Removed redundant check

Closes #997

ARCHITECTURE.md

@@ -0,0 +1,297 @@
+# Tantivy
+
+## What is tantivy?
+
+Tantivy is a library that is meant to build search engines. Although it is by no mean a port of Lucene, its architecture is strongly inspired by it. If you are familiar with Lucene, you may be struck by the overlapping vocabulary.
+This is not fortuitous.
+
+Tantivy's bread and butter is to address the problem of full-text search :
+
+Given a large set of textual documents, and a text query, return the K-most relevant documents in a very efficient way. In order to execute these queries rapidly, the tantivy need to build an index beforehand. The relevance score implemented in the tantivy is not configurable. Tantivy uses the same score as the default similarity used in Lucene / Elasticsearch, called [BM25](https://en.wikipedia.org/wiki/Okapi_BM25).
+
+But tantivy's scope does not stop there. Numerous features are required to power rich search applications. For instance, one may want to:
+- compute the count of documents matching a query in the different section of an e-commerce website,
+- display an average price per meter square for a real estate search engine,
+- take in account historical user data to rank documents in a specific way,
+- or even use tantivy to power an OLAP database.
+
+A more abstract description of the problem space tantivy is trying to address is the following.
+
+Ingest a large set of documents, create an index that makes it possible to
+rapidly select all documents matching a given predicate (also known as a query) and
+collect some information about them (See collector).
+
+Roughly speaking the design is following these guiding principles:
+- Search should be O(1) in memory.
+- Indexing should be O(1) in memory. (In practise it is just sublinear)
+- Search should be as fast as possible
+
+This comes at the cost of the dynamicity of the index : while it is possible to add, and delete documents from our corpus, the tantivy is designed to handle these updates in large batches.
+
+## [core/](src/core): Index, segments, searchers.
+
+Core contains all of the high level code to make it possible for to create an index, add documents, delete documents and commit.
+
+This is both the most high-level part of tantivy, the least performance sensitive one, the seemingly most mundane code... And paradoxically the most complicated part.
+
+### Index and Segments...
+
+A tantivy index is in fact a collection of smaller independent immutable segments.
+Each segment contains its own independent set of datastructures.
+
+A segment is identified by a segment id that is in fact a UUID.
+The file of a segment has the format
+
+ ```segment-id . ext ```
+
+The extension signals which datastructure (or [`SegmentComponent`](src/core/segment_component.rs)) is stored in the file.
+
+A small `meta.json` file is in charge keeping track of the list of segments, as well as the schema.
+
+On commit, one segment per indexing thread is written to disk, and the `meta.json` is then updated atomically.
+
+For a better idea of how indexing works, you may read the [following blog post](https://fulmicoton.com/posts/behold-tantivy-part2/).
+
+
+### Deletes
+
+Deletes happen by deleting a "term". Tantivy does not offer any notion of primary id, so it is up to the user to use a field in their schema as if it was a primary id, and delete the associated term if they want to delete only one specific document.
+
+On commit, tantivy will find all of the segments with documents matching this existing term and create a [tombstone file](src/fastfield/delete.rs) that represents the bitset of the document that are deleted.
+Like all segment files, this file is immutable. Because it is possible to have more than one tombstone file at a given instant, the tombstone filename has the format ``` segment_id . commit_opstamp . del```.
+
+An opstamp is simply an incremental id that identifies any operation applied to the index. For instance, performing a commit or adding a document.
+
+
+### DocId
+
+Within a segment, all documents are identified by a DocId that ranges within `[0, max_doc)`.
+where max doc is the number of documents in the segment, (deleted or not). Having such a compact `DocId` space is key to the compression of our datastructures.
+
+The DocIds are simply allocated in the order documents are added to the index.
+
+### Merges
+
+In separate threads, tantivy's index writer search for opportunities to merge segments.
+The point of segment merges is to:
+- eventually get rid of tombstoned documents
+- reduce the otherwise evergrowing number of segments.
+
+Indeed, while having several segments instead of one does not hurt search too much, having hundreds can have a measurable impact on the search performance.
+
+### Searcher
+
+The user of the library usually does not need to know about the existence of Segments.
+Searching is done through an object called a [`Searcher`](src/core/searcher.rs), that captures a
+snapshot of the index at one point of time, by holding a list of [SegmentReader](src/core/segment_reader.rs).
+
+In other words, regardless of commits, file garbage collection, or segment merge that might happen, as long as the user holds and reuse the same [Searcher](src/core/searcher.rs), search will happen on an immutable snapshot of the index.
+
+## [directory/](src/directory): Where should the data be stored?
+
+Tantivy, like Lucene, abstracts the place where the data should be stored in a key-trait
+called [`Directory`](src/directory/directory.rs).
+Contrary to Lucene however, "files" are quite different from some kind of `io::Read` object.
+Check out [`src/directory/directory.rs`](src/directory/directory.rs) trait for more details.
+
+Tantivy ships two main directory implementation: the `MMapDirectory` and the `RAMDirectory`,
+but users can extend tantivy with their own implementation.
+
+## [schema/](src/schema): What are documents?
+
+Tantivy's document follow a very strict schema , decided before building any index.
+
+The schema defines all of the fields that the indexes [`Document`](src/schema/document.rs) may and should contain, their types (`text`, `i64`, `u64`, `Date`, ...) as well as how it should be indexed / represented in tantivy.
+
+Depending on the type of the field, you can decide to
+- put it in the docstore
+- store it as a fast field
+- index it
+
+Practically, tantivy will push values associated to this type to up to 3 respective
+datastructures.
+
+*Limitations*
+
+As of today, tantivy's schema impose a 1:1 relationship between a field that is being ingested and a field represented in the search index. In sophisticated search application, it is fairly common to want to index a field twice using different tokenizers, or to index the concatenation of several fields together into one field.
+
+This is not something tantivy supports, and it is up to the user to duplicate field / concatenate fields before feeding them to tantivy.
+
+## General information about these datastructures.
+
+All datastructures in tantivy, have:
+- a writer
+- a serializer
+- a reader
+
+The writer builds a in-memory representation of a batch of documents. This representation is not searchable. It is just meant as intermediary mutable representation, to which we can sequentially add
+the document of a batch. At the end of the batch (or if a memory limit is reached), this representation
+is then converted in an on-disk immutable representation, that is extremely compact.
+This conversion is done by the serializer.
+
+Finally, the reader is in charge of offering an API to read on this on-disk read-only representation.
+In tantivy, readers are designed to require very little anonymous memory. The data is read straight from an mmapped file, and loading an index is as fast as mmapping its files.
+
+## [store/](src/store): Here is my DocId, Gimme my document!
+
+The docstore is a row-oriented storage that, for each documents, stores a subset of the fields
+that are marked as stored in the schema. The docstore is compressed using a general purpose algorithm
+like LZ4.
+
+**Useful for**
+
+In search engines, it is often used to display search results.
+Once the top 10 documents have been identified, we fetch them from the store, and display them or their snippet on the search result page (aka SERP).
+
+**Not useful for**
+
+Fetching a document from the store is typically a "slow" operation. It usually consists in
+- searching into a compact tree-like datastructure to find the position of the right block.
+- decompressing a small block
+- returning the document from this block.
+
+It is NOT meant to be called for every document matching a query.
+
+As a rule of thumb, if you hit the docstore more than 100 times per search query, you are probably misusing tantivy.
+
+
+## [fastfield/](src/fastfield): Here is my DocId, Gimme my value!
+
+Fast fields are stored in a column-oriented storage that allows for random access.
+The only compression applied is bitpacking. The column comes with two meta data.
+The minimum value in the column and the number of bits per doc.
+
+Fetching a value for a `DocId` is then as simple as computing
+
+```
+min_value + fetch_bits(num_bits * doc_id..num_bits * (doc_id+1))
+```
+
+This operation just requires one memory fetch.
+Because, DocSets are scanned through in order (DocId are iterated in a sorted manner) which
+also help locality.
+
+In Lucene's jargon, fast fields are called DocValues.
+
+**Useful for**
+
+They are typically integer values that are useful to either rank or compute aggregate over
+all of the documents matching a query (aka [DocSet](src/docset.rs)).
+
+For instance, one could define a function to combine upvotes with tantivy's internal relevancy score.
+This can be done by fetching a fast field during scoring.
+Once could also compute the mean price of the items matching a query in an e-commerce website.
+This can be done by fetching a fast field in a collector.
+Finally one could decide to post filter a docset to remove docset with a price within a specific range.
+If the ratio of filtered out documents is not too low, an efficient way to do this is to fetch the price, and apply the filter on the collector side.
+
+Aside from integer values, it is also possible to store an actual byte payload.
+For advanced search engine, it is possible to store all of the features required for learning-to-rank in a byte payload, access it during search, and apply the learning-to-rank model.
+
+Finally facets are a specific kind of fast field, and the associated source code is in [`fastfield/facet_reader.rs`](src/fastfield/facet_reader.rs).
+
+# The inverted search index.
+
+The inverted index is the core part of full-text search.
+When presented a new document with the text field "Hello, happy tax payer!", tantivy breaks it into a list of so-called token. In addition to just splitting this strings into tokens, it might also do different kind of operations like dropping the punctuation, converting the character to lowercase, apply stemming etc. Tantivy makes it possible to configure the operations to be applied in the schema
+(tokenizer/ is the place where these operations are implemented).
+
+For instance, the default tokenizer of tantivy would break our text into: `[hello, happy, tax, payer]`.
+The document will therefore be registered in the inverted index as containing the terms
+`[text:hello, text:happy, text:tax, text:payer]`.
+
+The role of the inverted index is, when given a term, supply us with a very fast iterator over
+the sorted doc ids that match the term.
+
+Such an iterator is called a posting list. In addition to giving us `DocId`, they can also give us optionally to the number of occurrence of the term for each document, also called term frequency or TF.
+
+These iterators being sorted by DocId, one can create an iterator over the document containing `text:tax AND text:payer`, `(text:tax AND text:payer) OR (text:contribuable)` or any boolean expression.
+
+In order to represent the function
+```Term ⟶ Posting```
+
+The inverted index actually consists of two datastructures chained together.
+
+- [Term](src/schema/term.rs) ⟶ [TermInfo](src/postings/term_info.rs) is addressed by the term dictionary.
+- [TermInfo](src/postings/term_info.rs) ⟶ [Posting](src/postings/postings.rs) is addressed by the posting lists.
+
+Where [TermInfo](src/postings/term_info.rs) is an object containing some meta data about a term.
+
+
+## [termdict/](src/termdict): Here is a term, give me the [TermInfo](src/postings/term_info.rs)!
+
+Tantivy's term dictionary is mainly in charge of supplying the function
+
+[Term](src/schema/term.rs) ⟶ [TermInfo](src/postings/term_info.rs)
+
+It is itself is broken into two parts.
+- [Term](src/schema/term.rs) ⟶ [TermOrdinal](src/termdict/mod.rs) is addressed by a finite state transducer, implemented by the fst crate.
+- [TermOrdinal](src/termdict/mod.rs) ⟶ [TermInfo](src/postings/term_info.rs) is addressed by the term info store.
+
+
+## [postings/](src/postings): Iterate over documents... very fast!
+
+A posting list makes it possible to store a sorted list of doc ids and for each doc store
+a term frequency as well.
+
+The posting list are stored in a separate file. The [TermInfo](src/postings/term_info.rs) contains an offset into that file and a number of documents for the given posting list. Both are required and sufficient to read the posting list.
+
+The posting list is organized in block of 128 documents.
+One block of doc ids is followed by one block of term frequencies.
+
+The doc ids are delta encoded and bitpacked.
+The term frequencies are bitpacked.
+
+Because the number of docs is rarely a multiple of 128, the last block my contain an arbitrary number of docs between 1 and 127 documents. We then use variable int encoding instead of bitpacking.
+
+## [positions/](src/positions): Where are my terms within the documents?
+
+Phrase queries make it possible to search for documents containing a specific sequence of document.
+For instance, when the phrase query "the art of war" does not match "the war of art".
+To make it possible, it is possible to specify in the schema that a field should store positions in addition to being indexed.
+
+The token positions of all of the terms are then stored in a separate file with the extension `.pos`.
+The [TermInfo](src/postings/term_info.rs) gives an offset (expressed in position this time) in this file. As we iterate throught the docset,
+we advance the position reader by the number of term frequencies of the current document.
+
+## [fieldnorms/](src/fieldnorms): Here is my doc, how many tokens in this field?
+
+The [BM25](https://en.wikipedia.org/wiki/Okapi_BM25) formula also requires to know the number of tokens stored in a specific field for a given document. We store this information on one byte per document in the fieldnorm.
+The fieldnorm is therefore compressed. Values up to 40 are encoded unchanged. There is then a logarithmic mapping that
+
+
+## [tokenizer/](src/tokenizer): How should we process text?
+
+Text processing is key to a good search experience.
+Splits or normalize your text too much, and the search results will have a less precision and a higher recall.
+Do not normalize, or under split your text, you will end up with a higher precision and a lesser recall.
+
+Text processing can be configured by selecting an off-the-shelf [`Tokenizer`](./src/tokenizer/tokenizer.rs) or implementing your own to first split the text into tokens, and then chain different [`TokenFilter`](src/tokenizer/tokenizer.rs)'s to it.
+
+Tantivy's comes with few tokenizers, but external crates are offering advanced tokenizers, such as [Lindera](https://crates.io/crates/lindera) for Japanese.
+
+
+## [query/](src/query): Define and compose queries
+
+The [Query](src/query/query.rs) trait defines what a query is.
+Due to the necessity for some query to compute some statistics over the entire index, and because the
+index is composed of several `SegmentReader`, the path from transforming a `Query` to a iterator over document is slightly convoluted, but fundamentally, this is what a Query is.
+
+The iterator over a document comes with some scoring function. The resulting trait is called a
+[Scorer](src/query/scorer.rs) and is specific to a segment.
+
+Different queries can be combined using the [BooleanQuery](src/query/boolean_query/).
+Tantivy comes with different types of queries, and can be extended by implementing
+the Query`, `Weight` and `Scorer` traits.
+
+## [collector](src/collector): Define what to do with matched documents
+
+Collectors define how to aggregate the documents matching a query, in the broadest sense possible.
+The search will push matched document one by one, calling their
+`fn collect(doc: DocId, score: Score);` method.
+
+Users may implement their own collectors by implementing the [Collector](src/collector/mod.rs) trait.
+
+## [query-grammar](query-grammar): Defines the grammar of the query parser
+
+While the [QueryParser](src/query/query_parser/query_parser.rs) struct is located in the `query/` directory, the actual parser combinator used to convert user queries into an AST is in an external crate called `query-grammar`. This part was externalize to lighten the work of the compiler.

CHANGELOG.md

@@ -1,11 +1,42 @@
+Tantivy 0.15.0
+=========================
+- API Changes. Using Range instead of (start, end) in the API and internals (`FileSlice`, `OwnedBytes`, `Snippets`, ...)
+  This change is breaking but migration is trivial.
+- Added an Histogram collector. (@fulmicoton) #994
+- Added support for Option<TCollector>.  (@fulmicoton) 
+
+
 Tantivy 0.14.0
 =========================
-- Remove dependency to atomicwrites #833 .Implemented by @pmasurel upon suggestion and research from @asafigan). 
+- Remove dependency to atomicwrites #833 .Implemented by @fulmicoton upon suggestion and research from @asafigan).
+- Migrated tantivy error from the now deprecated `failure` crate to `thiserror` #760. (@hirevo)
+- API Change. Accessing the typed value off a `Schema::Value` now returns an Option instead of panicking if the type does not match.
+- Large API Change in the Directory API. Tantivy used to assume that all files could be somehow memory mapped. After this change, Directory return a `FileSlice` that can be reduced and eventually read into an `OwnedBytes` object. Long and blocking io operation are still required by they do not span over the entire file.
+- Added support for Brotli compression in the DocStore. (@ppodolsky)
+- Added helper for building intersections and unions in BooleanQuery (@guilload)
+- Bugfix in `Query::explain`
+- Removed dependency on `notify` #924. Replaced with `FileWatcher` struct that polls meta file every 500ms in background thread. (@halvorboe @guilload)
+- Added `FilterCollector`, which wraps another collector and filters docs using a predicate over a fast field (@barrotsteindev)
+- Simplified the encoding of the skip reader struct. BlockWAND max tf is now encoded over a single byte. (@fulmicoton)
+- `FilterCollector` now supports all Fast Field value types (@barrotsteindev)
+- FastField are not all loaded when opening the segment reader. (@fulmicoton)
+
+This version breaks compatibility and requires users to reindex everything.
+
+Tantivy 0.13.2
+===================
+Bugfix. Acquiring a facet reader on a segment that does not contain any
+doc with this facet returns `None`. (#896)
+
+Tantivy 0.13.1
+===================
+Made `Query` and `Collector` `Send + Sync`.
+Updated misc dependency versions.
 
 Tantivy 0.13.0
 ======================
 Tantivy 0.13 introduce a change in the index format that will require
-you to reindex your index (BlockWAND information are added in the skiplist). 
+you to reindex your index (BlockWAND information are added in the skiplist).
 The index size increase is minor as this information is only added for
 full blocks.
 If you have a massive index for which reindexing is not an option, please contact me
@@ -14,7 +45,7 @@ so that we can discuss possible solutions.
 - Bugfix in `FuzzyTermQuery` not matching terms by prefix when it should (@Peachball)
 - Relaxed constraints on the custom/tweak score functions. At the segment level, they can be mut, and they are not required to be Sync + Send.
 - `MMapDirectory::open` does not return a `Result` anymore.
-- Change in the DocSet and Scorer API. (@fulmicoton). 
+- Change in the DocSet and Scorer API. (@fulmicoton).
 A freshly created DocSet point directly to their first doc. A sentinel value called TERMINATED marks the end of a DocSet.
 `.advance()` returns the new DocId. `Scorer::skip(target)` has been replaced by `Scorer::seek(target)` and returns the resulting DocId.
 As a result, iterating through DocSet now looks as follows
@@ -28,7 +59,7 @@ while doc != TERMINATED {
 The change made it possible to greatly simplify a lot of the docset's code.
 - Misc internal optimization and introduction of the `Scorer::for_each_pruning` function. (@fulmicoton)
 - Added an offset option to the Top(.*)Collectors. (@robyoung)
-- Added Block WAND. Performance on TOP-K on term-unions should be greatly increased. (@fulmicoton, and special thanks 
+- Added Block WAND. Performance on TOP-K on term-unions should be greatly increased. (@fulmicoton, and special thanks
 to the PISA team for answering all my questions!)
 
 Tantivy 0.12.0
@@ -36,14 +67,14 @@ Tantivy 0.12.0
 - Removing static dispatch in tokenizers for simplicity. (#762)
 - Added backward iteration for `TermDictionary` stream. (@halvorboe)
 - Fixed a performance issue when searching for the posting lists of a missing term (@audunhalland)
-- Added a configurable maximum number of docs (10M by default) for a segment to be considered for merge (@hntd187, landed by @halvorboe #713) 
+- Added a configurable maximum number of docs (10M by default) for a segment to be considered for merge (@hntd187, landed by @halvorboe #713)
 - Important Bugfix #777, causing tantivy to retain memory mapping. (diagnosed by @poljar)
 - Added support for field boosting. (#547, @fulmicoton)
 
 ## How to update?
 
-Crates relying on custom tokenizer, or registering tokenizer in the manager will require some 
-minor changes. Check https://github.com/tantivy-search/tantivy/blob/master/examples/custom_tokenizer.rs
+Crates relying on custom tokenizer, or registering tokenizer in the manager will require some
+minor changes. Check https://github.com/tantivy-search/tantivy/blob/main/examples/custom_tokenizer.rs
 to check for some code sample.
 
 Tantivy 0.11.3
@@ -79,7 +110,7 @@ Tantivy 0.11.0
 
 ## How to update?
 
-- The index format is changed. You are required to reindex your data to use tantivy 0.11. 
+- The index format is changed. You are required to reindex your data to use tantivy 0.11.
 - `Box<dyn BoxableTokenizer>` has been replaced by a `BoxedTokenizer` struct.
 - Regex are now compiled when the `RegexQuery` instance is built. As a result, it can now return
 an error and handling the `Result` is required.
@@ -103,26 +134,26 @@ Tantivy 0.10.0
 
 *Tantivy 0.10.0 index format is compatible with the index format in 0.9.0.*
 
-- Added an API to easily tweak or entirely replace the 
- default score. See `TopDocs::tweak_score`and `TopScore::custom_score` (@pmasurel)
+- Added an API to easily tweak or entirely replace the
+ default score. See `TopDocs::tweak_score`and `TopScore::custom_score` (@fulmicoton)
 - Added an ASCII folding filter (@drusellers)
-- Bugfix in `query.count` in presence of deletes (@pmasurel)
-- Added `.explain(...)` in `Query` and `Weight` to (@pmasurel)
-- Added an efficient way to `delete_all_documents` in `IndexWriter` (@petr-tik). 
+- Bugfix in `query.count` in presence of deletes (@fulmicoton)
+- Added `.explain(...)` in `Query` and `Weight` to (@fulmicoton)
+- Added an efficient way to `delete_all_documents` in `IndexWriter` (@petr-tik).
   All segments are simply removed.
 
 Minor
 ---------
 - Switched to Rust 2018 (@uvd)
-- Small simplification of the code. 
+- Small simplification of the code.
 Calling .freq() or .doc() when .advance() has never been called
 on segment postings should panic from now on.
 - Tokens exceeding `u16::max_value() - 4` chars are discarded silently instead of panicking.
 - Fast fields are now preloaded when the `SegmentReader` is created.
 - `IndexMeta` is now public.  (@hntd187)
 - `IndexWriter` `add_document`, `delete_term`. `IndexWriter` is `Sync`, making it possible to use it with a `
-Arc<RwLock<IndexWriter>>`. `add_document` and `delete_term` can 
-only require a read lock. (@pmasurel)
+Arc<RwLock<IndexWriter>>`. `add_document` and `delete_term` can
+only require a read lock. (@fulmicoton)
 - Introducing `Opstamp` as an expressive type alias for `u64`. (@petr-tik)
 - Stamper now relies on `AtomicU64` on all platforms (@petr-tik)
 - Bugfix - Files get deleted slightly earlier
@@ -136,7 +167,7 @@ Your program should be usable as is.
 
 Fast fields used to be accessed directly from the `SegmentReader`.
 The API changed, you are now required to acquire your fast field reader via the
-`segment_reader.fast_fields()`, and use one of the typed method: 
+`segment_reader.fast_fields()`, and use one of the typed method:
 - `.u64()`, `.i64()` if your field is single-valued ;
 - `.u64s()`, `.i64s()` if your field is multi-valued ;
 - `.bytes()` if your field is bytes fast field.
@@ -145,16 +176,16 @@ The API changed, you are now required to acquire your fast field reader via the
 
 Tantivy 0.9.0
 =====================
-*0.9.0 index format is not compatible with the 
+*0.9.0 index format is not compatible with the
 previous index format.*
-- MAJOR BUGFIX : 
+- MAJOR BUGFIX :
   Some `Mmap` objects were being leaked, and would never get released. (@fulmicoton)
 - Removed most unsafe (@fulmicoton)
 - Indexer memory footprint improved. (VInt comp, inlining the first block. (@fulmicoton)
 - Stemming in other language possible (@pentlander)
 - Segments with no docs are deleted earlier (@barrotsteindev)
-- Added grouped add and delete operations. 
-  They are guaranteed to happen together (i.e. they cannot be split by a commit). 
+- Added grouped add and delete operations.
+  They are guaranteed to happen together (i.e. they cannot be split by a commit).
   In addition, adds are guaranteed to happen on the same segment. (@elbow-jason)
 - Removed `INT_STORED` and `INT_INDEXED`. It is now possible to use `STORED` and `INDEXED`
   for int fields. (@fulmicoton)
@@ -168,26 +199,26 @@ tantivy 0.9 brought some API breaking change.
 To update from tantivy 0.8, you will need to go through the following steps.
 
 - `schema::INT_INDEXED` and `schema::INT_STORED`  should be replaced by `schema::INDEXED` and `schema::INT_STORED`.
-- The index now does not hold the pool of searcher anymore. You are required to create an intermediary object called 
-`IndexReader` for this. 
-    
+- The index now does not hold the pool of searcher anymore. You are required to create an intermediary object called
+`IndexReader` for this.
+
     ```rust
     // create the reader. You typically need to create 1 reader for the entire
     // lifetime of you program.
     let reader = index.reader()?;
-    
+
     // Acquire a searcher (previously `index.searcher()`) is now written:
     let searcher = reader.searcher();
-    
-    // With the default setting of the reader, you are not required to 
+
+    // With the default setting of the reader, you are not required to
     // call `index.load_searchers()` anymore.
     //
     // The IndexReader will pick up that change automatically, regardless
     // of whether the update was done in a different process or not.
-    // If this behavior is not wanted, you can create your reader with 
+    // If this behavior is not wanted, you can create your reader with
     // the `ReloadPolicy::Manual`, and manually decide when to reload the index
     // by calling `reader.reload()?`.
-  
+
     ```
 
 
@@ -202,7 +233,7 @@ Tantivy 0.8.1
 =====================
 Hotfix of #476.
 
-Merge was reflecting deletes before commit was passed. 
+Merge was reflecting deletes before commit was passed.
 Thanks @barrotsteindev  for reporting the bug.
 
 
@@ -210,7 +241,7 @@ Tantivy 0.8.0
 =====================
 *No change in the index format*
 - API Breaking change in the collector API. (@jwolfe, @fulmicoton)
-- Multithreaded search (@jwolfe, @fulmicoton) 
+- Multithreaded search (@jwolfe, @fulmicoton)
 
 
 Tantivy 0.7.1
@@ -238,7 +269,7 @@ Tantivy 0.6.1
         - Exclusive `field:{startExcl to endExcl}`
         - Mixed `field:[startIncl to endExcl}` and vice versa
         - Unbounded `field:[start to *]`, `field:[* to end]`
- 
+
 
 Tantivy 0.6
 ==========================
@@ -246,10 +277,10 @@ Tantivy 0.6
 Special thanks to @drusellers and @jason-wolfe for their contributions
 to this release!
 
-- Removed C code. Tantivy is now pure Rust. (@pmasurel)
-- BM25 (@pmasurel)
-- Approximate field norms encoded over 1 byte. (@pmasurel)
-- Compiles on stable rust (@pmasurel)
+- Removed C code. Tantivy is now pure Rust. (@fulmicoton)
+- BM25 (@fulmicoton)
+- Approximate field norms encoded over 1 byte. (@fulmicoton)
+- Compiles on stable rust (@fulmicoton)
 - Add &[u8] fastfield for associating arbitrary bytes to each document (@jason-wolfe) (#270)
     - Completely uncompressed
     - Internally: One u64 fast field for indexes, one fast field for the bytes themselves.
@@ -257,7 +288,7 @@ to this release!
 - Add Stopword Filter support (@drusellers)
 - Add a FuzzyTermQuery (@drusellers)
 - Add a RegexQuery (@drusellers)
-- Various performance improvements (@pmasurel)_
+- Various performance improvements (@fulmicoton)_
 
 
 Tantivy 0.5.2

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "tantivy"
-version = "0.14.0-dev"
+version = "0.14.0"
 authors = ["Paul Masurel <paul.masurel@gmail.com>"]
 license = "MIT"
 categories = ["database-implementations", "data-structures"]
@@ -13,51 +13,52 @@ keywords = ["search", "information", "retrieval"]
 edition = "2018"
 
 [dependencies]
-base64 = "0.12.0"
-byteorder = "1.0"
-crc32fast = "1.2.0"
-once_cell = "1.0"
-regex ={version = "1.3.0", default-features = false, features = ["std"]}
+base64 = "0.13"
+byteorder = "1"
+crc32fast = "1"
+once_cell = "1"
+regex ={version = "1", default-features = false, features = ["std"]}
 tantivy-fst = "0.3"
 memmap = {version = "0.7", optional=true}
-lz4 = {version="1.20", optional=true}
+lz4 = {version="1", optional=true}
+brotli = {version="3.3.0", optional=true}
 snap = "1"
-tempfile = {version="3.0", optional=true}
+tempfile = {version="3", optional=true}
 log = "0.4"
-serde = {version="1.0", features=["derive"]}
-serde_json = "1.0"
-num_cpus = "1.2"
+serde = {version="1", features=["derive"]}
+serde_json = "1"
+num_cpus = "1"
 fs2={version="0.4", optional=true}
 levenshtein_automata = "0.2"
-notify = {version="4", optional=true}
 uuid = { version = "0.8", features = ["v4", "serde"] }
-crossbeam = "0.7"
+crossbeam = "0.8"
 futures = {version = "0.3",  features=["thread-pool"] }
-owning_ref = "0.4"
-stable_deref_trait = "1.0.0"
-rust-stemmers = "1.2"
-downcast-rs = { version="1.0" }
-tantivy-query-grammar = { version="0.14.0-dev", path="./query-grammar" }
+tantivy-query-grammar = { version="0.14.0", path="./query-grammar" }
+stable_deref_trait = "1"
+rust-stemmers = "1"
+downcast-rs = "1"
 bitpacking = {version="0.8", default-features = false, features=["bitpacker4x"]}
 census = "0.4"
-fnv = "1.0.6"
-owned-read = "0.4"
-failure = "0.1"
-htmlescape = "0.3.1"
+fnv = "1"
+thiserror = "1.0"
+htmlescape = "0.3"
 fail = "0.4"
 murmurhash32 = "0.2"
 chrono = "0.4"
-smallvec = "1.0"
+smallvec = "1"
 rayon = "1"
+lru = "0.6"
+fastdivide = "0.3"
 
 [target.'cfg(windows)'.dependencies]
 winapi = "0.3"
 
 [dev-dependencies]
-rand = "0.7"
+rand = "0.8"
 maplit = "1"
 matches = "0.1.8"
-proptest = "0.10"
+proptest = "1.0"
+criterion = "0.3"
 
 [dev-dependencies.fail]
 version = "0.4"
@@ -74,12 +75,12 @@ overflow-checks = true
 
 [features]
 default = ["mmap"]
-mmap = ["fs2", "tempfile", "memmap", "notify"]
+mmap = ["fs2", "tempfile", "memmap"]
+brotli-compression = ["brotli"]
 lz4-compression = ["lz4"]
 failpoints = ["fail/failpoints"]
 unstable = [] # useful for benches.
 wasm-bindgen = ["uuid/wasm-bindgen"]
-scoref64 = [] # scores are f64 instead of f32. was introduced to debug blockwand.
 
 [workspace]
 members = ["query-grammar"]
@@ -98,3 +99,7 @@ travis-ci = { repository = "tantivy-search/tantivy" }
 name = "failpoints"
 path = "tests/failpoints/mod.rs"
 required-features = ["fail/failpoints"]
+
+[[bench]]
+name = "analyzer"
+harness = false

README.md

@@ -1,11 +1,10 @@
 
-[![Build Status](https://travis-ci.org/tantivy-search/tantivy.svg?branch=master)](https://travis-ci.org/tantivy-search/tantivy)
-[![codecov](https://codecov.io/gh/tantivy-search/tantivy/branch/master/graph/badge.svg)](https://codecov.io/gh/tantivy-search/tantivy)
+[![Build Status](https://travis-ci.org/tantivy-search/tantivy.svg?branch=main)](https://travis-ci.org/tantivy-search/tantivy)
+[![codecov](https://codecov.io/gh/tantivy-search/tantivy/branch/main/graph/badge.svg)](https://codecov.io/gh/tantivy-search/tantivy)
 [![Join the chat at https://gitter.im/tantivy-search/tantivy](https://badges.gitter.im/tantivy-search/tantivy.svg)](https://gitter.im/tantivy-search/tantivy?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
-[![Build status](https://ci.appveyor.com/api/projects/status/r7nb13kj23u8m9pj/branch/master?svg=true)](https://ci.appveyor.com/project/fulmicoton/tantivy/branch/master)
+[![Build status](https://ci.appveyor.com/api/projects/status/r7nb13kj23u8m9pj/branch/main?svg=true)](https://ci.appveyor.com/project/fulmicoton/tantivy/branch/main)
 [![Crates.io](https://img.shields.io/crates/v/tantivy.svg)](https://crates.io/crates/tantivy)
-[![Say Thanks!](https://img.shields.io/badge/Say%20Thanks-!-1EAEDB.svg)](https://saythanks.io/to/fulmicoton)
 
 ![Tantivy](https://tantivy-search.github.io/logo/tantivy-logo.png)
 
@@ -85,7 +84,7 @@ There are many ways to support this project.
 - Help with documentation by asking questions or submitting PRs
 - Contribute code (you can join [our Gitter](https://gitter.im/tantivy-search/tantivy))
 - Talk about Tantivy around you
-- Drop a word on on [![Say Thanks!](https://img.shields.io/badge/Say%20Thanks-!-1EAEDB.svg)](https://saythanks.io/to/fulmicoton) or even [![Become a patron](https://c5.patreon.com/external/logo/become_a_patron_button.png)](https://www.patreon.com/fulmicoton)
+- [![Become a patron](https://c5.patreon.com/external/logo/become_a_patron_button.png)](https://www.patreon.com/fulmicoton)
 
 # Contributing code
 

benches/analyzer.rs

@@ -0,0 +1,22 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+use tantivy::tokenizer::TokenizerManager;
+
+const ALICE_TXT: &'static str = include_str!("alice.txt");
+
+pub fn criterion_benchmark(c: &mut Criterion) {
+    let tokenizer_manager = TokenizerManager::default();
+    let tokenizer = tokenizer_manager.get("default").unwrap();
+    c.bench_function("default-tokenize-alice", |b| {
+        b.iter(|| {
+            let mut word_count = 0;
+            let mut token_stream = tokenizer.token_stream(ALICE_TXT);
+            while token_stream.advance() {
+                word_count += 1;
+            }
+            assert_eq!(word_count, 30_731);
+        })
+    });
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

examples/custom_collector.rs

@@ -14,7 +14,7 @@ use tantivy::fastfield::FastFieldReader;
 use tantivy::query::QueryParser;
 use tantivy::schema::Field;
 use tantivy::schema::{Schema, FAST, INDEXED, TEXT};
-use tantivy::{doc, Index, Score, SegmentReader, TantivyError};
+use tantivy::{doc, Index, Score, SegmentReader};
 
 #[derive(Default)]
 struct Stats {
@@ -72,16 +72,7 @@ impl Collector for StatsCollector {
         _segment_local_id: u32,
         segment_reader: &SegmentReader,
     ) -> tantivy::Result<StatsSegmentCollector> {
-        let fast_field_reader = segment_reader
-            .fast_fields()
-            .u64(self.field)
-            .ok_or_else(|| {
-                let field_name = segment_reader.schema().get_field_name(self.field);
-                TantivyError::SchemaError(format!(
-                    "Field {:?} is not a u64 fast field.",
-                    field_name
-                ))
-            })?;
+        let fast_field_reader = segment_reader.fast_fields().u64(self.field)?;
         Ok(StatsSegmentCollector {
             fast_field_reader,
             stats: Stats::default(),

examples/faceted_search.rs

@@ -23,7 +23,7 @@ fn main() -> tantivy::Result<()> {
 
     let name = schema_builder.add_text_field("felin_name", TEXT | STORED);
     // this is our faceted field: its scientific classification
-    let classification = schema_builder.add_facet_field("classification");
+    let classification = schema_builder.add_facet_field("classification", INDEXED);
 
     let schema = schema_builder.build();
     let index = Index::create_in_ram(schema);

examples/faceted_search_with_tweaked_score.rs

@@ -9,7 +9,7 @@ fn main() -> tantivy::Result<()> {
     let mut schema_builder = Schema::builder();
 
     let title = schema_builder.add_text_field("title", STORED);
-    let ingredient = schema_builder.add_facet_field("ingredient");
+    let ingredient = schema_builder.add_facet_field("ingredient", INDEXED);
 
     let schema = schema_builder.build();
     let index = Index::create_in_ram(schema.clone());
@@ -56,12 +56,12 @@ fn main() -> tantivy::Result<()> {
         );
         let top_docs_by_custom_score =
             TopDocs::with_limit(2).tweak_score(move |segment_reader: &SegmentReader| {
-                let mut ingredient_reader = segment_reader.facet_reader(ingredient).unwrap();
+                let ingredient_reader = segment_reader.facet_reader(ingredient).unwrap();
                 let facet_dict = ingredient_reader.facet_dict();
 
                 let query_ords: HashSet<u64> = facets
                     .iter()
-                    .filter_map(|key| facet_dict.term_ord(key.encoded_str()))
+                    .filter_map(|key| facet_dict.term_ord(key.encoded_str()).unwrap())
                     .collect();
 
                 let mut facet_ords_buffer: Vec<u64> = Vec::with_capacity(20);

examples/iterating_docs_and_positions.rs

@@ -1,4 +1,4 @@
-// # Iterating docs and positioms.
+// # Iterating docs and positions.
 //
 // At its core of tantivy, relies on a data structure
 // called an inverted index.
@@ -45,7 +45,7 @@ fn main() -> tantivy::Result<()> {
         // Inverted index stands for the combination of
         // - the term dictionary
         // - the inverted lists associated to each terms and their positions
-        let inverted_index = segment_reader.inverted_index(title);
+        let inverted_index = segment_reader.inverted_index(title)?;
 
         // A `Term` is a text token associated with a field.
         // Let's go through all docs containing the term `title:the` and access their position
@@ -58,7 +58,7 @@ fn main() -> tantivy::Result<()> {
         // If you don't need all this information, you may get better performance by decompressing less
         // information.
         if let Some(mut segment_postings) =
-            inverted_index.read_postings(&term_the, IndexRecordOption::WithFreqsAndPositions)
+            inverted_index.read_postings(&term_the, IndexRecordOption::WithFreqsAndPositions)?
         {
             // this buffer will be used to request for positions
             let mut positions: Vec<u32> = Vec::with_capacity(100);
@@ -106,7 +106,7 @@ fn main() -> tantivy::Result<()> {
         // Inverted index stands for the combination of
         // - the term dictionary
         // - the inverted lists associated to each terms and their positions
-        let inverted_index = segment_reader.inverted_index(title);
+        let inverted_index = segment_reader.inverted_index(title)?;
 
         // This segment posting object is like a cursor over the documents matching the term.
         // The `IndexRecordOption` arguments tells tantivy we will be interested in both term frequencies
@@ -115,7 +115,7 @@ fn main() -> tantivy::Result<()> {
         // If you don't need all this information, you may get better performance by decompressing less
         // information.
         if let Some(mut block_segment_postings) =
-            inverted_index.read_block_postings(&term_the, IndexRecordOption::Basic)
+            inverted_index.read_block_postings(&term_the, IndexRecordOption::Basic)?
         {
             loop {
                 let docs = block_segment_postings.docs();

examples/pre_tokenized_text.rs

@@ -1,6 +1,6 @@
 // # Pre-tokenized text example
 //
-// This example shows how to use pre-tokenized text. Sometimes yout might
+// This example shows how to use pre-tokenized text. Sometimes you might
 // want to index and search through text which is already split into
 // tokens by some external tool.
 //

examples/snippet.rs

@@ -69,12 +69,12 @@ fn highlight(snippet: Snippet) -> String {
     let mut result = String::new();
     let mut start_from = 0;
 
-    for (start, end) in snippet.highlighted().iter().map(|h| h.bounds()) {
-        result.push_str(&snippet.fragments()[start_from..start]);
+    for fragment_range in snippet.highlighted() {
+        result.push_str(&snippet.fragments()[start_from..fragment_range.start]);
         result.push_str(" --> ");
-        result.push_str(&snippet.fragments()[start..end]);
+        result.push_str(&snippet.fragments()[fragment_range.clone()]);
         result.push_str(" <-- ");
-        start_from = end;
+        start_from = fragment_range.end;
     }
 
     result.push_str(&snippet.fragments()[start_from..]);

query-grammar/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "tantivy-query-grammar"
-version = "0.14.0-dev"
+version = "0.14.0"
 authors = ["Paul Masurel <paul.masurel@gmail.com>"]
 license = "MIT"
 categories = ["database-implementations", "data-structures"]

src/collector/custom_score_top_collector.rs

@@ -46,7 +46,7 @@ pub trait CustomScorer<TScore>: Sync {
 
 impl<TCustomScorer, TScore> Collector for CustomScoreTopCollector<TCustomScorer, TScore>
 where
-    TCustomScorer: CustomScorer<TScore>,
+    TCustomScorer: CustomScorer<TScore> + Send + Sync,
     TScore: 'static + PartialOrd + Clone + Send + Sync,
 {
     type Fruit = Vec<(TScore, DocAddress)>;
@@ -58,10 +58,8 @@ where
         segment_local_id: u32,
         segment_reader: &SegmentReader,
     ) -> crate::Result<Self::Child> {
+        let segment_collector = self.collector.for_segment(segment_local_id, segment_reader);
         let segment_scorer = self.custom_scorer.segment_scorer(segment_reader)?;
-        let segment_collector = self
-            .collector
-            .for_segment(segment_local_id, segment_reader)?;
         Ok(CustomScoreTopSegmentCollector {
             segment_collector,
             segment_scorer,

src/collector/docset_collector.rs

@@ -0,0 +1,61 @@
+use std::collections::HashSet;
+
+use crate::{DocAddress, DocId, Score};
+
+use super::{Collector, SegmentCollector};
+
+/// Collectors that returns the set of DocAddress that matches the query.
+///
+/// This collector is mostly useful for tests.
+pub struct DocSetCollector;
+
+impl Collector for DocSetCollector {
+    type Fruit = HashSet<DocAddress>;
+    type Child = DocSetChildCollector;
+
+    fn for_segment(
+        &self,
+        segment_local_id: crate::SegmentLocalId,
+        _segment: &crate::SegmentReader,
+    ) -> crate::Result<Self::Child> {
+        Ok(DocSetChildCollector {
+            segment_local_id,
+            docs: HashSet::new(),
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        false
+    }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<(u32, HashSet<DocId>)>,
+    ) -> crate::Result<Self::Fruit> {
+        let len: usize = segment_fruits.iter().map(|(_, docset)| docset.len()).sum();
+        let mut result = HashSet::with_capacity(len);
+        for (segment_local_id, docs) in segment_fruits {
+            for doc in docs {
+                result.insert(DocAddress(segment_local_id, doc));
+            }
+        }
+        Ok(result)
+    }
+}
+
+pub struct DocSetChildCollector {
+    segment_local_id: u32,
+    docs: HashSet<DocId>,
+}
+
+impl SegmentCollector for DocSetChildCollector {
+    type Fruit = (u32, HashSet<DocId>);
+
+    fn collect(&mut self, doc: crate::DocId, _score: Score) {
+        self.docs.insert(doc);
+    }
+
+    fn harvest(self) -> (u32, HashSet<DocId>) {
+        (self.segment_local_id, self.docs)
+    }
+}

src/collector/facet_collector.rs

@@ -7,14 +7,13 @@ use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
 use crate::SegmentReader;
-use crate::TantivyError;
 use std::cmp::Ordering;
 use std::collections::btree_map;
 use std::collections::BTreeMap;
 use std::collections::BTreeSet;
 use std::collections::BinaryHeap;
-use std::collections::Bound;
 use std::iter::Peekable;
+use std::ops::Bound;
 use std::{u64, usize};
 
 struct Hit<'a> {
@@ -81,7 +80,7 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 /// ```rust
 /// use tantivy::collector::FacetCollector;
 /// use tantivy::query::AllQuery;
-/// use tantivy::schema::{Facet, Schema, TEXT};
+/// use tantivy::schema::{Facet, Schema, INDEXED, TEXT};
 /// use tantivy::{doc, Index};
 ///
 /// fn example() -> tantivy::Result<()> {
@@ -90,7 +89,7 @@ fn facet_depth(facet_bytes: &[u8]) -> usize {
 ///     // Facet have their own specific type.
 ///     // It is not a bad practise to put all of your
 ///     // facet information in the same field.
-///     let facet = schema_builder.add_facet_field("facet");
+///     let facet = schema_builder.add_facet_field("facet", INDEXED);
 ///     let title = schema_builder.add_text_field("title", TEXT);
 ///     let schema = schema_builder.build();
 ///     let index = Index::create_in_ram(schema);
@@ -266,10 +265,7 @@ impl Collector for FacetCollector {
         _: SegmentLocalId,
         reader: &SegmentReader,
     ) -> crate::Result<FacetSegmentCollector> {
-        let field_name = reader.schema().get_field_name(self.field);
-        let facet_reader = reader.facet_reader(self.field).ok_or_else(|| {
-            TantivyError::SchemaError(format!("Field {:?} is not a facet field.", field_name))
-        })?;
+        let facet_reader = reader.facet_reader(self.field)?;
 
         let mut collapse_mapping = Vec::new();
         let mut counts = Vec::new();
@@ -278,7 +274,7 @@ impl Collector for FacetCollector {
         let mut collapse_facet_it = self.facets.iter().peekable();
         collapse_facet_ords.push(0);
         {
-            let mut facet_streamer = facet_reader.facet_dict().range().into_stream();
+            let mut facet_streamer = facet_reader.facet_dict().range().into_stream()?;
             if facet_streamer.advance() {
                 'outer: loop {
                     // at the begining of this loop, facet_streamer
@@ -372,9 +368,12 @@ impl SegmentCollector for FacetSegmentCollector {
             }
             let mut facet = vec![];
             let facet_ord = self.collapse_facet_ords[collapsed_facet_ord];
-            facet_dict.ord_to_term(facet_ord as u64, &mut facet);
-            // TODO
-            facet_counts.insert(Facet::from_encoded(facet).unwrap(), count);
+            // TODO handle errors.
+            if facet_dict.ord_to_term(facet_ord as u64, &mut facet).is_ok() {
+                if let Ok(facet) = Facet::from_encoded(facet) {
+                    facet_counts.insert(facet, count);
+                }
+            }
         }
         FacetCounts { facet_counts }
     }
@@ -399,6 +398,8 @@ impl<'a> Iterator for FacetChildIterator<'a> {
 }
 
 impl FacetCounts {
+    /// Returns an iterator over all of the facet count pairs inside this result.
+    /// See the documentation for `FacetCollector` for a usage example.
     pub fn get<T>(&self, facet_from: T) -> FacetChildIterator<'_>
     where
         Facet: From<T>,
@@ -418,6 +419,8 @@ impl FacetCounts {
         FacetChildIterator { underlying }
     }
 
+    /// Returns a vector of top `k` facets with their counts, sorted highest-to-lowest by counts.
+    /// See the documentation for `FacetCollector` for a usage example.
     pub fn top_k<T>(&self, facet: T, k: usize) -> Vec<(&Facet, u64)>
     where
         Facet: From<T>,
@@ -458,7 +461,7 @@ mod tests {
     use crate::collector::Count;
     use crate::core::Index;
     use crate::query::{AllQuery, QueryParser, TermQuery};
-    use crate::schema::{Document, Facet, Field, IndexRecordOption, Schema};
+    use crate::schema::{Document, Facet, Field, IndexRecordOption, Schema, INDEXED};
     use crate::Term;
     use rand::distributions::Uniform;
     use rand::prelude::SliceRandom;
@@ -468,11 +471,11 @@ mod tests {
     #[test]
     fn test_facet_collector_drilldown() {
         let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
 
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         let num_facets: usize = 3 * 4 * 5;
         let facets: Vec<Facet> = (0..num_facets)
             .map(|mut n| {
@@ -528,10 +531,10 @@ mod tests {
     #[test]
     fn test_doc_unsorted_multifacet() {
         let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facets");
+        let facet_field = schema_builder.add_facet_field("facets", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(
             facet_field => Facet::from_text(&"/subjects/A/a"),
             facet_field => Facet::from_text(&"/subjects/B/a"),
@@ -550,12 +553,12 @@ mod tests {
     }
 
     #[test]
-    fn test_doc_search_by_facet() {
+    fn test_doc_search_by_facet() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.add_document(doc!(
             facet_field => Facet::from_text(&"/A/A"),
         ));
@@ -568,8 +571,8 @@ mod tests {
         index_writer.add_document(doc!(
             facet_field => Facet::from_text(&"/D/C/A"),
         ));
-        index_writer.commit().unwrap();
-        let reader = index.reader().unwrap();
+        index_writer.commit()?;
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         assert_eq!(searcher.num_docs(), 4);
 
@@ -586,17 +589,17 @@ mod tests {
         assert_eq!(count_facet("/A/C"), 1);
         assert_eq!(count_facet("/A/C/A"), 1);
         assert_eq!(count_facet("/C/A"), 0);
+
+        let query_parser = QueryParser::for_index(&index, vec![]);
         {
-            let query_parser = QueryParser::for_index(&index, vec![]);
-            {
-                let query = query_parser.parse_query("facet:/A/B").unwrap();
-                assert_eq!(1, searcher.search(&query, &Count).unwrap());
-            }
-            {
-                let query = query_parser.parse_query("facet:/A").unwrap();
-                assert_eq!(3, searcher.search(&query, &Count).unwrap());
-            }
+            let query = query_parser.parse_query("facet:/A/B")?;
+            assert_eq!(1, searcher.search(&query, &Count).unwrap());
         }
+        {
+            let query = query_parser.parse_query("facet:/A")?;
+            assert_eq!(3, searcher.search(&query, &Count)?);
+        }
+        Ok(())
     }
 
     #[test]
@@ -609,7 +612,7 @@ mod tests {
     #[test]
     fn test_facet_collector_topk() {
         let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
 
@@ -631,7 +634,7 @@ mod tests {
             .collect();
         docs[..].shuffle(&mut thread_rng());
 
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         for doc in docs {
             index_writer.add_document(doc);
         }
@@ -661,7 +664,7 @@ mod bench {
 
     use crate::collector::FacetCollector;
     use crate::query::AllQuery;
-    use crate::schema::{Facet, Schema};
+    use crate::schema::{Facet, Schema, INDEXED};
     use crate::Index;
     use rand::seq::SliceRandom;
     use rand::thread_rng;
@@ -670,7 +673,7 @@ mod bench {
     #[bench]
     fn bench_facet_collector(b: &mut Bencher) {
         let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
 
@@ -684,7 +687,7 @@ mod bench {
         // 40425 docs
         docs[..].shuffle(&mut thread_rng());
 
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         for doc in docs {
             index_writer.add_document(doc);
         }

src/collector/filter_collector_wrapper.rs

@@ -0,0 +1,183 @@
+// # Custom collector example
+//
+// This example shows how you can implement your own
+// collector. As an example, we will compute a collector
+// that computes the standard deviation of a given fast field.
+//
+// Of course, you can have a look at the tantivy's built-in collectors
+// such as the `CountCollector` for more examples.
+
+// ---
+// Importing tantivy...
+use std::marker::PhantomData;
+
+use crate::collector::{Collector, SegmentCollector};
+use crate::fastfield::{FastFieldReader, FastValue};
+use crate::schema::Field;
+use crate::{Score, SegmentReader, TantivyError};
+
+/// The `FilterCollector` collector filters docs using a u64 fast field value and a predicate.
+/// Only the documents for which the predicate returned "true" will be passed on to the next collector.
+///
+/// ```rust
+/// use tantivy::collector::{TopDocs, FilterCollector};
+/// use tantivy::query::QueryParser;
+/// use tantivy::schema::{Schema, TEXT, INDEXED, FAST};
+/// use tantivy::{doc, DocAddress, Index};
+///
+/// let mut schema_builder = Schema::builder();
+/// let title = schema_builder.add_text_field("title", TEXT);
+/// let price = schema_builder.add_u64_field("price", INDEXED | FAST);
+/// let schema = schema_builder.build();
+/// let index = Index::create_in_ram(schema);
+///
+/// let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
+/// index_writer.add_document(doc!(title => "The Name of the Wind", price => 30_200u64));
+/// index_writer.add_document(doc!(title => "The Diary of Muadib", price => 29_240u64));
+/// index_writer.add_document(doc!(title => "A Dairy Cow", price => 21_240u64));
+/// index_writer.add_document(doc!(title => "The Diary of a Young Girl", price => 20_120u64));
+/// assert!(index_writer.commit().is_ok());
+///
+/// let reader = index.reader().unwrap();
+/// let searcher = reader.searcher();
+///
+/// let query_parser = QueryParser::for_index(&index, vec![title]);
+/// let query = query_parser.parse_query("diary").unwrap();
+/// let no_filter_collector = FilterCollector::new(price, &|value: u64| value > 20_120u64, TopDocs::with_limit(2));
+/// let top_docs = searcher.search(&query, &no_filter_collector).unwrap();
+///
+/// assert_eq!(top_docs.len(), 1);
+/// assert_eq!(top_docs[0].1, DocAddress(0, 1));
+///
+/// let filter_all_collector: FilterCollector<_, _, u64> = FilterCollector::new(price, &|value| value < 5u64, TopDocs::with_limit(2));
+/// let filtered_top_docs = searcher.search(&query, &filter_all_collector).unwrap();
+///
+/// assert_eq!(filtered_top_docs.len(), 0);
+/// ```
+pub struct FilterCollector<TCollector, TPredicate, TPredicateValue: FastValue>
+where
+    TPredicate: 'static + Clone,
+{
+    field: Field,
+    collector: TCollector,
+    predicate: TPredicate,
+    t_predicate_value: PhantomData<TPredicateValue>,
+}
+
+impl<TCollector, TPredicate, TPredicateValue: FastValue>
+    FilterCollector<TCollector, TPredicate, TPredicateValue>
+where
+    TCollector: Collector + Send + Sync,
+    TPredicate: Fn(TPredicateValue) -> bool + Send + Sync + Clone,
+{
+    /// Create a new FilterCollector.
+    pub fn new(
+        field: Field,
+        predicate: TPredicate,
+        collector: TCollector,
+    ) -> FilterCollector<TCollector, TPredicate, TPredicateValue> {
+        FilterCollector {
+            field,
+            predicate,
+            collector,
+            t_predicate_value: PhantomData,
+        }
+    }
+}
+
+impl<TCollector, TPredicate, TPredicateValue: FastValue> Collector
+    for FilterCollector<TCollector, TPredicate, TPredicateValue>
+where
+    TCollector: Collector + Send + Sync,
+    TPredicate: 'static + Fn(TPredicateValue) -> bool + Send + Sync + Clone,
+    TPredicateValue: FastValue,
+{
+    // That's the type of our result.
+    // Our standard deviation will be a float.
+    type Fruit = TCollector::Fruit;
+
+    type Child = FilterSegmentCollector<TCollector::Child, TPredicate, TPredicateValue>;
+
+    fn for_segment(
+        &self,
+        segment_local_id: u32,
+        segment_reader: &SegmentReader,
+    ) -> crate::Result<FilterSegmentCollector<TCollector::Child, TPredicate, TPredicateValue>> {
+        let schema = segment_reader.schema();
+        let field_entry = schema.get_field_entry(self.field);
+        if !field_entry.is_fast() {
+            return Err(TantivyError::SchemaError(format!(
+                "Field {:?} is not a fast field.",
+                field_entry.name()
+            )));
+        }
+        let requested_type = TPredicateValue::to_type();
+        let field_schema_type = field_entry.field_type().value_type();
+        if requested_type != field_schema_type {
+            return Err(TantivyError::SchemaError(format!(
+                "Field {:?} is of type {:?}!={:?}",
+                field_entry.name(),
+                requested_type,
+                field_schema_type
+            )));
+        }
+
+        let fast_field_reader = segment_reader
+            .fast_fields()
+            .typed_fast_field_reader(self.field)?;
+
+        let segment_collector = self
+            .collector
+            .for_segment(segment_local_id, segment_reader)?;
+
+        Ok(FilterSegmentCollector {
+            fast_field_reader,
+            segment_collector,
+            predicate: self.predicate.clone(),
+            t_predicate_value: PhantomData,
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.collector.requires_scoring()
+    }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<<TCollector::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<TCollector::Fruit> {
+        self.collector.merge_fruits(segment_fruits)
+    }
+}
+
+pub struct FilterSegmentCollector<TSegmentCollector, TPredicate, TPredicateValue>
+where
+    TPredicate: 'static,
+    TPredicateValue: FastValue,
+{
+    fast_field_reader: FastFieldReader<TPredicateValue>,
+    segment_collector: TSegmentCollector,
+    predicate: TPredicate,
+    t_predicate_value: PhantomData<TPredicateValue>,
+}
+
+impl<TSegmentCollector, TPredicate, TPredicateValue> SegmentCollector
+    for FilterSegmentCollector<TSegmentCollector, TPredicate, TPredicateValue>
+where
+    TSegmentCollector: SegmentCollector,
+    TPredicate: 'static + Fn(TPredicateValue) -> bool + Send + Sync,
+    TPredicateValue: FastValue,
+{
+    type Fruit = TSegmentCollector::Fruit;
+
+    fn collect(&mut self, doc: u32, score: Score) {
+        let value = self.fast_field_reader.get(doc);
+        if (self.predicate)(value) {
+            self.segment_collector.collect(doc, score)
+        }
+    }
+
+    fn harvest(self) -> <TSegmentCollector as SegmentCollector>::Fruit {
+        self.segment_collector.harvest()
+    }
+}

src/collector/histogram_collector.rs

@@ -0,0 +1,291 @@
+use crate::collector::{Collector, SegmentCollector};
+use crate::fastfield::{FastFieldReader, FastValue};
+use crate::schema::{Field, Type};
+use crate::{DocId, Score};
+use fastdivide::DividerU64;
+
+/// Histogram builds an histogram of the values of a fastfield for the
+/// collected DocSet.
+///
+/// At construction, it is given parameters that define a partition of an interval
+/// [min_val, max_val) into N buckets with the same width.
+/// The ith bucket is then defined by `[min_val + i * bucket_width, min_val + (i+1) * bucket_width)`
+///
+/// An histogram is then defined as a `Vec<u64>` of length `num_buckets`, that contains a count of
+/// documents for each value bucket.
+///
+/// See also [`HistogramCollector::new()`].
+///
+/// # Warning
+///
+/// f64 field. are not supported.
+#[derive(Clone)]
+pub struct HistogramCollector {
+    min_value: u64,
+    num_buckets: usize,
+    divider: DividerU64,
+    field: Field,
+}
+
+impl HistogramCollector {
+    /// Builds a new HistogramCollector.
+    ///
+    /// The scale/range of the histogram is not dynamic. It is required to
+    /// define it by supplying following parameter:
+    ///  - `min_value`: the minimum value that can be recorded in the histogram.
+    ///  - `bucket_width`: the length of the interval that is associated to each buckets.
+    ///  - `num_buckets`: The overall number of buckets.
+    ///
+    /// Together, this parameters define a partition of `[min_value, min_value + num_buckets * bucket_width)`
+    /// into `num_buckets` intervals of width bucket that we call `bucket`.
+    ///
+    /// # Disclaimer
+    /// This function panics if the field given is of type f64.
+    pub fn new<TFastValue: FastValue>(
+        field: Field,
+        min_value: TFastValue,
+        bucket_width: u64,
+        num_buckets: usize,
+    ) -> HistogramCollector {
+        let fast_type = TFastValue::to_type();
+        assert!(fast_type == Type::U64 || fast_type == Type::I64 || fast_type == Type::Date);
+        HistogramCollector {
+            min_value: min_value.to_u64(),
+            num_buckets,
+            field,
+            divider: DividerU64::divide_by(bucket_width),
+        }
+    }
+}
+
+struct HistogramComputer {
+    counts: Vec<u64>,
+    min_value: u64,
+    divider: DividerU64,
+}
+
+impl HistogramComputer {
+    #[inline]
+    pub(crate) fn add_value(&mut self, value: u64) {
+        if value < self.min_value {
+            return;
+        }
+        let delta = value - self.min_value;
+        let delta_u64 = delta.to_u64();
+        let bucket_id: usize = self.divider.divide(delta_u64) as usize;
+        if bucket_id < self.counts.len() {
+            self.counts[bucket_id] += 1;
+        }
+    }
+
+    fn harvest(self) -> Vec<u64> {
+        self.counts
+    }
+}
+pub struct SegmentHistogramCollector {
+    histogram_computer: HistogramComputer,
+    ff_reader: FastFieldReader<u64>,
+}
+
+impl SegmentCollector for SegmentHistogramCollector {
+    type Fruit = Vec<u64>;
+
+    fn collect(&mut self, doc: DocId, _score: Score) {
+        let value = self.ff_reader.get(doc);
+        self.histogram_computer.add_value(value);
+    }
+
+    fn harvest(self) -> Self::Fruit {
+        self.histogram_computer.harvest()
+    }
+}
+
+impl Collector for HistogramCollector {
+    type Fruit = Vec<u64>;
+    type Child = SegmentHistogramCollector;
+
+    fn for_segment(
+        &self,
+        _segment_local_id: crate::SegmentLocalId,
+        segment: &crate::SegmentReader,
+    ) -> crate::Result<Self::Child> {
+        let ff_reader = segment.fast_fields().u64_lenient(self.field)?;
+        Ok(SegmentHistogramCollector {
+            histogram_computer: HistogramComputer {
+                counts: vec![0; self.num_buckets],
+                min_value: self.min_value,
+                divider: self.divider,
+            },
+            ff_reader,
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        false
+    }
+
+    fn merge_fruits(&self, child_histograms: Vec<Vec<u64>>) -> crate::Result<Vec<u64>> {
+        Ok(add_vecs(child_histograms, self.num_buckets))
+    }
+}
+
+pub fn add_arrays_into(acc: &mut [u64], add: &[u64]) {
+    assert_eq!(acc.len(), add.len());
+    for (dest_bucket, bucket_count) in acc.iter_mut().zip(add) {
+        *dest_bucket += bucket_count;
+    }
+}
+
+fn add_vecs(mut vals_list: Vec<Vec<u64>>, len: usize) -> Vec<u64> {
+    let mut acc = vals_list.pop().unwrap_or_else(|| vec![0u64; len]);
+    assert_eq!(acc.len(), len);
+    for vals in vals_list {
+        add_arrays_into(&mut acc, &vals);
+    }
+    acc
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{add_vecs, HistogramCollector, HistogramComputer};
+    use crate::chrono::{TimeZone, Utc};
+    use crate::schema::{Schema, FAST};
+    use crate::{doc, query, Index};
+    use fastdivide::DividerU64;
+    use query::AllQuery;
+
+    #[test]
+    fn test_add_histograms_simple() {
+        assert_eq!(
+            add_vecs(vec![vec![1, 0, 3], vec![11, 2, 3], vec![0, 0, 1]], 3),
+            vec![12, 2, 7]
+        )
+    }
+
+    #[test]
+    fn test_add_histograms_empty() {
+        assert_eq!(add_vecs(vec![], 3), vec![0, 0, 0])
+    }
+
+    #[test]
+    fn test_histogram_builder_simple() {
+        // [1..3)
+        // [3..5)
+        // ..
+        // [9..11)
+        let mut histogram_computer = HistogramComputer {
+            counts: vec![0; 5],
+            min_value: 1,
+            divider: DividerU64::divide_by(2),
+        };
+        histogram_computer.add_value(1);
+        histogram_computer.add_value(7);
+        assert_eq!(histogram_computer.harvest(), vec![1, 0, 0, 1, 0]);
+    }
+
+    #[test]
+    fn test_histogram_too_low_is_ignored() {
+        let mut histogram_computer = HistogramComputer {
+            counts: vec![0; 5],
+            min_value: 2,
+            divider: DividerU64::divide_by(2),
+        };
+        histogram_computer.add_value(0);
+        assert_eq!(histogram_computer.harvest(), vec![0, 0, 0, 0, 0]);
+    }
+
+    #[test]
+    fn test_histogram_too_high_is_ignored() {
+        let mut histogram_computer = HistogramComputer {
+            counts: vec![0u64; 5],
+            min_value: 0,
+            divider: DividerU64::divide_by(2),
+        };
+        histogram_computer.add_value(10);
+        assert_eq!(histogram_computer.harvest(), vec![0, 0, 0, 0, 0]);
+    }
+    #[test]
+    fn test_no_segments() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let val_field = schema_builder.add_u64_field("val_field", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let all_query = AllQuery;
+        let histogram_collector = HistogramCollector::new(val_field, 0u64, 2, 5);
+        let histogram = searcher.search(&all_query, &histogram_collector)?;
+        assert_eq!(histogram, vec![0; 5]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_histogram_i64() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let val_field = schema_builder.add_i64_field("val_field", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut writer = index.writer_with_num_threads(1, 4_000_000)?;
+        writer.add_document(doc!(val_field=>12i64));
+        writer.add_document(doc!(val_field=>-30i64));
+        writer.add_document(doc!(val_field=>-12i64));
+        writer.add_document(doc!(val_field=>-10i64));
+        writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let all_query = AllQuery;
+        let histogram_collector = HistogramCollector::new(val_field, -20i64, 10u64, 4);
+        let histogram = searcher.search(&all_query, &histogram_collector)?;
+        assert_eq!(histogram, vec![1, 1, 0, 1]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_histogram_merge() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let val_field = schema_builder.add_i64_field("val_field", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut writer = index.writer_with_num_threads(1, 4_000_000)?;
+        writer.add_document(doc!(val_field=>12i64));
+        writer.commit()?;
+        writer.add_document(doc!(val_field=>-30i64));
+        writer.commit()?;
+        writer.add_document(doc!(val_field=>-12i64));
+        writer.commit()?;
+        writer.add_document(doc!(val_field=>-10i64));
+        writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let all_query = AllQuery;
+        let histogram_collector = HistogramCollector::new(val_field, -20i64, 10u64, 4);
+        let histogram = searcher.search(&all_query, &histogram_collector)?;
+        assert_eq!(histogram, vec![1, 1, 0, 1]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_histogram_dates() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let date_field = schema_builder.add_date_field("date_field", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut writer = index.writer_with_num_threads(1, 4_000_000)?;
+        writer.add_document(doc!(date_field=>Utc.ymd(1982, 9, 17).and_hms(0, 0,0)));
+        writer.add_document(doc!(date_field=>Utc.ymd(1986, 3, 9).and_hms(0, 0, 0)));
+        writer.add_document(doc!(date_field=>Utc.ymd(1983, 9, 27).and_hms(0, 0, 0)));
+        writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let all_query = AllQuery;
+        let week_histogram_collector = HistogramCollector::new(
+            date_field,
+            Utc.ymd(1980, 1, 1).and_hms(0, 0, 0),
+            3600 * 24 * 365, // it is just for a unit test... sorry leap years.
+            10,
+        );
+        let week_histogram = searcher.search(&all_query, &week_histogram_collector)?;
+        assert_eq!(week_histogram, vec![0, 0, 1, 1, 0, 0, 1, 0, 0, 0]);
+        Ok(())
+    }
+}

src/collector/int_facet_collector.rs

@@ -1,127 +0,0 @@
-use std::cmp::Eq;
-use std::collections::HashMap;
-use std::hash::Hash;
-
-use collector::Collector;
-use fastfield::FastFieldReader;
-use schema::Field;
-
-use DocId;
-use Result;
-use Score;
-use SegmentReader;
-use SegmentLocalId;
-
-
-/// Facet collector  for i64/u64 fast field
-pub struct IntFacetCollector<T>
-where
-    T: FastFieldReader,
-    T::ValueType: Eq + Hash,
-{
-    counters: HashMap<T::ValueType, u64>,
-    field: Field,
-    ff_reader: Option<T>,
-}
-
-
-impl<T> IntFacetCollector<T>
-where
-    T: FastFieldReader,
-    T::ValueType: Eq + Hash,
-{
-    /// Creates a new facet collector for aggregating a given field.
-    pub fn new(field: Field) -> IntFacetCollector<T> {
-        IntFacetCollector {
-            counters: HashMap::new(),
-            field: field,
-            ff_reader: None,
-        }
-    }
-}
-
-
-impl<T> Collector for IntFacetCollector<T>
-where
-    T: FastFieldReader,
-    T::ValueType: Eq + Hash,
-{
-    fn set_segment(&mut self, _: SegmentLocalId, reader: &SegmentReader) -> Result<()> {
-        self.ff_reader = Some(reader.get_fast_field_reader(self.field)?);
-        Ok(())
-    }
-
-    fn collect(&mut self, doc: DocId, _: Score) {
-        let val = self.ff_reader
-            .as_ref()
-            .expect(
-                "collect() was called before set_segment. \
-                This should never happen.",
-            )
-            .get(doc);
-        *(self.counters.entry(val).or_insert(0)) += 1;
-    }
-}
-
-
-
-#[cfg(test)]
-mod tests {
-
-    use collector::{chain, IntFacetCollector};
-    use query::QueryParser;
-    use fastfield::{I64FastFieldReader, U64FastFieldReader};
-    use schema::{self, FAST, STRING};
-    use Index;
-
-    #[test]
-    // create 10 documents, set num field value to 0 or 1 for even/odd ones
-    // make sure we have facet counters correctly filled
-    fn test_facet_collector_results() {
-
-        let mut schema_builder = schema::Schema::builder();
-        let num_field_i64 = schema_builder.add_i64_field("num_i64", FAST);
-        let num_field_u64 = schema_builder.add_u64_field("num_u64", FAST);
-        let num_field_f64 = schema_builder.add_f64_field("num_f64", FAST);
-        let text_field = schema_builder.add_text_field("text", STRING);
-        let schema = schema_builder.build();
-
-        let index = Index::create_in_ram(schema.clone());
-
-        {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            {
-                for i in 0u64..10u64 {
-                    index_writer.add_document(doc!(
-                        num_field_i64 => ((i as i64) % 3i64) as i64,
-                        num_field_u64 => (i % 2u64) as u64,
-                        num_field_f64 => (i % 4u64) as f64,
-                        text_field => "text"
-                    ));
-                }
-            }
-            assert_eq!(index_writer.commit().unwrap(), 10u64);
-        }
-
-        let searcher = index.reader().searcher();
-        let mut ffvf_i64: IntFacetCollector<I64FastFieldReader> = IntFacetCollector::new(num_field_i64);
-        let mut ffvf_u64: IntFacetCollector<U64FastFieldReader> = IntFacetCollector::new(num_field_u64);
-        let mut ffvf_f64: IntFacetCollector<F64FastFieldReader> = IntFacetCollector::new(num_field_f64);
-
-        {
-            // perform the query
-            let mut facet_collectors = chain().push(&mut ffvf_i64).push(&mut ffvf_u64).push(&mut ffvf_f64);
-            let mut query_parser = QueryParser::for_index(index, vec![text_field]);
-            let query = query_parser.parse_query("text:text").unwrap();
-            query.search(&searcher, &mut facet_collectors).unwrap();
-        }
-
-        assert_eq!(ffvf_u64.counters[&0], 5);
-        assert_eq!(ffvf_u64.counters[&1], 5);
-        assert_eq!(ffvf_i64.counters[&0], 4);
-        assert_eq!(ffvf_i64.counters[&1], 3);
-        assert_eq!(ffvf_f64.counters[&0.0], 3);
-        assert_eq!(ffvf_f64.counters[&2.0], 2);
-
-    }
-}

src/collector/mod.rs

@@ -93,6 +93,9 @@ use downcast_rs::impl_downcast;
 mod count_collector;
 pub use self::count_collector::Count;
 
+mod histogram_collector;
+pub use histogram_collector::HistogramCollector;
+
 mod multi_collector;
 pub use self::multi_collector::MultiCollector;
 
@@ -109,8 +112,15 @@ pub use self::tweak_score_top_collector::{ScoreSegmentTweaker, ScoreTweaker};
 
 mod facet_collector;
 pub use self::facet_collector::FacetCollector;
+pub use self::facet_collector::FacetCounts;
 use crate::query::Weight;
 
+mod docset_collector;
+pub use self::docset_collector::DocSetCollector;
+
+mod filter_collector_wrapper;
+pub use self::filter_collector_wrapper::FilterCollector;
+
 /// `Fruit` is the type for the result of our collection.
 /// e.g. `usize` for the `Count` collector.
 pub trait Fruit: Send + downcast_rs::Downcast {}
@@ -133,13 +143,13 @@ impl<T> Fruit for T where T: Send + downcast_rs::Downcast {}
 /// The collection logic itself is in the `SegmentCollector`.
 ///
 /// Segments are not guaranteed to be visited in any specific order.
-pub trait Collector: Sync {
+pub trait Collector: Sync + Send {
     /// `Fruit` is the type for the result of our collection.
     /// e.g. `usize` for the `Count` collector.
     type Fruit: Fruit;
 
     /// Type of the `SegmentCollector` associated to this collector.
-    type Child: SegmentCollector<Fruit = Self::Fruit>;
+    type Child: SegmentCollector;
 
     /// `set_segment` is called before beginning to enumerate
     /// on this segment.
@@ -154,7 +164,10 @@ pub trait Collector: Sync {
 
     /// Combines the fruit associated to the collection of each segments
     /// into one fruit.
-    fn merge_fruits(&self, segment_fruits: Vec<Self::Fruit>) -> crate::Result<Self::Fruit>;
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit>;
 
     /// Created a segment collector and
     fn collect_segment(
@@ -180,6 +193,61 @@ pub trait Collector: Sync {
     }
 }
 
+impl<TSegmentCollector: SegmentCollector> SegmentCollector for Option<TSegmentCollector> {
+    type Fruit = Option<TSegmentCollector::Fruit>;
+
+    fn collect(&mut self, doc: DocId, score: Score) {
+        if let Some(segment_collector) = self {
+            segment_collector.collect(doc, score);
+        }
+    }
+
+    fn harvest(self) -> Self::Fruit {
+        self.map(|segment_collector| segment_collector.harvest())
+    }
+}
+
+impl<TCollector: Collector> Collector for Option<TCollector> {
+    type Fruit = Option<TCollector::Fruit>;
+
+    type Child = Option<<TCollector as Collector>::Child>;
+
+    fn for_segment(
+        &self,
+        segment_local_id: SegmentLocalId,
+        segment: &SegmentReader,
+    ) -> crate::Result<Self::Child> {
+        Ok(if let Some(inner) = self {
+            let inner_segment_collector = inner.for_segment(segment_local_id, segment)?;
+            Some(inner_segment_collector)
+        } else {
+            None
+        })
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.as_ref()
+            .map(|inner| inner.requires_scoring())
+            .unwrap_or(false)
+    }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit> {
+        if let Some(inner) = self.as_ref() {
+            let inner_segment_fruits: Vec<_> = segment_fruits
+                .into_iter()
+                .flat_map(|fruit_opt| fruit_opt.into_iter())
+                .collect();
+            let fruit = inner.merge_fruits(inner_segment_fruits)?;
+            Ok(Some(fruit))
+        } else {
+            Ok(None)
+        }
+    }
+}
+
 /// The `SegmentCollector` is the trait in charge of defining the
 /// collect operation at the scale of the segment.
 ///
@@ -224,11 +292,11 @@ where
 
     fn merge_fruits(
         &self,
-        children: Vec<(Left::Fruit, Right::Fruit)>,
+        segment_fruits: Vec<<Self::Child as SegmentCollector>::Fruit>,
     ) -> crate::Result<(Left::Fruit, Right::Fruit)> {
         let mut left_fruits = vec![];
         let mut right_fruits = vec![];
-        for (left_fruit, right_fruit) in children {
+        for (left_fruit, right_fruit) in segment_fruits {
             left_fruits.push(left_fruit);
             right_fruits.push(right_fruit);
         }
@@ -282,7 +350,10 @@ where
         self.0.requires_scoring() || self.1.requires_scoring() || self.2.requires_scoring()
     }
 
-    fn merge_fruits(&self, children: Vec<Self::Fruit>) -> crate::Result<Self::Fruit> {
+    fn merge_fruits(
+        &self,
+        children: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit> {
         let mut one_fruits = vec![];
         let mut two_fruits = vec![];
         let mut three_fruits = vec![];
@@ -349,7 +420,10 @@ where
             || self.3.requires_scoring()
     }
 
-    fn merge_fruits(&self, children: Vec<Self::Fruit>) -> crate::Result<Self::Fruit> {
+    fn merge_fruits(
+        &self,
+        children: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit> {
         let mut one_fruits = vec![];
         let mut two_fruits = vec![];
         let mut three_fruits = vec![];

src/collector/multi_collector.rs

@@ -34,13 +34,13 @@ impl<TCollector: Collector> Collector for CollectorWrapper<TCollector> {
 
     fn merge_fruits(
         &self,
-        children: Vec<<Self as Collector>::Fruit>,
+        children: Vec<<Self::Child as SegmentCollector>::Fruit>,
     ) -> crate::Result<Box<dyn Fruit>> {
-        let typed_fruit: Vec<TCollector::Fruit> = children
+        let typed_fruit: Vec<<TCollector::Child as SegmentCollector>::Fruit> = children
             .into_iter()
             .map(|untyped_fruit| {
                 untyped_fruit
-                    .downcast::<TCollector::Fruit>()
+                    .downcast::<<TCollector::Child as SegmentCollector>::Fruit>()
                     .map(|boxed_but_typed| *boxed_but_typed)
                     .map_err(|_| {
                         TantivyError::InvalidArgument("Failed to cast child fruit.".to_string())
@@ -259,7 +259,7 @@ mod tests {
 
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text=>"abc"));
             index_writer.add_document(doc!(text=>"abc abc abc"));
             index_writer.add_document(doc!(text=>"abc abc"));

src/collector/tests.rs

@@ -3,10 +3,17 @@ use crate::core::SegmentReader;
 use crate::fastfield::BytesFastFieldReader;
 use crate::fastfield::FastFieldReader;
 use crate::schema::Field;
-use crate::DocAddress;
 use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
+use crate::{DocAddress, Document, Searcher};
+
+use crate::collector::{Count, FilterCollector, TopDocs};
+use crate::query::{AllQuery, QueryParser};
+use crate::schema::{Schema, FAST, TEXT};
+use crate::DateTime;
+use crate::{doc, Index};
+use std::str::FromStr;
 
 pub const TEST_COLLECTOR_WITH_SCORE: TestCollector = TestCollector {
     compute_score: true,
@@ -16,6 +23,54 @@ pub const TEST_COLLECTOR_WITHOUT_SCORE: TestCollector = TestCollector {
     compute_score: true,
 };
 
+#[test]
+pub fn test_filter_collector() {
+    let mut schema_builder = Schema::builder();
+    let title = schema_builder.add_text_field("title", TEXT);
+    let price = schema_builder.add_u64_field("price", FAST);
+    let date = schema_builder.add_date_field("date", FAST);
+    let schema = schema_builder.build();
+    let index = Index::create_in_ram(schema);
+
+    let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
+    index_writer.add_document(doc!(title => "The Name of the Wind", price => 30_200u64, date => DateTime::from_str("1898-04-09T00:00:00+00:00").unwrap()));
+    index_writer.add_document(doc!(title => "The Diary of Muadib", price => 29_240u64, date => DateTime::from_str("2020-04-09T00:00:00+00:00").unwrap()));
+    index_writer.add_document(doc!(title => "The Diary of Anne Frank", price => 18_240u64, date => DateTime::from_str("2019-04-20T00:00:00+00:00").unwrap()));
+    index_writer.add_document(doc!(title => "A Dairy Cow", price => 21_240u64, date => DateTime::from_str("2019-04-09T00:00:00+00:00").unwrap()));
+    index_writer.add_document(doc!(title => "The Diary of a Young Girl", price => 20_120u64, date => DateTime::from_str("2018-04-09T00:00:00+00:00").unwrap()));
+    assert!(index_writer.commit().is_ok());
+
+    let reader = index.reader().unwrap();
+    let searcher = reader.searcher();
+
+    let query_parser = QueryParser::for_index(&index, vec![title]);
+    let query = query_parser.parse_query("diary").unwrap();
+    let filter_some_collector = FilterCollector::new(
+        price,
+        &|value: u64| value > 20_120u64,
+        TopDocs::with_limit(2),
+    );
+    let top_docs = searcher.search(&query, &filter_some_collector).unwrap();
+
+    assert_eq!(top_docs.len(), 1);
+    assert_eq!(top_docs[0].1, DocAddress(0, 1));
+
+    let filter_all_collector: FilterCollector<_, _, u64> =
+        FilterCollector::new(price, &|value| value < 5u64, TopDocs::with_limit(2));
+    let filtered_top_docs = searcher.search(&query, &filter_all_collector).unwrap();
+
+    assert_eq!(filtered_top_docs.len(), 0);
+
+    fn date_filter(value: DateTime) -> bool {
+        (value - DateTime::from_str("2019-04-09T00:00:00+00:00").unwrap()).num_weeks() > 0
+    }
+
+    let filter_dates_collector = FilterCollector::new(date, &date_filter, TopDocs::with_limit(5));
+    let filtered_date_docs = searcher.search(&query, &filter_dates_collector).unwrap();
+
+    assert_eq!(filtered_date_docs.len(), 2);
+}
+
 /// Stores all of the doc ids.
 /// This collector is only used for tests.
 /// It is unusable in pr
@@ -185,12 +240,10 @@ impl Collector for BytesFastFieldTestCollector {
         _segment_local_id: u32,
         segment_reader: &SegmentReader,
     ) -> crate::Result<BytesFastFieldSegmentCollector> {
+        let reader = segment_reader.fast_fields().bytes(self.field)?;
         Ok(BytesFastFieldSegmentCollector {
             vals: Vec::new(),
-            reader: segment_reader
-                .fast_fields()
-                .bytes(self.field)
-                .expect("Field is not a bytes fast field."),
+            reader,
         })
     }
 
@@ -215,3 +268,30 @@ impl SegmentCollector for BytesFastFieldSegmentCollector {
         self.vals
     }
 }
+
+fn make_test_searcher() -> crate::Result<crate::LeasedItem<Searcher>> {
+    let schema = Schema::builder().build();
+    let index = Index::create_in_ram(schema);
+    let mut index_writer = index.writer_for_tests()?;
+    index_writer.add_document(Document::default());
+    index_writer.add_document(Document::default());
+    index_writer.commit()?;
+    Ok(index.reader()?.searcher())
+}
+
+#[test]
+fn test_option_collector_some() -> crate::Result<()> {
+    let searcher = make_test_searcher()?;
+    let counts = searcher.search(&AllQuery, &Some(Count))?;
+    assert_eq!(counts, Some(2));
+    Ok(())
+}
+
+#[test]
+fn test_option_collector_none() -> crate::Result<()> {
+    let searcher = make_test_searcher()?;
+    let none_collector: Option<Count> = None;
+    let counts = searcher.search(&AllQuery, &none_collector)?;
+    assert_eq!(counts, None);
+    Ok(())
+}

src/collector/top_collector.rs

@@ -2,9 +2,9 @@ use crate::DocAddress;
 use crate::DocId;
 use crate::SegmentLocalId;
 use crate::SegmentReader;
-use serde::export::PhantomData;
 use std::cmp::Ordering;
 use std::collections::BinaryHeap;
+use std::marker::PhantomData;
 
 /// Contains a feature (field, score, etc.) of a document along with the document address.
 ///
@@ -120,11 +120,8 @@ where
         &self,
         segment_id: SegmentLocalId,
         _: &SegmentReader,
-    ) -> crate::Result<TopSegmentCollector<F>> {
-        Ok(TopSegmentCollector::new(
-            segment_id,
-            self.limit + self.offset,
-        ))
+    ) -> TopSegmentCollector<F> {
+        TopSegmentCollector::new(segment_id, self.limit + self.offset)
     }
 
     /// Create a new TopCollector with the same limit and offset.

src/collector/top_score_collector.rs

@@ -1,6 +1,4 @@
 use super::Collector;
-use crate::collector::custom_score_top_collector::CustomScoreTopCollector;
-use crate::collector::top_collector::TopSegmentCollector;
 use crate::collector::top_collector::{ComparableDoc, TopCollector};
 use crate::collector::tweak_score_top_collector::TweakedScoreTopCollector;
 use crate::collector::{
@@ -14,8 +12,71 @@ use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
 use crate::SegmentReader;
-use std::collections::BinaryHeap;
+use crate::{collector::custom_score_top_collector::CustomScoreTopCollector, fastfield::FastValue};
+use crate::{collector::top_collector::TopSegmentCollector, TantivyError};
 use std::fmt;
+use std::{collections::BinaryHeap, marker::PhantomData};
+
+struct FastFieldConvertCollector<
+    TCollector: Collector<Fruit = Vec<(u64, DocAddress)>>,
+    TFastValue: FastValue,
+> {
+    pub collector: TCollector,
+    pub field: Field,
+    pub fast_value: std::marker::PhantomData<TFastValue>,
+}
+
+impl<TCollector, TFastValue> Collector for FastFieldConvertCollector<TCollector, TFastValue>
+where
+    TCollector: Collector<Fruit = Vec<(u64, DocAddress)>>,
+    TFastValue: FastValue,
+{
+    type Fruit = Vec<(TFastValue, DocAddress)>;
+
+    type Child = TCollector::Child;
+
+    fn for_segment(
+        &self,
+        segment_local_id: crate::SegmentLocalId,
+        segment: &SegmentReader,
+    ) -> crate::Result<Self::Child> {
+        let schema = segment.schema();
+        let field_entry = schema.get_field_entry(self.field);
+        if !field_entry.is_fast() {
+            return Err(TantivyError::SchemaError(format!(
+                "Field {:?} is not a fast field.",
+                field_entry.name()
+            )));
+        }
+        let schema_type = TFastValue::to_type();
+        let requested_type = field_entry.field_type().value_type();
+        if schema_type != requested_type {
+            return Err(TantivyError::SchemaError(format!(
+                "Field {:?} is of type {:?}!={:?}",
+                field_entry.name(),
+                schema_type,
+                requested_type
+            )));
+        }
+        self.collector.for_segment(segment_local_id, segment)
+    }
+
+    fn requires_scoring(&self) -> bool {
+        self.collector.requires_scoring()
+    }
+
+    fn merge_fruits(
+        &self,
+        segment_fruits: Vec<<Self::Child as SegmentCollector>::Fruit>,
+    ) -> crate::Result<Self::Fruit> {
+        let raw_result = self.collector.merge_fruits(segment_fruits)?;
+        let transformed_result = raw_result
+            .into_iter()
+            .map(|(score, doc_address)| (TFastValue::from_u64(score), doc_address))
+            .collect::<Vec<_>>();
+        Ok(transformed_result)
+    }
+}
 
 /// The `TopDocs` collector keeps track of the top `K` documents
 /// sorted by their score.
@@ -38,7 +99,7 @@ use std::fmt;
 /// let schema = schema_builder.build();
 /// let index = Index::create_in_ram(schema);
 ///
-/// let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+/// let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
 /// index_writer.add_document(doc!(title => "The Name of the Wind"));
 /// index_writer.add_document(doc!(title => "The Diary of Muadib"));
 /// index_writer.add_document(doc!(title => "A Dairy Cow"));
@@ -73,7 +134,7 @@ struct ScorerByFastFieldReader {
 
 impl CustomSegmentScorer<u64> for ScorerByFastFieldReader {
     fn score(&mut self, doc: DocId) -> u64 {
-        self.ff_reader.get_u64(u64::from(doc))
+        self.ff_reader.get(doc)
     }
 }
 
@@ -85,15 +146,14 @@ impl CustomScorer<u64> for ScorerByField {
     type Child = ScorerByFastFieldReader;
 
     fn segment_scorer(&self, segment_reader: &SegmentReader) -> crate::Result<Self::Child> {
-        let ff_reader = segment_reader
+        // We interpret this field as u64, regardless of its type, that way,
+        // we avoid needless conversion. Regardless of the fast field type, the
+        // mapping is monotonic, so it is sufficient to compute our top-K docs.
+        //
+        // The conversion will then happen only on the top-K docs.
+        let ff_reader: FastFieldReader<u64> = segment_reader
             .fast_fields()
-            .u64(self.field)
-            .ok_or_else(|| {
-                crate::TantivyError::SchemaError(format!(
-                    "Field requested ({:?}) is not a i64/u64 fast field.",
-                    self.field
-                ))
-            })?;
+            .typed_fast_field_reader(self.field)?;
         Ok(ScorerByFastFieldReader { ff_reader })
     }
 }
@@ -112,6 +172,8 @@ impl TopDocs {
     /// This is equivalent to `OFFSET` in MySQL or PostgreSQL and `start` in
     /// Lucene's TopDocsCollector.
     ///
+    /// # Example
+    ///
     /// ```rust
     /// use tantivy::collector::TopDocs;
     /// use tantivy::query::QueryParser;
@@ -123,7 +185,7 @@ impl TopDocs {
     /// let schema = schema_builder.build();
     /// let index = Index::create_in_ram(schema);
     ///
-    /// let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+    /// let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
     /// index_writer.add_document(doc!(title => "The Name of the Wind"));
     /// index_writer.add_document(doc!(title => "The Diary of Muadib"));
     /// index_writer.add_document(doc!(title => "A Dairy Cow"));
@@ -148,6 +210,14 @@ impl TopDocs {
 
     /// Set top-K to rank documents by a given fast field.
     ///
+    /// If the field is not a fast or does not exist, this method returns successfully (it is not aware of any schema).
+    /// An error will be returned at the moment of search.
+    ///
+    /// If the field is a FAST field but not a u64 field, search will return successfully but it will return
+    /// returns a monotonic u64-representation (ie. the order is still correct) of the requested field type.
+    ///
+    /// # Example
+    ///
     /// ```rust
     /// # use tantivy::schema::{Schema, FAST, TEXT};
     /// # use tantivy::{doc, Index, DocAddress};
@@ -161,15 +231,15 @@ impl TopDocs {
     /// #   let title = schema_builder.add_text_field("title", TEXT);
     /// #   let rating = schema_builder.add_u64_field("rating", FAST);
     /// #   let schema = schema_builder.build();
-    /// #  
+    /// #
     /// #   let index = Index::create_in_ram(schema);
-    /// #   let mut index_writer = index.writer_with_num_threads(1, 3_000_000)?;
+    /// #   let mut index_writer = index.writer_with_num_threads(1, 10_000_000)?;
     /// #   index_writer.add_document(doc!(title => "The Name of the Wind", rating => 92u64));
     /// #   index_writer.add_document(doc!(title => "The Diary of Muadib", rating => 97u64));
     /// #   index_writer.add_document(doc!(title => "A Dairy Cow", rating => 63u64));
     /// #   index_writer.add_document(doc!(title => "The Diary of a Young Girl", rating => 80u64));
     /// #   assert!(index_writer.commit().is_ok());
-    /// #   let reader = index.reader().unwrap();
+    /// #   let reader = index.reader()?;
     /// #   let query = QueryParser::for_index(&index, vec![title]).parse_query("diary")?;
     /// #   let top_docs = docs_sorted_by_rating(&reader.searcher(), &query, rating)?;
     /// #   assert_eq!(top_docs,
@@ -177,26 +247,21 @@ impl TopDocs {
     /// #                 (80u64, DocAddress(0u32, 3))]);
     /// #   Ok(())
     /// # }
-    ///
-    ///
     /// /// Searches the document matching the given query, and
     /// /// collects the top 10 documents, order by the u64-`field`
     /// /// given in argument.
-    /// ///
-    /// /// `field` is required to be a FAST field.
     /// fn docs_sorted_by_rating(searcher: &Searcher,
     ///                          query: &dyn Query,
-    ///                          sort_by_field: Field)
+    ///                          rating_field: Field)
     ///     -> tantivy::Result<Vec<(u64, DocAddress)>> {
     ///
     ///     // This is where we build our topdocs collector
     ///     //
-    ///     // Note the generics parameter that needs to match the
-    ///     // type `sort_by_field`.
-    ///     let top_docs_by_rating = TopDocs
+    ///     // Note the `rating_field` needs to be a FAST field here.
+    ///     let top_books_by_rating = TopDocs
     ///                 ::with_limit(10)
-    ///                  .order_by_u64_field(sort_by_field);
-    ///     
+    ///                  .order_by_u64_field(rating_field);
+    ///
     ///     // ... and here are our documents. Note this is a simple vec.
     ///     // The `u64` in the pair is the value of our fast field for
     ///     // each documents.
@@ -205,21 +270,105 @@ impl TopDocs {
     ///     // length of 10, or less if not enough documents matched the
     ///     // query.
     ///     let resulting_docs: Vec<(u64, DocAddress)> =
-    ///          searcher.search(query, &top_docs_by_rating)?;
-    ///     
+    ///          searcher.search(query, &top_books_by_rating)?;
+    ///
     ///     Ok(resulting_docs)
     /// }
     /// ```
     ///
-    /// # Panics
-    ///
-    /// May panic if the field requested is not a fast field.
+    /// # See also
     ///
+    /// To confortably work with `u64`s, `i64`s, `f64`s, or `date`s, please refer to
+    /// [.order_by_fast_field(...)](#method.order_by_fast_field) method.
     pub fn order_by_u64_field(
         self,
         field: Field,
     ) -> impl Collector<Fruit = Vec<(u64, DocAddress)>> {
-        self.custom_score(ScorerByField { field })
+        CustomScoreTopCollector::new(ScorerByField { field }, self.0.into_tscore())
+    }
+
+    /// Set top-K to rank documents by a given fast field.
+    ///
+    /// If the field is not a fast field, or its field type does not match the generic type, this method does not panic,
+    /// but an explicit error will be returned at the moment of collection.
+    ///
+    /// Note that this method is a generic. The requested fast field type will be often
+    /// inferred in your code by the rust compiler.
+    ///
+    /// Implementation-wise, for performance reason, tantivy will manipulate the u64 representation of your fast
+    /// field until the last moment.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # use tantivy::schema::{Schema, FAST, TEXT};
+    /// # use tantivy::{doc, Index, DocAddress};
+    /// # use tantivy::query::{Query, AllQuery};
+    /// use tantivy::Searcher;
+    /// use tantivy::collector::TopDocs;
+    /// use tantivy::schema::Field;
+    ///
+    /// # fn main() -> tantivy::Result<()> {
+    /// #   let mut schema_builder = Schema::builder();
+    /// #   let title = schema_builder.add_text_field("company", TEXT);
+    /// #   let rating = schema_builder.add_i64_field("revenue", FAST);
+    /// #   let schema = schema_builder.build();
+    /// #
+    /// #   let index = Index::create_in_ram(schema);
+    /// #   let mut index_writer = index.writer_with_num_threads(1, 10_000_000)?;
+    /// #   index_writer.add_document(doc!(title => "MadCow Inc.", rating => 92_000_000i64));
+    /// #   index_writer.add_document(doc!(title => "Zozo Cow KKK", rating => 119_000_000i64));
+    /// #   index_writer.add_document(doc!(title => "Declining Cow", rating => -63_000_000i64));
+    /// #   assert!(index_writer.commit().is_ok());
+    /// #   let reader = index.reader()?;
+    /// #   let top_docs = docs_sorted_by_revenue(&reader.searcher(), &AllQuery, rating)?;
+    /// #   assert_eq!(top_docs,
+    /// #            vec![(119_000_000i64, DocAddress(0, 1)),
+    /// #                 (92_000_000i64, DocAddress(0, 0))]);
+    /// #   Ok(())
+    /// # }
+    /// /// Searches the document matching the given query, and
+    /// /// collects the top 10 documents, order by the u64-`field`
+    /// /// given in argument.
+    /// fn docs_sorted_by_revenue(searcher: &Searcher,
+    ///                          query: &dyn Query,
+    ///                          revenue_field: Field)
+    ///     -> tantivy::Result<Vec<(i64, DocAddress)>> {
+    ///
+    ///     // This is where we build our topdocs collector
+    ///     //
+    ///     // Note the generics parameter that needs to match the
+    ///     // type `sort_by_field`. revenue_field here is a FAST i64 field.
+    ///     let top_company_by_revenue = TopDocs
+    ///                 ::with_limit(2)
+    ///                  .order_by_fast_field(revenue_field);
+    ///
+    ///     // ... and here are our documents. Note this is a simple vec.
+    ///     // The `i64` in the pair is the value of our fast field for
+    ///     // each documents.
+    ///     //
+    ///     // The vec is sorted decreasingly by `sort_by_field`, and has a
+    ///     // length of 10, or less if not enough documents matched the
+    ///     // query.
+    ///     let resulting_docs: Vec<(i64, DocAddress)> =
+    ///          searcher.search(query, &top_company_by_revenue)?;
+    ///
+    ///     Ok(resulting_docs)
+    /// }
+    /// ```
+    pub fn order_by_fast_field<TFastValue>(
+        self,
+        fast_field: Field,
+    ) -> impl Collector<Fruit = Vec<(TFastValue, DocAddress)>>
+    where
+        TFastValue: FastValue,
+    {
+        let u64_collector = self.order_by_u64_field(fast_field);
+        FastFieldConvertCollector {
+            collector: u64_collector,
+            field: fast_field,
+            fast_value: PhantomData,
+        }
     }
 
     /// Ranks the documents using a custom score.
@@ -242,7 +391,7 @@ impl TopDocs {
     ///
     /// In the following example will will tweak our ranking a bit by
     /// boosting popular products a notch.
-    ///  
+    ///
     /// In more serious application, this tweaking could involved running a
     /// learning-to-rank model over various features
     ///
@@ -264,7 +413,7 @@ impl TopDocs {
     /// fn create_index() -> tantivy::Result<Index> {
     ///   let schema = create_schema();
     ///   let index = Index::create_in_ram(schema);
-    ///   let mut index_writer = index.writer_with_num_threads(1, 3_000_000)?;
+    ///   let mut index_writer = index.writer_with_num_threads(1, 10_000_000)?;
     ///   let product_name = index.schema().get_field("product_name").unwrap();
     ///   let popularity: Field = index.schema().get_field("popularity").unwrap();
     ///   index_writer.add_document(doc!(product_name => "The Diary of Muadib", popularity => 1u64));
@@ -324,7 +473,7 @@ impl TopDocs {
     where
         TScore: 'static + Send + Sync + Clone + PartialOrd,
         TScoreSegmentTweaker: ScoreSegmentTweaker<TScore> + 'static,
-        TScoreTweaker: ScoreTweaker<TScore, Child = TScoreSegmentTweaker>,
+        TScoreTweaker: ScoreTweaker<TScore, Child = TScoreSegmentTweaker> + Send + Sync,
     {
         TweakedScoreTopCollector::new(score_tweaker, self.0.into_tscore())
     }
@@ -371,9 +520,9 @@ impl TopDocs {
     /// # fn main() -> tantivy::Result<()> {
     /// #   let schema = create_schema();
     /// #   let index = Index::create_in_ram(schema);
-    /// #   let mut index_writer = index.writer_with_num_threads(1, 3_000_000)?;
+    /// #   let mut index_writer = index.writer_with_num_threads(1, 10_000_000)?;
     /// #   let product_name = index.schema().get_field("product_name").unwrap();
-    /// #   
+    /// #
     /// let popularity: Field = index.schema().get_field("popularity").unwrap();
     /// let boosted: Field = index.schema().get_field("boosted").unwrap();
     /// #   index_writer.add_document(doc!(boosted=>1u64, product_name => "The Diary of Muadib", popularity => 1u64));
@@ -407,7 +556,7 @@ impl TopDocs {
     ///                 segment_reader.fast_fields().u64(popularity).unwrap();
     ///             let boosted_reader =
     ///                 segment_reader.fast_fields().u64(boosted).unwrap();
-    ///    
+    ///
     ///             // We can now define our actual scoring function
     ///             move |doc: DocId| {
     ///                 let popularity: u64 = popularity_reader.get(doc);
@@ -438,7 +587,7 @@ impl TopDocs {
     where
         TScore: 'static + Send + Sync + Clone + PartialOrd,
         TCustomSegmentScorer: CustomSegmentScorer<TScore> + 'static,
-        TCustomScorer: CustomScorer<TScore, Child = TCustomSegmentScorer>,
+        TCustomScorer: CustomScorer<TScore, Child = TCustomSegmentScorer> + Send + Sync,
     {
         CustomScoreTopCollector::new(custom_score, self.0.into_tscore())
     }
@@ -454,7 +603,7 @@ impl Collector for TopDocs {
         segment_local_id: SegmentLocalId,
         reader: &SegmentReader,
     ) -> crate::Result<Self::Child> {
-        let collector = self.0.for_segment(segment_local_id, reader)?;
+        let collector = self.0.for_segment(segment_local_id, reader);
         Ok(TopScoreSegmentCollector(collector))
     }
 
@@ -561,7 +710,7 @@ mod tests {
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
             index_writer.add_document(doc!(text_field=>"Hello happy tax payer."));
             index_writer.add_document(doc!(text_field=>"Droopy says hello happy tax payer"));
             index_writer.add_document(doc!(text_field=>"I like Droopy"));
@@ -578,7 +727,7 @@ mod tests {
     }
 
     #[test]
-    fn test_top_collector_not_at_capacity() {
+    fn test_top_collector_not_at_capacity_without_offset() {
         let index = make_index();
         let field = index.schema().get_field("text").unwrap();
         let query_parser = QueryParser::for_index(&index, vec![field]);
@@ -722,6 +871,94 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_top_field_collector_datetime() -> crate::Result<()> {
+        use std::str::FromStr;
+        let mut schema_builder = Schema::builder();
+        let name = schema_builder.add_text_field("name", TEXT);
+        let birthday = schema_builder.add_date_field("birthday", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        let pr_birthday = crate::DateTime::from_str("1898-04-09T00:00:00+00:00")?;
+        index_writer.add_document(doc!(
+            name => "Paul Robeson",
+            birthday => pr_birthday
+        ));
+        let mr_birthday = crate::DateTime::from_str("1947-11-08T00:00:00+00:00")?;
+        index_writer.add_document(doc!(
+            name => "Minnie Riperton",
+            birthday => mr_birthday
+        ));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let top_collector = TopDocs::with_limit(3).order_by_fast_field(birthday);
+        let top_docs: Vec<(crate::DateTime, DocAddress)> =
+            searcher.search(&AllQuery, &top_collector)?;
+        assert_eq!(
+            &top_docs[..],
+            &[
+                (mr_birthday, DocAddress(0, 1)),
+                (pr_birthday, DocAddress(0, 0)),
+            ]
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn test_top_field_collector_i64() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let city = schema_builder.add_text_field("city", TEXT);
+        let altitude = schema_builder.add_i64_field("altitude", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(
+                city => "georgetown",
+                altitude =>  -1i64,
+        ));
+        index_writer.add_document(doc!(
+            city => "tokyo",
+            altitude =>  40i64,
+        ));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let top_collector = TopDocs::with_limit(3).order_by_fast_field(altitude);
+        let top_docs: Vec<(i64, DocAddress)> = searcher.search(&AllQuery, &top_collector)?;
+        assert_eq!(
+            &top_docs[..],
+            &[(40i64, DocAddress(0, 1)), (-1i64, DocAddress(0, 0)),]
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn test_top_field_collector_f64() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let city = schema_builder.add_text_field("city", TEXT);
+        let altitude = schema_builder.add_f64_field("altitude", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(
+                city => "georgetown",
+                altitude =>  -1.0f64,
+        ));
+        index_writer.add_document(doc!(
+            city => "tokyo",
+            altitude =>  40f64,
+        ));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let top_collector = TopDocs::with_limit(3).order_by_fast_field(altitude);
+        let top_docs: Vec<(f64, DocAddress)> = searcher.search(&AllQuery, &top_collector)?;
+        assert_eq!(
+            &top_docs[..],
+            &[(40f64, DocAddress(0, 1)), (-1.0f64, DocAddress(0, 0)),]
+        );
+        Ok(())
+    }
+
     #[test]
     #[should_panic]
     fn test_field_does_not_exist() {
@@ -744,29 +981,39 @@ mod tests {
     }
 
     #[test]
-    fn test_field_not_fast_field() {
+    fn test_field_not_fast_field() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
-        let title = schema_builder.add_text_field(TITLE, TEXT);
         let size = schema_builder.add_u64_field(SIZE, STORED);
         let schema = schema_builder.build();
-        let (index, _) = index("beer", title, schema, |index_writer| {
-            index_writer.add_document(doc!(
-                title => "bottle of beer",
-                size => 12u64,
-            ));
-        });
-        let searcher = index.reader().unwrap().searcher();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(size=>1u64));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
         let segment = searcher.segment_reader(0);
         let top_collector = TopDocs::with_limit(4).order_by_u64_field(size);
-        let err = top_collector.for_segment(0, segment);
-        if let Err(crate::TantivyError::SchemaError(msg)) = err {
-            assert_eq!(
-                msg,
-                "Field requested (Field(1)) is not a i64/u64 fast field."
-            );
-        } else {
-            assert!(false);
-        }
+        let err = top_collector.for_segment(0, segment).err().unwrap();
+        assert!(matches!(err, crate::TantivyError::SchemaError(_)));
+        Ok(())
+    }
+
+    #[test]
+    fn test_field_wrong_type() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let size = schema_builder.add_u64_field(SIZE, STORED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(size=>1u64));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let segment = searcher.segment_reader(0);
+        let top_collector = TopDocs::with_limit(4).order_by_fast_field::<i64>(size);
+        let err = top_collector.for_segment(0, segment).err().unwrap();
+        assert!(
+            matches!(err, crate::TantivyError::SchemaError(msg) if msg == "Field \"size\" is not a fast field.")
+        );
+        Ok(())
     }
 
     #[test]
@@ -820,8 +1067,7 @@ mod tests {
         mut doc_adder: impl FnMut(&mut IndexWriter) -> (),
     ) -> (Index, Box<dyn Query>) {
         let index = Index::create_in_ram(schema);
-
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
         doc_adder(&mut index_writer);
         index_writer.commit().unwrap();
         let query_parser = QueryParser::for_index(&index, vec![query_field]);

src/collector/tweak_score_top_collector.rs

@@ -49,7 +49,7 @@ pub trait ScoreTweaker<TScore>: Sync {
 
 impl<TScoreTweaker, TScore> Collector for TweakedScoreTopCollector<TScoreTweaker, TScore>
 where
-    TScoreTweaker: ScoreTweaker<TScore>,
+    TScoreTweaker: ScoreTweaker<TScore> + Send + Sync,
     TScore: 'static + PartialOrd + Clone + Send + Sync,
 {
     type Fruit = Vec<(TScore, DocAddress)>;
@@ -62,9 +62,7 @@ where
         segment_reader: &SegmentReader,
     ) -> Result<Self::Child> {
         let segment_scorer = self.score_tweaker.segment_tweaker(segment_reader)?;
-        let segment_collector = self
-            .collector
-            .for_segment(segment_local_id, segment_reader)?;
+        let segment_collector = self.collector.for_segment(segment_local_id, segment_reader);
         Ok(TopTweakedScoreSegmentCollector {
             segment_collector,
             segment_scorer,

src/common/bitpacker.rs

@@ -1,6 +1,7 @@
 use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
 use std::io;
-use std::ops::Deref;
+
+use crate::directory::OwnedBytes;
 
 pub(crate) struct BitPacker {
     mini_buffer: u64,
@@ -60,20 +61,14 @@ impl BitPacker {
 }
 
 #[derive(Clone)]
-pub struct BitUnpacker<Data>
-where
-    Data: Deref<Target = [u8]>,
-{
+pub struct BitUnpacker {
     num_bits: u64,
     mask: u64,
-    data: Data,
+    data: OwnedBytes,
 }
 
-impl<Data> BitUnpacker<Data>
-where
-    Data: Deref<Target = [u8]>,
-{
-    pub fn new(data: Data, num_bits: u8) -> BitUnpacker<Data> {
+impl BitUnpacker {
+    pub fn new(data: OwnedBytes, num_bits: u8) -> BitUnpacker {
         let mask: u64 = if num_bits == 64 {
             !0u64
         } else {
@@ -90,7 +85,7 @@ where
         if self.num_bits == 0 {
             return 0u64;
         }
-        let data: &[u8] = &*self.data;
+        let data: &[u8] = self.data.as_slice();
         let num_bits = self.num_bits;
         let mask = self.mask;
         let addr_in_bits = idx * num_bits;
@@ -109,8 +104,9 @@ where
 #[cfg(test)]
 mod test {
     use super::{BitPacker, BitUnpacker};
+    use crate::directory::OwnedBytes;
 
-    fn create_fastfield_bitpacker(len: usize, num_bits: u8) -> (BitUnpacker<Vec<u8>>, Vec<u64>) {
+    fn create_fastfield_bitpacker(len: usize, num_bits: u8) -> (BitUnpacker, Vec<u64>) {
         let mut data = Vec::new();
         let mut bitpacker = BitPacker::new();
         let max_val: u64 = (1u64 << num_bits as u64) - 1u64;
@@ -122,7 +118,7 @@ mod test {
         }
         bitpacker.close(&mut data).unwrap();
         assert_eq!(data.len(), ((num_bits as usize) * len + 7) / 8 + 7);
-        let bitunpacker = BitUnpacker::new(data, num_bits);
+        let bitunpacker = BitUnpacker::new(OwnedBytes::new(data), num_bits);
         (bitunpacker, vals)
     }
 

src/common/composite_file.rs

@@ -1,14 +1,17 @@
 use crate::common::BinarySerializable;
 use crate::common::CountingWriter;
 use crate::common::VInt;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{TerminatingWrite, WritePtr};
 use crate::schema::Field;
 use crate::space_usage::FieldUsage;
 use crate::space_usage::PerFieldSpaceUsage;
 use std::collections::HashMap;
-use std::io::Write;
-use std::io::{self, Read};
+use std::io::{self, Read, Write};
+use std::iter::ExactSizeIterator;
+use std::ops::Range;
+
+use super::HasLen;
 
 #[derive(Eq, PartialEq, Hash, Copy, Ord, PartialOrd, Clone, Debug)]
 pub struct FileAddr {
@@ -103,25 +106,26 @@ impl<W: TerminatingWrite + Write> CompositeWrite<W> {
 /// for each field.
 #[derive(Clone)]
 pub struct CompositeFile {
-    data: ReadOnlySource,
-    offsets_index: HashMap<FileAddr, (usize, usize)>,
+    data: FileSlice,
+    offsets_index: HashMap<FileAddr, Range<usize>>,
 }
 
 impl CompositeFile {
     /// Opens a composite file stored in a given
-    /// `ReadOnlySource`.
-    pub fn open(data: &ReadOnlySource) -> io::Result<CompositeFile> {
+    /// `FileSlice`.
+    pub fn open(data: &FileSlice) -> io::Result<CompositeFile> {
         let end = data.len();
-        let footer_len_data = data.slice_from(end - 4);
+        let footer_len_data = data.slice_from(end - 4).read_bytes()?;
         let footer_len = u32::deserialize(&mut footer_len_data.as_slice())? as usize;
         let footer_start = end - 4 - footer_len;
-        let footer_data = data.slice(footer_start, footer_start + footer_len);
+        let footer_data = data
+            .slice(footer_start..footer_start + footer_len)
+            .read_bytes()?;
         let mut footer_buffer = footer_data.as_slice();
         let num_fields = VInt::deserialize(&mut footer_buffer)?.0 as usize;
 
         let mut file_addrs = vec![];
         let mut offsets = vec![];
-
         let mut field_index = HashMap::new();
 
         let mut offset = 0;
@@ -136,7 +140,7 @@ impl CompositeFile {
             let file_addr = file_addrs[i];
             let start_offset = offsets[i];
             let end_offset = offsets[i + 1];
-            field_index.insert(file_addr, (start_offset, end_offset));
+            field_index.insert(file_addr, start_offset..end_offset);
         }
 
         Ok(CompositeFile {
@@ -150,31 +154,31 @@ impl CompositeFile {
     pub fn empty() -> CompositeFile {
         CompositeFile {
             offsets_index: HashMap::new(),
-            data: ReadOnlySource::empty(),
+            data: FileSlice::empty(),
         }
     }
 
-    /// Returns the `ReadOnlySource` associated
+    /// Returns the `FileSlice` associated
     /// to a given `Field` and stored in a `CompositeFile`.
-    pub fn open_read(&self, field: Field) -> Option<ReadOnlySource> {
+    pub fn open_read(&self, field: Field) -> Option<FileSlice> {
         self.open_read_with_idx(field, 0)
     }
 
-    /// Returns the `ReadOnlySource` associated
+    /// Returns the `FileSlice` associated
     /// to a given `Field` and stored in a `CompositeFile`.
-    pub fn open_read_with_idx(&self, field: Field, idx: usize) -> Option<ReadOnlySource> {
+    pub fn open_read_with_idx(&self, field: Field, idx: usize) -> Option<FileSlice> {
         self.offsets_index
             .get(&FileAddr { field, idx })
-            .map(|&(from, to)| self.data.slice(from, to))
+            .map(|byte_range| self.data.slice(byte_range.clone()))
     }
 
     pub fn space_usage(&self) -> PerFieldSpaceUsage {
         let mut fields = HashMap::new();
-        for (&field_addr, &(start, end)) in self.offsets_index.iter() {
+        for (&field_addr, byte_range) in &self.offsets_index {
             fields
                 .entry(field_addr.field)
                 .or_insert_with(|| FieldUsage::empty(field_addr.field))
-                .add_field_idx(field_addr.idx, end - start);
+                .add_field_idx(field_addr.idx, byte_range.len());
         }
         PerFieldSpaceUsage::new(fields)
     }
@@ -192,46 +196,44 @@ mod test {
     use std::path::Path;
 
     #[test]
-    fn test_composite_file() {
+    fn test_composite_file() -> crate::Result<()> {
         let path = Path::new("test_path");
-        let mut directory = RAMDirectory::create();
+        let directory = RAMDirectory::create();
         {
             let w = directory.open_write(path).unwrap();
             let mut composite_write = CompositeWrite::wrap(w);
-            {
-                let mut write_0 = composite_write.for_field(Field::from_field_id(0u32));
-                VInt(32431123u64).serialize(&mut write_0).unwrap();
-                write_0.flush().unwrap();
-            }
-
-            {
-                let mut write_4 = composite_write.for_field(Field::from_field_id(4u32));
-                VInt(2).serialize(&mut write_4).unwrap();
-                write_4.flush().unwrap();
-            }
-            composite_write.close().unwrap();
+            let mut write_0 = composite_write.for_field(Field::from_field_id(0u32));
+            VInt(32431123u64).serialize(&mut write_0)?;
+            write_0.flush()?;
+            let mut write_4 = composite_write.for_field(Field::from_field_id(4u32));
+            VInt(2).serialize(&mut write_4)?;
+            write_4.flush()?;
+            composite_write.close()?;
         }
         {
-            let r = directory.open_read(path).unwrap();
-            let composite_file = CompositeFile::open(&r).unwrap();
+            let r = directory.open_read(path)?;
+            let composite_file = CompositeFile::open(&r)?;
             {
                 let file0 = composite_file
                     .open_read(Field::from_field_id(0u32))
-                    .unwrap();
+                    .unwrap()
+                    .read_bytes()?;
                 let mut file0_buf = file0.as_slice();
-                let payload_0 = VInt::deserialize(&mut file0_buf).unwrap().0;
+                let payload_0 = VInt::deserialize(&mut file0_buf)?.0;
                 assert_eq!(file0_buf.len(), 0);
                 assert_eq!(payload_0, 32431123u64);
             }
             {
                 let file4 = composite_file
                     .open_read(Field::from_field_id(4u32))
-                    .unwrap();
+                    .unwrap()
+                    .read_bytes()?;
                 let mut file4_buf = file4.as_slice();
-                let payload_4 = VInt::deserialize(&mut file4_buf).unwrap().0;
+                let payload_4 = VInt::deserialize(&mut file4_buf)?.0;
                 assert_eq!(file4_buf.len(), 0);
                 assert_eq!(payload_4, 2u64);
             }
         }
+        Ok(())
     }
 }

src/common/counting_writer.rs

@@ -20,9 +20,10 @@ impl<W: Write> CountingWriter<W> {
         self.written_bytes
     }
 
-    pub fn finish(mut self) -> io::Result<(W, u64)> {
-        self.flush()?;
-        Ok((self.underlying, self.written_bytes))
+    /// Returns the underlying write object.
+    /// Note that this method does not trigger any flushing.
+    pub fn finish(self) -> W {
+        self.underlying
     }
 }
 
@@ -46,7 +47,6 @@ impl<W: Write> Write for CountingWriter<W> {
 
 impl<W: TerminatingWrite> TerminatingWrite for CountingWriter<W> {
     fn terminate_ref(&mut self, token: AntiCallToken) -> io::Result<()> {
-        self.flush()?;
         self.underlying.terminate_ref(token)
     }
 }
@@ -63,8 +63,9 @@ mod test {
         let mut counting_writer = CountingWriter::wrap(buffer);
         let bytes = (0u8..10u8).collect::<Vec<u8>>();
         counting_writer.write_all(&bytes).unwrap();
-        let (w, len): (Vec<u8>, u64) = counting_writer.finish().unwrap();
+        let len = counting_writer.written_bytes();
+        let buffer_restituted: Vec<u8> = counting_writer.finish();
         assert_eq!(len, 10u64);
-        assert_eq!(w.len(), 10);
+        assert_eq!(buffer_restituted.len(), 10);
     }
 }

src/common/mod.rs

@@ -66,10 +66,6 @@ pub(crate) fn compute_num_bits(n: u64) -> u8 {
     }
 }
 
-pub(crate) fn is_power_of_2(n: usize) -> bool {
-    (n > 0) && (n & (n - 1) == 0)
-}
-
 /// Has length trait
 pub trait HasLen {
     /// Return length
@@ -119,11 +115,16 @@ pub fn u64_to_i64(val: u64) -> i64 {
 /// For simplicity, tantivy internally handles `f64` as `u64`.
 /// The mapping is defined by this function.
 ///
-/// Maps `f64` to `u64` so that lexical order is preserved.
+/// Maps `f64` to `u64` in a monotonic manner, so that bytes lexical order is preserved.
 ///
 /// This is more suited than simply casting (`val as u64`)
 /// which would truncate the result
 ///
+/// # Reference
+///
+/// Daniel Lemire's [blog post](https://lemire.me/blog/2020/12/14/converting-floating-point-numbers-to-integers-while-preserving-order/)
+/// explains the mapping in a clear manner.
+///
 /// # See also
 /// The [reverse mapping is `u64_to_f64`](./fn.u64_to_f64.html).
 #[inline(always)]
@@ -152,6 +153,7 @@ pub(crate) mod test {
     pub use super::minmax;
     pub use super::serialize::test::fixed_size_test;
     use super::{compute_num_bits, f64_to_u64, i64_to_u64, u64_to_f64, u64_to_i64};
+    use proptest::prelude::*;
     use std::f64;
 
     fn test_i64_converter_helper(val: i64) {
@@ -162,6 +164,15 @@ pub(crate) mod test {
         assert_eq!(u64_to_f64(f64_to_u64(val)), val);
     }
 
+    proptest! {
+        #[test]
+        fn test_f64_converter_monotonicity_proptest((left, right) in (proptest::num::f64::NORMAL, proptest::num::f64::NORMAL)) {
+            let left_u64 = f64_to_u64(left);
+            let right_u64 = f64_to_u64(right);
+            assert_eq!(left_u64 < right_u64,  left < right);
+        }
+    }
+
     #[test]
     fn test_i64_converter() {
         assert_eq!(i64_to_u64(i64::min_value()), u64::min_value());

src/core/index.rs

@@ -5,6 +5,7 @@ use crate::core::SegmentId;
 use crate::core::SegmentMeta;
 use crate::core::SegmentMetaInventory;
 use crate::core::META_FILEPATH;
+use crate::directory::error::OpenReadError;
 use crate::directory::ManagedDirectory;
 #[cfg(feature = "mmap")]
 use crate::directory::MmapDirectory;
@@ -21,7 +22,6 @@ use crate::schema::FieldType;
 use crate::schema::Schema;
 use crate::tokenizer::{TextAnalyzer, TokenizerManager};
 use crate::IndexWriter;
-use std::borrow::BorrowMut;
 use std::collections::HashSet;
 use std::fmt;
 
@@ -35,12 +35,21 @@ fn load_metas(
     inventory: &SegmentMetaInventory,
 ) -> crate::Result<IndexMeta> {
     let meta_data = directory.atomic_read(&META_FILEPATH)?;
-    let meta_string = String::from_utf8_lossy(&meta_data);
+    let meta_string = String::from_utf8(meta_data).map_err(|_utf8_err| {
+        error!("Meta data is not valid utf8.");
+        DataCorruption::new(
+            META_FILEPATH.to_path_buf(),
+            "Meta file does not contain valid utf8 file.".to_string(),
+        )
+    })?;
     IndexMeta::deserialize(&meta_string, &inventory)
         .map_err(|e| {
             DataCorruption::new(
                 META_FILEPATH.to_path_buf(),
-                format!("Meta file cannot be deserialized. {:?}.", e),
+                format!(
+                    "Meta file cannot be deserialized. {:?}. Content: {:?}",
+                    e, meta_string
+                ),
             )
         })
         .map_err(From::from)
@@ -57,8 +66,10 @@ pub struct Index {
 }
 
 impl Index {
-    /// Examines the director to see if it contains an index
-    pub fn exists<Dir: Directory>(dir: &Dir) -> bool {
+    /// Examines the directory to see if it contains an index.
+    ///
+    /// Effectively, it only checks for the presence of the `meta.json` file.
+    pub fn exists<Dir: Directory>(dir: &Dir) -> Result<bool, OpenReadError> {
         dir.exists(&META_FILEPATH)
     }
 
@@ -105,7 +116,7 @@ impl Index {
         schema: Schema,
     ) -> crate::Result<Index> {
         let mmap_directory = MmapDirectory::open(directory_path)?;
-        if Index::exists(&mmap_directory) {
+        if Index::exists(&mmap_directory)? {
             return Err(TantivyError::IndexAlreadyExists);
         }
         Index::create(mmap_directory, schema)
@@ -113,7 +124,7 @@ impl Index {
 
     /// Opens or creates a new index in the provided directory
     pub fn open_or_create<Dir: Directory>(dir: Dir, schema: Schema) -> crate::Result<Index> {
-        if !Index::exists(&dir) {
+        if !Index::exists(&dir)? {
             return Index::create(dir, schema);
         }
         let index = Index::open(dir)?;
@@ -140,7 +151,9 @@ impl Index {
         Index::create(mmap_directory, schema)
     }
 
-    /// Creates a new index given an implementation of the trait `Directory`
+    /// Creates a new index given an implementation of the trait `Directory`.
+    ///
+    /// If a directory previously existed, it will be erased.
     pub fn create<Dir: Directory>(dir: Dir, schema: Schema) -> crate::Result<Index> {
         let directory = ManagedDirectory::wrap(dir)?;
         Index::from_directory(directory, schema)
@@ -149,10 +162,11 @@ impl Index {
     /// Create a new index from a directory.
     ///
     /// This will overwrite existing meta.json
-    fn from_directory(mut directory: ManagedDirectory, schema: Schema) -> crate::Result<Index> {
-        save_new_metas(schema.clone(), directory.borrow_mut())?;
+    fn from_directory(directory: ManagedDirectory, schema: Schema) -> crate::Result<Index> {
+        save_new_metas(schema.clone(), &directory)?;
         let metas = IndexMeta::with_schema(schema);
-        Index::create_from_metas(directory, &metas, SegmentMetaInventory::default())
+        let index = Index::create_from_metas(directory, &metas, SegmentMetaInventory::default());
+        Ok(index)
     }
 
     /// Creates a new index given a directory and an `IndexMeta`.
@@ -160,15 +174,15 @@ impl Index {
         directory: ManagedDirectory,
         metas: &IndexMeta,
         inventory: SegmentMetaInventory,
-    ) -> crate::Result<Index> {
+    ) -> Index {
         let schema = metas.schema.clone();
-        Ok(Index {
+        Index {
             directory,
             schema,
             tokenizers: TokenizerManager::default(),
             executor: Arc::new(Executor::single_thread()),
             inventory,
-        })
+        }
     }
 
     /// Accessor for the tokenizer manager.
@@ -243,7 +257,8 @@ impl Index {
         let directory = ManagedDirectory::wrap(directory)?;
         let inventory = SegmentMetaInventory::default();
         let metas = load_metas(&directory, &inventory)?;
-        Index::create_from_metas(directory, &metas, inventory)
+        let index = Index::create_from_metas(directory, &metas, inventory);
+        Ok(index)
     }
 
     /// Reads the index meta file from the directory.
@@ -300,6 +315,15 @@ impl Index {
         )
     }
 
+    /// Helper to create an index writer for tests.
+    ///
+    /// That index writer only simply has a single thread and a heap of 5 MB.
+    /// Using a single thread gives us a deterministic allocation of DocId.
+    #[cfg(test)]
+    pub fn writer_for_tests(&self) -> crate::Result<IndexWriter> {
+        self.writer_with_num_threads(1, 10_000_000)
+    }
+
     /// Creates a multithreaded writer
     ///
     /// Tantivy will automatically define the number of threads to use.
@@ -387,7 +411,7 @@ impl fmt::Debug for Index {
 
 #[cfg(test)]
 mod tests {
-    use crate::directory::RAMDirectory;
+    use crate::directory::{RAMDirectory, WatchCallback};
     use crate::schema::Field;
     use crate::schema::{Schema, INDEXED, TEXT};
     use crate::IndexReader;
@@ -411,24 +435,24 @@ mod tests {
     #[test]
     fn test_index_exists() {
         let directory = RAMDirectory::create();
-        assert!(!Index::exists(&directory));
+        assert!(!Index::exists(&directory).unwrap());
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
     }
 
     #[test]
     fn open_or_create_should_create() {
         let directory = RAMDirectory::create();
-        assert!(!Index::exists(&directory));
+        assert!(!Index::exists(&directory).unwrap());
         assert!(Index::open_or_create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
     }
 
     #[test]
     fn open_or_create_should_open() {
         let directory = RAMDirectory::create();
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
         assert!(Index::open_or_create(directory, throw_away_schema()).is_ok());
     }
 
@@ -436,7 +460,7 @@ mod tests {
     fn create_should_wipeoff_existing() {
         let directory = RAMDirectory::create();
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
         assert!(Index::create(directory.clone(), Schema::builder().build()).is_ok());
     }
 
@@ -444,7 +468,7 @@ mod tests {
     fn open_or_create_exists_but_schema_does_not_match() {
         let directory = RAMDirectory::create();
         assert!(Index::create(directory.clone(), throw_away_schema()).is_ok());
-        assert!(Index::exists(&directory));
+        assert!(Index::exists(&directory).unwrap());
         assert!(Index::open_or_create(directory.clone(), throw_away_schema()).is_ok());
         let err = Index::open_or_create(directory, Schema::builder().build());
         assert_eq!(
@@ -498,28 +522,28 @@ mod tests {
         }
 
         #[test]
-        fn test_index_manual_policy_mmap() {
+        fn test_index_manual_policy_mmap() -> crate::Result<()> {
             let schema = throw_away_schema();
             let field = schema.get_field("num_likes").unwrap();
-            let mut index = Index::create_from_tempdir(schema).unwrap();
-            let mut writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            writer.commit().unwrap();
+            let mut index = Index::create_from_tempdir(schema)?;
+            let mut writer = index.writer_for_tests()?;
+            writer.commit()?;
             let reader = index
                 .reader_builder()
                 .reload_policy(ReloadPolicy::Manual)
-                .try_into()
-                .unwrap();
+                .try_into()?;
             assert_eq!(reader.searcher().num_docs(), 0);
             writer.add_document(doc!(field=>1u64));
             let (sender, receiver) = crossbeam::channel::unbounded();
-            let _handle = index.directory_mut().watch(Box::new(move || {
+            let _handle = index.directory_mut().watch(WatchCallback::new(move || {
                 let _ = sender.send(());
             }));
-            writer.commit().unwrap();
+            writer.commit()?;
             assert!(receiver.recv().is_ok());
             assert_eq!(reader.searcher().num_docs(), 0);
-            reader.reload().unwrap();
+            reader.reload()?;
             assert_eq!(reader.searcher().num_docs(), 1);
+            Ok(())
         }
 
         #[test]
@@ -542,10 +566,12 @@ mod tests {
     fn test_index_on_commit_reload_policy_aux(field: Field, index: &Index, reader: &IndexReader) {
         let mut reader_index = reader.index();
         let (sender, receiver) = crossbeam::channel::unbounded();
-        let _watch_handle = reader_index.directory_mut().watch(Box::new(move || {
-            let _ = sender.send(());
-        }));
-        let mut writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let _watch_handle = reader_index
+            .directory_mut()
+            .watch(WatchCallback::new(move || {
+                let _ = sender.send(());
+            }));
+        let mut writer = index.writer_for_tests().unwrap();
         assert_eq!(reader.searcher().num_docs(), 0);
         writer.add_document(doc!(field=>1u64));
         writer.commit().unwrap();
@@ -583,7 +609,7 @@ mod tests {
             writer.add_document(doc!(field => i));
         }
         let (sender, receiver) = crossbeam::channel::unbounded();
-        let _handle = directory.watch(Box::new(move || {
+        let _handle = directory.watch(WatchCallback::new(move || {
             let _ = sender.send(());
         }));
         writer.commit().unwrap();

src/core/inverted_index_reader.rs

@@ -1,9 +1,10 @@
+use std::io;
+
 use crate::common::BinarySerializable;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::positions::PositionReader;
 use crate::postings::TermInfo;
 use crate::postings::{BlockSegmentPostings, SegmentPostings};
-use crate::schema::FieldType;
 use crate::schema::IndexRecordOption;
 use crate::schema::Term;
 use crate::termdict::TermDictionary;
@@ -15,7 +16,7 @@ use crate::termdict::TermDictionary;
 ///
 /// It is safe to delete the segment associated to
 /// an `InvertedIndexReader`. As long as it is open,
-/// the `ReadOnlySource` it is relying on should
+/// the `FileSlice` it is relying on should
 /// stay available.
 ///
 ///
@@ -23,9 +24,9 @@ use crate::termdict::TermDictionary;
 /// the `SegmentReader`'s [`.inverted_index(...)`] method
 pub struct InvertedIndexReader {
     termdict: TermDictionary,
-    postings_source: ReadOnlySource,
-    positions_source: ReadOnlySource,
-    positions_idx_source: ReadOnlySource,
+    postings_file_slice: FileSlice,
+    positions_file_slice: FileSlice,
+    positions_idx_file_slice: FileSlice,
     record_option: IndexRecordOption,
     total_num_tokens: u64,
 }
@@ -34,42 +35,38 @@ impl InvertedIndexReader {
     #[cfg_attr(feature = "cargo-clippy", allow(clippy::needless_pass_by_value))] // for symmetry
     pub(crate) fn new(
         termdict: TermDictionary,
-        postings_source: ReadOnlySource,
-        positions_source: ReadOnlySource,
-        positions_idx_source: ReadOnlySource,
+        postings_file_slice: FileSlice,
+        positions_file_slice: FileSlice,
+        positions_idx_file_slice: FileSlice,
         record_option: IndexRecordOption,
-    ) -> InvertedIndexReader {
-        let total_num_tokens_data = postings_source.slice(0, 8);
-        let mut total_num_tokens_cursor = total_num_tokens_data.as_slice();
-        let total_num_tokens = u64::deserialize(&mut total_num_tokens_cursor).unwrap_or(0u64);
-        InvertedIndexReader {
+    ) -> io::Result<InvertedIndexReader> {
+        let (total_num_tokens_slice, postings_body) = postings_file_slice.split(8);
+        let total_num_tokens = u64::deserialize(&mut total_num_tokens_slice.read_bytes()?)?;
+        Ok(InvertedIndexReader {
             termdict,
-            postings_source: postings_source.slice_from(8),
-            positions_source,
-            positions_idx_source,
+            postings_file_slice: postings_body,
+            positions_file_slice,
+            positions_idx_file_slice,
             record_option,
             total_num_tokens,
-        }
+        })
     }
 
     /// Creates an empty `InvertedIndexReader` object, which
     /// contains no terms at all.
-    pub fn empty(field_type: &FieldType) -> InvertedIndexReader {
-        let record_option = field_type
-            .get_index_record_option()
-            .unwrap_or(IndexRecordOption::Basic);
+    pub fn empty(record_option: IndexRecordOption) -> InvertedIndexReader {
         InvertedIndexReader {
             termdict: TermDictionary::empty(),
-            postings_source: ReadOnlySource::empty(),
-            positions_source: ReadOnlySource::empty(),
-            positions_idx_source: ReadOnlySource::empty(),
+            postings_file_slice: FileSlice::empty(),
+            positions_file_slice: FileSlice::empty(),
+            positions_idx_file_slice: FileSlice::empty(),
             record_option,
             total_num_tokens: 0u64,
         }
     }
 
     /// Returns the term info associated with the term.
-    pub fn get_term_info(&self, term: &Term) -> Option<TermInfo> {
+    pub fn get_term_info(&self, term: &Term) -> io::Result<Option<TermInfo>> {
         self.termdict.get(term.value_bytes())
     }
 
@@ -92,11 +89,12 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         block_postings: &mut BlockSegmentPostings,
-    ) {
-        let offset = term_info.postings_offset as usize;
-        let end_source = self.postings_source.len();
-        let postings_slice = self.postings_source.slice(offset, end_source);
-        block_postings.reset(term_info.doc_freq, postings_slice);
+    ) -> io::Result<()> {
+        let postings_slice = self
+            .postings_file_slice
+            .slice(term_info.postings_range.clone());
+        block_postings.reset(term_info.doc_freq, postings_slice.read_bytes()?);
+        Ok(())
     }
 
     /// Returns a block postings given a `Term`.
@@ -107,9 +105,10 @@ impl InvertedIndexReader {
         &self,
         term: &Term,
         option: IndexRecordOption,
-    ) -> Option<BlockSegmentPostings> {
-        self.get_term_info(term)
+    ) -> io::Result<Option<BlockSegmentPostings>> {
+        self.get_term_info(term)?
             .map(move |term_info| self.read_block_postings_from_terminfo(&term_info, option))
+            .transpose()
     }
 
     /// Returns a block postings given a `term_info`.
@@ -120,10 +119,11 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         requested_option: IndexRecordOption,
-    ) -> BlockSegmentPostings {
-        let offset = term_info.postings_offset as usize;
-        let postings_data = self.postings_source.slice_from(offset);
-        BlockSegmentPostings::from_data(
+    ) -> io::Result<BlockSegmentPostings> {
+        let postings_data = self
+            .postings_file_slice
+            .slice(term_info.postings_range.clone());
+        BlockSegmentPostings::open(
             term_info.doc_freq,
             postings_data,
             self.record_option,
@@ -139,20 +139,23 @@ impl InvertedIndexReader {
         &self,
         term_info: &TermInfo,
         option: IndexRecordOption,
-    ) -> SegmentPostings {
-        let block_postings = self.read_block_postings_from_terminfo(term_info, option);
+    ) -> io::Result<SegmentPostings> {
+        let block_postings = self.read_block_postings_from_terminfo(term_info, option)?;
         let position_stream = {
             if option.has_positions() {
-                let position_reader = self.positions_source.clone();
-                let skip_reader = self.positions_idx_source.clone();
+                let position_reader = self.positions_file_slice.clone();
+                let skip_reader = self.positions_idx_file_slice.clone();
                 let position_reader =
-                    PositionReader::new(position_reader, skip_reader, term_info.positions_idx);
+                    PositionReader::new(position_reader, skip_reader, term_info.positions_idx)?;
                 Some(position_reader)
             } else {
                 None
             }
         };
-        SegmentPostings::from_block_postings(block_postings, position_stream)
+        Ok(SegmentPostings::from_block_postings(
+            block_postings,
+            position_stream,
+        ))
     }
 
     /// Returns the total number of tokens recorded for all documents
@@ -171,24 +174,31 @@ impl InvertedIndexReader {
     /// For instance, requesting `IndexRecordOption::Freq` for a
     /// `TextIndexingOptions` that does not index position will return a `SegmentPostings`
     /// with `DocId`s and frequencies.
-    pub fn read_postings(&self, term: &Term, option: IndexRecordOption) -> Option<SegmentPostings> {
-        self.get_term_info(term)
+    pub fn read_postings(
+        &self,
+        term: &Term,
+        option: IndexRecordOption,
+    ) -> io::Result<Option<SegmentPostings>> {
+        self.get_term_info(term)?
             .map(move |term_info| self.read_postings_from_terminfo(&term_info, option))
+            .transpose()
     }
 
     pub(crate) fn read_postings_no_deletes(
         &self,
         term: &Term,
         option: IndexRecordOption,
-    ) -> Option<SegmentPostings> {
-        self.get_term_info(term)
+    ) -> io::Result<Option<SegmentPostings>> {
+        self.get_term_info(term)?
             .map(|term_info| self.read_postings_from_terminfo(&term_info, option))
+            .transpose()
     }
 
     /// Returns the number of documents containing the term.
-    pub fn doc_freq(&self, term: &Term) -> u32 {
-        self.get_term_info(term)
+    pub fn doc_freq(&self, term: &Term) -> io::Result<u32> {
+        Ok(self
+            .get_term_info(term)?
             .map(|term_info| term_info.doc_freq)
-            .unwrap_or(0u32)
+            .unwrap_or(0u32))
     }
 }

src/core/searcher.rs

@@ -1,18 +1,17 @@
 use crate::collector::Collector;
 use crate::core::Executor;
-use crate::core::InvertedIndexReader;
+
 use crate::core::SegmentReader;
 use crate::query::Query;
 use crate::schema::Document;
 use crate::schema::Schema;
-use crate::schema::{Field, Term};
+use crate::schema::Term;
 use crate::space_usage::SearcherSpaceUsage;
 use crate::store::StoreReader;
-use crate::termdict::TermMerger;
 use crate::DocAddress;
 use crate::Index;
-use std::fmt;
-use std::sync::Arc;
+
+use std::{fmt, io};
 
 /// Holds a list of `SegmentReader`s ready for search.
 ///
@@ -32,17 +31,17 @@ impl Searcher {
         schema: Schema,
         index: Index,
         segment_readers: Vec<SegmentReader>,
-    ) -> Searcher {
-        let store_readers = segment_readers
+    ) -> io::Result<Searcher> {
+        let store_readers: Vec<StoreReader> = segment_readers
             .iter()
             .map(SegmentReader::get_store_reader)
-            .collect();
-        Searcher {
+            .collect::<io::Result<Vec<_>>>()?;
+        Ok(Searcher {
             schema,
             index,
             segment_readers,
             store_readers,
-        }
+        })
     }
 
     /// Returns the `Index` associated to the `Searcher`
@@ -75,13 +74,14 @@ impl Searcher {
 
     /// Return the overall number of documents containing
     /// the given term.
-    pub fn doc_freq(&self, term: &Term) -> u64 {
-        self.segment_readers
-            .iter()
-            .map(|segment_reader| {
-                u64::from(segment_reader.inverted_index(term.field()).doc_freq(term))
-            })
-            .sum::<u64>()
+    pub fn doc_freq(&self, term: &Term) -> crate::Result<u64> {
+        let mut total_doc_freq = 0;
+        for segment_reader in &self.segment_readers {
+            let inverted_index = segment_reader.inverted_index(term.field())?;
+            let doc_freq = inverted_index.doc_freq(term)?;
+            total_doc_freq += u64::from(doc_freq);
+        }
+        Ok(total_doc_freq)
     }
 
     /// Return the list of segment readers
@@ -147,44 +147,13 @@ impl Searcher {
         collector.merge_fruits(fruits)
     }
 
-    /// Return the field searcher associated to a `Field`.
-    pub fn field(&self, field: Field) -> FieldSearcher {
-        let inv_index_readers = self
-            .segment_readers
-            .iter()
-            .map(|segment_reader| segment_reader.inverted_index(field))
-            .collect::<Vec<_>>();
-        FieldSearcher::new(inv_index_readers)
-    }
-
     /// Summarize total space usage of this searcher.
-    pub fn space_usage(&self) -> SearcherSpaceUsage {
+    pub fn space_usage(&self) -> io::Result<SearcherSpaceUsage> {
         let mut space_usage = SearcherSpaceUsage::new();
-        for segment_reader in self.segment_readers.iter() {
-            space_usage.add_segment(segment_reader.space_usage());
+        for segment_reader in &self.segment_readers {
+            space_usage.add_segment(segment_reader.space_usage()?);
         }
-        space_usage
-    }
-}
-
-pub struct FieldSearcher {
-    inv_index_readers: Vec<Arc<InvertedIndexReader>>,
-}
-
-impl FieldSearcher {
-    fn new(inv_index_readers: Vec<Arc<InvertedIndexReader>>) -> FieldSearcher {
-        FieldSearcher { inv_index_readers }
-    }
-
-    /// Returns a Stream over all of the sorted unique terms of
-    /// for the given field.
-    pub fn terms(&self) -> TermMerger<'_> {
-        let term_streamers: Vec<_> = self
-            .inv_index_readers
-            .iter()
-            .map(|inverted_index| inverted_index.terms().stream())
-            .collect();
-        TermMerger::new(term_streamers)
+        Ok(space_usage)
     }
 }
 

src/core/segment.rs

@@ -4,7 +4,7 @@ use crate::core::SegmentId;
 use crate::core::SegmentMeta;
 use crate::directory::error::{OpenReadError, OpenWriteError};
 use crate::directory::Directory;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{FileSlice, WritePtr};
 use crate::indexer::segment_serializer::SegmentSerializer;
 use crate::schema::Schema;
 use crate::Opstamp;
@@ -78,10 +78,9 @@ impl Segment {
     }
 
     /// Open one of the component file for a *regular* read.
-    pub fn open_read(&self, component: SegmentComponent) -> Result<ReadOnlySource, OpenReadError> {
+    pub fn open_read(&self, component: SegmentComponent) -> Result<FileSlice, OpenReadError> {
         let path = self.relative_path(component);
-        let source = self.index.directory().open_read(&path)?;
-        Ok(source)
+        self.index.directory().open_read(&path)
     }
 
     /// Open one of the component file for *regular* write.

src/core/segment_component.rs

@@ -20,7 +20,7 @@ pub enum SegmentComponent {
     /// Dictionary associating `Term`s to `TermInfo`s which is
     /// simply an address into the `postings` file and the `positions` file.
     TERMS,
-    /// Row-oriented, LZ4-compressed storage of the documents.
+    /// Row-oriented, compressed storage of the documents.
     /// Accessing a document from the store is relatively slow, as it
     /// requires to decompress the entire block it belongs to.
     STORE,

src/core/segment_reader.rs

@@ -1,26 +1,26 @@
-use crate::common::CompositeFile;
 use crate::common::HasLen;
 use crate::core::InvertedIndexReader;
 use crate::core::Segment;
 use crate::core::SegmentComponent;
 use crate::core::SegmentId;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::fastfield::DeleteBitSet;
 use crate::fastfield::FacetReader;
 use crate::fastfield::FastFieldReaders;
 use crate::fieldnorm::{FieldNormReader, FieldNormReaders};
-use crate::schema::Field;
 use crate::schema::FieldType;
 use crate::schema::Schema;
+use crate::schema::{Field, IndexRecordOption};
 use crate::space_usage::SegmentSpaceUsage;
 use crate::store::StoreReader;
 use crate::termdict::TermDictionary;
 use crate::DocId;
+use crate::{common::CompositeFile, error::DataCorruption};
 use fail::fail_point;
-use std::collections::HashMap;
 use std::fmt;
 use std::sync::Arc;
 use std::sync::RwLock;
+use std::{collections::HashMap, io};
 
 /// Entry point to access all of the datastructures of the `Segment`
 ///
@@ -50,7 +50,7 @@ pub struct SegmentReader {
     fast_fields_readers: Arc<FastFieldReaders>,
     fieldnorm_readers: FieldNormReaders,
 
-    store_source: ReadOnlySource,
+    store_file: FileSlice,
     delete_bitset_opt: Option<DeleteBitSet>,
     schema: Schema,
 }
@@ -106,16 +106,24 @@ impl SegmentReader {
     }
 
     /// Accessor to the `FacetReader` associated to a given `Field`.
-    pub fn facet_reader(&self, field: Field) -> Option<FacetReader> {
+    pub fn facet_reader(&self, field: Field) -> crate::Result<FacetReader> {
         let field_entry = self.schema.get_field_entry(field);
-        if field_entry.field_type() != &FieldType::HierarchicalFacet {
-            return None;
+
+        match field_entry.field_type() {
+            FieldType::HierarchicalFacet(_) => {
+                let term_ords_reader = self.fast_fields().u64s(field)?;
+                let termdict = self
+                    .termdict_composite
+                    .open_read(field)
+                    .map(TermDictionary::open)
+                    .unwrap_or_else(|| Ok(TermDictionary::empty()))?;
+                Ok(FacetReader::new(term_ords_reader, termdict))
+            }
+            _ => Err(crate::TantivyError::InvalidArgument(format!(
+                "Field {:?} is not a facet field.",
+                field_entry.name()
+            ))),
         }
-        let term_ords_reader = self.fast_fields().u64s(field)?;
-        let termdict_source = self.termdict_composite.open_read(field)?;
-        let termdict = TermDictionary::from_source(&termdict_source);
-        let facet_reader = FacetReader::new(term_ords_reader, termdict);
-        Some(facet_reader)
     }
 
     /// Accessor to the segment's `Field norms`'s reader.
@@ -125,47 +133,45 @@ impl SegmentReader {
     ///
     /// They are simply stored as a fast field, serialized in
     /// the `.fieldnorm` file of the segment.
-    pub fn get_fieldnorms_reader(&self, field: Field) -> FieldNormReader {
-        if let Some(fieldnorm_reader) = self.fieldnorm_readers.get_field(field) {
-            fieldnorm_reader
-        } else {
+    pub fn get_fieldnorms_reader(&self, field: Field) -> crate::Result<FieldNormReader> {
+        self.fieldnorm_readers.get_field(field)?.ok_or_else(|| {
             let field_name = self.schema.get_field_name(field);
             let err_msg = format!(
-                "Field norm not found for field {:?}. Was it market as indexed during indexing.",
+                "Field norm not found for field {:?}. Was it marked as indexed during indexing?",
                 field_name
             );
-            panic!(err_msg);
-        }
+            crate::TantivyError::SchemaError(err_msg)
+        })
     }
 
     /// Accessor to the segment's `StoreReader`.
-    pub fn get_store_reader(&self) -> StoreReader {
-        StoreReader::from_source(self.store_source.clone())
+    pub fn get_store_reader(&self) -> io::Result<StoreReader> {
+        StoreReader::open(self.store_file.clone())
     }
 
     /// Open a new segment for reading.
     pub fn open(segment: &Segment) -> crate::Result<SegmentReader> {
-        let termdict_source = segment.open_read(SegmentComponent::TERMS)?;
-        let termdict_composite = CompositeFile::open(&termdict_source)?;
+        let termdict_file = segment.open_read(SegmentComponent::TERMS)?;
+        let termdict_composite = CompositeFile::open(&termdict_file)?;
 
-        let store_source = segment.open_read(SegmentComponent::STORE)?;
+        let store_file = segment.open_read(SegmentComponent::STORE)?;
 
         fail_point!("SegmentReader::open#middle");
 
-        let postings_source = segment.open_read(SegmentComponent::POSTINGS)?;
-        let postings_composite = CompositeFile::open(&postings_source)?;
+        let postings_file = segment.open_read(SegmentComponent::POSTINGS)?;
+        let postings_composite = CompositeFile::open(&postings_file)?;
 
         let positions_composite = {
-            if let Ok(source) = segment.open_read(SegmentComponent::POSITIONS) {
-                CompositeFile::open(&source)?
+            if let Ok(positions_file) = segment.open_read(SegmentComponent::POSITIONS) {
+                CompositeFile::open(&positions_file)?
             } else {
                 CompositeFile::empty()
             }
         };
 
         let positions_idx_composite = {
-            if let Ok(source) = segment.open_read(SegmentComponent::POSITIONSSKIP) {
-                CompositeFile::open(&source)?
+            if let Ok(positions_skip_file) = segment.open_read(SegmentComponent::POSITIONSSKIP) {
+                CompositeFile::open(&positions_skip_file)?
             } else {
                 CompositeFile::empty()
             }
@@ -176,20 +182,21 @@ impl SegmentReader {
         let fast_fields_data = segment.open_read(SegmentComponent::FASTFIELDS)?;
         let fast_fields_composite = CompositeFile::open(&fast_fields_data)?;
         let fast_field_readers =
-            Arc::new(FastFieldReaders::load_all(&schema, &fast_fields_composite)?);
+            Arc::new(FastFieldReaders::new(schema.clone(), fast_fields_composite));
 
         let fieldnorm_data = segment.open_read(SegmentComponent::FIELDNORMS)?;
         let fieldnorm_readers = FieldNormReaders::open(fieldnorm_data)?;
 
         let delete_bitset_opt = if segment.meta().has_deletes() {
             let delete_data = segment.open_read(SegmentComponent::DELETE)?;
-            Some(DeleteBitSet::open(delete_data))
+            let delete_bitset = DeleteBitSet::open(delete_data)?;
+            Some(delete_bitset)
         } else {
             None
         };
 
         Ok(SegmentReader {
-            inv_idx_reader_cache: Arc::new(RwLock::new(HashMap::new())),
+            inv_idx_reader_cache: Default::default(),
             max_doc: segment.meta().max_doc(),
             num_docs: segment.meta().num_docs(),
             termdict_composite,
@@ -197,7 +204,7 @@ impl SegmentReader {
             fast_fields_readers: fast_field_readers,
             fieldnorm_readers,
             segment_id: segment.id(),
-            store_source,
+            store_file,
             delete_bitset_opt,
             positions_composite,
             positions_idx_composite,
@@ -212,58 +219,64 @@ impl SegmentReader {
     /// The field reader is in charge of iterating through the
     /// term dictionary associated to a specific field,
     /// and opening the posting list associated to any term.
-    pub fn inverted_index(&self, field: Field) -> Arc<InvertedIndexReader> {
+    ///
+    /// If the field is marked as index, a warn is logged and an empty `InvertedIndexReader`
+    /// is returned.
+    /// Similarly if the field is marked as indexed but no term has been indexed for the given
+    /// index. an empty `InvertedIndexReader` is returned (but no warning is logged).
+    pub fn inverted_index(&self, field: Field) -> crate::Result<Arc<InvertedIndexReader>> {
         if let Some(inv_idx_reader) = self
             .inv_idx_reader_cache
             .read()
             .expect("Lock poisoned. This should never happen")
             .get(&field)
         {
-            return Arc::clone(inv_idx_reader);
+            return Ok(Arc::clone(inv_idx_reader));
         }
         let field_entry = self.schema.get_field_entry(field);
         let field_type = field_entry.field_type();
         let record_option_opt = field_type.get_index_record_option();
 
         if record_option_opt.is_none() {
-            panic!("Field {:?} does not seem indexed.", field_entry.name());
+            warn!("Field {:?} does not seem indexed.", field_entry.name());
         }
 
-        let record_option = record_option_opt.unwrap();
+        let postings_file_opt = self.postings_composite.open_read(field);
 
-        let postings_source_opt = self.postings_composite.open_read(field);
-
-        if postings_source_opt.is_none() {
+        if postings_file_opt.is_none() || record_option_opt.is_none() {
             // no documents in the segment contained this field.
             // As a result, no data is associated to the inverted index.
             //
             // Returns an empty inverted index.
-            return Arc::new(InvertedIndexReader::empty(field_type));
+            let record_option = record_option_opt.unwrap_or(IndexRecordOption::Basic);
+            return Ok(Arc::new(InvertedIndexReader::empty(record_option)));
         }
 
-        let postings_source = postings_source_opt.unwrap();
+        let record_option = record_option_opt.unwrap();
+        let postings_file = postings_file_opt.unwrap();
 
-        let termdict_source = self.termdict_composite.open_read(field).expect(
-            "Failed to open field term dictionary in composite file. Is the field indexed?",
-        );
+        let termdict_file: FileSlice = self.termdict_composite.open_read(field)
+            .ok_or_else(||
+               DataCorruption::comment_only(format!("Failed to open field {:?}'s term dictionary in the composite file. Has the schema been modified?", field_entry.name()))
+            )?;
 
-        let positions_source = self
+        let positions_file = self
             .positions_composite
             .open_read(field)
             .expect("Index corrupted. Failed to open field positions in composite file.");
 
-        let positions_idx_source = self
+        let positions_idx_file = self
             .positions_idx_composite
             .open_read(field)
             .expect("Index corrupted. Failed to open field positions in composite file.");
 
         let inv_idx_reader = Arc::new(InvertedIndexReader::new(
-            TermDictionary::from_source(&termdict_source),
-            postings_source,
-            positions_source,
-            positions_idx_source,
+            TermDictionary::open(termdict_file)?,
+            postings_file,
+            positions_file,
+            positions_idx_file,
             record_option,
-        ));
+        )?);
 
         // by releasing the lock in between, we may end up opening the inverting index
         // twice, but this is fine.
@@ -272,7 +285,7 @@ impl SegmentReader {
             .expect("Field reader cache lock poisoned. This should never happen.")
             .insert(field, Arc::clone(&inv_idx_reader));
 
-        inv_idx_reader
+        Ok(inv_idx_reader)
     }
 
     /// Returns the segment id
@@ -295,13 +308,13 @@ impl SegmentReader {
     }
 
     /// Returns an iterator that will iterate over the alive document ids
-    pub fn doc_ids_alive<'a>(&'a self) -> impl Iterator<Item = DocId> + 'a {
+    pub fn doc_ids_alive(&self) -> impl Iterator<Item = DocId> + '_ {
         (0u32..self.max_doc).filter(move |doc| !self.is_deleted(*doc))
     }
 
     /// Summarize total space usage of this segment.
-    pub fn space_usage(&self) -> SegmentSpaceUsage {
-        SegmentSpaceUsage::new(
+    pub fn space_usage(&self) -> io::Result<SegmentSpaceUsage> {
+        Ok(SegmentSpaceUsage::new(
             self.num_docs(),
             self.termdict_composite.space_usage(),
             self.postings_composite.space_usage(),
@@ -309,12 +322,12 @@ impl SegmentReader {
             self.positions_idx_composite.space_usage(),
             self.fast_fields_readers.space_usage(),
             self.fieldnorm_readers.space_usage(),
-            self.get_store_reader().space_usage(),
+            self.get_store_reader()?.space_usage(),
             self.delete_bitset_opt
                 .as_ref()
                 .map(DeleteBitSet::space_usage)
                 .unwrap_or(0),
-        )
+        ))
     }
 }
 
@@ -331,7 +344,7 @@ mod test {
     use crate::DocId;
 
     #[test]
-    fn test_alive_docs_iterator() {
+    fn test_alive_docs_iterator() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         schema_builder.add_text_field("name", TEXT | STORED);
         let schema = schema_builder.build();
@@ -339,26 +352,26 @@ mod test {
         let name = schema.get_field("name").unwrap();
 
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.add_document(doc!(name => "tantivy"));
             index_writer.add_document(doc!(name => "horse"));
             index_writer.add_document(doc!(name => "jockey"));
             index_writer.add_document(doc!(name => "cap"));
-
             // we should now have one segment with two docs
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
 
         {
-            let mut index_writer2 = index.writer(50_000_000).unwrap();
+            let mut index_writer2 = index.writer(50_000_000)?;
             index_writer2.delete_term(Term::from_field_text(name, "horse"));
             index_writer2.delete_term(Term::from_field_text(name, "cap"));
 
             // ok, now we should have a deleted doc
-            index_writer2.commit().unwrap();
+            index_writer2.commit()?;
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         let docs: Vec<DocId> = searcher.segment_reader(0).doc_ids_alive().collect();
         assert_eq!(vec![0u32, 2u32], docs);
+        Ok(())
     }
 }

src/directory/directory.rs

@@ -1,9 +1,9 @@
 use crate::directory::directory_lock::Lock;
 use crate::directory::error::LockError;
 use crate::directory::error::{DeleteError, OpenReadError, OpenWriteError};
-use crate::directory::WatchCallback;
 use crate::directory::WatchHandle;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{FileHandle, WatchCallback};
+use crate::directory::{FileSlice, WritePtr};
 use std::fmt;
 use std::io;
 use std::io::Write;
@@ -11,7 +11,6 @@ use std::marker::Send;
 use std::marker::Sync;
 use std::path::Path;
 use std::path::PathBuf;
-use std::result;
 use std::thread;
 use std::time::Duration;
 
@@ -80,7 +79,7 @@ fn try_acquire_lock(
 ) -> Result<DirectoryLock, TryAcquireLockError> {
     let mut write = directory.open_write(filepath).map_err(|e| match e {
         OpenWriteError::FileAlreadyExists(_) => TryAcquireLockError::FileExists,
-        OpenWriteError::IOError(io_error) => TryAcquireLockError::IOError(io_error.into()),
+        OpenWriteError::IOError { io_error, .. } => TryAcquireLockError::IOError(io_error),
     })?;
     write.flush().map_err(TryAcquireLockError::IOError)?;
     Ok(DirectoryLock::from(Box::new(DirectoryLockGuard {
@@ -109,37 +108,43 @@ fn retry_policy(is_blocking: bool) -> RetryPolicy {
 /// should be your default choice.
 /// - The [`RAMDirectory`](struct.RAMDirectory.html), which
 /// should be used mostly for tests.
-///
 pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
-    /// Opens a virtual file for read.
+    /// Opens a file and returns a boxed `FileHandle`.
     ///
+    /// Users of `Directory` should typically call `Directory::open_read(...)`,
+    /// while `Directory` implementor should implement `get_file_handle()`.
+    fn get_file_handle(&self, path: &Path) -> Result<Box<dyn FileHandle>, OpenReadError>;
+
     /// Once a virtual file is open, its data may not
     /// change.
     ///
     /// Specifically, subsequent writes or flushes should
-    /// have no effect on the returned `ReadOnlySource` object.
+    /// have no effect on the returned `FileSlice` object.
     ///
     /// You should only use this to read files create with [Directory::open_write].
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError>;
+    fn open_read(&self, path: &Path) -> Result<FileSlice, OpenReadError> {
+        let file_handle = self.get_file_handle(path)?;
+        Ok(FileSlice::new(file_handle))
+    }
 
     /// Removes a file
     ///
     /// Removing a file will not affect an eventual
-    /// existing ReadOnlySource pointing to it.
+    /// existing FileSlice pointing to it.
     ///
     /// Removing a nonexistent file, yields a
     /// `DeleteError::DoesNotExist`.
-    fn delete(&self, path: &Path) -> result::Result<(), DeleteError>;
+    fn delete(&self, path: &Path) -> Result<(), DeleteError>;
 
     /// Returns true iff the file exists
-    fn exists(&self, path: &Path) -> bool;
+    fn exists(&self, path: &Path) -> Result<bool, OpenReadError>;
 
     /// Opens a writer for the *virtual file* associated with
     /// a Path.
     ///
     /// Right after this call, the file should be created
     /// and any subsequent call to `open_read` for the
-    /// same path should return a `ReadOnlySource`.
+    /// same path should return a `FileSlice`.
     ///
     /// Write operations may be aggressively buffered.
     /// The client of this trait is responsible for calling flush
@@ -153,7 +158,7 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     /// was not called.
     ///
     /// The file may not previously exist.
-    fn open_write(&mut self, path: &Path) -> Result<WritePtr, OpenWriteError>;
+    fn open_write(&self, path: &Path) -> Result<WritePtr, OpenWriteError>;
 
     /// Reads the full content file that has been written using
     /// atomic_write.
@@ -169,7 +174,7 @@ pub trait Directory: DirectoryClone + fmt::Debug + Send + Sync + 'static {
     /// a partially written file.
     ///
     /// The file may or may not previously exist.
-    fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()>;
+    fn atomic_write(&self, path: &Path, data: &[u8]) -> io::Result<()>;
 
     /// Acquire a lock in the given directory.
     ///

src/directory/error.rs

@@ -1,162 +1,68 @@
 use crate::Version;
-use std::error::Error as StdError;
 use std::fmt;
 use std::io;
 use std::path::PathBuf;
 
 /// Error while trying to acquire a directory lock.
-#[derive(Debug, Fail)]
+#[derive(Debug, Error)]
 pub enum LockError {
     /// Failed to acquired a lock as it is already held by another
     /// client.
     /// - In the context of a blocking lock, this means the lock was not released within some `timeout` period.
     /// - In the context of a non-blocking lock, this means the lock was busy at the moment of the call.
-    #[fail(
-        display = "Could not acquire lock as it is already held, possibly by a different process."
-    )]
+    #[error("Could not acquire lock as it is already held, possibly by a different process.")]
     LockBusy,
     /// Trying to acquire a lock failed with an `IOError`
-    #[fail(display = "Failed to acquire the lock due to an io:Error.")]
+    #[error("Failed to acquire the lock due to an io:Error.")]
     IOError(io::Error),
 }
 
-/// General IO error with an optional path to the offending file.
-#[derive(Debug)]
-pub struct IOError {
-    path: Option<PathBuf>,
-    err: io::Error,
-}
-
-impl Into<io::Error> for IOError {
-    fn into(self) -> io::Error {
-        self.err
-    }
-}
-
-impl fmt::Display for IOError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.path {
-            Some(ref path) => write!(f, "io error occurred on path '{:?}': '{}'", path, self.err),
-            None => write!(f, "io error occurred: '{}'", self.err),
-        }
-    }
-}
-
-impl StdError for IOError {
-    fn description(&self) -> &str {
-        "io error occurred"
-    }
-
-    fn cause(&self) -> Option<&dyn StdError> {
-        Some(&self.err)
-    }
-}
-
-impl IOError {
-    pub(crate) fn with_path(path: PathBuf, err: io::Error) -> Self {
-        IOError {
-            path: Some(path),
-            err,
-        }
-    }
-}
-
-impl From<io::Error> for IOError {
-    fn from(err: io::Error) -> IOError {
-        IOError { path: None, err }
-    }
-}
-
 /// Error that may occur when opening a directory
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum OpenDirectoryError {
     /// The underlying directory does not exists.
+    #[error("Directory does not exist: '{0}'.")]
     DoesNotExist(PathBuf),
     /// The path exists but is not a directory.
+    #[error("Path exists but is not a directory: '{0}'.")]
     NotADirectory(PathBuf),
+    /// Failed to create a temp directory.
+    #[error("Failed to create a temporary directory: '{0}'.")]
+    FailedToCreateTempDir(io::Error),
     /// IoError
-    IoError(io::Error),
-}
-
-impl From<io::Error> for OpenDirectoryError {
-    fn from(io_err: io::Error) -> Self {
-        OpenDirectoryError::IoError(io_err)
-    }
-}
-
-impl fmt::Display for OpenDirectoryError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            OpenDirectoryError::DoesNotExist(ref path) => {
-                write!(f, "the underlying directory '{:?}' does not exist", path)
-            }
-            OpenDirectoryError::NotADirectory(ref path) => {
-                write!(f, "the path '{:?}' exists but is not a directory", path)
-            }
-            OpenDirectoryError::IoError(ref err) => write!(
-                f,
-                "IOError while trying to open/create the directory. {:?}",
-                err
-            ),
-        }
-    }
-}
-
-impl StdError for OpenDirectoryError {
-    fn description(&self) -> &str {
-        "error occurred while opening a directory"
-    }
-
-    fn cause(&self) -> Option<&dyn StdError> {
-        None
-    }
+    #[error("IOError '{io_error:?}' while create directory in: '{directory_path:?}'.")]
+    IoError {
+        /// underlying io Error.
+        io_error: io::Error,
+        /// directory we tried to open.
+        directory_path: PathBuf,
+    },
 }
 
 /// Error that may occur when starting to write in a file
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum OpenWriteError {
     /// Our directory is WORM, writing an existing file is forbidden.
     /// Checkout the `Directory` documentation.
+    #[error("File already exists: '{0}'")]
     FileAlreadyExists(PathBuf),
     /// Any kind of IO error that happens when
     /// writing in the underlying IO device.
-    IOError(IOError),
+    #[error("IOError '{io_error:?}' while opening file for write: '{filepath}'.")]
+    IOError {
+        /// The underlying `io::Error`.
+        io_error: io::Error,
+        /// File path of the file that tantivy failed to open for write.
+        filepath: PathBuf,
+    },
 }
 
-impl From<IOError> for OpenWriteError {
-    fn from(err: IOError) -> OpenWriteError {
-        OpenWriteError::IOError(err)
+impl OpenWriteError {
+    /// Wraps an io error.
+    pub fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
+        Self::IOError { io_error, filepath }
     }
 }
-
-impl fmt::Display for OpenWriteError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            OpenWriteError::FileAlreadyExists(ref path) => {
-                write!(f, "the file '{:?}' already exists", path)
-            }
-            OpenWriteError::IOError(ref err) => write!(
-                f,
-                "an io error occurred while opening a file for writing: '{}'",
-                err
-            ),
-        }
-    }
-}
-
-impl StdError for OpenWriteError {
-    fn description(&self) -> &str {
-        "error occurred while opening a file for writing"
-    }
-
-    fn cause(&self) -> Option<&dyn StdError> {
-        match *self {
-            OpenWriteError::FileAlreadyExists(_) => None,
-            OpenWriteError::IOError(ref err) => Some(err),
-        }
-    }
-}
-
 /// Type of index incompatibility between the library and the index found on disk
 /// Used to catch and provide a hint to solve this incompatibility issue
 pub enum Incompatibility {
@@ -217,55 +123,47 @@ impl fmt::Debug for Incompatibility {
 }
 
 /// Error that may occur when accessing a file read
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum OpenReadError {
     /// The file does not exists.
+    #[error("Files does not exists: {0:?}")]
     FileDoesNotExist(PathBuf),
-    /// Any kind of IO error that happens when
-    /// interacting with the underlying IO device.
-    IOError(IOError),
-    /// This library doesn't support the index version found on disk
+    /// Any kind of io::Error.
+    #[error(
+        "IOError: '{io_error:?}' happened while opening the following file for Read: {filepath}."
+    )]
+    IOError {
+        /// The underlying `io::Error`.
+        io_error: io::Error,
+        /// File path of the file that tantivy failed to open for read.
+        filepath: PathBuf,
+    },
+    /// This library does not support the index version found in file footer.
+    #[error("Index version unsupported: {0:?}")]
     IncompatibleIndex(Incompatibility),
 }
 
-impl From<IOError> for OpenReadError {
-    fn from(err: IOError) -> OpenReadError {
-        OpenReadError::IOError(err)
+impl OpenReadError {
+    /// Wraps an io error.
+    pub fn wrap_io_error(io_error: io::Error, filepath: PathBuf) -> Self {
+        Self::IOError { io_error, filepath }
     }
 }
-
-impl fmt::Display for OpenReadError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            OpenReadError::FileDoesNotExist(ref path) => {
-                write!(f, "the file '{:?}' does not exist", path)
-            }
-            OpenReadError::IOError(ref err) => write!(
-                f,
-                "an io error occurred while opening a file for reading: '{}'",
-                err
-            ),
-            OpenReadError::IncompatibleIndex(ref footer) => {
-                write!(f, "Incompatible index format: {:?}", footer)
-            }
-        }
-    }
-}
-
 /// Error that may occur when trying to delete a file
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum DeleteError {
     /// The file does not exists.
+    #[error("File does not exists: '{0}'.")]
     FileDoesNotExist(PathBuf),
     /// Any kind of IO error that happens when
     /// interacting with the underlying IO device.
-    IOError(IOError),
-}
-
-impl From<IOError> for DeleteError {
-    fn from(err: IOError) -> DeleteError {
-        DeleteError::IOError(err)
-    }
+    #[error("The following IO error happened while deleting file '{filepath}': '{io_error:?}'.")]
+    IOError {
+        /// The underlying `io::Error`.
+        io_error: io::Error,
+        /// File path of the file that tantivy failed to delete.
+        filepath: PathBuf,
+    },
 }
 
 impl From<Incompatibility> for OpenReadError {
@@ -273,29 +171,3 @@ impl From<Incompatibility> for OpenReadError {
         OpenReadError::IncompatibleIndex(incompatibility)
     }
 }
-
-impl fmt::Display for DeleteError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            DeleteError::FileDoesNotExist(ref path) => {
-                write!(f, "the file '{:?}' does not exist", path)
-            }
-            DeleteError::IOError(ref err) => {
-                write!(f, "an io error occurred while deleting a file: '{}'", err)
-            }
-        }
-    }
-}
-
-impl StdError for DeleteError {
-    fn description(&self) -> &str {
-        "error occurred while deleting a file"
-    }
-
-    fn cause(&self) -> Option<&dyn StdError> {
-        match *self {
-            DeleteError::FileDoesNotExist(_) => None,
-            DeleteError::IOError(ref err) => Some(err),
-        }
-    }
-}

src/directory/file_slice.rs

@@ -0,0 +1,246 @@
+use stable_deref_trait::StableDeref;
+
+use crate::common::HasLen;
+use crate::directory::OwnedBytes;
+use std::fmt;
+use std::ops::Range;
+use std::sync::{Arc, Weak};
+use std::{io, ops::Deref};
+
+pub type ArcBytes = Arc<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
+pub type WeakArcBytes = Weak<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
+
+/// Objects that represents files sections in tantivy.
+///
+/// By contract, whatever happens to the directory file, as long as a FileHandle
+/// is alive, the data associated with it cannot be altered or destroyed.
+///
+/// The underlying behavior is therefore specific to the `Directory` that created it.
+/// Despite its name, a `FileSlice` may or may not directly map to an actual file
+/// on the filesystem.
+pub trait FileHandle: 'static + Send + Sync + HasLen + fmt::Debug {
+    /// Reads a slice of bytes.
+    ///
+    /// This method may panic if the range requested is invalid.
+    fn read_bytes(&self, range: Range<usize>) -> io::Result<OwnedBytes>;
+}
+
+impl FileHandle for &'static [u8] {
+    fn read_bytes(&self, range: Range<usize>) -> io::Result<OwnedBytes> {
+        let bytes = &self[range];
+        Ok(OwnedBytes::new(bytes))
+    }
+}
+
+impl<T: Deref<Target = [u8]>> HasLen for T {
+    fn len(&self) -> usize {
+        self.deref().len()
+    }
+}
+
+impl<B> From<B> for FileSlice
+where
+    B: StableDeref + Deref<Target = [u8]> + 'static + Send + Sync,
+{
+    fn from(bytes: B) -> FileSlice {
+        FileSlice::new(Box::new(OwnedBytes::new(bytes)))
+    }
+}
+
+/// Logical slice of read only file in tantivy.
+///
+/// It can be cloned and sliced cheaply.
+///
+#[derive(Clone)]
+pub struct FileSlice {
+    data: Arc<dyn FileHandle>,
+    range: Range<usize>,
+}
+
+impl fmt::Debug for FileSlice {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "FileSlice({:?}, {:?})", &self.data, self.range)
+    }
+}
+
+impl FileSlice {
+    /// Wraps a FileHandle.
+    pub fn new(file_handle: Box<dyn FileHandle>) -> Self {
+        let num_bytes = file_handle.len();
+        FileSlice::new_with_num_bytes(file_handle, num_bytes)
+    }
+
+    /// Wraps a FileHandle.
+    #[doc(hidden)]
+    pub fn new_with_num_bytes(file_handle: Box<dyn FileHandle>, num_bytes: usize) -> Self {
+        FileSlice {
+            data: Arc::from(file_handle),
+            range: 0..num_bytes,
+        }
+    }
+
+    /// Creates a fileslice that is just a view over a slice of the data.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `byte_range.end` exceeds the filesize.
+    pub fn slice(&self, byte_range: Range<usize>) -> FileSlice {
+        assert!(byte_range.end <= self.len());
+        FileSlice {
+            data: self.data.clone(),
+            range: self.range.start + byte_range.start..self.range.start + byte_range.end,
+        }
+    }
+
+    /// Creates an empty FileSlice
+    pub fn empty() -> FileSlice {
+        const EMPTY_SLICE: &[u8] = &[];
+        FileSlice::from(EMPTY_SLICE)
+    }
+
+    /// Returns a `OwnedBytes` with all of the data in the `FileSlice`.
+    ///
+    /// The behavior is strongly dependant on the implementation of the underlying
+    /// `Directory` and the `FileSliceTrait` it creates.
+    /// In particular, it is  up to the `Directory` implementation
+    /// to handle caching if needed.
+    pub fn read_bytes(&self) -> io::Result<OwnedBytes> {
+        self.data.read_bytes(self.range.clone())
+    }
+
+    /// Reads a specific slice of data.
+    ///
+    /// This is equivalent to running `file_slice.slice(from, to).read_bytes()`.
+    pub fn read_bytes_slice(&self, range: Range<usize>) -> io::Result<OwnedBytes> {
+        assert!(
+            range.end <= self.len(),
+            "end of requested range exceeds the fileslice length ({} > {})",
+            range.end,
+            self.len()
+        );
+        self.data
+            .read_bytes(self.range.start + range.start..self.range.start + range.end)
+    }
+
+    /// Splits the FileSlice at the given offset and return two file slices.
+    /// `file_slice[..split_offset]` and `file_slice[split_offset..]`.
+    ///
+    /// This operation is cheap and must not copy any underlying data.
+    pub fn split(self, left_len: usize) -> (FileSlice, FileSlice) {
+        let left = self.slice_to(left_len);
+        let right = self.slice_from(left_len);
+        (left, right)
+    }
+
+    /// Splits the file slice at the given offset and return two file slices.
+    /// `file_slice[..split_offset]` and `file_slice[split_offset..]`.
+    pub fn split_from_end(self, right_len: usize) -> (FileSlice, FileSlice) {
+        let left_len = self.len() - right_len;
+        self.split(left_len)
+    }
+
+    /// Like `.slice(...)` but enforcing only the `from`
+    /// boundary.
+    ///
+    /// Equivalent to `.slice(from_offset, self.len())`
+    pub fn slice_from(&self, from_offset: usize) -> FileSlice {
+        self.slice(from_offset..self.len())
+    }
+
+    /// Like `.slice(...)` but enforcing only the `to`
+    /// boundary.
+    ///
+    /// Equivalent to `.slice(0, to_offset)`
+    pub fn slice_to(&self, to_offset: usize) -> FileSlice {
+        self.slice(0..to_offset)
+    }
+}
+
+impl FileHandle for FileSlice {
+    fn read_bytes(&self, range: Range<usize>) -> io::Result<OwnedBytes> {
+        self.read_bytes_slice(range)
+    }
+}
+
+impl HasLen for FileSlice {
+    fn len(&self) -> usize {
+        self.range.len()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{FileHandle, FileSlice};
+    use crate::common::HasLen;
+    use std::io;
+
+    #[test]
+    fn test_file_slice() -> io::Result<()> {
+        let file_slice = FileSlice::new(Box::new(b"abcdef".as_ref()));
+        assert_eq!(file_slice.len(), 6);
+        assert_eq!(file_slice.slice_from(2).read_bytes()?.as_slice(), b"cdef");
+        assert_eq!(file_slice.slice_to(2).read_bytes()?.as_slice(), b"ab");
+        assert_eq!(
+            file_slice
+                .slice_from(1)
+                .slice_to(2)
+                .read_bytes()?
+                .as_slice(),
+            b"bc"
+        );
+        {
+            let (left, right) = file_slice.clone().split(0);
+            assert_eq!(left.read_bytes()?.as_slice(), b"");
+            assert_eq!(right.read_bytes()?.as_slice(), b"abcdef");
+        }
+        {
+            let (left, right) = file_slice.clone().split(2);
+            assert_eq!(left.read_bytes()?.as_slice(), b"ab");
+            assert_eq!(right.read_bytes()?.as_slice(), b"cdef");
+        }
+        {
+            let (left, right) = file_slice.clone().split_from_end(0);
+            assert_eq!(left.read_bytes()?.as_slice(), b"abcdef");
+            assert_eq!(right.read_bytes()?.as_slice(), b"");
+        }
+        {
+            let (left, right) = file_slice.clone().split_from_end(2);
+            assert_eq!(left.read_bytes()?.as_slice(), b"abcd");
+            assert_eq!(right.read_bytes()?.as_slice(), b"ef");
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_file_slice_trait_slice_len() {
+        let blop: &'static [u8] = b"abc";
+        let owned_bytes: Box<dyn FileHandle> = Box::new(blop);
+        assert_eq!(owned_bytes.len(), 3);
+    }
+
+    #[test]
+    fn test_slice_simple_read() -> io::Result<()> {
+        let slice = FileSlice::new(Box::new(&b"abcdef"[..]));
+        assert_eq!(slice.len(), 6);
+        assert_eq!(slice.read_bytes()?.as_ref(), b"abcdef");
+        assert_eq!(slice.slice(1..4).read_bytes()?.as_ref(), b"bcd");
+        Ok(())
+    }
+
+    #[test]
+    fn test_slice_read_slice() -> io::Result<()> {
+        let slice_deref = FileSlice::new(Box::new(&b"abcdef"[..]));
+        assert_eq!(slice_deref.read_bytes_slice(1..4)?.as_ref(), b"bcd");
+        Ok(())
+    }
+
+    #[test]
+    #[should_panic(expected = "end of requested range exceeds the fileslice length (10 > 6)")]
+    fn test_slice_read_slice_invalid_range_exceeds() {
+        let slice_deref = FileSlice::new(Box::new(&b"abcdef"[..]));
+        assert_eq!(
+            slice_deref.read_bytes_slice(0..10).unwrap().as_ref(),
+            b"bcd"
+        );
+    }
+}

src/directory/file_watcher.rs

@@ -0,0 +1,182 @@
+use crate::directory::{WatchCallback, WatchCallbackList, WatchHandle};
+use crc32fast::Hasher;
+use std::fs;
+use std::io;
+use std::io::BufRead;
+use std::path::Path;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::Arc;
+use std::thread;
+use std::time::Duration;
+
+pub const POLLING_INTERVAL: Duration = Duration::from_millis(if cfg!(test) { 1 } else { 500 });
+
+// Watches a file and executes registered callbacks when the file is modified.
+pub struct FileWatcher {
+    path: Arc<Path>,
+    callbacks: Arc<WatchCallbackList>,
+    state: Arc<AtomicUsize>, // 0: new, 1: runnable, 2: terminated
+}
+
+impl FileWatcher {
+    pub fn new(path: &Path) -> FileWatcher {
+        FileWatcher {
+            path: Arc::from(path),
+            callbacks: Default::default(),
+            state: Default::default(),
+        }
+    }
+
+    pub fn spawn(&self) {
+        if self
+            .state
+            .compare_exchange(0, 1, Ordering::SeqCst, Ordering::SeqCst)
+            .is_err()
+        {
+            return;
+        }
+
+        let path = self.path.clone();
+        let callbacks = self.callbacks.clone();
+        let state = self.state.clone();
+
+        thread::Builder::new()
+            .name("thread-tantivy-meta-file-watcher".to_string())
+            .spawn(move || {
+                let mut current_checksum = None;
+
+                while state.load(Ordering::SeqCst) == 1 {
+                    if let Ok(checksum) = FileWatcher::compute_checksum(&path) {
+                        // `None.unwrap_or_else(|| !checksum) != checksum` evaluates to `true`
+                        if current_checksum.unwrap_or_else(|| !checksum) != checksum {
+                            info!("Meta file {:?} was modified", path);
+                            current_checksum = Some(checksum);
+                            futures::executor::block_on(callbacks.broadcast());
+                        }
+                    }
+
+                    thread::sleep(POLLING_INTERVAL);
+                }
+            })
+            .expect("Failed to spawn meta file watcher thread");
+    }
+
+    pub fn watch(&self, callback: WatchCallback) -> WatchHandle {
+        let handle = self.callbacks.subscribe(callback);
+        self.spawn();
+        handle
+    }
+
+    fn compute_checksum(path: &Path) -> Result<u32, io::Error> {
+        let reader = match fs::File::open(path) {
+            Ok(f) => io::BufReader::new(f),
+            Err(e) => {
+                warn!("Failed to open meta file {:?}: {:?}", path, e);
+                return Err(e);
+            }
+        };
+
+        let mut hasher = Hasher::new();
+
+        for line in reader.lines() {
+            hasher.update(line?.as_bytes())
+        }
+
+        Ok(hasher.finalize())
+    }
+}
+
+impl Drop for FileWatcher {
+    fn drop(&mut self) {
+        self.state.store(2, Ordering::SeqCst);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use std::mem;
+
+    use crate::directory::mmap_directory::atomic_write;
+
+    use super::*;
+
+    #[test]
+    fn test_file_watcher_drop_watcher() -> crate::Result<()> {
+        let tmp_dir = tempfile::TempDir::new()?;
+        let tmp_file = tmp_dir.path().join("watched.txt");
+
+        let counter: Arc<AtomicUsize> = Default::default();
+        let (tx, rx) = crossbeam::channel::unbounded();
+        let timeout = Duration::from_millis(100);
+
+        let watcher = FileWatcher::new(&tmp_file);
+
+        let state = watcher.state.clone();
+        assert_eq!(state.load(Ordering::SeqCst), 0);
+
+        let counter_clone = counter.clone();
+
+        let _handle = watcher.watch(WatchCallback::new(move || {
+            let val = counter_clone.fetch_add(1, Ordering::SeqCst);
+            tx.send(val + 1).unwrap();
+        }));
+
+        assert_eq!(counter.load(Ordering::SeqCst), 0);
+        assert_eq!(state.load(Ordering::SeqCst), 1);
+
+        atomic_write(&tmp_file, b"foo")?;
+        assert_eq!(rx.recv_timeout(timeout), Ok(1));
+
+        atomic_write(&tmp_file, b"foo")?;
+        assert!(rx.recv_timeout(timeout).is_err());
+
+        atomic_write(&tmp_file, b"bar")?;
+        assert_eq!(rx.recv_timeout(timeout), Ok(2));
+
+        mem::drop(watcher);
+
+        atomic_write(&tmp_file, b"qux")?;
+        thread::sleep(Duration::from_millis(10));
+        assert_eq!(counter.load(Ordering::SeqCst), 2);
+        assert_eq!(state.load(Ordering::SeqCst), 2);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_file_watcher_drop_handle() -> crate::Result<()> {
+        let tmp_dir = tempfile::TempDir::new()?;
+        let tmp_file = tmp_dir.path().join("watched.txt");
+
+        let counter: Arc<AtomicUsize> = Default::default();
+        let (tx, rx) = crossbeam::channel::unbounded();
+        let timeout = Duration::from_millis(100);
+
+        let watcher = FileWatcher::new(&tmp_file);
+
+        let state = watcher.state.clone();
+        assert_eq!(state.load(Ordering::SeqCst), 0);
+
+        let counter_clone = counter.clone();
+
+        let handle = watcher.watch(WatchCallback::new(move || {
+            let val = counter_clone.fetch_add(1, Ordering::SeqCst);
+            tx.send(val + 1).unwrap();
+        }));
+
+        assert_eq!(counter.load(Ordering::SeqCst), 0);
+        assert_eq!(state.load(Ordering::SeqCst), 1);
+
+        atomic_write(&tmp_file, b"foo")?;
+        assert_eq!(rx.recv_timeout(timeout), Ok(1));
+
+        mem::drop(handle);
+
+        atomic_write(&tmp_file, b"qux")?;
+        assert_eq!(counter.load(Ordering::SeqCst), 1);
+        assert_eq!(state.load(Ordering::SeqCst), 1);
+
+        Ok(())
+    }
+}

src/directory/footer.rs

@@ -1,9 +1,8 @@
-use crate::common::{BinarySerializable, CountingWriter, FixedSize, VInt};
+use crate::common::{BinarySerializable, CountingWriter, FixedSize, HasLen, VInt};
 use crate::directory::error::Incompatibility;
-use crate::directory::read_only_source::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{AntiCallToken, TerminatingWrite};
 use crate::Version;
-use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
 use crc32fast::Hasher;
 use std::io;
 use std::io::Write;
@@ -64,26 +63,26 @@ impl Footer {
         let mut counting_write = CountingWriter::wrap(&mut write);
         self.serialize(&mut counting_write)?;
         let written_len = counting_write.written_bytes();
-        write.write_u32::<LittleEndian>(written_len as u32)?;
+        (written_len as u32).serialize(write)?;
         Ok(())
     }
 
-    pub fn extract_footer(source: ReadOnlySource) -> Result<(Footer, ReadOnlySource), io::Error> {
-        if source.len() < 4 {
+    pub fn extract_footer(file: FileSlice) -> io::Result<(Footer, FileSlice)> {
+        if file.len() < 4 {
             return Err(io::Error::new(
                 io::ErrorKind::UnexpectedEof,
                 format!(
                     "File corrupted. The file is smaller than 4 bytes (len={}).",
-                    source.len()
+                    file.len()
                 ),
             ));
         }
-        let (body_footer, footer_len_bytes) = source.split_from_end(u32::SIZE_IN_BYTES);
-        let footer_len = LittleEndian::read_u32(footer_len_bytes.as_slice()) as usize;
-        let body_len = body_footer.len() - footer_len;
-        let (body, footer_data) = body_footer.split(body_len);
-        let mut cursor = footer_data.as_slice();
-        let footer = Footer::deserialize(&mut cursor)?;
+        let (body_footer, footer_len_file) = file.split_from_end(u32::SIZE_IN_BYTES);
+        let mut footer_len_bytes = footer_len_file.read_bytes()?;
+        let footer_len = u32::deserialize(&mut footer_len_bytes)? as usize;
+        let (body, footer) = body_footer.split_from_end(footer_len);
+        let mut footer_bytes = footer.read_bytes()?;
+        let footer = Footer::deserialize(&mut footer_bytes)?;
         Ok((footer, body))
     }
 
@@ -116,6 +115,18 @@ impl Footer {
                 }
                 Ok(())
             }
+            VersionedFooter::V3 {
+                crc32: _crc,
+                store_compression,
+            } => {
+                if &library_version.store_compression != store_compression {
+                    return Err(Incompatibility::CompressionMismatch {
+                        library_compression_format: library_version.store_compression.to_string(),
+                        index_compression_format: store_compression.to_string(),
+                    });
+                }
+                Ok(())
+            }
             VersionedFooter::UnknownVersion => Err(Incompatibility::IndexMismatch {
                 library_version: library_version.clone(),
                 index_version: self.version.clone(),
@@ -137,24 +148,31 @@ pub enum VersionedFooter {
         crc32: CrcHashU32,
         store_compression: String,
     },
+    // Block wand max termfred on 1 byte
+    V3 {
+        crc32: CrcHashU32,
+        store_compression: String,
+    },
 }
 
 impl BinarySerializable for VersionedFooter {
     fn serialize<W: io::Write>(&self, writer: &mut W) -> io::Result<()> {
         let mut buf = Vec::new();
         match self {
-            VersionedFooter::V2 {
+            VersionedFooter::V3 {
                 crc32,
                 store_compression: compression,
             } => {
                 // Serializes a valid `VersionedFooter` or panics if the version is unknown
                 // [   version    |   crc_hash  | compression_mode ]
                 // [    0..4      |     4..8    |     variable     ]
-                BinarySerializable::serialize(&2u32, &mut buf)?;
+                BinarySerializable::serialize(&3u32, &mut buf)?;
                 BinarySerializable::serialize(crc32, &mut buf)?;
                 BinarySerializable::serialize(compression, &mut buf)?;
             }
-            VersionedFooter::V1 { .. } | VersionedFooter::UnknownVersion => {
+            VersionedFooter::V2 { .. }
+            | VersionedFooter::V1 { .. }
+            | VersionedFooter::UnknownVersion => {
                 return Err(io::Error::new(
                     io::ErrorKind::InvalidInput,
                     "Cannot serialize an unknown versioned footer ",
@@ -183,7 +201,7 @@ impl BinarySerializable for VersionedFooter {
         reader.read_exact(&mut buf[..])?;
         let mut cursor = &buf[..];
         let version = u32::deserialize(&mut cursor)?;
-        if version != 1 && version != 2 {
+        if version > 3 {
             return Ok(VersionedFooter::UnknownVersion);
         }
         let crc32 = u32::deserialize(&mut cursor)?;
@@ -193,12 +211,17 @@ impl BinarySerializable for VersionedFooter {
                 crc32,
                 store_compression,
             }
-        } else {
-            assert_eq!(version, 2);
+        } else if version == 2 {
             VersionedFooter::V2 {
                 crc32,
                 store_compression,
             }
+        } else {
+            assert_eq!(version, 3);
+            VersionedFooter::V3 {
+                crc32,
+                store_compression,
+            }
         })
     }
 }
@@ -206,6 +229,7 @@ impl BinarySerializable for VersionedFooter {
 impl VersionedFooter {
     pub fn crc(&self) -> Option<CrcHashU32> {
         match self {
+            VersionedFooter::V3 { crc32, .. } => Some(*crc32),
             VersionedFooter::V2 { crc32, .. } => Some(*crc32),
             VersionedFooter::V1 { crc32, .. } => Some(*crc32),
             VersionedFooter::UnknownVersion { .. } => None,
@@ -244,7 +268,7 @@ impl<W: TerminatingWrite> Write for FooterProxy<W> {
 impl<W: TerminatingWrite> TerminatingWrite for FooterProxy<W> {
     fn terminate_ref(&mut self, _: AntiCallToken) -> io::Result<()> {
         let crc32 = self.hasher.take().unwrap().finalize();
-        let footer = Footer::new(VersionedFooter::V2 {
+        let footer = Footer::new(VersionedFooter::V3 {
             crc32,
             store_compression: crate::store::COMPRESSION.to_string(),
         });
@@ -271,11 +295,15 @@ mod tests {
         let mut vec = Vec::new();
         let footer_proxy = FooterProxy::new(&mut vec);
         assert!(footer_proxy.terminate().is_ok());
-        assert_eq!(vec.len(), 167);
+        if crate::store::COMPRESSION == "lz4" {
+            assert_eq!(vec.len(), 158);
+        } else {
+            assert_eq!(vec.len(), 167);
+        }
         let footer = Footer::deserialize(&mut &vec[..]).unwrap();
         assert!(matches!(
            footer.versioned_footer,
-           VersionedFooter::V2 { store_compression, .. }
+           VersionedFooter::V3 { store_compression, .. }
            if store_compression == crate::store::COMPRESSION
         ));
         assert_eq!(&footer.version, crate::version());
@@ -285,7 +313,7 @@ mod tests {
     fn test_serialize_deserialize_footer() {
         let mut buffer = Vec::new();
         let crc32 = 123456u32;
-        let footer: Footer = Footer::new(VersionedFooter::V2 {
+        let footer: Footer = Footer::new(VersionedFooter::V3 {
             crc32,
             store_compression: "lz4".to_string(),
         });
@@ -297,7 +325,7 @@ mod tests {
     #[test]
     fn footer_length() {
         let crc32 = 1111111u32;
-        let versioned_footer = VersionedFooter::V2 {
+        let versioned_footer = VersionedFooter::V3 {
             crc32,
             store_compression: "lz4".to_string(),
         };
@@ -318,7 +346,7 @@ mod tests {
             // versionned footer length
             12 | 128,
             // index format version
-            2,
+            3,
             0,
             0,
             0,
@@ -337,7 +365,7 @@ mod tests {
         let versioned_footer = VersionedFooter::deserialize(&mut cursor).unwrap();
         assert!(cursor.is_empty());
         let expected_crc: u32 = LittleEndian::read_u32(&v_footer_bytes[5..9]) as CrcHashU32;
-        let expected_versioned_footer: VersionedFooter = VersionedFooter::V2 {
+        let expected_versioned_footer: VersionedFooter = VersionedFooter::V3 {
             crc32: expected_crc,
             store_compression: "lz4".to_string(),
         };

src/directory/managed_directory.rs

@@ -1,11 +1,11 @@
 use crate::core::{MANAGED_FILEPATH, META_FILEPATH};
-use crate::directory::error::{DeleteError, IOError, LockError, OpenReadError, OpenWriteError};
+use crate::directory::error::{DeleteError, LockError, OpenReadError, OpenWriteError};
 use crate::directory::footer::{Footer, FooterProxy};
-use crate::directory::DirectoryLock;
 use crate::directory::GarbageCollectionResult;
 use crate::directory::Lock;
 use crate::directory::META_LOCK;
-use crate::directory::{ReadOnlySource, WritePtr};
+use crate::directory::{DirectoryLock, FileHandle};
+use crate::directory::{FileSlice, WritePtr};
 use crate::directory::{WatchCallback, WatchHandle};
 use crate::error::DataCorruption;
 use crate::Directory;
@@ -53,7 +53,7 @@ struct MetaInformation {
 /// Saves the file containing the list of existing files
 /// that were created by tantivy.
 fn save_managed_paths(
-    directory: &mut dyn Directory,
+    directory: &dyn Directory,
     wlock: &RwLockWriteGuard<'_, MetaInformation>,
 ) -> io::Result<()> {
     let mut w = serde_json::to_vec(&wlock.managed_paths)?;
@@ -86,7 +86,7 @@ impl ManagedDirectory {
                 directory: Box::new(directory),
                 meta_informations: Arc::default(),
             }),
-            Err(OpenReadError::IOError(e)) => Err(From::from(e)),
+            io_err @ Err(OpenReadError::IOError { .. }) => Err(io_err.err().unwrap().into()),
             Err(OpenReadError::IncompatibleIndex(incompatibility)) => {
                 // For the moment, this should never happen  `meta.json`
                 // do not have any footer and cannot detect incompatibility.
@@ -168,7 +168,7 @@ impl ManagedDirectory {
                         DeleteError::FileDoesNotExist(_) => {
                             deleted_files.push(file_to_delete.clone());
                         }
-                        DeleteError::IOError(_) => {
+                        DeleteError::IOError { .. } => {
                             failed_to_delete_files.push(file_to_delete.clone());
                             if !cfg!(target_os = "windows") {
                                 // On windows, delete is expected to fail if the file
@@ -212,7 +212,7 @@ impl ManagedDirectory {
     /// File starting by "." are reserved to locks.
     /// They are not managed and cannot be subjected
     /// to garbage collection.
-    fn register_file_as_managed(&mut self, filepath: &Path) -> io::Result<()> {
+    fn register_file_as_managed(&self, filepath: &Path) -> io::Result<()> {
         // Files starting by "." (e.g. lock files) are not managed.
         if !is_managed(filepath) {
             return Ok(());
@@ -223,7 +223,7 @@ impl ManagedDirectory {
             .expect("Managed file lock poisoned");
         let has_changed = meta_wlock.managed_paths.insert(filepath.to_owned());
         if has_changed {
-            save_managed_paths(self.directory.as_mut(), &meta_wlock)?;
+            save_managed_paths(self.directory.as_ref(), &meta_wlock)?;
         }
         Ok(())
     }
@@ -231,10 +231,19 @@ impl ManagedDirectory {
     /// Verify checksum of a managed file
     pub fn validate_checksum(&self, path: &Path) -> result::Result<bool, OpenReadError> {
         let reader = self.directory.open_read(path)?;
-        let (footer, data) = Footer::extract_footer(reader)
-            .map_err(|err| IOError::with_path(path.to_path_buf(), err))?;
+        let (footer, data) =
+            Footer::extract_footer(reader).map_err(|io_error| OpenReadError::IOError {
+                io_error,
+                filepath: path.to_path_buf(),
+            })?;
+        let bytes = data
+            .read_bytes()
+            .map_err(|io_error| OpenReadError::IOError {
+                filepath: path.to_path_buf(),
+                io_error,
+            })?;
         let mut hasher = Hasher::new();
-        hasher.update(data.as_slice());
+        hasher.update(bytes.as_slice());
         let crc = hasher.finalize();
         Ok(footer
             .versioned_footer
@@ -245,7 +254,6 @@ impl ManagedDirectory {
 
     /// List files for which checksum does not match content
     pub fn list_damaged(&self) -> result::Result<HashSet<PathBuf>, OpenReadError> {
-        let mut hashset = HashSet::new();
         let mut managed_paths = self
             .meta_informations
             .read()
@@ -255,27 +263,33 @@ impl ManagedDirectory {
 
         managed_paths.remove(*META_FILEPATH);
 
-        for path in managed_paths.into_iter() {
+        let mut damaged_files = HashSet::new();
+        for path in managed_paths {
             if !self.validate_checksum(&path)? {
-                hashset.insert(path);
+                damaged_files.insert(path);
             }
         }
-        Ok(hashset)
+        Ok(damaged_files)
     }
 }
 
 impl Directory for ManagedDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
-        let read_only_source = self.directory.open_read(path)?;
-        let (footer, reader) = Footer::extract_footer(read_only_source)
-            .map_err(|err| IOError::with_path(path.to_path_buf(), err))?;
+    fn get_file_handle(&self, path: &Path) -> Result<Box<dyn FileHandle>, OpenReadError> {
+        let file_slice = self.open_read(path)?;
+        Ok(Box::new(file_slice))
+    }
+
+    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
+        let file_slice = self.directory.open_read(path)?;
+        let (footer, reader) = Footer::extract_footer(file_slice)
+            .map_err(|io_error| OpenReadError::wrap_io_error(io_error, path.to_path_buf()))?;
         footer.is_compatible()?;
         Ok(reader)
     }
 
-    fn open_write(&mut self, path: &Path) -> result::Result<WritePtr, OpenWriteError> {
+    fn open_write(&self, path: &Path) -> result::Result<WritePtr, OpenWriteError> {
         self.register_file_as_managed(path)
-            .map_err(|e| IOError::with_path(path.to_owned(), e))?;
+            .map_err(|io_error| OpenWriteError::wrap_io_error(io_error, path.to_path_buf()))?;
         Ok(io::BufWriter::new(Box::new(FooterProxy::new(
             self.directory
                 .open_write(path)?
@@ -285,7 +299,7 @@ impl Directory for ManagedDirectory {
         ))))
     }
 
-    fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()> {
+    fn atomic_write(&self, path: &Path, data: &[u8]) -> io::Result<()> {
         self.register_file_as_managed(path)?;
         self.directory.atomic_write(path, data)
     }
@@ -298,7 +312,7 @@ impl Directory for ManagedDirectory {
         self.directory.delete(path)
     }
 
-    fn exists(&self, path: &Path) -> bool {
+    fn exists(&self, path: &Path) -> Result<bool, OpenReadError> {
         self.directory.exists(path)
     }
 
@@ -346,22 +360,22 @@ mod tests_mmap_specific {
             managed_directory
                 .atomic_write(test_path2, &[0u8, 1u8])
                 .unwrap();
-            assert!(managed_directory.exists(test_path1));
-            assert!(managed_directory.exists(test_path2));
+            assert!(managed_directory.exists(test_path1).unwrap());
+            assert!(managed_directory.exists(test_path2).unwrap());
             let living_files: HashSet<PathBuf> = [test_path1.to_owned()].iter().cloned().collect();
             assert!(managed_directory.garbage_collect(|| living_files).is_ok());
-            assert!(managed_directory.exists(test_path1));
-            assert!(!managed_directory.exists(test_path2));
+            assert!(managed_directory.exists(test_path1).unwrap());
+            assert!(!managed_directory.exists(test_path2).unwrap());
         }
         {
             let mmap_directory = MmapDirectory::open(&tempdir_path).unwrap();
             let mut managed_directory = ManagedDirectory::wrap(mmap_directory).unwrap();
-            assert!(managed_directory.exists(test_path1));
-            assert!(!managed_directory.exists(test_path2));
+            assert!(managed_directory.exists(test_path1).unwrap());
+            assert!(!managed_directory.exists(test_path2).unwrap());
             let living_files: HashSet<PathBuf> = HashSet::new();
             assert!(managed_directory.garbage_collect(|| living_files).is_ok());
-            assert!(!managed_directory.exists(test_path1));
-            assert!(!managed_directory.exists(test_path2));
+            assert!(!managed_directory.exists(test_path1).unwrap());
+            assert!(!managed_directory.exists(test_path2).unwrap());
         }
     }
 
@@ -378,7 +392,7 @@ mod tests_mmap_specific {
         let mut write = managed_directory.open_write(test_path1).unwrap();
         write.write_all(&[0u8, 1u8]).unwrap();
         write.terminate().unwrap();
-        assert!(managed_directory.exists(test_path1));
+        assert!(managed_directory.exists(test_path1).unwrap());
 
         let _mmap_read = managed_directory.open_read(test_path1).unwrap();
         assert!(managed_directory
@@ -386,52 +400,50 @@ mod tests_mmap_specific {
             .is_ok());
         if cfg!(target_os = "windows") {
             // On Windows, gc should try and fail the file as it is mmapped.
-            assert!(managed_directory.exists(test_path1));
+            assert!(managed_directory.exists(test_path1).unwrap());
             // unmap should happen here.
             drop(_mmap_read);
             // The file should still be in the list of managed file and
             // eventually be deleted once mmap is released.
             assert!(managed_directory.garbage_collect(|| living_files).is_ok());
-            assert!(!managed_directory.exists(test_path1));
+            assert!(!managed_directory.exists(test_path1).unwrap());
         } else {
-            assert!(!managed_directory.exists(test_path1));
+            assert!(!managed_directory.exists(test_path1).unwrap());
         }
     }
 
     #[test]
-    fn test_checksum() {
+    fn test_checksum() -> crate::Result<()> {
         let test_path1: &'static Path = Path::new("some_path_for_test");
         let test_path2: &'static Path = Path::new("other_test_path");
 
         let tempdir = TempDir::new().unwrap();
         let tempdir_path = PathBuf::from(tempdir.path());
 
-        let mmap_directory = MmapDirectory::open(&tempdir_path).unwrap();
-        let mut managed_directory = ManagedDirectory::wrap(mmap_directory).unwrap();
-        let mut write = managed_directory.open_write(test_path1).unwrap();
-        write.write_all(&[0u8, 1u8]).unwrap();
-        write.terminate().unwrap();
+        let mmap_directory = MmapDirectory::open(&tempdir_path)?;
+        let managed_directory = ManagedDirectory::wrap(mmap_directory)?;
+        let mut write = managed_directory.open_write(test_path1)?;
+        write.write_all(&[0u8, 1u8])?;
+        write.terminate()?;
 
-        let mut write = managed_directory.open_write(test_path2).unwrap();
-        write.write_all(&[3u8, 4u8, 5u8]).unwrap();
-        write.terminate().unwrap();
+        let mut write = managed_directory.open_write(test_path2)?;
+        write.write_all(&[3u8, 4u8, 5u8])?;
+        write.terminate()?;
 
-        let read_source = managed_directory.open_read(test_path2).unwrap();
-        assert_eq!(read_source.as_slice(), &[3u8, 4u8, 5u8]);
+        let read_file = managed_directory.open_read(test_path2)?.read_bytes()?;
+        assert_eq!(read_file.as_slice(), &[3u8, 4u8, 5u8]);
         assert!(managed_directory.list_damaged().unwrap().is_empty());
 
         let mut corrupted_path = tempdir_path.clone();
         corrupted_path.push(test_path2);
-        let mut file = OpenOptions::new()
-            .write(true)
-            .open(&corrupted_path)
-            .unwrap();
-        file.write_all(&[255u8]).unwrap();
-        file.flush().unwrap();
+        let mut file = OpenOptions::new().write(true).open(&corrupted_path)?;
+        file.write_all(&[255u8])?;
+        file.flush()?;
         drop(file);
 
-        let damaged = managed_directory.list_damaged().unwrap();
+        let damaged = managed_directory.list_damaged()?;
         assert_eq!(damaged.len(), 1);
         assert!(damaged.contains(test_path2));
+        Ok(())
     }
 }

src/directory/mmap_directory.rs

@@ -1,25 +1,19 @@
 use crate::core::META_FILEPATH;
 use crate::directory::error::LockError;
-use crate::directory::error::{
-    DeleteError, IOError, OpenDirectoryError, OpenReadError, OpenWriteError,
-};
-use crate::directory::read_only_source::BoxedData;
-use crate::directory::AntiCallToken;
+use crate::directory::error::{DeleteError, OpenDirectoryError, OpenReadError, OpenWriteError};
+use crate::directory::file_watcher::FileWatcher;
 use crate::directory::Directory;
 use crate::directory::DirectoryLock;
 use crate::directory::Lock;
-use crate::directory::ReadOnlySource;
 use crate::directory::WatchCallback;
-use crate::directory::WatchCallbackList;
 use crate::directory::WatchHandle;
+use crate::directory::{AntiCallToken, FileHandle, OwnedBytes};
+use crate::directory::{ArcBytes, WeakArcBytes};
 use crate::directory::{TerminatingWrite, WritePtr};
 use fs2::FileExt;
 use memmap::Mmap;
-use notify::RawEvent;
-use notify::RecursiveMode;
-use notify::Watcher;
 use serde::{Deserialize, Serialize};
-use std::collections::HashMap;
+use stable_deref_trait::StableDeref;
 use std::convert::From;
 use std::fmt;
 use std::fs::OpenOptions;
@@ -28,13 +22,9 @@ use std::io::{self, Seek, SeekFrom};
 use std::io::{BufWriter, Read, Write};
 use std::path::{Path, PathBuf};
 use std::result;
-use std::sync::mpsc::{channel, Receiver, Sender};
 use std::sync::Arc;
-use std::sync::Mutex;
 use std::sync::RwLock;
-use std::sync::Weak;
-use std::thread;
-use tempfile;
+use std::{collections::HashMap, ops::Deref};
 use tempfile::TempDir;
 
 /// Create a default io error given a string.
@@ -45,17 +35,17 @@ pub(crate) fn make_io_err(msg: String) -> io::Error {
 /// Returns None iff the file exists, can be read, but is empty (and hence
 /// cannot be mmapped)
 fn open_mmap(full_path: &Path) -> result::Result<Option<Mmap>, OpenReadError> {
-    let file = File::open(full_path).map_err(|e| {
-        if e.kind() == io::ErrorKind::NotFound {
-            OpenReadError::FileDoesNotExist(full_path.to_owned())
+    let file = File::open(full_path).map_err(|io_err| {
+        if io_err.kind() == io::ErrorKind::NotFound {
+            OpenReadError::FileDoesNotExist(full_path.to_path_buf())
         } else {
-            OpenReadError::IOError(IOError::with_path(full_path.to_owned(), e))
+            OpenReadError::wrap_io_error(io_err, full_path.to_path_buf())
         }
     })?;
 
     let meta_data = file
         .metadata()
-        .map_err(|e| IOError::with_path(full_path.to_owned(), e))?;
+        .map_err(|io_err| OpenReadError::wrap_io_error(io_err, full_path.to_owned()))?;
     if meta_data.len() == 0 {
         // if the file size is 0, it will not be possible
         // to mmap the file, so we return None
@@ -65,7 +55,7 @@ fn open_mmap(full_path: &Path) -> result::Result<Option<Mmap>, OpenReadError> {
     unsafe {
         memmap::Mmap::map(&file)
             .map(Some)
-            .map_err(|e| From::from(IOError::with_path(full_path.to_owned(), e)))
+            .map_err(|io_err| OpenReadError::wrap_io_error(io_err, full_path.to_path_buf()))
     }
 }
 
@@ -86,7 +76,7 @@ pub struct CacheInfo {
 
 struct MmapCache {
     counters: CacheCounters,
-    cache: HashMap<PathBuf, Weak<BoxedData>>,
+    cache: HashMap<PathBuf, WeakArcBytes>,
 }
 
 impl Default for MmapCache {
@@ -120,7 +110,7 @@ impl MmapCache {
     }
 
     // Returns None if the file exists but as a len of 0 (and hence is not mmappable).
-    fn get_mmap(&mut self, full_path: &Path) -> Result<Option<Arc<BoxedData>>, OpenReadError> {
+    fn get_mmap(&mut self, full_path: &Path) -> Result<Option<ArcBytes>, OpenReadError> {
         if let Some(mmap_weak) = self.cache.get(full_path) {
             if let Some(mmap_arc) = mmap_weak.upgrade() {
                 self.counters.hit += 1;
@@ -131,7 +121,7 @@ impl MmapCache {
         self.counters.miss += 1;
         let mmap_opt = open_mmap(full_path)?;
         Ok(mmap_opt.map(|mmap| {
-            let mmap_arc: Arc<BoxedData> = Arc::new(Box::new(mmap));
+            let mmap_arc: ArcBytes = Arc::new(mmap);
             let mmap_weak = Arc::downgrade(&mmap_arc);
             self.cache.insert(full_path.to_owned(), mmap_weak);
             mmap_arc
@@ -139,63 +129,6 @@ impl MmapCache {
     }
 }
 
-struct WatcherWrapper {
-    _watcher: Mutex<notify::RecommendedWatcher>,
-    watcher_router: Arc<WatchCallbackList>,
-}
-
-impl WatcherWrapper {
-    pub fn new(path: &Path) -> Result<Self, OpenDirectoryError> {
-        let (tx, watcher_recv): (Sender<RawEvent>, Receiver<RawEvent>) = channel();
-        // We need to initialize the
-        let watcher = notify::raw_watcher(tx)
-            .and_then(|mut watcher| {
-                watcher.watch(path, RecursiveMode::Recursive)?;
-                Ok(watcher)
-            })
-            .map_err(|err| match err {
-                notify::Error::PathNotFound => OpenDirectoryError::DoesNotExist(path.to_owned()),
-                _ => {
-                    panic!("Unknown error while starting watching directory {:?}", path);
-                }
-            })?;
-        let watcher_router: Arc<WatchCallbackList> = Default::default();
-        let watcher_router_clone = watcher_router.clone();
-        thread::Builder::new()
-            .name("meta-file-watch-thread".to_string())
-            .spawn(move || {
-                loop {
-                    match watcher_recv.recv().map(|evt| evt.path) {
-                        Ok(Some(changed_path)) => {
-                            // ... Actually subject to false positive.
-                            // We might want to be more accurate than this at one point.
-                            if let Some(filename) = changed_path.file_name() {
-                                if filename == *META_FILEPATH {
-                                    let _ = watcher_router_clone.broadcast();
-                                }
-                            }
-                        }
-                        Ok(None) => {
-                            // not an event we are interested in.
-                        }
-                        Err(_e) => {
-                            // the watch send channel was dropped
-                            break;
-                        }
-                    }
-                }
-            })?;
-        Ok(WatcherWrapper {
-            _watcher: Mutex::new(watcher),
-            watcher_router,
-        })
-    }
-
-    pub fn watch(&mut self, watch_callback: WatchCallback) -> WatchHandle {
-        self.watcher_router.subscribe(watch_callback)
-    }
-}
-
 /// Directory storing data in files, read via mmap.
 ///
 /// The Mmap object are cached to limit the
@@ -217,40 +150,21 @@ struct MmapDirectoryInner {
     root_path: PathBuf,
     mmap_cache: RwLock<MmapCache>,
     _temp_directory: Option<TempDir>,
-    watcher: RwLock<Option<WatcherWrapper>>,
+    watcher: FileWatcher,
 }
 
 impl MmapDirectoryInner {
     fn new(root_path: PathBuf, temp_directory: Option<TempDir>) -> MmapDirectoryInner {
         MmapDirectoryInner {
-            root_path,
             mmap_cache: Default::default(),
             _temp_directory: temp_directory,
-            watcher: RwLock::new(None),
+            watcher: FileWatcher::new(&root_path.join(*META_FILEPATH)),
+            root_path,
         }
     }
 
-    fn watch(&self, watch_callback: WatchCallback) -> crate::Result<WatchHandle> {
-        // a lot of juggling here, to ensure we don't do anything that panics
-        // while the rwlock is held. That way we ensure that the rwlock cannot
-        // be poisoned.
-        //
-        // The downside is that we might create a watch wrapper that is not useful.
-        let need_initialization = self.watcher.read().unwrap().is_none();
-        if need_initialization {
-            let watch_wrapper = WatcherWrapper::new(&self.root_path)?;
-            let mut watch_wlock = self.watcher.write().unwrap();
-            // the watcher could have been initialized when we released the lock, and
-            // we do not want to lose the watched files that were set.
-            if watch_wlock.is_none() {
-                *watch_wlock = Some(watch_wrapper);
-            }
-        }
-        if let Some(watch_wrapper) = self.watcher.write().unwrap().as_mut() {
-            Ok(watch_wrapper.watch(watch_callback))
-        } else {
-            unreachable!("At this point, watch wrapper is supposed to be initialized");
-        }
+    fn watch(&self, callback: WatchCallback) -> WatchHandle {
+        self.watcher.watch(callback)
     }
 }
 
@@ -273,9 +187,11 @@ impl MmapDirectory {
     /// This is mostly useful to test the MmapDirectory itself.
     /// For your unit tests, prefer the RAMDirectory.
     pub fn create_from_tempdir() -> Result<MmapDirectory, OpenDirectoryError> {
-        let tempdir = TempDir::new().map_err(OpenDirectoryError::IoError)?;
-        let tempdir_path = PathBuf::from(tempdir.path());
-        Ok(MmapDirectory::new(tempdir_path, Some(tempdir)))
+        let tempdir = TempDir::new().map_err(OpenDirectoryError::FailedToCreateTempDir)?;
+        Ok(MmapDirectory::new(
+            tempdir.path().to_path_buf(),
+            Some(tempdir),
+        ))
     }
 
     /// Opens a MmapDirectory in a directory.
@@ -397,8 +313,38 @@ impl TerminatingWrite for SafeFileWriter {
     }
 }
 
+#[derive(Clone)]
+struct MmapArc(Arc<dyn Deref<Target = [u8]> + Send + Sync>);
+
+impl Deref for MmapArc {
+    type Target = [u8];
+
+    fn deref(&self) -> &[u8] {
+        self.0.deref()
+    }
+}
+unsafe impl StableDeref for MmapArc {}
+
+/// Writes a file in an atomic manner.
+pub(crate) fn atomic_write(path: &Path, content: &[u8]) -> io::Result<()> {
+    // We create the temporary file in the same directory as the target file.
+    // Indeed the canonical temp directory and the target file might sit in different
+    // filesystem, in which case the atomic write may actually not work.
+    let parent_path = path.parent().ok_or_else(|| {
+        io::Error::new(
+            io::ErrorKind::InvalidInput,
+            "Path {:?} does not have parent directory.",
+        )
+    })?;
+    let mut tempfile = tempfile::Builder::new().tempfile_in(&parent_path)?;
+    tempfile.write_all(content)?;
+    tempfile.flush()?;
+    tempfile.into_temp_path().persist(path)?;
+    Ok(())
+}
+
 impl Directory for MmapDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
+    fn get_file_handle(&self, path: &Path) -> result::Result<Box<dyn FileHandle>, OpenReadError> {
         debug!("Open Read {:?}", path);
         let full_path = self.resolve_path(path);
 
@@ -408,12 +354,19 @@ impl Directory for MmapDirectory {
                  on mmap cache while reading {:?}",
                 path
             );
-            IOError::with_path(path.to_owned(), make_io_err(msg))
+            let io_err = make_io_err(msg);
+            OpenReadError::wrap_io_error(io_err, path.to_path_buf())
         })?;
-        Ok(mmap_cache
+
+        let owned_bytes = mmap_cache
             .get_mmap(&full_path)?
-            .map(ReadOnlySource::from)
-            .unwrap_or_else(ReadOnlySource::empty))
+            .map(|mmap_arc| {
+                let mmap_arc_obj = MmapArc(mmap_arc);
+                OwnedBytes::new(mmap_arc_obj)
+            })
+            .unwrap_or_else(OwnedBytes::empty);
+
+        Ok(Box::new(owned_bytes))
     }
 
     /// Any entry associated to the path in the mmap will be
@@ -421,25 +374,29 @@ impl Directory for MmapDirectory {
     fn delete(&self, path: &Path) -> result::Result<(), DeleteError> {
         let full_path = self.resolve_path(path);
         match fs::remove_file(&full_path) {
-            Ok(_) => self
-                .sync_directory()
-                .map_err(|e| IOError::with_path(path.to_owned(), e).into()),
+            Ok(_) => self.sync_directory().map_err(|e| DeleteError::IOError {
+                io_error: e,
+                filepath: path.to_path_buf(),
+            }),
             Err(e) => {
                 if e.kind() == io::ErrorKind::NotFound {
                     Err(DeleteError::FileDoesNotExist(path.to_owned()))
                 } else {
-                    Err(IOError::with_path(path.to_owned(), e).into())
+                    Err(DeleteError::IOError {
+                        io_error: e,
+                        filepath: path.to_path_buf(),
+                    })
                 }
             }
         }
     }
 
-    fn exists(&self, path: &Path) -> bool {
+    fn exists(&self, path: &Path) -> Result<bool, OpenReadError> {
         let full_path = self.resolve_path(path);
-        full_path.exists()
+        Ok(full_path.exists())
     }
 
-    fn open_write(&mut self, path: &Path) -> Result<WritePtr, OpenWriteError> {
+    fn open_write(&self, path: &Path) -> Result<WritePtr, OpenWriteError> {
         debug!("Open Write {:?}", path);
         let full_path = self.resolve_path(path);
 
@@ -448,22 +405,22 @@ impl Directory for MmapDirectory {
             .create_new(true)
             .open(full_path);
 
-        let mut file = open_res.map_err(|err| {
-            if err.kind() == io::ErrorKind::AlreadyExists {
-                OpenWriteError::FileAlreadyExists(path.to_owned())
+        let mut file = open_res.map_err(|io_err| {
+            if io_err.kind() == io::ErrorKind::AlreadyExists {
+                OpenWriteError::FileAlreadyExists(path.to_path_buf())
             } else {
-                IOError::with_path(path.to_owned(), err).into()
+                OpenWriteError::wrap_io_error(io_err, path.to_path_buf())
             }
         })?;
 
         // making sure the file is created.
         file.flush()
-            .map_err(|e| IOError::with_path(path.to_owned(), e))?;
+            .map_err(|io_error| OpenWriteError::wrap_io_error(io_error, path.to_path_buf()))?;
 
         // Apparetntly, on some filesystem syncing the parent
         // directory is required.
         self.sync_directory()
-            .map_err(|e| IOError::with_path(path.to_owned(), e))?;
+            .map_err(|io_err| OpenWriteError::wrap_io_error(io_err, path.to_path_buf()))?;
 
         let writer = SafeFileWriter::new(file);
         Ok(BufWriter::new(Box::new(writer)))
@@ -474,28 +431,26 @@ impl Directory for MmapDirectory {
         let mut buffer = Vec::new();
         match File::open(&full_path) {
             Ok(mut file) => {
-                file.read_to_end(&mut buffer)
-                    .map_err(|e| IOError::with_path(path.to_owned(), e))?;
+                file.read_to_end(&mut buffer).map_err(|io_error| {
+                    OpenReadError::wrap_io_error(io_error, path.to_path_buf())
+                })?;
                 Ok(buffer)
             }
-            Err(e) => {
-                if e.kind() == io::ErrorKind::NotFound {
+            Err(io_error) => {
+                if io_error.kind() == io::ErrorKind::NotFound {
                     Err(OpenReadError::FileDoesNotExist(path.to_owned()))
                 } else {
-                    Err(IOError::with_path(path.to_owned(), e).into())
+                    Err(OpenReadError::wrap_io_error(io_error, path.to_path_buf()))
                 }
             }
         }
     }
 
-    fn atomic_write(&mut self, path: &Path, content: &[u8]) -> io::Result<()> {
+    fn atomic_write(&self, path: &Path, content: &[u8]) -> io::Result<()> {
         debug!("Atomic Write {:?}", path);
-        let mut tempfile = tempfile::Builder::new().tempfile_in(&self.inner.root_path)?;
-        tempfile.write_all(content)?;
-        tempfile.flush()?;
         let full_path = self.resolve_path(path);
-        tempfile.into_temp_path().persist(full_path)?;
-        Ok(())
+        atomic_write(&full_path, content)?;
+        self.sync_directory()
     }
 
     fn acquire_lock(&self, lock: &Lock) -> Result<DirectoryLock, LockError> {
@@ -519,7 +474,7 @@ impl Directory for MmapDirectory {
     }
 
     fn watch(&self, watch_callback: WatchCallback) -> crate::Result<WatchHandle> {
-        self.inner.watch(watch_callback)
+        Ok(self.inner.watch(watch_callback))
     }
 }
 
@@ -530,12 +485,10 @@ mod tests {
     // The following tests are specific to the MmapDirectory
 
     use super::*;
-    use crate::indexer::LogMergePolicy;
     use crate::schema::{Schema, SchemaBuilder, TEXT};
     use crate::Index;
     use crate::ReloadPolicy;
-    use std::fs;
-    use std::sync::atomic::{AtomicUsize, Ordering};
+    use crate::{common::HasLen, indexer::LogMergePolicy};
 
     #[test]
     fn test_open_non_existent_path() {
@@ -548,7 +501,7 @@ mod tests {
         // cannot be mmapped.
         //
         // In that case the directory returns a SharedVecSlice.
-        let mut mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
+        let mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
         let path = PathBuf::from("test");
         {
             let mut w = mmap_directory.open_write(&path).unwrap();
@@ -564,7 +517,7 @@ mod tests {
 
         // here we test if the cache releases
         // mmaps correctly.
-        let mut mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
+        let mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
         let num_paths = 10;
         let paths: Vec<PathBuf> = (0..num_paths)
             .map(|i| PathBuf::from(&*format!("file_{}", i)))
@@ -624,27 +577,6 @@ mod tests {
         assert_eq!(mmap_directory.get_cache_info().mmapped.len(), 0);
     }
 
-    #[test]
-    fn test_watch_wrapper() {
-        let counter: Arc<AtomicUsize> = Default::default();
-        let counter_clone = counter.clone();
-        let tmp_dir = tempfile::TempDir::new().unwrap();
-        let tmp_dirpath = tmp_dir.path().to_owned();
-        let mut watch_wrapper = WatcherWrapper::new(&tmp_dirpath).unwrap();
-        let tmp_file = tmp_dirpath.join(*META_FILEPATH);
-        let _handle = watch_wrapper.watch(Box::new(move || {
-            counter_clone.fetch_add(1, Ordering::SeqCst);
-        }));
-        let (sender, receiver) = crossbeam::channel::unbounded();
-        let _handle2 = watch_wrapper.watch(Box::new(move || {
-            let _ = sender.send(());
-        }));
-        assert_eq!(counter.load(Ordering::SeqCst), 0);
-        fs::write(&tmp_file, b"whateverwilldo").unwrap();
-        assert!(receiver.recv().is_ok());
-        assert!(counter.load(Ordering::SeqCst) >= 1);
-    }
-
     #[test]
     fn test_mmap_released() {
         let mmap_directory = MmapDirectory::create_from_tempdir().unwrap();
@@ -655,7 +587,7 @@ mod tests {
         {
             let index = Index::create(mmap_directory.clone(), schema).unwrap();
 
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             let mut log_merge_policy = LogMergePolicy::default();
             log_merge_policy.set_min_merge_size(3);
             index_writer.set_merge_policy(Box::new(log_merge_policy));

src/directory/mod.rs

@@ -9,10 +9,12 @@ mod mmap_directory;
 
 mod directory;
 mod directory_lock;
+mod file_slice;
+mod file_watcher;
 mod footer;
 mod managed_directory;
+mod owned_bytes;
 mod ram_directory;
-mod read_only_source;
 mod watch_event_router;
 
 /// Errors specific to the directory module.
@@ -21,11 +23,14 @@ pub mod error;
 pub use self::directory::DirectoryLock;
 pub use self::directory::{Directory, DirectoryClone};
 pub use self::directory_lock::{Lock, INDEX_WRITER_LOCK, META_LOCK};
+pub(crate) use self::file_slice::{ArcBytes, WeakArcBytes};
+pub use self::file_slice::{FileHandle, FileSlice};
+pub use self::owned_bytes::OwnedBytes;
 pub use self::ram_directory::RAMDirectory;
-pub use self::read_only_source::ReadOnlySource;
 pub use self::watch_event_router::{WatchCallback, WatchCallbackList, WatchHandle};
 use std::io::{self, BufWriter, Write};
 use std::path::PathBuf;
+
 /// Outcome of the Garbage collection
 pub struct GarbageCollectionResult {
     /// List of files that were deleted in this cycle

src/directory/owned_bytes.rs

@@ -0,0 +1,290 @@
+use crate::directory::FileHandle;
+use stable_deref_trait::StableDeref;
+use std::convert::TryInto;
+use std::mem;
+use std::ops::{Deref, Range};
+use std::sync::Arc;
+use std::{fmt, io};
+
+/// An OwnedBytes simply wraps an object that owns a slice of data and exposes
+/// this data as a static slice.
+///
+/// The backing object is required to be `StableDeref`.
+#[derive(Clone)]
+pub struct OwnedBytes {
+    data: &'static [u8],
+    box_stable_deref: Arc<dyn Deref<Target = [u8]> + Sync + Send>,
+}
+
+impl FileHandle for OwnedBytes {
+    fn read_bytes(&self, range: Range<usize>) -> io::Result<OwnedBytes> {
+        Ok(self.slice(range))
+    }
+}
+
+impl OwnedBytes {
+    /// Creates an empty `OwnedBytes`.
+    pub fn empty() -> OwnedBytes {
+        OwnedBytes::new(&[][..])
+    }
+
+    /// Creates an `OwnedBytes` intance given a `StableDeref` object.
+    pub fn new<T: StableDeref + Deref<Target = [u8]> + 'static + Send + Sync>(
+        data_holder: T,
+    ) -> OwnedBytes {
+        let box_stable_deref = Arc::new(data_holder);
+        let bytes: &[u8] = box_stable_deref.as_ref();
+        let data = unsafe { mem::transmute::<_, &'static [u8]>(bytes.deref()) };
+        OwnedBytes {
+            box_stable_deref,
+            data,
+        }
+    }
+
+    /// creates a fileslice that is just a view over a slice of the data.
+    pub fn slice(&self, range: Range<usize>) -> Self {
+        OwnedBytes {
+            data: &self.data[range],
+            box_stable_deref: self.box_stable_deref.clone(),
+        }
+    }
+
+    /// Returns the underlying slice of data.
+    /// `Deref` and `AsRef` are also available.
+    #[inline(always)]
+    pub fn as_slice(&self) -> &[u8] {
+        self.data
+    }
+
+    /// Returns the len of the slice.
+    #[inline(always)]
+    pub fn len(&self) -> usize {
+        self.data.len()
+    }
+
+    /// Splits the OwnedBytes into two OwnedBytes `(left, right)`.
+    ///
+    /// Left will hold `split_len` bytes.
+    ///
+    /// This operation is cheap and does not require to copy any memory.
+    /// On the other hand, both `left` and `right` retain a handle over
+    /// the entire slice of memory. In other words, the memory will only
+    /// be released when both left and right are dropped.
+    pub fn split(self, split_len: usize) -> (OwnedBytes, OwnedBytes) {
+        let right_box_stable_deref = self.box_stable_deref.clone();
+        let left = OwnedBytes {
+            data: &self.data[..split_len],
+            box_stable_deref: self.box_stable_deref,
+        };
+        let right = OwnedBytes {
+            data: &self.data[split_len..],
+            box_stable_deref: right_box_stable_deref,
+        };
+        (left, right)
+    }
+
+    /// Returns true iff this `OwnedBytes` is empty.
+    #[inline(always)]
+    pub fn is_empty(&self) -> bool {
+        self.as_slice().is_empty()
+    }
+
+    /// Drops the left most `advance_len` bytes.
+    ///
+    /// See also [.clip(clip_len: usize))](#method.clip).
+    #[inline(always)]
+    pub fn advance(&mut self, advance_len: usize) {
+        self.data = &self.data[advance_len..]
+    }
+
+    /// Reads an `u8` from the `OwnedBytes` and advance by one byte.
+    pub fn read_u8(&mut self) -> u8 {
+        assert!(!self.is_empty());
+
+        let byte = self.as_slice()[0];
+        self.advance(1);
+        byte
+    }
+
+    /// Reads an `u64` encoded as little-endian from the `OwnedBytes` and advance by 8 bytes.
+    pub fn read_u64(&mut self) -> u64 {
+        assert!(self.len() > 7);
+
+        let octlet: [u8; 8] = self.as_slice()[..8].try_into().unwrap();
+        self.advance(8);
+        u64::from_le_bytes(octlet)
+    }
+}
+
+impl fmt::Debug for OwnedBytes {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // We truncate the bytes in order to make sure the debug string
+        // is not too long.
+        let bytes_truncated: &[u8] = if self.len() > 8 {
+            &self.as_slice()[..10]
+        } else {
+            self.as_slice()
+        };
+        write!(f, "OwnedBytes({:?}, len={})", bytes_truncated, self.len())
+    }
+}
+
+impl Deref for OwnedBytes {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        self.as_slice()
+    }
+}
+
+impl io::Read for OwnedBytes {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let read_len = {
+            let data = self.as_slice();
+            if data.len() >= buf.len() {
+                let buf_len = buf.len();
+                buf.copy_from_slice(&data[..buf_len]);
+                buf.len()
+            } else {
+                let data_len = data.len();
+                buf[..data_len].copy_from_slice(data);
+                data_len
+            }
+        };
+        self.advance(read_len);
+        Ok(read_len)
+    }
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        let read_len = {
+            let data = self.as_slice();
+            buf.extend(data);
+            data.len()
+        };
+        self.advance(read_len);
+        Ok(read_len)
+    }
+    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
+        let read_len = self.read(buf)?;
+        if read_len != buf.len() {
+            return Err(io::Error::new(
+                io::ErrorKind::UnexpectedEof,
+                "failed to fill whole buffer",
+            ));
+        }
+        Ok(())
+    }
+}
+
+impl AsRef<[u8]> for OwnedBytes {
+    fn as_ref(&self) -> &[u8] {
+        self.as_slice()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io::{self, Read};
+
+    use super::OwnedBytes;
+
+    #[test]
+    fn test_owned_bytes_debug() {
+        let short_bytes = OwnedBytes::new(b"abcd".as_ref());
+        assert_eq!(
+            format!("{:?}", short_bytes),
+            "OwnedBytes([97, 98, 99, 100], len=4)"
+        );
+        let long_bytes = OwnedBytes::new(b"abcdefghijklmnopq".as_ref());
+        assert_eq!(
+            format!("{:?}", long_bytes),
+            "OwnedBytes([97, 98, 99, 100, 101, 102, 103, 104, 105, 106], len=17)"
+        );
+    }
+
+    #[test]
+    fn test_owned_bytes_read() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcdefghiklmnopqrstuvwxyz".as_ref());
+        {
+            let mut buf = [0u8; 5];
+            bytes.read_exact(&mut buf[..]).unwrap();
+            assert_eq!(&buf, b"abcde");
+            assert_eq!(bytes.as_slice(), b"fghiklmnopqrstuvwxyz")
+        }
+        {
+            let mut buf = [0u8; 2];
+            bytes.read_exact(&mut buf[..]).unwrap();
+            assert_eq!(&buf, b"fg");
+            assert_eq!(bytes.as_slice(), b"hiklmnopqrstuvwxyz")
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_right_at_the_end() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = [0u8; 5];
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 5);
+        assert_eq!(&buf, b"abcde");
+        assert_eq!(bytes.as_slice(), b"");
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 0);
+        assert_eq!(&buf, b"abcde");
+        Ok(())
+    }
+    #[test]
+    fn test_owned_bytes_read_incomplete() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = [0u8; 7];
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 5);
+        assert_eq!(&buf[..5], b"abcde");
+        assert_eq!(bytes.read(&mut buf[..]).unwrap(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_to_end() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"abcde".as_ref());
+        let mut buf = Vec::new();
+        bytes.read_to_end(&mut buf)?;
+        assert_eq!(buf.as_slice(), b"abcde".as_ref());
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_u8() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"\xFF".as_ref());
+        assert_eq!(bytes.read_u8(), 255);
+        assert_eq!(bytes.len(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_read_u64() -> io::Result<()> {
+        let mut bytes = OwnedBytes::new(b"\0\xFF\xFF\xFF\xFF\xFF\xFF\xFF".as_ref());
+        assert_eq!(bytes.read_u64(), u64::MAX - 255);
+        assert_eq!(bytes.len(), 0);
+        Ok(())
+    }
+
+    #[test]
+    fn test_owned_bytes_split() {
+        let bytes = OwnedBytes::new(b"abcdefghi".as_ref());
+        let (left, right) = bytes.split(3);
+        assert_eq!(left.as_slice(), b"abc");
+        assert_eq!(right.as_slice(), b"defghi");
+    }
+
+    #[test]
+    fn test_owned_bytes_split_boundary() {
+        let bytes = OwnedBytes::new(b"abcdefghi".as_ref());
+        {
+            let (left, right) = bytes.clone().split(0);
+            assert_eq!(left.as_slice(), b"");
+            assert_eq!(right.as_slice(), b"abcdefghi");
+        }
+        {
+            let (left, right) = bytes.split(9);
+            assert_eq!(left.as_slice(), b"abcdefghi");
+            assert_eq!(right.as_slice(), b"");
+        }
+    }
+}

src/directory/ram_directory.rs

@@ -1,9 +1,9 @@
-use crate::core::META_FILEPATH;
 use crate::directory::error::{DeleteError, OpenReadError, OpenWriteError};
 use crate::directory::AntiCallToken;
 use crate::directory::WatchCallbackList;
-use crate::directory::{Directory, ReadOnlySource, WatchCallback, WatchHandle};
+use crate::directory::{Directory, FileSlice, WatchCallback, WatchHandle};
 use crate::directory::{TerminatingWrite, WritePtr};
+use crate::{common::HasLen, core::META_FILEPATH};
 use fail::fail_point;
 use std::collections::HashMap;
 use std::fmt;
@@ -12,6 +12,8 @@ use std::path::{Path, PathBuf};
 use std::result;
 use std::sync::{Arc, RwLock};
 
+use super::FileHandle;
+
 /// Writer associated with the `RAMDirectory`
 ///
 /// The Writer just writes a buffer.
@@ -80,17 +82,17 @@ impl TerminatingWrite for VecWriter {
 
 #[derive(Default)]
 struct InnerDirectory {
-    fs: HashMap<PathBuf, ReadOnlySource>,
+    fs: HashMap<PathBuf, FileSlice>,
     watch_router: WatchCallbackList,
 }
 
 impl InnerDirectory {
     fn write(&mut self, path: PathBuf, data: &[u8]) -> bool {
-        let data = ReadOnlySource::new(Vec::from(data));
+        let data = FileSlice::from(data.to_vec());
         self.fs.insert(path, data).is_some()
     }
 
-    fn open_read(&self, path: &Path) -> Result<ReadOnlySource, OpenReadError> {
+    fn open_read(&self, path: &Path) -> Result<FileSlice, OpenReadError> {
         self.fs
             .get(path)
             .ok_or_else(|| OpenReadError::FileDoesNotExist(PathBuf::from(path)))
@@ -151,11 +153,11 @@ impl RAMDirectory {
     /// written using the `atomic_write` api.
     ///
     /// If an error is encounterred, files may be persisted partially.
-    pub fn persist(&self, dest: &mut dyn Directory) -> crate::Result<()> {
+    pub fn persist(&self, dest: &dyn Directory) -> crate::Result<()> {
         let wlock = self.fs.write().unwrap();
-        for (path, source) in wlock.fs.iter() {
+        for (path, file) in wlock.fs.iter() {
             let mut dest_wrt = dest.open_write(path)?;
-            dest_wrt.write_all(source.as_slice())?;
+            dest_wrt.write_all(file.read_bytes()?.as_slice())?;
             dest_wrt.terminate()?;
         }
         Ok(())
@@ -163,24 +165,37 @@ impl RAMDirectory {
 }
 
 impl Directory for RAMDirectory {
-    fn open_read(&self, path: &Path) -> result::Result<ReadOnlySource, OpenReadError> {
+    fn get_file_handle(&self, path: &Path) -> Result<Box<dyn FileHandle>, OpenReadError> {
+        let file_slice = self.open_read(path)?;
+        Ok(Box::new(file_slice))
+    }
+
+    fn open_read(&self, path: &Path) -> result::Result<FileSlice, OpenReadError> {
         self.fs.read().unwrap().open_read(path)
     }
 
     fn delete(&self, path: &Path) -> result::Result<(), DeleteError> {
         fail_point!("RAMDirectory::delete", |_| {
-            use crate::directory::error::IOError;
-            let io_error = IOError::from(io::Error::from(io::ErrorKind::Other));
-            Err(DeleteError::from(io_error))
+            Err(DeleteError::IOError {
+                io_error: io::Error::from(io::ErrorKind::Other),
+                filepath: path.to_path_buf(),
+            })
         });
         self.fs.write().unwrap().delete(path)
     }
 
-    fn exists(&self, path: &Path) -> bool {
-        self.fs.read().unwrap().exists(path)
+    fn exists(&self, path: &Path) -> Result<bool, OpenReadError> {
+        Ok(self
+            .fs
+            .read()
+            .map_err(|e| OpenReadError::IOError {
+                io_error: io::Error::new(io::ErrorKind::Other, e.to_string()),
+                filepath: path.to_path_buf(),
+            })?
+            .exists(path))
     }
 
-    fn open_write(&mut self, path: &Path) -> Result<WritePtr, OpenWriteError> {
+    fn open_write(&self, path: &Path) -> Result<WritePtr, OpenWriteError> {
         let mut fs = self.fs.write().unwrap();
         let path_buf = PathBuf::from(path);
         let vec_writer = VecWriter::new(path_buf.clone(), self.clone());
@@ -194,23 +209,26 @@ impl Directory for RAMDirectory {
     }
 
     fn atomic_read(&self, path: &Path) -> Result<Vec<u8>, OpenReadError> {
-        Ok(self.open_read(path)?.as_slice().to_owned())
+        let bytes =
+            self.open_read(path)?
+                .read_bytes()
+                .map_err(|io_error| OpenReadError::IOError {
+                    io_error,
+                    filepath: path.to_path_buf(),
+                })?;
+        Ok(bytes.as_slice().to_owned())
     }
 
-    fn atomic_write(&mut self, path: &Path, data: &[u8]) -> io::Result<()> {
+    fn atomic_write(&self, path: &Path, data: &[u8]) -> io::Result<()> {
         fail_point!("RAMDirectory::atomic_write", |msg| Err(io::Error::new(
             io::ErrorKind::Other,
             msg.unwrap_or_else(|| "Undefined".to_string())
         )));
         let path_buf = PathBuf::from(path);
 
-        // Reserve the path to prevent calls to .write() to succeed.
-        self.fs.write().unwrap().write(path_buf.clone(), &[]);
+        self.fs.write().unwrap().write(path_buf, data);
 
-        let mut vec_writer = VecWriter::new(path_buf, self.clone());
-        vec_writer.write_all(data)?;
-        vec_writer.flush()?;
-        if path == Path::new(&*META_FILEPATH) {
+        if path == *META_FILEPATH {
             let _ = self.fs.write().unwrap().watch_router.broadcast();
         }
         Ok(())
@@ -234,13 +252,13 @@ mod tests {
         let msg_seq: &'static [u8] = b"sequential is the way";
         let path_atomic: &'static Path = Path::new("atomic");
         let path_seq: &'static Path = Path::new("seq");
-        let mut directory = RAMDirectory::create();
+        let directory = RAMDirectory::create();
         assert!(directory.atomic_write(path_atomic, msg_atomic).is_ok());
         let mut wrt = directory.open_write(path_seq).unwrap();
         assert!(wrt.write_all(msg_seq).is_ok());
         assert!(wrt.flush().is_ok());
-        let mut directory_copy = RAMDirectory::create();
-        assert!(directory.persist(&mut directory_copy).is_ok());
+        let directory_copy = RAMDirectory::create();
+        assert!(directory.persist(&directory_copy).is_ok());
         assert_eq!(directory_copy.atomic_read(path_atomic).unwrap(), msg_atomic);
         assert_eq!(directory_copy.atomic_read(path_seq).unwrap(), msg_seq);
     }

src/directory/read_only_source.rs

@@ -1,137 +0,0 @@
-use crate::common::HasLen;
-use stable_deref_trait::{CloneStableDeref, StableDeref};
-use std::ops::Deref;
-use std::sync::Arc;
-
-pub type BoxedData = Box<dyn Deref<Target = [u8]> + Send + Sync + 'static>;
-
-/// Read object that represents files in tantivy.
-///
-/// These read objects are only in charge to deliver
-/// the data in the form of a constant read-only `&[u8]`.
-/// Whatever happens to the directory file, the data
-/// hold by this object should never be altered or destroyed.
-pub struct ReadOnlySource {
-    data: Arc<BoxedData>,
-    start: usize,
-    stop: usize,
-}
-
-unsafe impl StableDeref for ReadOnlySource {}
-unsafe impl CloneStableDeref for ReadOnlySource {}
-
-impl Deref for ReadOnlySource {
-    type Target = [u8];
-
-    fn deref(&self) -> &[u8] {
-        self.as_slice()
-    }
-}
-
-impl From<Arc<BoxedData>> for ReadOnlySource {
-    fn from(data: Arc<BoxedData>) -> Self {
-        let len = data.len();
-        ReadOnlySource {
-            data,
-            start: 0,
-            stop: len,
-        }
-    }
-}
-
-impl ReadOnlySource {
-    pub(crate) fn new<D>(data: D) -> ReadOnlySource
-    where
-        D: Deref<Target = [u8]> + Send + Sync + 'static,
-    {
-        let len = data.len();
-        ReadOnlySource {
-            data: Arc::new(Box::new(data)),
-            start: 0,
-            stop: len,
-        }
-    }
-
-    /// Creates an empty ReadOnlySource
-    pub fn empty() -> ReadOnlySource {
-        ReadOnlySource::new(&[][..])
-    }
-
-    /// Returns the data underlying the ReadOnlySource object.
-    pub fn as_slice(&self) -> &[u8] {
-        &self.data[self.start..self.stop]
-    }
-
-    /// Splits into 2 `ReadOnlySource`, at the offset given
-    /// as an argument.
-    pub fn split(self, addr: usize) -> (ReadOnlySource, ReadOnlySource) {
-        let left = self.slice(0, addr);
-        let right = self.slice_from(addr);
-        (left, right)
-    }
-
-    /// Splits into 2 `ReadOnlySource`, at the offset `end - right_len`.
-    pub fn split_from_end(self, right_len: usize) -> (ReadOnlySource, ReadOnlySource) {
-        let left_len = self.len() - right_len;
-        self.split(left_len)
-    }
-
-    /// Creates a ReadOnlySource that is just a
-    /// view over a slice of the data.
-    ///
-    /// Keep in mind that any living slice extends
-    /// the lifetime of the original ReadOnlySource,
-    ///
-    /// For instance, if `ReadOnlySource` wraps 500MB
-    /// worth of data in anonymous memory, and only a
-    /// 1KB slice is remaining, the whole `500MBs`
-    /// are retained in memory.
-    pub fn slice(&self, start: usize, stop: usize) -> ReadOnlySource {
-        assert!(
-            start <= stop,
-            "Requested negative slice [{}..{}]",
-            start,
-            stop
-        );
-        assert!(stop <= self.len());
-        ReadOnlySource {
-            data: self.data.clone(),
-            start: self.start + start,
-            stop: self.start + stop,
-        }
-    }
-
-    /// Like `.slice(...)` but enforcing only the `from`
-    /// boundary.
-    ///
-    /// Equivalent to `.slice(from_offset, self.len())`
-    pub fn slice_from(&self, from_offset: usize) -> ReadOnlySource {
-        self.slice(from_offset, self.len())
-    }
-
-    /// Like `.slice(...)` but enforcing only the `to`
-    /// boundary.
-    ///
-    /// Equivalent to `.slice(0, to_offset)`
-    pub fn slice_to(&self, to_offset: usize) -> ReadOnlySource {
-        self.slice(0, to_offset)
-    }
-}
-
-impl HasLen for ReadOnlySource {
-    fn len(&self) -> usize {
-        self.stop - self.start
-    }
-}
-
-impl Clone for ReadOnlySource {
-    fn clone(&self) -> Self {
-        self.slice_from(0)
-    }
-}
-
-impl From<Vec<u8>> for ReadOnlySource {
-    fn from(data: Vec<u8>) -> ReadOnlySource {
-        ReadOnlySource::new(data)
-    }
-}

src/directory/tests.rs

@@ -20,45 +20,47 @@ mod mmap_directory_tests {
     }
 
     #[test]
-    fn test_simple() {
-        let mut directory = make_directory();
-        super::test_simple(&mut directory);
+    fn test_simple() -> crate::Result<()> {
+        let directory = make_directory();
+        super::test_simple(&directory)
     }
 
     #[test]
     fn test_write_create_the_file() {
-        let mut directory = make_directory();
-        super::test_write_create_the_file(&mut directory);
+        let directory = make_directory();
+        super::test_write_create_the_file(&directory);
     }
 
     #[test]
-    fn test_rewrite_forbidden() {
-        let mut directory = make_directory();
-        super::test_rewrite_forbidden(&mut directory);
+    fn test_rewrite_forbidden() -> crate::Result<()> {
+        let directory = make_directory();
+        super::test_rewrite_forbidden(&directory)?;
+        Ok(())
     }
 
     #[test]
-    fn test_directory_delete() {
-        let mut directory = make_directory();
-        super::test_directory_delete(&mut directory);
+    fn test_directory_delete() -> crate::Result<()> {
+        let directory = make_directory();
+        super::test_directory_delete(&directory)?;
+        Ok(())
     }
 
     #[test]
     fn test_lock_non_blocking() {
-        let mut directory = make_directory();
-        super::test_lock_non_blocking(&mut directory);
+        let directory = make_directory();
+        super::test_lock_non_blocking(&directory);
     }
 
     #[test]
     fn test_lock_blocking() {
-        let mut directory = make_directory();
-        super::test_lock_blocking(&mut directory);
+        let directory = make_directory();
+        super::test_lock_blocking(&directory);
     }
 
     #[test]
     fn test_watch() {
-        let mut directory = make_directory();
-        super::test_watch(&mut directory);
+        let directory = make_directory();
+        super::test_watch(&directory);
     }
 }
 
@@ -72,45 +74,47 @@ mod ram_directory_tests {
     }
 
     #[test]
-    fn test_simple() {
-        let mut directory = make_directory();
-        super::test_simple(&mut directory);
+    fn test_simple() -> crate::Result<()> {
+        let directory = make_directory();
+        super::test_simple(&directory)
     }
 
     #[test]
     fn test_write_create_the_file() {
-        let mut directory = make_directory();
-        super::test_write_create_the_file(&mut directory);
+        let directory = make_directory();
+        super::test_write_create_the_file(&directory);
     }
 
     #[test]
-    fn test_rewrite_forbidden() {
-        let mut directory = make_directory();
-        super::test_rewrite_forbidden(&mut directory);
+    fn test_rewrite_forbidden() -> crate::Result<()> {
+        let directory = make_directory();
+        super::test_rewrite_forbidden(&directory)?;
+        Ok(())
     }
 
     #[test]
-    fn test_directory_delete() {
-        let mut directory = make_directory();
-        super::test_directory_delete(&mut directory);
+    fn test_directory_delete() -> crate::Result<()> {
+        let directory = make_directory();
+        super::test_directory_delete(&directory)?;
+        Ok(())
     }
 
     #[test]
     fn test_lock_non_blocking() {
-        let mut directory = make_directory();
-        super::test_lock_non_blocking(&mut directory);
+        let directory = make_directory();
+        super::test_lock_non_blocking(&directory);
     }
 
     #[test]
     fn test_lock_blocking() {
-        let mut directory = make_directory();
-        super::test_lock_blocking(&mut directory);
+        let directory = make_directory();
+        super::test_lock_blocking(&directory);
     }
 
     #[test]
     fn test_watch() {
-        let mut directory = make_directory();
-        super::test_watch(&mut directory);
+        let directory = make_directory();
+        super::test_watch(&directory);
     }
 }
 
@@ -118,68 +122,61 @@ mod ram_directory_tests {
 #[should_panic]
 fn ram_directory_panics_if_flush_forgotten() {
     let test_path: &'static Path = Path::new("some_path_for_test");
-    let mut ram_directory = RAMDirectory::create();
+    let ram_directory = RAMDirectory::create();
     let mut write_file = ram_directory.open_write(test_path).unwrap();
     assert!(write_file.write_all(&[4]).is_ok());
 }
 
-fn test_simple(directory: &mut dyn Directory) {
+fn test_simple(directory: &dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
-    {
-        let mut write_file = directory.open_write(test_path).unwrap();
-        assert!(directory.exists(test_path));
-        write_file.write_all(&[4]).unwrap();
-        write_file.write_all(&[3]).unwrap();
-        write_file.write_all(&[7, 3, 5]).unwrap();
-        write_file.flush().unwrap();
-    }
-    {
-        let read_file = directory.open_read(test_path).unwrap();
-        let data: &[u8] = &*read_file;
-        assert_eq!(data, &[4u8, 3u8, 7u8, 3u8, 5u8]);
-    }
+    let mut write_file = directory.open_write(test_path)?;
+    assert!(directory.exists(test_path).unwrap());
+    write_file.write_all(&[4])?;
+    write_file.write_all(&[3])?;
+    write_file.write_all(&[7, 3, 5])?;
+    write_file.flush()?;
+    let read_file = directory.open_read(test_path)?.read_bytes()?;
+    assert_eq!(read_file.as_slice(), &[4u8, 3u8, 7u8, 3u8, 5u8]);
+    mem::drop(read_file);
     assert!(directory.delete(test_path).is_ok());
-    assert!(!directory.exists(test_path));
+    assert!(!directory.exists(test_path).unwrap());
+    Ok(())
 }
 
-fn test_rewrite_forbidden(directory: &mut dyn Directory) {
+fn test_rewrite_forbidden(directory: &dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
-    {
-        directory.open_write(test_path).unwrap();
-        assert!(directory.exists(test_path));
-    }
-    {
-        assert!(directory.open_write(test_path).is_err());
-    }
+    directory.open_write(test_path)?;
+    assert!(directory.exists(test_path).unwrap());
+    assert!(directory.open_write(test_path).is_err());
     assert!(directory.delete(test_path).is_ok());
+    Ok(())
 }
 
-fn test_write_create_the_file(directory: &mut dyn Directory) {
+fn test_write_create_the_file(directory: &dyn Directory) {
     let test_path: &'static Path = Path::new("some_path_for_test");
     {
         assert!(directory.open_read(test_path).is_err());
         let _w = directory.open_write(test_path).unwrap();
-        assert!(directory.exists(test_path));
+        assert!(directory.exists(test_path).unwrap());
         assert!(directory.open_read(test_path).is_ok());
         assert!(directory.delete(test_path).is_ok());
     }
 }
 
-fn test_directory_delete(directory: &mut dyn Directory) {
+fn test_directory_delete(directory: &dyn Directory) -> crate::Result<()> {
     let test_path: &'static Path = Path::new("some_path_for_test");
     assert!(directory.open_read(test_path).is_err());
-    let mut write_file = directory.open_write(&test_path).unwrap();
-    write_file.write_all(&[1, 2, 3, 4]).unwrap();
-    write_file.flush().unwrap();
+    let mut write_file = directory.open_write(&test_path)?;
+    write_file.write_all(&[1, 2, 3, 4])?;
+    write_file.flush()?;
     {
-        let read_handle = directory.open_read(&test_path).unwrap();
-        assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
+        let read_handle = directory.open_read(&test_path)?.read_bytes()?;
+        assert_eq!(read_handle.as_slice(), &[1u8, 2u8, 3u8, 4u8]);
         // Mapped files can't be deleted on Windows
         if !cfg!(windows) {
             assert!(directory.delete(&test_path).is_ok());
-            assert_eq!(&*read_handle, &[1u8, 2u8, 3u8, 4u8]);
+            assert_eq!(read_handle.as_slice(), &[1u8, 2u8, 3u8, 4u8]);
         }
-
         assert!(directory.delete(Path::new("SomeOtherPath")).is_err());
     }
 
@@ -189,43 +186,40 @@ fn test_directory_delete(directory: &mut dyn Directory) {
 
     assert!(directory.open_read(&test_path).is_err());
     assert!(directory.delete(&test_path).is_err());
+    Ok(())
 }
 
-fn test_watch(directory: &mut dyn Directory) {
-    let num_progress: Arc<AtomicUsize> = Default::default();
+fn test_watch(directory: &dyn Directory) {
     let counter: Arc<AtomicUsize> = Default::default();
-    let counter_clone = counter.clone();
-    let (sender, receiver) = crossbeam::channel::unbounded();
-    let watch_callback = Box::new(move || {
-        counter_clone.fetch_add(1, SeqCst);
-    });
-    // This callback is used to synchronize watching in our unit test.
-    // We bind it to a variable because the callback is removed when that
-    // handle is dropped.
-    let watch_handle = directory.watch(watch_callback).unwrap();
-    let _progress_listener = directory
-        .watch(Box::new(move || {
-            let val = num_progress.fetch_add(1, SeqCst);
-            let _ = sender.send(val);
+    let (tx, rx) = crossbeam::channel::unbounded();
+    let timeout = Duration::from_millis(500);
+
+    let handle = directory
+        .watch(WatchCallback::new(move || {
+            let val = counter.fetch_add(1, SeqCst);
+            tx.send(val + 1).unwrap();
         }))
         .unwrap();
 
-    for i in 0..10 {
-        assert!(i <= counter.load(SeqCst));
-        assert!(directory
-            .atomic_write(Path::new("meta.json"), b"random_test_data_2")
-            .is_ok());
-        assert!(i + 1 <= counter.load(SeqCst)); // notify can trigger more than once.
-    }
-    mem::drop(watch_handle);
     assert!(directory
-        .atomic_write(Path::new("meta.json"), b"random_test_data")
+        .atomic_write(Path::new("meta.json"), b"foo")
         .is_ok());
-    assert!(receiver.recv_timeout(Duration::from_millis(500)).is_ok());
-    assert!(10 <= counter.load(SeqCst));
+    assert_eq!(rx.recv_timeout(timeout), Ok(1));
+
+    assert!(directory
+        .atomic_write(Path::new("meta.json"), b"bar")
+        .is_ok());
+    assert_eq!(rx.recv_timeout(timeout), Ok(2));
+
+    mem::drop(handle);
+
+    assert!(directory
+        .atomic_write(Path::new("meta.json"), b"qux")
+        .is_ok());
+    assert!(rx.recv_timeout(timeout).is_err());
 }
 
-fn test_lock_non_blocking(directory: &mut dyn Directory) {
+fn test_lock_non_blocking(directory: &dyn Directory) {
     {
         let lock_a_res = directory.acquire_lock(&Lock {
             filepath: PathBuf::from("a.lock"),
@@ -250,7 +244,7 @@ fn test_lock_non_blocking(directory: &mut dyn Directory) {
     assert!(lock_a_res.is_ok());
 }
 
-fn test_lock_blocking(directory: &mut dyn Directory) {
+fn test_lock_blocking(directory: &dyn Directory) {
     let lock_a_res = directory.acquire_lock(&Lock {
         filepath: PathBuf::from("a.lock"),
         is_blocking: true,

src/directory/watch_event_router.rs

@@ -4,8 +4,20 @@ use std::sync::Arc;
 use std::sync::RwLock;
 use std::sync::Weak;
 
-/// Type alias for callbacks registered when watching files of a `Directory`.
-pub type WatchCallback = Box<dyn Fn() + Sync + Send>;
+/// Cloneable wrapper for callbacks registered when watching files of a `Directory`.
+#[derive(Clone)]
+pub struct WatchCallback(Arc<dyn Fn() + Sync + Send>);
+
+impl WatchCallback {
+    /// Wraps a `Fn()` to create a WatchCallback.
+    pub fn new<F: Fn() + Sync + Send + 'static>(op: F) -> Self {
+        WatchCallback(Arc::new(op))
+    }
+
+    fn call(&self) {
+        self.0()
+    }
+}
 
 /// Helper struct to implement the watch method in `Directory` implementations.
 ///
@@ -29,6 +41,13 @@ impl WatchHandle {
     pub fn new(watch_callback: Arc<WatchCallback>) -> WatchHandle {
         WatchHandle(watch_callback)
     }
+
+    /// Returns an empty watch handle.
+    ///
+    /// This function is only useful when implementing a readonly directory.
+    pub fn empty() -> WatchHandle {
+        WatchHandle::new(Arc::new(WatchCallback::new(|| {})))
+    }
 }
 
 impl WatchCallbackList {
@@ -40,13 +59,13 @@ impl WatchCallbackList {
         WatchHandle::new(watch_callback_arc)
     }
 
-    fn list_callback(&self) -> Vec<Arc<WatchCallback>> {
-        let mut callbacks = vec![];
+    fn list_callback(&self) -> Vec<WatchCallback> {
+        let mut callbacks: Vec<WatchCallback> = vec![];
         let mut router_wlock = self.router.write().unwrap();
         let mut i = 0;
         while i < router_wlock.len() {
             if let Some(watch) = router_wlock[i].upgrade() {
-                callbacks.push(watch);
+                callbacks.push(watch.as_ref().clone());
                 i += 1;
             } else {
                 router_wlock.swap_remove(i);
@@ -68,7 +87,7 @@ impl WatchCallbackList {
             .name("watch-callbacks".to_string())
             .spawn(move || {
                 for callback in callbacks {
-                    callback();
+                    callback.call();
                 }
                 let _ = sender.send(());
             });
@@ -84,7 +103,7 @@ impl WatchCallbackList {
 
 #[cfg(test)]
 mod tests {
-    use crate::directory::WatchCallbackList;
+    use crate::directory::{WatchCallback, WatchCallbackList};
     use futures::executor::block_on;
     use std::mem;
     use std::sync::atomic::{AtomicUsize, Ordering};
@@ -95,7 +114,7 @@ mod tests {
         let watch_event_router = WatchCallbackList::default();
         let counter: Arc<AtomicUsize> = Default::default();
         let counter_clone = counter.clone();
-        let inc_callback = Box::new(move || {
+        let inc_callback = WatchCallback::new(move || {
             counter_clone.fetch_add(1, Ordering::SeqCst);
         });
         block_on(watch_event_router.broadcast());
@@ -123,7 +142,7 @@ mod tests {
         let counter: Arc<AtomicUsize> = Default::default();
         let inc_callback = |inc: usize| {
             let counter_clone = counter.clone();
-            Box::new(move || {
+            WatchCallback::new(move || {
                 counter_clone.fetch_add(inc, Ordering::SeqCst);
             })
         };
@@ -151,7 +170,7 @@ mod tests {
         let watch_event_router = WatchCallbackList::default();
         let counter: Arc<AtomicUsize> = Default::default();
         let counter_clone = counter.clone();
-        let inc_callback = Box::new(move || {
+        let inc_callback = WatchCallback::new(move || {
             counter_clone.fetch_add(1, Ordering::SeqCst);
         });
         let handle_a = watch_event_router.subscribe(inc_callback);

src/docset.rs

@@ -10,7 +10,7 @@ use std::borrow::BorrowMut;
 pub const TERMINATED: DocId = std::i32::MAX as u32;
 
 /// Represents an iterable set of sorted doc ids.
-pub trait DocSet {
+pub trait DocSet: Send {
     /// Goes to the next element.
     ///
     /// The DocId of the next element is returned.
@@ -129,6 +129,14 @@ impl<'a> DocSet for &'a mut dyn DocSet {
     fn size_hint(&self) -> u32 {
         (**self).size_hint()
     }
+
+    fn count(&mut self, delete_bitset: &DeleteBitSet) -> u32 {
+        (**self).count(delete_bitset)
+    }
+
+    fn count_including_deleted(&mut self) -> u32 {
+        (**self).count_including_deleted()
+    }
 }
 
 impl<TDocSet: DocSet + ?Sized> DocSet for Box<TDocSet> {

src/error.rs

@@ -2,21 +2,27 @@
 
 use std::io;
 
-use crate::directory::error::{IOError, OpenDirectoryError, OpenReadError, OpenWriteError};
 use crate::directory::error::{Incompatibility, LockError};
 use crate::fastfield::FastFieldNotAvailableError;
 use crate::query;
-use crate::schema;
+use crate::{
+    directory::error::{OpenDirectoryError, OpenReadError, OpenWriteError},
+    schema,
+};
 use std::fmt;
 use std::path::PathBuf;
 use std::sync::PoisonError;
 
+/// Represents a `DataCorruption` error.
+///
+/// When facing data corruption, tantivy  actually panic or return this error.
 pub struct DataCorruption {
     filepath: Option<PathBuf>,
     comment: String,
 }
 
 impl DataCorruption {
+    /// Creates a `DataCorruption` Error.
     pub fn new(filepath: PathBuf, comment: String) -> DataCorruption {
         DataCorruption {
             filepath: Some(filepath),
@@ -24,10 +30,11 @@ impl DataCorruption {
         }
     }
 
-    pub fn comment_only(comment: String) -> DataCorruption {
+    /// Creates a `DataCorruption` Error, when the filepath is irrelevant.
+    pub fn comment_only<TStr: ToString>(comment: TStr) -> DataCorruption {
         DataCorruption {
             filepath: None,
-            comment,
+            comment: comment.to_string(),
         }
     }
 }
@@ -43,44 +50,47 @@ impl fmt::Debug for DataCorruption {
     }
 }
 
-/// The library's failure based error enum
-#[derive(Debug, Fail)]
+/// The library's error enum
+#[derive(Debug, Error)]
 pub enum TantivyError {
-    /// Path does not exist.
-    #[fail(display = "Path does not exist: '{:?}'", _0)]
-    PathDoesNotExist(PathBuf),
-    /// File already exists, this is a problem when we try to write into a new file.
-    #[fail(display = "File already exists: '{:?}'", _0)]
-    FileAlreadyExists(PathBuf),
+    /// Failed to open the directory.
+    #[error("Failed to open the directory: '{0:?}'")]
+    OpenDirectoryError(#[from] OpenDirectoryError),
+    /// Failed to open a file for read.
+    #[error("Failed to open file for read: '{0:?}'")]
+    OpenReadError(#[from] OpenReadError),
+    /// Failed to open a file for write.
+    #[error("Failed to open file for write: '{0:?}'")]
+    OpenWriteError(#[from] OpenWriteError),
     /// Index already exists in this directory
-    #[fail(display = "Index already exists")]
+    #[error("Index already exists")]
     IndexAlreadyExists,
     /// Failed to acquire file lock
-    #[fail(display = "Failed to acquire Lockfile: {:?}. {:?}", _0, _1)]
+    #[error("Failed to acquire Lockfile: {0:?}. {1:?}")]
     LockFailure(LockError, Option<String>),
     /// IO Error.
-    #[fail(display = "An IO error occurred: '{}'", _0)]
-    IOError(#[cause] IOError),
+    #[error("An IO error occurred: '{0}'")]
+    IOError(#[from] io::Error),
     /// Data corruption.
-    #[fail(display = "{:?}", _0)]
+    #[error("Data corrupted: '{0:?}'")]
     DataCorruption(DataCorruption),
     /// A thread holding the locked panicked and poisoned the lock.
-    #[fail(display = "A thread holding the locked panicked and poisoned the lock")]
+    #[error("A thread holding the locked panicked and poisoned the lock")]
     Poisoned,
     /// Invalid argument was passed by the user.
-    #[fail(display = "An invalid argument was passed: '{}'", _0)]
+    #[error("An invalid argument was passed: '{0}'")]
     InvalidArgument(String),
     /// An Error happened in one of the thread.
-    #[fail(display = "An error occurred in a thread: '{}'", _0)]
+    #[error("An error occurred in a thread: '{0}'")]
     ErrorInThread(String),
     /// An Error appeared related to the schema.
-    #[fail(display = "Schema error: '{}'", _0)]
+    #[error("Schema error: '{0}'")]
     SchemaError(String),
     /// System error. (e.g.: We failed spawning a new thread)
-    #[fail(display = "System error.'{}'", _0)]
+    #[error("System error.'{0}'")]
     SystemError(String),
     /// Index incompatible with current version of tantivy
-    #[fail(display = "{:?}", _0)]
+    #[error("{0:?}")]
     IncompatibleIndex(Incompatibility),
 }
 
@@ -89,31 +99,17 @@ impl From<DataCorruption> for TantivyError {
         TantivyError::DataCorruption(data_corruption)
     }
 }
-
 impl From<FastFieldNotAvailableError> for TantivyError {
     fn from(fastfield_error: FastFieldNotAvailableError) -> TantivyError {
         TantivyError::SchemaError(format!("{}", fastfield_error))
     }
 }
-
 impl From<LockError> for TantivyError {
     fn from(lock_error: LockError) -> TantivyError {
         TantivyError::LockFailure(lock_error, None)
     }
 }
 
-impl From<IOError> for TantivyError {
-    fn from(io_error: IOError) -> TantivyError {
-        TantivyError::IOError(io_error)
-    }
-}
-
-impl From<io::Error> for TantivyError {
-    fn from(io_error: io::Error) -> TantivyError {
-        TantivyError::IOError(io_error.into())
-    }
-}
-
 impl From<query::QueryParserError> for TantivyError {
     fn from(parsing_error: query::QueryParserError) -> TantivyError {
         TantivyError::InvalidArgument(format!("Query is invalid. {:?}", parsing_error))
@@ -126,15 +122,9 @@ impl<Guard> From<PoisonError<Guard>> for TantivyError {
     }
 }
 
-impl From<OpenReadError> for TantivyError {
-    fn from(error: OpenReadError) -> TantivyError {
-        match error {
-            OpenReadError::FileDoesNotExist(filepath) => TantivyError::PathDoesNotExist(filepath),
-            OpenReadError::IOError(io_error) => TantivyError::IOError(io_error),
-            OpenReadError::IncompatibleIndex(incompatibility) => {
-                TantivyError::IncompatibleIndex(incompatibility)
-            }
-        }
+impl From<chrono::ParseError> for TantivyError {
+    fn from(err: chrono::ParseError) -> TantivyError {
+        TantivyError::InvalidArgument(err.to_string())
     }
 }
 
@@ -144,35 +134,9 @@ impl From<schema::DocParsingError> for TantivyError {
     }
 }
 
-impl From<OpenWriteError> for TantivyError {
-    fn from(error: OpenWriteError) -> TantivyError {
-        match error {
-            OpenWriteError::FileAlreadyExists(filepath) => {
-                TantivyError::FileAlreadyExists(filepath)
-            }
-            OpenWriteError::IOError(io_error) => TantivyError::IOError(io_error),
-        }
-    }
-}
-
-impl From<OpenDirectoryError> for TantivyError {
-    fn from(error: OpenDirectoryError) -> TantivyError {
-        match error {
-            OpenDirectoryError::DoesNotExist(directory_path) => {
-                TantivyError::PathDoesNotExist(directory_path)
-            }
-            OpenDirectoryError::NotADirectory(directory_path) => {
-                TantivyError::InvalidArgument(format!("{:?} is not a directory", directory_path))
-            }
-            OpenDirectoryError::IoError(err) => TantivyError::IOError(IOError::from(err)),
-        }
-    }
-}
-
 impl From<serde_json::Error> for TantivyError {
     fn from(error: serde_json::Error) -> TantivyError {
-        let io_err = io::Error::from(error);
-        TantivyError::IOError(io_err.into())
+        TantivyError::IOError(error.into())
     }
 }
 

src/fastfield/bytes/mod.rs

@@ -6,31 +6,114 @@ pub use self::writer::BytesFastFieldWriter;
 
 #[cfg(test)]
 mod tests {
-    use crate::schema::Schema;
-    use crate::Index;
+    use crate::schema::{BytesOptions, IndexRecordOption, Schema, Value};
+    use crate::{query::TermQuery, schema::FAST, schema::INDEXED, schema::STORED};
+    use crate::{DocAddress, DocSet, Index, Searcher, Term};
+    use std::ops::Deref;
 
     #[test]
-    fn test_bytes() {
+    fn test_bytes() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
-        let field = schema_builder.add_bytes_field("bytesfield");
+        let bytes_field = schema_builder.add_bytes_field("bytesfield", FAST);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-        index_writer.add_document(doc!(field=>vec![0u8, 1, 2, 3]));
-        index_writer.add_document(doc!(field=>vec![]));
-        index_writer.add_document(doc!(field=>vec![255u8]));
-        index_writer.add_document(doc!(field=>vec![1u8, 3, 5, 7, 9]));
-        index_writer.add_document(doc!(field=>vec![0u8; 1000]));
-        assert!(index_writer.commit().is_ok());
-        let searcher = index.reader().unwrap().searcher();
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(bytes_field=>vec![0u8, 1, 2, 3]));
+        index_writer.add_document(doc!(bytes_field=>vec![]));
+        index_writer.add_document(doc!(bytes_field=>vec![255u8]));
+        index_writer.add_document(doc!(bytes_field=>vec![1u8, 3, 5, 7, 9]));
+        index_writer.add_document(doc!(bytes_field=>vec![0u8; 1000]));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
         let segment_reader = searcher.segment_reader(0);
-        let bytes_reader = segment_reader.fast_fields().bytes(field).unwrap();
-
+        let bytes_reader = segment_reader.fast_fields().bytes(bytes_field).unwrap();
         assert_eq!(bytes_reader.get_bytes(0), &[0u8, 1, 2, 3]);
         assert!(bytes_reader.get_bytes(1).is_empty());
         assert_eq!(bytes_reader.get_bytes(2), &[255u8]);
         assert_eq!(bytes_reader.get_bytes(3), &[1u8, 3, 5, 7, 9]);
         let long = vec![0u8; 1000];
         assert_eq!(bytes_reader.get_bytes(4), long.as_slice());
+        Ok(())
+    }
+
+    fn create_index_for_test<T: Into<BytesOptions>>(
+        byte_options: T,
+    ) -> crate::Result<impl Deref<Target = Searcher>> {
+        let mut schema_builder = Schema::builder();
+        let field = schema_builder.add_bytes_field("string_bytes", byte_options.into());
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(
+                field => b"tantivy".as_ref(),
+                field => b"lucene".as_ref()
+        ));
+        index_writer.commit()?;
+        Ok(index.reader()?.searcher())
+    }
+
+    #[test]
+    fn test_stored_bytes() -> crate::Result<()> {
+        let searcher = create_index_for_test(STORED)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let retrieved_doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        let values: Vec<&Value> = retrieved_doc.get_all(field).collect();
+        assert_eq!(values.len(), 2);
+        let values_bytes: Vec<&[u8]> = values
+            .into_iter()
+            .flat_map(|value| value.bytes_value())
+            .collect();
+        assert_eq!(values_bytes, &[&b"tantivy"[..], &b"lucene"[..]]);
+        Ok(())
+    }
+
+    #[test]
+    fn test_non_stored_bytes() -> crate::Result<()> {
+        let searcher = create_index_for_test(INDEXED)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let retrieved_doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        assert!(retrieved_doc.get_first(field).is_none());
+        Ok(())
+    }
+
+    #[test]
+    fn test_index_bytes() -> crate::Result<()> {
+        let searcher = create_index_for_test(INDEXED)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        let term = Term::from_field_bytes(field, b"lucene".as_ref());
+        let term_query = TermQuery::new(term, IndexRecordOption::Basic);
+        let term_weight = term_query.specialized_weight(&searcher, true)?;
+        let term_scorer = term_weight.specialized_scorer(searcher.segment_reader(0), 1.0)?;
+        assert_eq!(term_scorer.doc(), 0u32);
+        Ok(())
+    }
+
+    #[test]
+    fn test_non_index_bytes() -> crate::Result<()> {
+        let searcher = create_index_for_test(STORED)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        let term = Term::from_field_bytes(field, b"lucene".as_ref());
+        let term_query = TermQuery::new(term, IndexRecordOption::Basic);
+        let term_weight_err = term_query.specialized_weight(&searcher, false);
+        assert!(matches!(
+            term_weight_err,
+            Err(crate::TantivyError::SchemaError(_))
+        ));
+        Ok(())
+    }
+
+    #[test]
+    fn test_fast_bytes_multivalue_value() -> crate::Result<()> {
+        let searcher = create_index_for_test(FAST)?;
+        assert_eq!(searcher.num_docs(), 1);
+        let fast_fields = searcher.segment_reader(0u32).fast_fields();
+        let field = searcher.schema().get_field("string_bytes").unwrap();
+        let fast_field_reader = fast_fields.bytes(field).unwrap();
+        assert_eq!(fast_field_reader.get_bytes(0u32), b"tantivy");
+        Ok(())
     }
 }

src/fastfield/bytes/reader.rs

@@ -1,6 +1,5 @@
-use owning_ref::OwningRef;
-
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::fastfield::FastFieldReader;
 use crate::DocId;
 
@@ -17,16 +16,16 @@ use crate::DocId;
 #[derive(Clone)]
 pub struct BytesFastFieldReader {
     idx_reader: FastFieldReader<u64>,
-    values: OwningRef<ReadOnlySource, [u8]>,
+    values: OwnedBytes,
 }
 
 impl BytesFastFieldReader {
     pub(crate) fn open(
         idx_reader: FastFieldReader<u64>,
-        values_source: ReadOnlySource,
-    ) -> BytesFastFieldReader {
-        let values = OwningRef::new(values_source).map(|source| &source[..]);
-        BytesFastFieldReader { idx_reader, values }
+        values_file: FileSlice,
+    ) -> crate::Result<BytesFastFieldReader> {
+        let values = values_file.read_bytes()?;
+        Ok(BytesFastFieldReader { idx_reader, values })
     }
 
     fn range(&self, doc: DocId) -> (usize, usize) {
@@ -38,7 +37,7 @@ impl BytesFastFieldReader {
     /// Returns the bytes associated to the given `doc`
     pub fn get_bytes(&self, doc: DocId) -> &[u8] {
         let (start, stop) = self.range(doc);
-        &self.values[start..stop]
+        &self.values.as_slice()[start..stop]
     }
 
     /// Returns the overall number of bytes in this bytes fast field.

src/fastfield/bytes/writer.rs

@@ -49,16 +49,10 @@ impl BytesFastFieldWriter {
     /// matching field values present in the document.
     pub fn add_document(&mut self, doc: &Document) {
         self.next_doc();
-        for field_value in doc.field_values() {
-            if field_value.field() == self.field {
-                if let Value::Bytes(ref bytes) = *field_value.value() {
-                    self.vals.extend_from_slice(bytes);
-                } else {
-                    panic!(
-                        "Bytes field contained non-Bytes Value!. Field {:?} = {:?}",
-                        self.field, field_value
-                    );
-                }
+        for field_value in doc.get_all(self.field) {
+            if let Value::Bytes(ref bytes) = field_value {
+                self.vals.extend_from_slice(bytes);
+                return;
             }
         }
     }
@@ -76,21 +70,18 @@ impl BytesFastFieldWriter {
 
     /// Serializes the fast field values by pushing them to the `FastFieldSerializer`.
     pub fn serialize(&self, serializer: &mut FastFieldSerializer) -> io::Result<()> {
-        {
-            // writing the offset index
-            let mut doc_index_serializer =
-                serializer.new_u64_fast_field_with_idx(self.field, 0, self.vals.len() as u64, 0)?;
-            for &offset in &self.doc_index {
-                doc_index_serializer.add_val(offset)?;
-            }
-            doc_index_serializer.add_val(self.vals.len() as u64)?;
-            doc_index_serializer.close_field()?;
-        }
-        {
-            // writing the values themselves
-            let mut value_serializer = serializer.new_bytes_fast_field_with_idx(self.field, 1)?;
-            value_serializer.write_all(&self.vals)?;
+        // writing the offset index
+        let mut doc_index_serializer =
+            serializer.new_u64_fast_field_with_idx(self.field, 0, self.vals.len() as u64, 0)?;
+        for &offset in &self.doc_index {
+            doc_index_serializer.add_val(offset)?;
         }
+        doc_index_serializer.add_val(self.vals.len() as u64)?;
+        doc_index_serializer.close_field()?;
+        // writing the values themselves
+        serializer
+            .new_bytes_fast_field_with_idx(self.field, 1)
+            .write_all(&self.vals)?;
         Ok(())
     }
 }

src/fastfield/delete.rs

@@ -1,5 +1,6 @@
 use crate::common::{BitSet, HasLen};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::directory::WritePtr;
 use crate::space_usage::ByteCount;
 use crate::DocId;
@@ -39,7 +40,7 @@ pub fn write_delete_bitset(
 /// Set of deleted `DocId`s.
 #[derive(Clone)]
 pub struct DeleteBitSet {
-    data: ReadOnlySource,
+    data: OwnedBytes,
     len: usize,
 }
 
@@ -53,26 +54,27 @@ impl DeleteBitSet {
         for &doc in docs {
             bitset.insert(doc);
         }
-        let mut directory = RAMDirectory::create();
+        let directory = RAMDirectory::create();
         let path = Path::new("dummydeletebitset");
         let mut wrt = directory.open_write(path).unwrap();
         write_delete_bitset(&bitset, max_doc, &mut wrt).unwrap();
         wrt.terminate().unwrap();
-        let source = directory.open_read(path).unwrap();
-        Self::open(source)
+        let file = directory.open_read(path).unwrap();
+        Self::open(file).unwrap()
     }
 
-    /// Opens a delete bitset given its data source.
-    pub fn open(data: ReadOnlySource) -> DeleteBitSet {
-        let num_deleted: usize = data
+    /// Opens a delete bitset given its file.
+    pub fn open(file: FileSlice) -> crate::Result<DeleteBitSet> {
+        let bytes = file.read_bytes()?;
+        let num_deleted: usize = bytes
             .as_slice()
             .iter()
             .map(|b| b.count_ones() as usize)
             .sum();
-        DeleteBitSet {
-            data,
+        Ok(DeleteBitSet {
+            data: bytes,
             len: num_deleted,
-        }
+        })
     }
 
     /// Returns true iff the document is still "alive". In other words, if it has not been deleted.
@@ -84,7 +86,7 @@ impl DeleteBitSet {
     #[inline(always)]
     pub fn is_deleted(&self, doc: DocId) -> bool {
         let byte_offset = doc / 8u32;
-        let b: u8 = (*self.data)[byte_offset as usize];
+        let b: u8 = self.data.as_slice()[byte_offset as usize];
         let shift = (doc & 7u32) as u8;
         b & (1u8 << shift) != 0
     }

src/fastfield/error.rs

@@ -4,8 +4,8 @@ use std::result;
 /// `FastFieldNotAvailableError` is returned when the
 /// user requested for a fast field reader, and the field was not
 /// defined in the schema as a fast field.
-#[derive(Debug, Fail)]
-#[fail(display = "Fast field not available: '{:?}'", field_name)]
+#[derive(Debug, Error)]
+#[error("Fast field not available: '{field_name:?}'")]
 pub struct FastFieldNotAvailableError {
     field_name: String,
 }

src/fastfield/facet_reader.rs

@@ -1,4 +1,5 @@
-use super::MultiValueIntFastFieldReader;
+use super::MultiValuedFastFieldReader;
+use crate::error::DataCorruption;
 use crate::schema::Facet;
 use crate::termdict::TermDictionary;
 use crate::termdict::TermOrdinal;
@@ -19,7 +20,7 @@ use std::str;
 /// list of facets. This ordinal is segment local and
 /// only makes sense for a given segment.
 pub struct FacetReader {
-    term_ords: MultiValueIntFastFieldReader<u64>,
+    term_ords: MultiValuedFastFieldReader<u64>,
     term_dict: TermDictionary,
     buffer: Vec<u8>,
 }
@@ -28,12 +29,12 @@ impl FacetReader {
     /// Creates a new `FacetReader`.
     ///
     /// A facet reader just wraps :
-    /// - a `MultiValueIntFastFieldReader` that makes it possible to
+    /// - a `MultiValuedFastFieldReader` that makes it possible to
     /// access the list of facet ords for a given document.
     /// - a `TermDictionary` that helps associating a facet to
     /// an ordinal and vice versa.
     pub fn new(
-        term_ords: MultiValueIntFastFieldReader<u64>,
+        term_ords: MultiValuedFastFieldReader<u64>,
         term_dict: TermDictionary,
     ) -> FacetReader {
         FacetReader {
@@ -62,18 +63,166 @@ impl FacetReader {
         &mut self,
         facet_ord: TermOrdinal,
         output: &mut Facet,
-    ) -> Result<(), str::Utf8Error> {
+    ) -> crate::Result<()> {
         let found_term = self
             .term_dict
-            .ord_to_term(facet_ord as u64, &mut self.buffer);
+            .ord_to_term(facet_ord as u64, &mut self.buffer)?;
         assert!(found_term, "Term ordinal {} no found.", facet_ord);
-        let facet_str = str::from_utf8(&self.buffer[..])?;
+        let facet_str = str::from_utf8(&self.buffer[..])
+            .map_err(|utf8_err| DataCorruption::comment_only(utf8_err.to_string()))?;
         output.set_facet_str(facet_str);
         Ok(())
     }
 
     /// Return the list of facet ordinals associated to a document.
-    pub fn facet_ords(&mut self, doc: DocId, output: &mut Vec<u64>) {
+    pub fn facet_ords(&self, doc: DocId, output: &mut Vec<u64>) {
         self.term_ords.get_vals(doc, output);
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::Index;
+    use crate::{
+        schema::{Facet, FacetOptions, SchemaBuilder, Value, INDEXED, STORED},
+        DocAddress, Document,
+    };
+
+    #[test]
+    fn test_facet_only_indexed() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert_eq!(&facet_ords, &[2u64]);
+        let doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let value = doc.get_first(facet_field).and_then(Value::path);
+        assert_eq!(value, None);
+        Ok(())
+    }
+
+    #[test]
+    fn test_facet_only_stored() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", STORED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        let doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let value = doc.get_first(facet_field).and_then(Value::path);
+        assert_eq!(value, Some("/a/b".to_string()));
+        Ok(())
+    }
+
+    #[test]
+    fn test_facet_stored_and_indexed() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", STORED | INDEXED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert_eq!(&facet_ords, &[2u64]);
+        let doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let value = doc.get_first(facet_field).and_then(Value::path);
+        assert_eq!(value, Some("/a/b".to_string()));
+        Ok(())
+    }
+
+    #[test]
+    fn test_facet_neither_stored_and_indexed() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", FacetOptions::default());
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        let doc = searcher.doc(DocAddress(0u32, 0u32))?;
+        let value = doc.get_first(facet_field).and_then(Value::path);
+        assert_eq!(value, None);
+        Ok(())
+    }
+
+    #[test]
+    fn test_facet_not_populated_for_all_docs() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(facet_field=>Facet::from_text("/a/b")));
+        index_writer.add_document(Document::default());
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert_eq!(&facet_ords, &[2u64]);
+        facet_reader.facet_ords(1u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        Ok(())
+    }
+
+    #[test]
+    fn test_facet_not_populated_for_any_docs() -> crate::Result<()> {
+        let mut schema_builder = SchemaBuilder::default();
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(Document::default());
+        index_writer.add_document(Document::default());
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let facet_reader = searcher
+            .segment_reader(0u32)
+            .facet_reader(facet_field)
+            .unwrap();
+        let mut facet_ords = Vec::new();
+        facet_reader.facet_ords(0u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        facet_reader.facet_ords(1u32, &mut facet_ords);
+        assert!(facet_ords.is_empty());
+        Ok(())
+    }
+}

src/fastfield/mod.rs

@@ -28,16 +28,19 @@ pub use self::delete::write_delete_bitset;
 pub use self::delete::DeleteBitSet;
 pub use self::error::{FastFieldNotAvailableError, Result};
 pub use self::facet_reader::FacetReader;
-pub use self::multivalued::{MultiValueIntFastFieldReader, MultiValueIntFastFieldWriter};
+pub use self::multivalued::{MultiValuedFastFieldReader, MultiValuedFastFieldWriter};
 pub use self::reader::FastFieldReader;
 pub use self::readers::FastFieldReaders;
 pub use self::serializer::FastFieldSerializer;
 pub use self::writer::{FastFieldsWriter, IntFastFieldWriter};
-use crate::chrono::{NaiveDateTime, Utc};
 use crate::common;
 use crate::schema::Cardinality;
 use crate::schema::FieldType;
 use crate::schema::Value;
+use crate::{
+    chrono::{NaiveDateTime, Utc},
+    schema::Type,
+};
 
 mod bytes;
 mod delete;
@@ -50,7 +53,7 @@ mod serializer;
 mod writer;
 
 /// Trait for types that are allowed for fast fields: (u64, i64 and f64).
-pub trait FastValue: Clone + Copy + Send + Sync + PartialOrd {
+pub trait FastValue: Clone + Copy + Send + Sync + PartialOrd + 'static {
     /// Converts a value from u64
     ///
     /// Internally all fast field values are encoded as u64.
@@ -76,6 +79,9 @@ pub trait FastValue: Clone + Copy + Send + Sync + PartialOrd {
     fn make_zero() -> Self {
         Self::from_u64(0i64.to_u64())
     }
+
+    /// Returns the `schema::Type` for this FastValue.
+    fn to_type() -> Type;
 }
 
 impl FastValue for u64 {
@@ -90,7 +96,7 @@ impl FastValue for u64 {
     fn fast_field_cardinality(field_type: &FieldType) -> Option<Cardinality> {
         match *field_type {
             FieldType::U64(ref integer_options) => integer_options.get_fastfield_cardinality(),
-            FieldType::HierarchicalFacet => Some(Cardinality::MultiValues),
+            FieldType::HierarchicalFacet(_) => Some(Cardinality::MultiValues),
             _ => None,
         }
     }
@@ -98,6 +104,10 @@ impl FastValue for u64 {
     fn as_u64(&self) -> u64 {
         *self
     }
+
+    fn to_type() -> Type {
+        Type::U64
+    }
 }
 
 impl FastValue for i64 {
@@ -119,6 +129,10 @@ impl FastValue for i64 {
     fn as_u64(&self) -> u64 {
         *self as u64
     }
+
+    fn to_type() -> Type {
+        Type::I64
+    }
 }
 
 impl FastValue for f64 {
@@ -140,6 +154,10 @@ impl FastValue for f64 {
     fn as_u64(&self) -> u64 {
         self.to_bits()
     }
+
+    fn to_type() -> Type {
+        Type::F64
+    }
 }
 
 impl FastValue for crate::DateTime {
@@ -162,6 +180,10 @@ impl FastValue for crate::DateTime {
     fn as_u64(&self) -> u64 {
         self.timestamp().as_u64()
     }
+
+    fn to_type() -> Type {
+        Type::Date
+    }
 }
 
 fn value_to_u64(value: &Value) -> u64 {
@@ -187,6 +209,7 @@ mod tests {
     use crate::schema::FAST;
     use crate::schema::{Document, IntOptions};
     use crate::{Index, SegmentId, SegmentReader};
+    use common::HasLen;
     use once_cell::sync::Lazy;
     use rand::prelude::SliceRandom;
     use rand::rngs::StdRng;
@@ -217,9 +240,9 @@ mod tests {
     }
 
     #[test]
-    fn test_intfastfield_small() {
+    fn test_intfastfield_small() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
             let mut serializer = FastFieldSerializer::from_write(write).unwrap();
@@ -232,27 +255,24 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
-        {
-            assert_eq!(source.len(), 36 as usize);
-        }
-        {
-            let composite_file = CompositeFile::open(&source).unwrap();
-            let field_source = composite_file.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(field_source);
-            assert_eq!(fast_field_reader.get(0), 13u64);
-            assert_eq!(fast_field_reader.get(1), 14u64);
-            assert_eq!(fast_field_reader.get(2), 2u64);
-        }
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 36 as usize);
+        let composite_file = CompositeFile::open(&file)?;
+        let file = composite_file.open_read(*FIELD).unwrap();
+        let fast_field_reader = FastFieldReader::<u64>::open(file)?;
+        assert_eq!(fast_field_reader.get(0), 13u64);
+        assert_eq!(fast_field_reader.get(1), 14u64);
+        assert_eq!(fast_field_reader.get(2), 2u64);
+        Ok(())
     }
 
     #[test]
-    fn test_intfastfield_large() {
+    fn test_intfastfield_large() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
-            let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
-            let mut serializer = FastFieldSerializer::from_write(write).unwrap();
+            let write: WritePtr = directory.open_write(Path::new("test"))?;
+            let mut serializer = FastFieldSerializer::from_write(write)?;
             let mut fast_field_writers = FastFieldsWriter::from_schema(&SCHEMA);
             fast_field_writers.add_document(&doc!(*FIELD=>4u64));
             fast_field_writers.add_document(&doc!(*FIELD=>14_082_001u64));
@@ -263,19 +283,15 @@ mod tests {
             fast_field_writers.add_document(&doc!(*FIELD=>1_002u64));
             fast_field_writers.add_document(&doc!(*FIELD=>1_501u64));
             fast_field_writers.add_document(&doc!(*FIELD=>215u64));
-            fast_field_writers
-                .serialize(&mut serializer, &HashMap::new())
-                .unwrap();
-            serializer.close().unwrap();
+            fast_field_writers.serialize(&mut serializer, &HashMap::new())?;
+            serializer.close()?;
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path)?;
+        assert_eq!(file.len(), 61 as usize);
         {
-            assert_eq!(source.len(), 61 as usize);
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             assert_eq!(fast_field_reader.get(0), 4u64);
             assert_eq!(fast_field_reader.get(1), 14_082_001u64);
             assert_eq!(fast_field_reader.get(2), 3_052u64);
@@ -286,12 +302,13 @@ mod tests {
             assert_eq!(fast_field_reader.get(7), 1_501u64);
             assert_eq!(fast_field_reader.get(8), 215u64);
         }
+        Ok(())
     }
 
     #[test]
-    fn test_intfastfield_null_amplitude() {
+    fn test_intfastfield_null_amplitude() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
 
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
@@ -305,24 +322,23 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 34 as usize);
         {
-            assert_eq!(source.len(), 34 as usize);
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             for doc in 0..10_000 {
                 assert_eq!(fast_field_reader.get(doc), 100_000u64);
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_intfastfield_large_numbers() {
+    fn test_intfastfield_large_numbers() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
 
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
@@ -338,14 +354,12 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 80042 as usize);
         {
-            assert_eq!(source.len(), 80042 as usize);
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
             assert_eq!(fast_field_reader.get(0), 0u64);
             for doc in 1..10_001 {
                 assert_eq!(
@@ -354,12 +368,13 @@ mod tests {
                 );
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_signed_intfastfield() {
+    fn test_signed_intfastfield() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         let mut schema_builder = Schema::builder();
 
         let i64_field = schema_builder.add_i64_field("field", FAST);
@@ -378,14 +393,12 @@ mod tests {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
+        assert_eq!(file.len(), 17709 as usize);
         {
-            assert_eq!(source.len(), 17709 as usize);
-        }
-        {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(i64_field).unwrap();
-            let fast_field_reader = FastFieldReader::<i64>::open(data);
+            let fast_field_reader = FastFieldReader::<i64>::open(data)?;
 
             assert_eq!(fast_field_reader.min_value(), -100i64);
             assert_eq!(fast_field_reader.max_value(), 9_999i64);
@@ -398,12 +411,13 @@ mod tests {
                 assert_eq!(buffer[i], -100i64 + 53i64 + i as i64);
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_signed_intfastfield_default_val() {
+    fn test_signed_intfastfield_default_val() -> crate::Result<()> {
         let path = Path::new("test");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         let mut schema_builder = Schema::builder();
         let i64_field = schema_builder.add_i64_field("field", FAST);
         let schema = schema_builder.build();
@@ -420,13 +434,14 @@ mod tests {
             serializer.close().unwrap();
         }
 
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(i64_field).unwrap();
-            let fast_field_reader = FastFieldReader::<i64>::open(data);
+            let fast_field_reader = FastFieldReader::<i64>::open(data)?;
             assert_eq!(fast_field_reader.get(0u32), 0i64);
         }
+        Ok(())
     }
 
     // Warning: this generates the same permutation at each call
@@ -437,28 +452,26 @@ mod tests {
     }
 
     #[test]
-    fn test_intfastfield_permutation() {
+    fn test_intfastfield_permutation() -> crate::Result<()> {
         let path = Path::new("test");
         let permutation = generate_permutation();
         let n = permutation.len();
-        let mut directory = RAMDirectory::create();
+        let directory = RAMDirectory::create();
         {
-            let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
-            let mut serializer = FastFieldSerializer::from_write(write).unwrap();
+            let write: WritePtr = directory.open_write(Path::new("test"))?;
+            let mut serializer = FastFieldSerializer::from_write(write)?;
             let mut fast_field_writers = FastFieldsWriter::from_schema(&SCHEMA);
             for &x in &permutation {
                 fast_field_writers.add_document(&doc!(*FIELD=>x));
             }
-            fast_field_writers
-                .serialize(&mut serializer, &HashMap::new())
-                .unwrap();
-            serializer.close().unwrap();
+            fast_field_writers.serialize(&mut serializer, &HashMap::new())?;
+            serializer.close()?;
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path)?;
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file)?;
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data)?;
 
             let mut a = 0u64;
             for _ in 0..n {
@@ -466,6 +479,7 @@ mod tests {
                 a = fast_field_reader.get(a as u32);
             }
         }
+        Ok(())
     }
 
     #[test]
@@ -474,7 +488,7 @@ mod tests {
         let date_field = schema_builder.add_date_field("date", FAST);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.set_merge_policy(Box::new(NoMergePolicy));
         index_writer.add_document(doc!(date_field =>crate::chrono::prelude::Utc::now()));
         index_writer.commit().unwrap();
@@ -511,7 +525,7 @@ mod tests {
         );
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.set_merge_policy(Box::new(NoMergePolicy));
         index_writer.add_document(doc!(
             date_field => crate::DateTime::from_u64(1i64.to_u64()),
@@ -598,7 +612,7 @@ mod bench {
     fn bench_intfastfield_linear_fflookup(b: &mut Bencher) {
         let path = Path::new("test");
         let permutation = generate_permutation();
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
             let mut serializer = FastFieldSerializer::from_write(write).unwrap();
@@ -611,11 +625,11 @@ mod bench {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data).unwrap();
 
             b.iter(|| {
                 let n = test::black_box(7000u32);
@@ -632,7 +646,7 @@ mod bench {
     fn bench_intfastfield_fflookup(b: &mut Bencher) {
         let path = Path::new("test");
         let permutation = generate_permutation();
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
             let write: WritePtr = directory.open_write(Path::new("test")).unwrap();
             let mut serializer = FastFieldSerializer::from_write(write).unwrap();
@@ -645,11 +659,11 @@ mod bench {
                 .unwrap();
             serializer.close().unwrap();
         }
-        let source = directory.open_read(&path).unwrap();
+        let file = directory.open_read(&path).unwrap();
         {
-            let fast_fields_composite = CompositeFile::open(&source).unwrap();
+            let fast_fields_composite = CompositeFile::open(&file).unwrap();
             let data = fast_fields_composite.open_read(*FIELD).unwrap();
-            let fast_field_reader = FastFieldReader::<u64>::open(data);
+            let fast_field_reader = FastFieldReader::<u64>::open(data).unwrap();
 
             b.iter(|| {
                 let n = test::black_box(1000u32);

src/fastfield/multivalued/mod.rs

@@ -1,8 +1,8 @@
 mod reader;
 mod writer;
 
-pub use self::reader::MultiValueIntFastFieldReader;
-pub use self::writer::MultiValueIntFastFieldWriter;
+pub use self::reader::MultiValuedFastFieldReader;
+pub use self::writer::MultiValuedFastFieldWriter;
 
 #[cfg(test)]
 mod tests {
@@ -13,6 +13,7 @@ mod tests {
     use crate::schema::Facet;
     use crate::schema::IntOptions;
     use crate::schema::Schema;
+    use crate::schema::INDEXED;
     use crate::Index;
     use chrono::Duration;
 
@@ -25,7 +26,7 @@ mod tests {
         );
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(field=>1u64, field=>3u64));
         index_writer.add_document(doc!());
         index_writer.add_document(doc!(field=>4u64));
@@ -64,7 +65,7 @@ mod tests {
             schema_builder.add_i64_field("time_stamp_i", IntOptions::default().set_stored());
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         let first_time_stamp = chrono::Utc::now();
         index_writer.add_document(
             doc!(date_field=>first_time_stamp, date_field=>first_time_stamp, time_i=>1i64),
@@ -100,6 +101,7 @@ mod tests {
                         .get_first(date_field)
                         .expect("cannot find value")
                         .date_value()
+                        .unwrap()
                         .timestamp(),
                     first_time_stamp.timestamp()
                 );
@@ -108,7 +110,7 @@ mod tests {
                         .get_first(time_i)
                         .expect("cannot find value")
                         .i64_value(),
-                    1i64
+                    Some(1i64)
                 );
             }
         }
@@ -131,6 +133,7 @@ mod tests {
                         .get_first(date_field)
                         .expect("cannot find value")
                         .date_value()
+                        .unwrap()
                         .timestamp(),
                     two_secs_ahead.timestamp()
                 );
@@ -139,7 +142,7 @@ mod tests {
                         .get_first(time_i)
                         .expect("cannot find value")
                         .i64_value(),
-                    3i64
+                    Some(3i64)
                 );
             }
         }
@@ -186,7 +189,7 @@ mod tests {
         );
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(field=> 1i64, field => 3i64));
         index_writer.add_document(doc!());
         index_writer.add_document(doc!(field=> -4i64));
@@ -197,31 +200,23 @@ mod tests {
         let segment_reader = searcher.segment_reader(0);
         let mut vals = Vec::new();
         let multi_value_reader = segment_reader.fast_fields().i64s(field).unwrap();
-        {
-            multi_value_reader.get_vals(2, &mut vals);
-            assert_eq!(&vals, &[-4i64]);
-        }
-        {
-            multi_value_reader.get_vals(0, &mut vals);
-            assert_eq!(&vals, &[1i64, 3i64]);
-        }
-        {
-            multi_value_reader.get_vals(1, &mut vals);
-            assert!(vals.is_empty());
-        }
-        {
-            multi_value_reader.get_vals(3, &mut vals);
-            assert_eq!(&vals, &[-5i64, -20i64, 1i64]);
-        }
+        multi_value_reader.get_vals(2, &mut vals);
+        assert_eq!(&vals, &[-4i64]);
+        multi_value_reader.get_vals(0, &mut vals);
+        assert_eq!(&vals, &[1i64, 3i64]);
+        multi_value_reader.get_vals(1, &mut vals);
+        assert!(vals.is_empty());
+        multi_value_reader.get_vals(3, &mut vals);
+        assert_eq!(&vals, &[-5i64, -20i64, 1i64]);
     }
     #[test]
     #[ignore]
     fn test_many_facets() {
         let mut schema_builder = Schema::builder();
-        let field = schema_builder.add_facet_field("facetfield");
+        let field = schema_builder.add_facet_field("facetfield", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         for i in 0..100_000 {
             index_writer.add_document(doc!(field=> Facet::from(format!("/lang/{}", i).as_str())));
         }

src/fastfield/multivalued/reader.rs

@@ -1,3 +1,5 @@
+use std::ops::Range;
+
 use crate::fastfield::{FastFieldReader, FastValue};
 use crate::DocId;
 
@@ -10,49 +12,42 @@ use crate::DocId;
 /// The `idx_reader` associated, for each document, the index of its first value.
 ///
 #[derive(Clone)]
-pub struct MultiValueIntFastFieldReader<Item: FastValue> {
+pub struct MultiValuedFastFieldReader<Item: FastValue> {
     idx_reader: FastFieldReader<u64>,
     vals_reader: FastFieldReader<Item>,
 }
 
-impl<Item: FastValue> MultiValueIntFastFieldReader<Item> {
+impl<Item: FastValue> MultiValuedFastFieldReader<Item> {
     pub(crate) fn open(
         idx_reader: FastFieldReader<u64>,
         vals_reader: FastFieldReader<Item>,
-    ) -> MultiValueIntFastFieldReader<Item> {
-        MultiValueIntFastFieldReader {
+    ) -> MultiValuedFastFieldReader<Item> {
+        MultiValuedFastFieldReader {
             idx_reader,
             vals_reader,
         }
     }
 
-    pub(crate) fn into_u64s_reader(self) -> MultiValueIntFastFieldReader<u64> {
-        MultiValueIntFastFieldReader {
-            idx_reader: self.idx_reader,
-            vals_reader: self.vals_reader.into_u64_reader(),
-        }
-    }
-
     /// Returns `(start, stop)`, such that the values associated
     /// to the given document are `start..stop`.
-    fn range(&self, doc: DocId) -> (u64, u64) {
+    fn range(&self, doc: DocId) -> Range<u64> {
         let start = self.idx_reader.get(doc);
         let stop = self.idx_reader.get(doc + 1);
-        (start, stop)
+        start..stop
     }
 
     /// Returns the array of values associated to the given `doc`.
     pub fn get_vals(&self, doc: DocId, vals: &mut Vec<Item>) {
-        let (start, stop) = self.range(doc);
-        let len = (stop - start) as usize;
+        let range = self.range(doc);
+        let len = (range.end - range.start) as usize;
         vals.resize(len, Item::make_zero());
-        self.vals_reader.get_range_u64(start, &mut vals[..]);
+        self.vals_reader.get_range_u64(range.start, &mut vals[..]);
     }
 
     /// Returns the number of values associated with the document `DocId`.
     pub fn num_vals(&self, doc: DocId) -> usize {
-        let (start, stop) = self.range(doc);
-        (stop - start) as usize
+        let range = self.range(doc);
+        (range.end - range.start) as usize
     }
 
     /// Returns the overall number of values in this field  .
@@ -65,16 +60,16 @@ impl<Item: FastValue> MultiValueIntFastFieldReader<Item> {
 mod tests {
 
     use crate::core::Index;
-    use crate::schema::{Facet, Schema};
+    use crate::schema::{Facet, Schema, INDEXED};
 
     #[test]
     fn test_multifastfield_reader() {
         let mut schema_builder = Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facets");
+        let facet_field = schema_builder.add_facet_field("facets", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         let mut index_writer = index
-            .writer_with_num_threads(1, 30_000_000)
+            .writer_for_tests()
             .expect("Failed to create index writer.");
         index_writer.add_document(doc!(
             facet_field => Facet::from("/category/cat2"),

src/fastfield/multivalued/writer.rs

@@ -7,6 +7,7 @@ use crate::termdict::TermOrdinal;
 use crate::DocId;
 use fnv::FnvHashMap;
 use std::io;
+use std::iter::once;
 
 /// Writer for multi-valued (as in, more than one value per document)
 /// int fast field.
@@ -18,7 +19,7 @@ use std::io;
 /// in your schema
 /// - add your document simply by calling `.add_document(...)`.
 ///
-/// The `MultiValueIntFastFieldWriter` can be acquired from the
+/// The `MultiValuedFastFieldWriter` can be acquired from the
 /// fastfield writer, by calling [`.get_multivalue_writer(...)`](./struct.FastFieldsWriter.html#method.get_multivalue_writer).
 ///
 /// Once acquired, writing is done by calling calls to
@@ -29,17 +30,17 @@ use std::io;
 /// This makes it possible to push unordered term ids,
 /// during indexing and remap them to their respective
 /// term ids when the segment is getting serialized.
-pub struct MultiValueIntFastFieldWriter {
+pub struct MultiValuedFastFieldWriter {
     field: Field,
     vals: Vec<UnorderedTermId>,
     doc_index: Vec<u64>,
     is_facet: bool,
 }
 
-impl MultiValueIntFastFieldWriter {
+impl MultiValuedFastFieldWriter {
     /// Creates a new `IntFastFieldWriter`
     pub(crate) fn new(field: Field, is_facet: bool) -> Self {
-        MultiValueIntFastFieldWriter {
+        MultiValuedFastFieldWriter {
             field,
             vals: Vec::new(),
             doc_index: Vec::new(),
@@ -47,7 +48,7 @@ impl MultiValueIntFastFieldWriter {
         }
     }
 
-    /// Access the field associated to the `MultiValueIntFastFieldWriter`
+    /// Access the field associated to the `MultiValuedFastFieldWriter`
     pub fn field(&self) -> Field {
         self.field
     }
@@ -125,25 +126,22 @@ impl MultiValueIntFastFieldWriter {
                         1,
                     )?;
 
-                    let last_interval = (
-                        self.doc_index.last().cloned().unwrap(),
-                        self.vals.len() as u64,
-                    );
+                    let last_interval =
+                        self.doc_index.last().cloned().unwrap() as usize..self.vals.len();
 
                     let mut doc_vals: Vec<u64> = Vec::with_capacity(100);
-                    for (start, stop) in self
+                    for range in self
                         .doc_index
                         .windows(2)
-                        .map(|interval| (interval[0], interval[1]))
-                        .chain(Some(last_interval).into_iter())
-                        .map(|(start, stop)| (start as usize, stop as usize))
+                        .map(|interval| interval[0] as usize..interval[1] as usize)
+                        .chain(once(last_interval))
                     {
                         doc_vals.clear();
-                        let remapped_vals = self.vals[start..stop]
+                        let remapped_vals = self.vals[range]
                             .iter()
                             .map(|val| *mapping.get(val).expect("Missing term ordinal"));
                         doc_vals.extend(remapped_vals);
-                        doc_vals.sort();
+                        doc_vals.sort_unstable();
                         for &val in &doc_vals {
                             value_serializer.add_val(val)?;
                         }

src/fastfield/reader.rs

@@ -3,13 +3,12 @@ use crate::common::bitpacker::BitUnpacker;
 use crate::common::compute_num_bits;
 use crate::common::BinarySerializable;
 use crate::common::CompositeFile;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
 use crate::directory::{Directory, RAMDirectory, WritePtr};
 use crate::fastfield::{FastFieldSerializer, FastFieldsWriter};
 use crate::schema::Schema;
 use crate::schema::FAST;
 use crate::DocId;
-use owning_ref::OwningRef;
 use std::collections::HashMap;
 use std::marker::PhantomData;
 use std::path::Path;
@@ -20,43 +19,27 @@ use std::path::Path;
 /// fast field is required.
 #[derive(Clone)]
 pub struct FastFieldReader<Item: FastValue> {
-    bit_unpacker: BitUnpacker<OwningRef<ReadOnlySource, [u8]>>,
+    bit_unpacker: BitUnpacker,
     min_value_u64: u64,
     max_value_u64: u64,
     _phantom: PhantomData<Item>,
 }
 
 impl<Item: FastValue> FastFieldReader<Item> {
-    /// Opens a fast field given a source.
-    pub fn open(data: ReadOnlySource) -> Self {
-        let min_value: u64;
-        let amplitude: u64;
-        {
-            let mut cursor = data.as_slice();
-            min_value =
-                u64::deserialize(&mut cursor).expect("Failed to read the min_value of fast field.");
-            amplitude =
-                u64::deserialize(&mut cursor).expect("Failed to read the amplitude of fast field.");
-        }
+    /// Opens a fast field given a file.
+    pub fn open(file: FileSlice) -> crate::Result<Self> {
+        let mut bytes = file.read_bytes()?;
+        let min_value = u64::deserialize(&mut bytes)?;
+        let amplitude = u64::deserialize(&mut bytes)?;
         let max_value = min_value + amplitude;
         let num_bits = compute_num_bits(amplitude);
-        let owning_ref = OwningRef::new(data).map(|data| &data[16..]);
-        let bit_unpacker = BitUnpacker::new(owning_ref, num_bits);
-        FastFieldReader {
+        let bit_unpacker = BitUnpacker::new(bytes, num_bits);
+        Ok(FastFieldReader {
             min_value_u64: min_value,
             max_value_u64: max_value,
             bit_unpacker,
             _phantom: PhantomData,
-        }
-    }
-
-    pub(crate) fn into_u64_reader(self) -> FastFieldReader<u64> {
-        FastFieldReader {
-            bit_unpacker: self.bit_unpacker,
-            min_value_u64: self.min_value_u64,
-            max_value_u64: self.max_value_u64,
-            _phantom: PhantomData,
-        }
+        })
     }
 
     /// Return the value associated to the given document.
@@ -135,7 +118,7 @@ impl<Item: FastValue> From<Vec<Item>> for FastFieldReader<Item> {
         let field = schema_builder.add_u64_field("field", FAST);
         let schema = schema_builder.build();
         let path = Path::new("__dummy__");
-        let mut directory: RAMDirectory = RAMDirectory::create();
+        let directory: RAMDirectory = RAMDirectory::create();
         {
             let write: WritePtr = directory
                 .open_write(path)
@@ -157,12 +140,11 @@ impl<Item: FastValue> From<Vec<Item>> for FastFieldReader<Item> {
             serializer.close().unwrap();
         }
 
-        let source = directory.open_read(path).expect("Failed to open the file");
-        let composite_file =
-            CompositeFile::open(&source).expect("Failed to read the composite file");
-        let field_source = composite_file
+        let file = directory.open_read(path).expect("Failed to open the file");
+        let composite_file = CompositeFile::open(&file).expect("Failed to read the composite file");
+        let field_file = composite_file
             .open_read(field)
             .expect("File component not found");
-        FastFieldReader::open(field_source)
+        FastFieldReader::open(field_file).unwrap()
     }
 }

src/fastfield/readers.rs

@@ -1,28 +1,22 @@
 use crate::common::CompositeFile;
-use crate::fastfield::BytesFastFieldReader;
-use crate::fastfield::MultiValueIntFastFieldReader;
+use crate::directory::FileSlice;
+use crate::fastfield::MultiValuedFastFieldReader;
+use crate::fastfield::{BytesFastFieldReader, FastValue};
 use crate::fastfield::{FastFieldNotAvailableError, FastFieldReader};
 use crate::schema::{Cardinality, Field, FieldType, Schema};
 use crate::space_usage::PerFieldSpaceUsage;
-use std::collections::HashMap;
+use crate::TantivyError;
 
 /// Provides access to all of the FastFieldReader.
 ///
 /// Internally, `FastFieldReaders` have preloaded fast field readers,
 /// and just wraps several `HashMap`.
+#[derive(Clone)]
 pub struct FastFieldReaders {
-    fast_field_i64: HashMap<Field, FastFieldReader<i64>>,
-    fast_field_u64: HashMap<Field, FastFieldReader<u64>>,
-    fast_field_f64: HashMap<Field, FastFieldReader<f64>>,
-    fast_field_date: HashMap<Field, FastFieldReader<crate::DateTime>>,
-    fast_field_i64s: HashMap<Field, MultiValueIntFastFieldReader<i64>>,
-    fast_field_u64s: HashMap<Field, MultiValueIntFastFieldReader<u64>>,
-    fast_field_f64s: HashMap<Field, MultiValueIntFastFieldReader<f64>>,
-    fast_field_dates: HashMap<Field, MultiValueIntFastFieldReader<crate::DateTime>>,
-    fast_bytes: HashMap<Field, BytesFastFieldReader>,
+    schema: Schema,
     fast_fields_composite: CompositeFile,
 }
-
+#[derive(Eq, PartialEq, Debug)]
 enum FastType {
     I64,
     U64,
@@ -44,227 +38,178 @@ fn type_and_cardinality(field_type: &FieldType) -> Option<(FastType, Cardinality
         FieldType::Date(options) => options
             .get_fastfield_cardinality()
             .map(|cardinality| (FastType::Date, cardinality)),
-        FieldType::HierarchicalFacet => Some((FastType::U64, Cardinality::MultiValues)),
+        FieldType::HierarchicalFacet(_) => Some((FastType::U64, Cardinality::MultiValues)),
         _ => None,
     }
 }
 
 impl FastFieldReaders {
-    pub(crate) fn load_all(
-        schema: &Schema,
-        fast_fields_composite: &CompositeFile,
-    ) -> crate::Result<FastFieldReaders> {
-        let mut fast_field_readers = FastFieldReaders {
-            fast_field_i64: Default::default(),
-            fast_field_u64: Default::default(),
-            fast_field_f64: Default::default(),
-            fast_field_date: Default::default(),
-            fast_field_i64s: Default::default(),
-            fast_field_u64s: Default::default(),
-            fast_field_f64s: Default::default(),
-            fast_field_dates: Default::default(),
-            fast_bytes: Default::default(),
-            fast_fields_composite: fast_fields_composite.clone(),
-        };
-        for (field, field_entry) in schema.fields() {
-            let field_type = field_entry.field_type();
-            if field_type == &FieldType::Bytes {
-                let idx_reader = fast_fields_composite
-                    .open_read_with_idx(field, 0)
-                    .ok_or_else(|| FastFieldNotAvailableError::new(field_entry))
-                    .map(FastFieldReader::open)?;
-                let data = fast_fields_composite
-                    .open_read_with_idx(field, 1)
-                    .ok_or_else(|| FastFieldNotAvailableError::new(field_entry))?;
-                fast_field_readers
-                    .fast_bytes
-                    .insert(field, BytesFastFieldReader::open(idx_reader, data));
-            } else if let Some((fast_type, cardinality)) = type_and_cardinality(field_type) {
-                match cardinality {
-                    Cardinality::SingleValue => {
-                        if let Some(fast_field_data) = fast_fields_composite.open_read(field) {
-                            match fast_type {
-                                FastType::U64 => {
-                                    let fast_field_reader = FastFieldReader::open(fast_field_data);
-                                    fast_field_readers
-                                        .fast_field_u64
-                                        .insert(field, fast_field_reader);
-                                }
-                                FastType::I64 => {
-                                    fast_field_readers.fast_field_i64.insert(
-                                        field,
-                                        FastFieldReader::open(fast_field_data.clone()),
-                                    );
-                                }
-                                FastType::F64 => {
-                                    fast_field_readers.fast_field_f64.insert(
-                                        field,
-                                        FastFieldReader::open(fast_field_data.clone()),
-                                    );
-                                }
-                                FastType::Date => {
-                                    fast_field_readers.fast_field_date.insert(
-                                        field,
-                                        FastFieldReader::open(fast_field_data.clone()),
-                                    );
-                                }
-                            }
-                        } else {
-                            return Err(From::from(FastFieldNotAvailableError::new(field_entry)));
-                        }
-                    }
-                    Cardinality::MultiValues => {
-                        let idx_opt = fast_fields_composite.open_read_with_idx(field, 0);
-                        let data_opt = fast_fields_composite.open_read_with_idx(field, 1);
-                        if let (Some(fast_field_idx), Some(fast_field_data)) = (idx_opt, data_opt) {
-                            let idx_reader = FastFieldReader::open(fast_field_idx);
-                            match fast_type {
-                                FastType::I64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
-                                    let multivalued_int_fast_field =
-                                        MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
-                                    fast_field_readers
-                                        .fast_field_i64s
-                                        .insert(field, multivalued_int_fast_field);
-                                }
-                                FastType::U64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
-                                    let multivalued_int_fast_field =
-                                        MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
-                                    fast_field_readers
-                                        .fast_field_u64s
-                                        .insert(field, multivalued_int_fast_field);
-                                }
-                                FastType::F64 => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
-                                    let multivalued_int_fast_field =
-                                        MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
-                                    fast_field_readers
-                                        .fast_field_f64s
-                                        .insert(field, multivalued_int_fast_field);
-                                }
-                                FastType::Date => {
-                                    let vals_reader = FastFieldReader::open(fast_field_data);
-                                    let multivalued_int_fast_field =
-                                        MultiValueIntFastFieldReader::open(idx_reader, vals_reader);
-                                    fast_field_readers
-                                        .fast_field_dates
-                                        .insert(field, multivalued_int_fast_field);
-                                }
-                            }
-                        } else {
-                            return Err(From::from(FastFieldNotAvailableError::new(field_entry)));
-                        }
-                    }
-                }
-            }
+    pub(crate) fn new(schema: Schema, fast_fields_composite: CompositeFile) -> FastFieldReaders {
+        FastFieldReaders {
+            fast_fields_composite,
+            schema,
         }
-        Ok(fast_field_readers)
     }
 
     pub(crate) fn space_usage(&self) -> PerFieldSpaceUsage {
         self.fast_fields_composite.space_usage()
     }
 
+    fn fast_field_data(&self, field: Field, idx: usize) -> crate::Result<FileSlice> {
+        self.fast_fields_composite
+            .open_read_with_idx(field, idx)
+            .ok_or_else(|| {
+                let field_name = self.schema.get_field_entry(field).name();
+                TantivyError::SchemaError(format!("Field({}) data was not found", field_name))
+            })
+    }
+
+    fn check_type(
+        &self,
+        field: Field,
+        expected_fast_type: FastType,
+        expected_cardinality: Cardinality,
+    ) -> crate::Result<()> {
+        let field_entry = self.schema.get_field_entry(field);
+        let (fast_type, cardinality) =
+            type_and_cardinality(field_entry.field_type()).ok_or_else(|| {
+                crate::TantivyError::SchemaError(format!(
+                    "Field {:?} is not a fast field.",
+                    field_entry.name()
+                ))
+            })?;
+        if fast_type != expected_fast_type {
+            return Err(crate::TantivyError::SchemaError(format!(
+                "Field {:?} is of type {:?}, expected {:?}.",
+                field_entry.name(),
+                fast_type,
+                expected_fast_type
+            )));
+        }
+        if cardinality != expected_cardinality {
+            return Err(crate::TantivyError::SchemaError(format!(
+                "Field {:?} is of cardinality {:?}, expected {:?}.",
+                field_entry.name(),
+                cardinality,
+                expected_cardinality
+            )));
+        }
+        Ok(())
+    }
+
+    pub(crate) fn typed_fast_field_reader<TFastValue: FastValue>(
+        &self,
+        field: Field,
+    ) -> crate::Result<FastFieldReader<TFastValue>> {
+        let fast_field_slice = self.fast_field_data(field, 0)?;
+        FastFieldReader::open(fast_field_slice)
+    }
+
+    pub(crate) fn typed_fast_field_multi_reader<TFastValue: FastValue>(
+        &self,
+        field: Field,
+    ) -> crate::Result<MultiValuedFastFieldReader<TFastValue>> {
+        let fast_field_slice_idx = self.fast_field_data(field, 0)?;
+        let fast_field_slice_vals = self.fast_field_data(field, 1)?;
+        let idx_reader = FastFieldReader::open(fast_field_slice_idx)?;
+        let vals_reader: FastFieldReader<TFastValue> =
+            FastFieldReader::open(fast_field_slice_vals)?;
+        Ok(MultiValuedFastFieldReader::open(idx_reader, vals_reader))
+    }
+
     /// Returns the `u64` fast field reader reader associated to `field`.
     ///
     /// If `field` is not a u64 fast field, this method returns `None`.
-    pub fn u64(&self, field: Field) -> Option<FastFieldReader<u64>> {
-        self.fast_field_u64.get(&field).cloned()
+    pub fn u64(&self, field: Field) -> crate::Result<FastFieldReader<u64>> {
+        self.check_type(field, FastType::U64, Cardinality::SingleValue)?;
+        self.typed_fast_field_reader(field)
     }
 
-    /// If the field is a u64-fast field return the associated reader.
-    /// If the field is a i64-fast field, return the associated u64 reader. Values are
-    /// mapped from i64 to u64 using a (well the, it is unique) monotonic mapping.    ///
+    /// Returns the `u64` fast field reader reader associated to `field`, regardless of whether the given
+    /// field is effectively of type `u64` or not.
     ///
-    /// This method is useful when merging segment reader.
-    pub(crate) fn u64_lenient(&self, field: Field) -> Option<FastFieldReader<u64>> {
-        if let Some(u64_ff_reader) = self.u64(field) {
-            return Some(u64_ff_reader);
-        }
-        if let Some(i64_ff_reader) = self.i64(field) {
-            return Some(i64_ff_reader.into_u64_reader());
-        }
-        if let Some(f64_ff_reader) = self.f64(field) {
-            return Some(f64_ff_reader.into_u64_reader());
-        }
-        if let Some(date_ff_reader) = self.date(field) {
-            return Some(date_ff_reader.into_u64_reader());
-        }
-        None
+    /// If not, the fastfield reader will returns the u64-value associated to the original FastValue.
+    pub fn u64_lenient(&self, field: Field) -> crate::Result<FastFieldReader<u64>> {
+        self.typed_fast_field_reader(field)
     }
 
     /// Returns the `i64` fast field reader reader associated to `field`.
     ///
     /// If `field` is not a i64 fast field, this method returns `None`.
-    pub fn i64(&self, field: Field) -> Option<FastFieldReader<i64>> {
-        self.fast_field_i64.get(&field).cloned()
+    pub fn i64(&self, field: Field) -> crate::Result<FastFieldReader<i64>> {
+        self.check_type(field, FastType::I64, Cardinality::SingleValue)?;
+        self.typed_fast_field_reader(field)
     }
 
     /// Returns the `i64` fast field reader reader associated to `field`.
     ///
     /// If `field` is not a i64 fast field, this method returns `None`.
-    pub fn date(&self, field: Field) -> Option<FastFieldReader<crate::DateTime>> {
-        self.fast_field_date.get(&field).cloned()
+    pub fn date(&self, field: Field) -> crate::Result<FastFieldReader<crate::DateTime>> {
+        self.check_type(field, FastType::Date, Cardinality::SingleValue)?;
+        self.typed_fast_field_reader(field)
     }
 
     /// Returns the `f64` fast field reader reader associated to `field`.
     ///
     /// If `field` is not a f64 fast field, this method returns `None`.
-    pub fn f64(&self, field: Field) -> Option<FastFieldReader<f64>> {
-        self.fast_field_f64.get(&field).cloned()
+    pub fn f64(&self, field: Field) -> crate::Result<FastFieldReader<f64>> {
+        self.check_type(field, FastType::F64, Cardinality::SingleValue)?;
+        self.typed_fast_field_reader(field)
     }
 
     /// Returns a `u64s` multi-valued fast field reader reader associated to `field`.
     ///
     /// If `field` is not a u64 multi-valued fast field, this method returns `None`.
-    pub fn u64s(&self, field: Field) -> Option<MultiValueIntFastFieldReader<u64>> {
-        self.fast_field_u64s.get(&field).cloned()
-    }
-
-    /// If the field is a u64s-fast field return the associated reader.
-    /// If the field is a i64s-fast field, return the associated u64s reader. Values are
-    /// mapped from i64 to u64 using a (well the, it is unique) monotonic mapping.
-    ///
-    /// This method is useful when merging segment reader.
-    pub(crate) fn u64s_lenient(&self, field: Field) -> Option<MultiValueIntFastFieldReader<u64>> {
-        if let Some(u64s_ff_reader) = self.u64s(field) {
-            return Some(u64s_ff_reader);
-        }
-        if let Some(i64s_ff_reader) = self.i64s(field) {
-            return Some(i64s_ff_reader.into_u64s_reader());
-        }
-        if let Some(f64s_ff_reader) = self.f64s(field) {
-            return Some(f64s_ff_reader.into_u64s_reader());
-        }
-        None
+    pub fn u64s(&self, field: Field) -> crate::Result<MultiValuedFastFieldReader<u64>> {
+        self.check_type(field, FastType::U64, Cardinality::MultiValues)?;
+        self.typed_fast_field_multi_reader(field)
     }
 
     /// Returns a `i64s` multi-valued fast field reader reader associated to `field`.
     ///
     /// If `field` is not a i64 multi-valued fast field, this method returns `None`.
-    pub fn i64s(&self, field: Field) -> Option<MultiValueIntFastFieldReader<i64>> {
-        self.fast_field_i64s.get(&field).cloned()
+    pub fn i64s(&self, field: Field) -> crate::Result<MultiValuedFastFieldReader<i64>> {
+        self.check_type(field, FastType::I64, Cardinality::MultiValues)?;
+        self.typed_fast_field_multi_reader(field)
     }
 
     /// Returns a `f64s` multi-valued fast field reader reader associated to `field`.
     ///
     /// If `field` is not a f64 multi-valued fast field, this method returns `None`.
-    pub fn f64s(&self, field: Field) -> Option<MultiValueIntFastFieldReader<f64>> {
-        self.fast_field_f64s.get(&field).cloned()
+    pub fn f64s(&self, field: Field) -> crate::Result<MultiValuedFastFieldReader<f64>> {
+        self.check_type(field, FastType::F64, Cardinality::MultiValues)?;
+        self.typed_fast_field_multi_reader(field)
     }
 
     /// Returns a `crate::DateTime` multi-valued fast field reader reader associated to `field`.
     ///
     /// If `field` is not a `crate::DateTime` multi-valued fast field, this method returns `None`.
-    pub fn dates(&self, field: Field) -> Option<MultiValueIntFastFieldReader<crate::DateTime>> {
-        self.fast_field_dates.get(&field).cloned()
+    pub fn dates(
+        &self,
+        field: Field,
+    ) -> crate::Result<MultiValuedFastFieldReader<crate::DateTime>> {
+        self.check_type(field, FastType::Date, Cardinality::MultiValues)?;
+        self.typed_fast_field_multi_reader(field)
     }
 
     /// Returns the `bytes` fast field reader associated to `field`.
     ///
     /// If `field` is not a bytes fast field, returns `None`.
-    pub fn bytes(&self, field: Field) -> Option<BytesFastFieldReader> {
-        self.fast_bytes.get(&field).cloned()
+    pub fn bytes(&self, field: Field) -> crate::Result<BytesFastFieldReader> {
+        let field_entry = self.schema.get_field_entry(field);
+        if let FieldType::Bytes(bytes_option) = field_entry.field_type() {
+            if !bytes_option.is_fast() {
+                return Err(crate::TantivyError::SchemaError(format!(
+                    "Field {:?} is not a fast field.",
+                    field_entry.name()
+                )));
+            }
+            let fast_field_idx_file = self.fast_field_data(field, 0)?;
+            let idx_reader = FastFieldReader::open(fast_field_idx_file)?;
+            let data = self.fast_field_data(field, 1)?;
+            BytesFastFieldReader::open(idx_reader, data)
+        } else {
+            Err(FastFieldNotAvailableError::new(field_entry).into())
+        }
     }
 }

src/fastfield/serializer.rs

@@ -66,9 +66,9 @@ impl FastFieldSerializer {
         &mut self,
         field: Field,
         idx: usize,
-    ) -> io::Result<FastBytesFieldSerializer<'_, CountingWriter<WritePtr>>> {
+    ) -> FastBytesFieldSerializer<'_, CountingWriter<WritePtr>> {
         let field_write = self.composite_write.for_field_with_idx(field, idx);
-        FastBytesFieldSerializer::open(field_write)
+        FastBytesFieldSerializer { write: field_write }
     }
 
     /// Closes the serializer
@@ -132,10 +132,6 @@ pub struct FastBytesFieldSerializer<'a, W: Write> {
 }
 
 impl<'a, W: Write> FastBytesFieldSerializer<'a, W> {
-    fn open(write: &'a mut W) -> io::Result<FastBytesFieldSerializer<'a, W>> {
-        Ok(FastBytesFieldSerializer { write })
-    }
-
     pub fn write_all(&mut self, vals: &[u8]) -> io::Result<()> {
         self.write.write_all(vals)
     }

src/fastfield/writer.rs

@@ -1,4 +1,4 @@
-use super::multivalued::MultiValueIntFastFieldWriter;
+use super::multivalued::MultiValuedFastFieldWriter;
 use crate::common;
 use crate::common::BinarySerializable;
 use crate::common::VInt;
@@ -13,7 +13,7 @@ use std::io;
 /// The fastfieldswriter regroup all of the fast field writers.
 pub struct FastFieldsWriter {
     single_value_writers: Vec<IntFastFieldWriter>,
-    multi_values_writers: Vec<MultiValueIntFastFieldWriter>,
+    multi_values_writers: Vec<MultiValuedFastFieldWriter>,
     bytes_value_writers: Vec<BytesFastFieldWriter>,
 }
 
@@ -33,7 +33,7 @@ impl FastFieldsWriter {
         let mut bytes_value_writers = Vec::new();
 
         for (field, field_entry) in schema.fields() {
-            match *field_entry.field_type() {
+            match field_entry.field_type() {
                 FieldType::I64(ref int_options)
                 | FieldType::U64(ref int_options)
                 | FieldType::F64(ref int_options)
@@ -46,19 +46,21 @@ impl FastFieldsWriter {
                             single_value_writers.push(fast_field_writer);
                         }
                         Some(Cardinality::MultiValues) => {
-                            let fast_field_writer = MultiValueIntFastFieldWriter::new(field, false);
+                            let fast_field_writer = MultiValuedFastFieldWriter::new(field, false);
                             multi_values_writers.push(fast_field_writer);
                         }
                         None => {}
                     }
                 }
-                FieldType::HierarchicalFacet => {
-                    let fast_field_writer = MultiValueIntFastFieldWriter::new(field, true);
+                FieldType::HierarchicalFacet(_) => {
+                    let fast_field_writer = MultiValuedFastFieldWriter::new(field, true);
                     multi_values_writers.push(fast_field_writer);
                 }
-                FieldType::Bytes => {
-                    let fast_field_writer = BytesFastFieldWriter::new(field);
-                    bytes_value_writers.push(fast_field_writer);
+                FieldType::Bytes(bytes_option) => {
+                    if bytes_option.is_fast() {
+                        let fast_field_writer = BytesFastFieldWriter::new(field);
+                        bytes_value_writers.push(fast_field_writer);
+                    }
                 }
                 _ => {}
             }
@@ -85,7 +87,7 @@ impl FastFieldsWriter {
     pub fn get_multivalue_writer(
         &mut self,
         field: Field,
-    ) -> Option<&mut MultiValueIntFastFieldWriter> {
+    ) -> Option<&mut MultiValuedFastFieldWriter> {
         // TODO optimize
         self.multi_values_writers
             .iter_mut()
@@ -126,6 +128,7 @@ impl FastFieldsWriter {
         for field_writer in &self.single_value_writers {
             field_writer.serialize(serializer)?;
         }
+
         for field_writer in &self.multi_values_writers {
             let field = field_writer.field();
             field_writer.serialize(serializer, mapping.get(&field))?;

src/fieldnorm/reader.rs

@@ -1,6 +1,7 @@
 use super::{fieldnorm_to_id, id_to_fieldnorm};
 use crate::common::CompositeFile;
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::schema::Field;
 use crate::space_usage::PerFieldSpaceUsage;
 use crate::DocId;
@@ -19,16 +20,21 @@ pub struct FieldNormReaders {
 
 impl FieldNormReaders {
     /// Creates a field norm reader.
-    pub fn open(source: ReadOnlySource) -> crate::Result<FieldNormReaders> {
-        let data = CompositeFile::open(&source)?;
+    pub fn open(file: FileSlice) -> crate::Result<FieldNormReaders> {
+        let data = CompositeFile::open(&file)?;
         Ok(FieldNormReaders {
             data: Arc::new(data),
         })
     }
 
     /// Returns the FieldNormReader for a specific field.
-    pub fn get_field(&self, field: Field) -> Option<FieldNormReader> {
-        self.data.open_read(field).map(FieldNormReader::open)
+    pub fn get_field(&self, field: Field) -> crate::Result<Option<FieldNormReader>> {
+        if let Some(file) = self.data.open_read(field) {
+            let fieldnorm_reader = FieldNormReader::open(file)?;
+            Ok(Some(fieldnorm_reader))
+        } else {
+            Ok(None)
+        }
     }
 
     /// Return a break down of the space usage per field.
@@ -55,19 +61,56 @@ impl FieldNormReaders {
 /// precompute computationally expensive functions of the fieldnorm
 /// in a very short array.
 #[derive(Clone)]
-pub struct FieldNormReader {
-    data: ReadOnlySource,
+pub struct FieldNormReader(ReaderImplEnum);
+
+impl From<ReaderImplEnum> for FieldNormReader {
+    fn from(reader_enum: ReaderImplEnum) -> FieldNormReader {
+        FieldNormReader(reader_enum)
+    }
+}
+
+#[derive(Clone)]
+enum ReaderImplEnum {
+    FromData(OwnedBytes),
+    Const {
+        num_docs: u32,
+        fieldnorm_id: u8,
+        fieldnorm: u32,
+    },
 }
 
 impl FieldNormReader {
-    /// Opens a field norm reader given its data source.
-    pub fn open(data: ReadOnlySource) -> Self {
-        FieldNormReader { data }
+    /// Creates a `FieldNormReader` with a constant fieldnorm.
+    ///
+    /// The fieldnorm will be subjected to compression as if it was coming
+    /// from an array-backed fieldnorm reader.
+    pub fn constant(num_docs: u32, fieldnorm: u32) -> FieldNormReader {
+        let fieldnorm_id = fieldnorm_to_id(fieldnorm);
+        let fieldnorm = id_to_fieldnorm(fieldnorm_id);
+        ReaderImplEnum::Const {
+            num_docs,
+            fieldnorm_id,
+            fieldnorm,
+        }
+        .into()
+    }
+
+    /// Opens a field norm reader given its file.
+    pub fn open(fieldnorm_file: FileSlice) -> crate::Result<Self> {
+        let data = fieldnorm_file.read_bytes()?;
+        Ok(FieldNormReader::new(data))
+    }
+
+    fn new(data: OwnedBytes) -> Self {
+        ReaderImplEnum::FromData(data).into()
     }
 
     /// Returns the number of documents in this segment.
     pub fn num_docs(&self) -> u32 {
-        self.data.len() as u32
+        match &self.0 {
+            ReaderImplEnum::FromData(data) => data.len() as u32,
+            ReaderImplEnum::Const { num_docs, .. } => *num_docs,
+        }
     }
 
     /// Returns the `fieldnorm` associated to a doc id.
@@ -80,15 +123,25 @@ impl FieldNormReader {
     /// The fieldnorm is effectively decoded from the
     /// `fieldnorm_id` by doing a simple table lookup.
     pub fn fieldnorm(&self, doc_id: DocId) -> u32 {
-        let fieldnorm_id = self.fieldnorm_id(doc_id);
-        id_to_fieldnorm(fieldnorm_id)
+        match &self.0 {
+            ReaderImplEnum::FromData(data) => {
+                let fieldnorm_id = data.as_slice()[doc_id as usize];
+                id_to_fieldnorm(fieldnorm_id)
+            }
+            ReaderImplEnum::Const { fieldnorm, .. } => *fieldnorm,
+        }
     }
 
     /// Returns the `fieldnorm_id` associated to a document.
     #[inline(always)]
     pub fn fieldnorm_id(&self, doc_id: DocId) -> u8 {
-        let fielnorms_data = self.data.as_slice();
-        fielnorms_data[doc_id as usize]
+        match &self.0 {
+            ReaderImplEnum::FromData(data) => {
+                let fieldnorm_id = data.as_slice()[doc_id as usize];
+                fieldnorm_id
+            }
+            ReaderImplEnum::Const { fieldnorm_id, .. } => *fieldnorm_id,
+        }
     }
 
     /// Converts a `fieldnorm_id` into a fieldnorm.
@@ -111,10 +164,8 @@ impl FieldNormReader {
             .cloned()
             .map(FieldNormReader::fieldnorm_to_id)
             .collect::<Vec<u8>>();
-        let field_norms_data = ReadOnlySource::from(field_norms_id);
-        FieldNormReader {
-            data: field_norms_data,
-        }
+        let field_norms_data = OwnedBytes::new(field_norms_id);
+        FieldNormReader::new(field_norms_data)
     }
 }
 
@@ -133,4 +184,20 @@ mod tests {
         assert_eq!(fieldnorm_reader.fieldnorm(3), 4);
         assert_eq!(fieldnorm_reader.fieldnorm(4), 983_064);
     }
+
+    #[test]
+    fn test_const_fieldnorm_reader_small_fieldnorm_id() {
+        let fieldnorm_reader = FieldNormReader::constant(1_000_000u32, 10u32);
+        assert_eq!(fieldnorm_reader.num_docs(), 1_000_000u32);
+        assert_eq!(fieldnorm_reader.fieldnorm(0u32), 10u32);
+        assert_eq!(fieldnorm_reader.fieldnorm_id(0u32), 10u8);
+    }
+
+    #[test]
+    fn test_const_fieldnorm_reader_large_fieldnorm_id() {
+        let fieldnorm_reader = FieldNormReader::constant(1_000_000u32, 300u32);
+        assert_eq!(fieldnorm_reader.num_docs(), 1_000_000u32);
+        assert_eq!(fieldnorm_reader.fieldnorm(0u32), 280u32);
+        assert_eq!(fieldnorm_reader.fieldnorm_id(0u32), 72u8);
+    }
 }

src/fieldnorm/writer.rs

@@ -4,7 +4,7 @@ use super::fieldnorm_to_id;
 use super::FieldNormsSerializer;
 use crate::schema::Field;
 use crate::schema::Schema;
-use std::io;
+use std::{io, iter};
 
 /// The `FieldNormsWriter` is in charge of tracking the fieldnorm byte
 /// of each document for each field with field norms.
@@ -44,7 +44,9 @@ impl FieldNormsWriter {
             .unwrap_or(0);
         FieldNormsWriter {
             fields,
-            fieldnorms_buffer: (0..max_field).map(|_| Vec::new()).collect::<Vec<_>>(),
+            fieldnorms_buffer: iter::repeat_with(Vec::new)
+                .take(max_field)
+                .collect::<Vec<_>>(),
         }
     }
 

src/functional_test.rs

@@ -1,45 +1,93 @@
-use rand::thread_rng;
-use std::collections::HashSet;
-
-use crate::schema::*;
 use crate::Index;
 use crate::Searcher;
+use crate::{doc, schema::*};
+use rand::thread_rng;
 use rand::Rng;
+use std::collections::HashSet;
 
-fn check_index_content(searcher: &Searcher, vals: &HashSet<u64>) {
+fn check_index_content(searcher: &Searcher, vals: &[u64]) -> crate::Result<()> {
     assert!(searcher.segment_readers().len() < 20);
     assert_eq!(searcher.num_docs() as usize, vals.len());
+    for segment_reader in searcher.segment_readers() {
+        let store_reader = segment_reader.get_store_reader()?;
+        for doc_id in 0..segment_reader.max_doc() {
+            let _doc = store_reader.get(doc_id)?;
+        }
+    }
+    Ok(())
 }
 
 #[test]
 #[ignore]
-fn test_indexing() {
+fn test_functional_store() -> crate::Result<()> {
+    let mut schema_builder = Schema::builder();
+
+    let id_field = schema_builder.add_u64_field("id", INDEXED | STORED);
+    let schema = schema_builder.build();
+
+    let index = Index::create_in_ram(schema);
+    let reader = index.reader()?;
+
+    let mut rng = thread_rng();
+
+    let mut index_writer = index.writer_with_num_threads(3, 12_000_000)?;
+
+    let mut doc_set: Vec<u64> = Vec::new();
+
+    let mut doc_id = 0u64;
+    for iteration in 0..500 {
+        dbg!(iteration);
+        let num_docs: usize = rng.gen_range(0..4);
+        if doc_set.len() >= 1 {
+            let doc_to_remove_id = rng.gen_range(0..doc_set.len());
+            let removed_doc_id = doc_set.swap_remove(doc_to_remove_id);
+            index_writer.delete_term(Term::from_field_u64(id_field, removed_doc_id));
+        }
+        for _ in 0..num_docs {
+            doc_set.push(doc_id);
+            index_writer.add_document(doc!(id_field=>doc_id));
+            doc_id += 1;
+        }
+        index_writer.commit()?;
+        reader.reload()?;
+        let searcher = reader.searcher();
+        check_index_content(&searcher, &doc_set)?;
+    }
+    Ok(())
+}
+
+#[test]
+#[ignore]
+fn test_functional_indexing() -> crate::Result<()> {
     let mut schema_builder = Schema::builder();
 
     let id_field = schema_builder.add_u64_field("id", INDEXED);
     let multiples_field = schema_builder.add_u64_field("multiples", INDEXED);
     let schema = schema_builder.build();
 
-    let index = Index::create_from_tempdir(schema).unwrap();
-    let reader = index.reader().unwrap();
+    let index = Index::create_from_tempdir(schema)?;
+    let reader = index.reader()?;
 
     let mut rng = thread_rng();
 
-    let mut index_writer = index.writer_with_num_threads(3, 120_000_000).unwrap();
+    let mut index_writer = index.writer_with_num_threads(3, 120_000_000)?;
 
     let mut committed_docs: HashSet<u64> = HashSet::new();
     let mut uncommitted_docs: HashSet<u64> = HashSet::new();
 
     for _ in 0..200 {
-        let random_val = rng.gen_range(0, 20);
+        let random_val = rng.gen_range(0..20);
         if random_val == 0 {
-            index_writer.commit().expect("Commit failed");
+            index_writer.commit()?;
             committed_docs.extend(&uncommitted_docs);
             uncommitted_docs.clear();
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             // check that everything is correct.
-            check_index_content(&searcher, &committed_docs);
+            check_index_content(
+                &searcher,
+                &committed_docs.iter().cloned().collect::<Vec<u64>>(),
+            )?;
         } else {
             if committed_docs.remove(&random_val) || uncommitted_docs.remove(&random_val) {
                 let doc_id_term = Term::from_field_u64(id_field, random_val);
@@ -55,4 +103,5 @@ fn test_indexing() {
             }
         }
     }
+    Ok(())
 }

src/indexer/delete_queue.rs

@@ -53,7 +53,7 @@ impl DeleteQueue {
             return block;
         }
         let block = Arc::new(Block {
-            operations: Arc::default(),
+            operations: Arc::new([]),
             next: NextBlock::from(self.clone()),
         });
         wlock.last_block = Arc::downgrade(&block);
@@ -108,7 +108,7 @@ impl DeleteQueue {
         let delete_operations = mem::replace(&mut self_wlock.writer, vec![]);
 
         let new_block = Arc::new(Block {
-            operations: Arc::new(delete_operations.into_boxed_slice()),
+            operations: Arc::from(delete_operations.into_boxed_slice()),
             next: NextBlock::from(self.clone()),
         });
 
@@ -167,7 +167,7 @@ impl NextBlock {
 }
 
 struct Block {
-    operations: Arc<Box<[DeleteOperation]>>,
+    operations: Arc<[DeleteOperation]>,
     next: NextBlock,
 }
 

src/indexer/index_writer.rs

@@ -108,9 +108,9 @@ fn compute_deleted_bitset(
         // Limit doc helps identify the first document
         // that may be affected by the delete operation.
         let limit_doc = doc_opstamps.compute_doc_limit(delete_op.opstamp);
-        let inverted_index = segment_reader.inverted_index(delete_op.term.field());
+        let inverted_index = segment_reader.inverted_index(delete_op.term.field())?;
         if let Some(mut docset) =
-            inverted_index.read_postings(&delete_op.term, IndexRecordOption::Basic)
+            inverted_index.read_postings(&delete_op.term, IndexRecordOption::Basic)?
         {
             let mut deleted_doc = docset.doc();
             while deleted_doc != TERMINATED {
@@ -449,7 +449,7 @@ impl IndexWriter {
     }
 
     /// Accessor to the merge policy.
-    pub fn get_merge_policy(&self) -> Arc<Box<dyn MergePolicy>> {
+    pub fn get_merge_policy(&self) -> Arc<dyn MergePolicy> {
         self.segment_updater.get_merge_policy()
     }
 
@@ -800,7 +800,7 @@ mod tests {
         let mut schema_builder = schema::Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
-        let index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let index_writer = index.writer_for_tests().unwrap();
         let operations = vec![
             UserOperation::Add(doc!(text_field=>"a")),
             UserOperation::Add(doc!(text_field=>"b")),
@@ -815,7 +815,7 @@ mod tests {
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_in_ram(schema_builder.build());
 
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(text_field => "hello1"));
         index_writer.add_document(doc!(text_field => "hello2"));
         assert!(index_writer.commit().is_ok());
@@ -864,7 +864,7 @@ mod tests {
             .reload_policy(ReloadPolicy::Manual)
             .try_into()
             .unwrap();
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         let a_term = Term::from_field_text(text_field, "a");
         let b_term = Term::from_field_text(text_field, "b");
         let operations = vec![
@@ -926,8 +926,8 @@ mod tests {
     fn test_lockfile_already_exists_error_msg() {
         let schema_builder = schema::Schema::builder();
         let index = Index::create_in_ram(schema_builder.build());
-        let _index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-        match index.writer_with_num_threads(1, 3_000_000) {
+        let _index_writer = index.writer_for_tests().unwrap();
+        match index.writer_for_tests() {
             Err(err) => {
                 let err_msg = err.to_string();
                 assert!(err_msg.contains("already an `IndexWriter`"));
@@ -979,7 +979,7 @@ mod tests {
         let num_docs_containing = |s: &str| {
             let searcher = reader.searcher();
             let term = Term::from_field_text(text_field, s);
-            searcher.doc_freq(&term)
+            searcher.doc_freq(&term).unwrap()
         };
 
         {
@@ -1015,7 +1015,7 @@ mod tests {
             .unwrap();
         let num_docs_containing = |s: &str| {
             let term_a = Term::from_field_text(text_field, s);
-            reader.searcher().doc_freq(&term_a)
+            reader.searcher().doc_freq(&term_a).unwrap()
         };
         {
             // writing the segment
@@ -1110,6 +1110,7 @@ mod tests {
                 .unwrap()
                 .searcher()
                 .doc_freq(&term_a)
+                .unwrap()
         };
         assert_eq!(num_docs_containing("a"), 0);
         assert_eq!(num_docs_containing("b"), 100);
@@ -1129,7 +1130,7 @@ mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let term = Term::from_field_text(text_field, s);
-            searcher.doc_freq(&term)
+            searcher.doc_freq(&term).unwrap()
         };
         let mut index_writer = index.writer_with_num_threads(4, 12_000_000).unwrap();
 
@@ -1180,7 +1181,15 @@ mod tests {
 
         // working with an empty index == no documents
         let term_b = Term::from_field_text(text_field, "b");
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_b), 0);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_b)
+                .unwrap(),
+            0
+        );
     }
 
     #[test]
@@ -1200,7 +1209,15 @@ mod tests {
 
         let term_a = Term::from_field_text(text_field, "a");
         // expect the document with that term to be in the index
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_a), 1);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_a)
+                .unwrap(),
+            1
+        );
     }
 
     #[test]
@@ -1226,7 +1243,15 @@ mod tests {
         // Find original docs in the index
         let term_a = Term::from_field_text(text_field, "a");
         // expect the document with that term to be in the index
-        assert_eq!(index.reader().unwrap().searcher().doc_freq(&term_a), 1);
+        assert_eq!(
+            index
+                .reader()
+                .unwrap()
+                .searcher()
+                .doc_freq(&term_a)
+                .unwrap(),
+            1
+        );
     }
 
     #[test]
@@ -1261,7 +1286,7 @@ mod tests {
         let idfield = schema_builder.add_text_field("id", STRING);
         schema_builder.add_text_field("optfield", STRING);
         let index = Index::create_in_ram(schema_builder.build());
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(idfield=>"myid"));
         let commit = index_writer.commit();
         assert!(commit.is_ok());

src/indexer/log_merge_policy.rs

@@ -8,7 +8,7 @@ const DEFAULT_MIN_LAYER_SIZE: u32 = 10_000;
 const DEFAULT_MIN_MERGE_SIZE: usize = 8;
 const DEFAULT_MAX_MERGE_SIZE: usize = 10_000_000;
 
-/// `LogMergePolicy` tries tries to merge segments that have a similar number of
+/// `LogMergePolicy` tries to merge segments that have a similar number of
 /// documents.
 #[derive(Debug, Clone)]
 pub struct LogMergePolicy {

src/indexer/merger.rs

@@ -7,7 +7,7 @@ use crate::fastfield::BytesFastFieldReader;
 use crate::fastfield::DeleteBitSet;
 use crate::fastfield::FastFieldReader;
 use crate::fastfield::FastFieldSerializer;
-use crate::fastfield::MultiValueIntFastFieldReader;
+use crate::fastfield::MultiValuedFastFieldReader;
 use crate::fieldnorm::FieldNormsSerializer;
 use crate::fieldnorm::FieldNormsWriter;
 use crate::fieldnorm::{FieldNormReader, FieldNormReaders};
@@ -25,23 +25,23 @@ use std::cmp;
 use std::collections::HashMap;
 use std::sync::Arc;
 
-fn compute_total_num_tokens(readers: &[SegmentReader], field: Field) -> u64 {
+fn compute_total_num_tokens(readers: &[SegmentReader], field: Field) -> crate::Result<u64> {
     let mut total_tokens = 0u64;
     let mut count: [usize; 256] = [0; 256];
     for reader in readers {
         if reader.has_deletes() {
             // if there are deletes, then we use an approximation
             // using the fieldnorm
-            let fieldnorms_reader = reader.get_fieldnorms_reader(field);
+            let fieldnorms_reader = reader.get_fieldnorms_reader(field)?;
             for doc in reader.doc_ids_alive() {
                 let fieldnorm_id = fieldnorms_reader.fieldnorm_id(doc);
                 count[fieldnorm_id as usize] += 1;
             }
         } else {
-            total_tokens += reader.inverted_index(field).total_num_tokens();
+            total_tokens += reader.inverted_index(field)?.total_num_tokens();
         }
     }
-    total_tokens
+    Ok(total_tokens
         + count
             .iter()
             .cloned()
@@ -49,7 +49,7 @@ fn compute_total_num_tokens(readers: &[SegmentReader], field: Field) -> u64 {
             .map(|(fieldnorm_ord, count)| {
                 count as u64 * u64::from(FieldNormReader::id_to_fieldnorm(fieldnorm_ord as u8))
             })
-            .sum::<u64>()
+            .sum::<u64>())
 }
 
 pub struct IndexMerger {
@@ -175,7 +175,7 @@ impl IndexMerger {
         for field in fields {
             fieldnorms_data.clear();
             for reader in &self.readers {
-                let fieldnorms_reader = reader.get_fieldnorms_reader(field);
+                let fieldnorms_reader = reader.get_fieldnorms_reader(field)?;
                 for doc_id in reader.doc_ids_alive() {
                     let fieldnorm_id = fieldnorms_reader.fieldnorm_id(doc_id);
                     fieldnorms_data.push(fieldnorm_id);
@@ -194,8 +194,8 @@ impl IndexMerger {
     ) -> crate::Result<()> {
         for (field, field_entry) in self.schema.fields() {
             let field_type = field_entry.field_type();
-            match *field_type {
-                FieldType::HierarchicalFacet => {
+            match field_type {
+                FieldType::HierarchicalFacet(_) => {
                     let term_ordinal_mapping = term_ord_mappings
                         .remove(&field)
                         .expect("Logic Error in Tantivy (Please report). HierarchicalFact field should have required a\
@@ -223,8 +223,10 @@ impl IndexMerger {
                     // They can be implemented using what is done
                     // for facets in the future.
                 }
-                FieldType::Bytes => {
-                    self.write_bytes_fast_field(field, fast_field_serializer)?;
+                FieldType::Bytes(byte_options) => {
+                    if byte_options.is_fast() {
+                        self.write_bytes_fast_field(field, fast_field_serializer)?;
+                    }
                 }
             }
         }
@@ -244,7 +246,7 @@ impl IndexMerger {
         for reader in &self.readers {
             let u64_reader: FastFieldReader<u64> = reader
                 .fast_fields()
-                .u64_lenient(field)
+                .typed_fast_field_reader(field)
                 .expect("Failed to find a reader for single fast field. This is a tantivy bug and it should never happen.");
             if let Some((seg_min_val, seg_max_val)) =
                 compute_min_max_val(&u64_reader, reader.max_doc(), reader.delete_bitset())
@@ -288,7 +290,7 @@ impl IndexMerger {
         fast_field_serializer: &mut FastFieldSerializer,
     ) -> crate::Result<()> {
         let mut total_num_vals = 0u64;
-        let mut u64s_readers: Vec<MultiValueIntFastFieldReader<u64>> = Vec::new();
+        let mut u64s_readers: Vec<MultiValuedFastFieldReader<u64>> = Vec::new();
 
         // In the first pass, we compute the total number of vals.
         //
@@ -296,9 +298,8 @@ impl IndexMerger {
         // what should be the bit length use for bitpacking.
         for reader in &self.readers {
             let u64s_reader = reader.fast_fields()
-                .u64s_lenient(field)
+                .typed_fast_field_multi_reader(field)
                 .expect("Failed to find index for multivalued field. This is a bug in tantivy, please report.");
-
             if let Some(delete_bitset) = reader.delete_bitset() {
                 for doc in 0u32..reader.max_doc() {
                     if delete_bitset.is_alive(doc) {
@@ -351,7 +352,7 @@ impl IndexMerger {
             for (segment_ord, segment_reader) in self.readers.iter().enumerate() {
                 let term_ordinal_mapping: &[TermOrdinal] =
                     term_ordinal_mappings.get_segment(segment_ord);
-                let ff_reader: MultiValueIntFastFieldReader<u64> = segment_reader
+                let ff_reader: MultiValuedFastFieldReader<u64> = segment_reader
                     .fast_fields()
                     .u64s(field)
                     .expect("Could not find multivalued u64 fast value reader.");
@@ -395,8 +396,10 @@ impl IndexMerger {
         // We go through a complete first pass to compute the minimum and the
         // maximum value and initialize our Serializer.
         for reader in &self.readers {
-            let ff_reader: MultiValueIntFastFieldReader<u64> =
-                reader.fast_fields().u64s_lenient(field).expect(
+            let ff_reader: MultiValuedFastFieldReader<u64> = reader
+                .fast_fields()
+                .typed_fast_field_multi_reader(field)
+                .expect(
                     "Failed to find multivalued fast field reader. This is a bug in \
                      tantivy. Please report.",
                 );
@@ -443,9 +446,7 @@ impl IndexMerger {
         let mut bytes_readers: Vec<BytesFastFieldReader> = Vec::new();
 
         for reader in &self.readers {
-            let bytes_reader = reader.fast_fields().bytes(field).expect(
-                "Failed to find bytes fast field reader. This is a bug in tantivy, please report.",
-            );
+            let bytes_reader = reader.fast_fields().bytes(field)?;
             if let Some(delete_bitset) = reader.delete_bitset() {
                 for doc in 0u32..reader.max_doc() {
                     if delete_bitset.is_alive(doc) {
@@ -475,7 +476,7 @@ impl IndexMerger {
             serialize_idx.close_field()?;
         }
 
-        let mut serialize_vals = fast_field_serializer.new_bytes_fast_field_with_idx(field, 1)?;
+        let mut serialize_vals = fast_field_serializer.new_bytes_fast_field_with_idx(field, 1);
         for segment_reader in &self.readers {
             let bytes_reader = segment_reader.fast_fields().bytes(field)
                 .expect("Failed to find bytes field in fast field reader. This is a bug in tantivy. Please report.");
@@ -498,25 +499,25 @@ impl IndexMerger {
     ) -> crate::Result<Option<TermOrdinalMapping>> {
         let mut positions_buffer: Vec<u32> = Vec::with_capacity(1_000);
         let mut delta_computer = DeltaComputer::new();
+
+        let mut max_term_ords: Vec<TermOrdinal> = Vec::new();
+
         let field_readers: Vec<Arc<InvertedIndexReader>> = self
             .readers
             .iter()
             .map(|reader| reader.inverted_index(indexed_field))
-            .collect::<Vec<_>>();
+            .collect::<crate::Result<Vec<_>>>()?;
 
         let mut field_term_streams = Vec::new();
-        let mut max_term_ords: Vec<TermOrdinal> = Vec::new();
-
         for field_reader in &field_readers {
             let terms = field_reader.terms();
-            field_term_streams.push(terms.stream());
+            field_term_streams.push(terms.stream()?);
             max_term_ords.push(terms.num_terms() as u64);
         }
 
-        let mut term_ord_mapping_opt = if *field_type == FieldType::HierarchicalFacet {
-            Some(TermOrdinalMapping::new(max_term_ords))
-        } else {
-            None
+        let mut term_ord_mapping_opt = match field_type {
+            FieldType::HierarchicalFacet(_) => Some(TermOrdinalMapping::new(max_term_ords)),
+            _ => None,
         };
 
         let mut merged_terms = TermMerger::new(field_term_streams);
@@ -541,7 +542,7 @@ impl IndexMerger {
         // The total number of tokens will only be exact when there has been no deletes.
         //
         // Otherwise, we approximate by removing deleted documents proportionally.
-        let total_num_tokens: u64 = compute_total_num_tokens(&self.readers, indexed_field);
+        let total_num_tokens: u64 = compute_total_num_tokens(&self.readers, indexed_field)?;
 
         // Create the total list of doc ids
         // by stacking the doc ids from the different segment.
@@ -578,8 +579,8 @@ impl IndexMerger {
                 let term_info = heap_item.streamer.value();
                 let segment_reader = &self.readers[heap_item.segment_ord];
                 let inverted_index: &InvertedIndexReader = &*field_readers[segment_ord];
-                let segment_postings =
-                    inverted_index.read_postings_from_terminfo(term_info, segment_postings_option);
+                let segment_postings = inverted_index
+                    .read_postings_from_terminfo(term_info, segment_postings_option)?;
                 let delete_bitset_opt = segment_reader.delete_bitset();
                 let doc_freq = if let Some(delete_bitset) = delete_bitset_opt {
                     segment_postings.doc_freq_given_deletes(delete_bitset)
@@ -648,7 +649,7 @@ impl IndexMerger {
     ) -> crate::Result<HashMap<Field, TermOrdinalMapping>> {
         let mut term_ordinal_mappings = HashMap::new();
         for (field, field_entry) in self.schema.fields() {
-            let fieldnorm_reader = fieldnorm_readers.get_field(field);
+            let fieldnorm_reader = fieldnorm_readers.get_field(field)?;
             if field_entry.is_indexed() {
                 if let Some(term_ordinal_mapping) = self.write_postings_for_field(
                     field,
@@ -665,7 +666,7 @@ impl IndexMerger {
 
     fn write_storable_fields(&self, store_writer: &mut StoreWriter) -> crate::Result<()> {
         for reader in &self.readers {
-            let store_reader = reader.get_store_reader();
+            let store_reader = reader.get_store_reader()?;
             if reader.num_deleted_docs() > 0 {
                 for doc_id in reader.doc_ids_alive() {
                     let doc = store_reader.get(doc_id)?;
@@ -720,12 +721,12 @@ mod tests {
     use crate::IndexWriter;
     use crate::Searcher;
     use crate::{schema, DocSet, SegmentId};
-    use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
+    use byteorder::{BigEndian, ReadBytesExt};
     use futures::executor::block_on;
-    use std::io::Cursor;
+    use schema::FAST;
 
     #[test]
-    fn test_index_merger_no_deletes() {
+    fn test_index_merger_no_deletes() -> crate::Result<()> {
         let mut schema_builder = schema::Schema::builder();
         let text_fieldtype = schema::TextOptions::default()
             .set_indexing_options(
@@ -738,98 +739,77 @@ mod tests {
         let date_field = schema_builder.add_date_field("date", INDEXED);
         let score_fieldtype = schema::IntOptions::default().set_fast(Cardinality::SingleValue);
         let score_field = schema_builder.add_u64_field("score", score_fieldtype);
-        let bytes_score_field = schema_builder.add_bytes_field("score_bytes");
+        let bytes_score_field = schema_builder.add_bytes_field("score_bytes", FAST);
         let index = Index::create_in_ram(schema_builder.build());
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let curr_time = chrono::Utc::now();
-        let add_score_bytes = |doc: &mut Document, score: u32| {
-            let mut bytes = Vec::new();
-            bytes
-                .write_u32::<BigEndian>(score)
-                .expect("failed to write u32 bytes to Vec...");
-            doc.add_bytes(bytes_score_field, bytes);
-        };
-
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            {
-                // writing the segment
-                {
-                    let mut doc = Document::default();
-                    doc.add_text(text_field, "af b");
-                    doc.add_u64(score_field, 3);
-                    doc.add_date(date_field, &curr_time);
-                    add_score_bytes(&mut doc, 3);
-                    index_writer.add_document(doc);
-                }
-                {
-                    let mut doc = Document::default();
-                    doc.add_text(text_field, "a b c");
-                    doc.add_u64(score_field, 5);
-                    add_score_bytes(&mut doc, 5);
-                    index_writer.add_document(doc);
-                }
-                {
-                    let mut doc = Document::default();
-                    doc.add_text(text_field, "a b c d");
-                    doc.add_u64(score_field, 7);
-                    add_score_bytes(&mut doc, 7);
-                    index_writer.add_document(doc);
-                }
-                index_writer.commit().expect("committed");
-            }
+            let mut index_writer = index.writer_for_tests()?;
+            // writing the segment
+            index_writer.add_document(doc!(
+                text_field => "af b",
+                score_field => 3u64,
+                date_field => curr_time,
+                bytes_score_field => 3u32.to_be_bytes().as_ref()
+            ));
 
-            {
-                // writing the segment
-                {
-                    let mut doc = Document::default();
-                    doc.add_text(text_field, "af b");
-                    doc.add_date(date_field, &curr_time);
-                    doc.add_u64(score_field, 11);
-                    add_score_bytes(&mut doc, 11);
-                    index_writer.add_document(doc);
-                }
-                {
-                    let mut doc = Document::default();
-                    doc.add_text(text_field, "a b c g");
-                    doc.add_u64(score_field, 13);
-                    add_score_bytes(&mut doc, 13);
-                    index_writer.add_document(doc);
-                }
-                index_writer.commit().expect("Commit failed");
-            }
+            index_writer.add_document(doc!(
+                text_field => "a b c",
+                score_field => 5u64,
+                bytes_score_field => 5u32.to_be_bytes().as_ref()
+            ));
+            index_writer.add_document(doc!(
+                text_field => "a b c d",
+                score_field => 7u64,
+                bytes_score_field => 7u32.to_be_bytes().as_ref()
+            ));
+            index_writer.commit()?;
+            // writing the segment
+            index_writer.add_document(doc!(
+                text_field => "af b",
+                date_field => curr_time,
+                score_field => 11u64,
+                bytes_score_field => 11u32.to_be_bytes().as_ref()
+            ));
+            index_writer.add_document(doc!(
+                text_field => "a b c g",
+                score_field => 13u64,
+                bytes_score_field => 13u32.to_be_bytes().as_ref()
+            ));
+            index_writer.commit()?;
         }
         {
             let segment_ids = index
                 .searchable_segment_ids()
                 .expect("Searchable segments failed.");
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            block_on(index_writer.merge(&segment_ids)).expect("Merging failed");
-            index_writer.wait_merging_threads().unwrap();
+            let mut index_writer = index.writer_for_tests()?;
+            block_on(index_writer.merge(&segment_ids))?;
+            index_writer.wait_merging_threads()?;
         }
         {
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             let get_doc_ids = |terms: Vec<Term>| {
                 let query = BooleanQuery::new_multiterms_query(terms);
-                let top_docs = searcher.search(&query, &TEST_COLLECTOR_WITH_SCORE).unwrap();
-                top_docs.docs().to_vec()
+                searcher
+                    .search(&query, &TEST_COLLECTOR_WITH_SCORE)
+                    .map(|top_docs| top_docs.docs().to_vec())
             };
             {
                 assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "a")]),
+                    get_doc_ids(vec![Term::from_field_text(text_field, "a")])?,
                     vec![DocAddress(0, 1), DocAddress(0, 2), DocAddress(0, 4)]
                 );
                 assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "af")]),
+                    get_doc_ids(vec![Term::from_field_text(text_field, "af")])?,
                     vec![DocAddress(0, 0), DocAddress(0, 3)]
                 );
                 assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "g")]),
+                    get_doc_ids(vec![Term::from_field_text(text_field, "g")])?,
                     vec![DocAddress(0, 4)]
                 );
                 assert_eq!(
-                    get_doc_ids(vec![Term::from_field_text(text_field, "b")]),
+                    get_doc_ids(vec![Term::from_field_text(text_field, "b")])?,
                     vec![
                         DocAddress(0, 0),
                         DocAddress(0, 1),
@@ -839,60 +819,57 @@ mod tests {
                     ]
                 );
                 assert_eq!(
-                    get_doc_ids(vec![Term::from_field_date(date_field, &curr_time)]),
+                    get_doc_ids(vec![Term::from_field_date(date_field, &curr_time)])?,
                     vec![DocAddress(0, 0), DocAddress(0, 3)]
                 );
             }
             {
-                let doc = searcher.doc(DocAddress(0, 0)).unwrap();
+                let doc = searcher.doc(DocAddress(0, 0))?;
                 assert_eq!(doc.get_first(text_field).unwrap().text(), Some("af b"));
             }
             {
-                let doc = searcher.doc(DocAddress(0, 1)).unwrap();
+                let doc = searcher.doc(DocAddress(0, 1))?;
                 assert_eq!(doc.get_first(text_field).unwrap().text(), Some("a b c"));
             }
             {
-                let doc = searcher.doc(DocAddress(0, 2)).unwrap();
+                let doc = searcher.doc(DocAddress(0, 2))?;
                 assert_eq!(doc.get_first(text_field).unwrap().text(), Some("a b c d"));
             }
             {
-                let doc = searcher.doc(DocAddress(0, 3)).unwrap();
+                let doc = searcher.doc(DocAddress(0, 3))?;
                 assert_eq!(doc.get_first(text_field).unwrap().text(), Some("af b"));
             }
             {
-                let doc = searcher.doc(DocAddress(0, 4)).unwrap();
+                let doc = searcher.doc(DocAddress(0, 4))?;
                 assert_eq!(doc.get_first(text_field).unwrap().text(), Some("a b c g"));
             }
             {
                 let get_fast_vals = |terms: Vec<Term>| {
                     let query = BooleanQuery::new_multiterms_query(terms);
-                    searcher
-                        .search(&query, &FastFieldTestCollector::for_field(score_field))
-                        .unwrap()
+                    searcher.search(&query, &FastFieldTestCollector::for_field(score_field))
                 };
                 let get_fast_vals_bytes = |terms: Vec<Term>| {
                     let query = BooleanQuery::new_multiterms_query(terms);
-                    searcher
-                        .search(
-                            &query,
-                            &BytesFastFieldTestCollector::for_field(bytes_score_field),
-                        )
-                        .expect("failed to search")
+                    searcher.search(
+                        &query,
+                        &BytesFastFieldTestCollector::for_field(bytes_score_field),
+                    )
                 };
                 assert_eq!(
-                    get_fast_vals(vec![Term::from_field_text(text_field, "a")]),
+                    get_fast_vals(vec![Term::from_field_text(text_field, "a")])?,
                     vec![5, 7, 13]
                 );
                 assert_eq!(
-                    get_fast_vals_bytes(vec![Term::from_field_text(text_field, "a")]),
+                    get_fast_vals_bytes(vec![Term::from_field_text(text_field, "a")])?,
                     vec![0, 0, 0, 5, 0, 0, 0, 7, 0, 0, 0, 13]
                 );
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_index_merger_with_deletes() {
+    fn test_index_merger_with_deletes() -> crate::Result<()> {
         let mut schema_builder = schema::Schema::builder();
         let text_fieldtype = schema::TextOptions::default()
             .set_indexing_options(
@@ -902,27 +879,26 @@ mod tests {
         let text_field = schema_builder.add_text_field("text", text_fieldtype);
         let score_fieldtype = schema::IntOptions::default().set_fast(Cardinality::SingleValue);
         let score_field = schema_builder.add_u64_field("score", score_fieldtype);
-        let bytes_score_field = schema_builder.add_bytes_field("score_bytes");
+        let bytes_score_field = schema_builder.add_bytes_field("score_bytes", FAST);
         let index = Index::create_in_ram(schema_builder.build());
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         let reader = index.reader().unwrap();
         let search_term = |searcher: &Searcher, term: Term| {
             let collector = FastFieldTestCollector::for_field(score_field);
             let bytes_collector = BytesFastFieldTestCollector::for_field(bytes_score_field);
             let term_query = TermQuery::new(term, IndexRecordOption::Basic);
-            let (scores, bytes) = searcher
+            searcher
                 .search(&term_query, &(collector, bytes_collector))
-                .unwrap();
-            let mut score_bytes = Cursor::new(bytes);
-            for &score in &scores {
-                assert_eq!(score as u32, score_bytes.read_u32::<BigEndian>().unwrap());
-            }
-
-            scores
+                .map(|(scores, bytes)| {
+                    let mut score_bytes = &bytes[..];
+                    for &score in &scores {
+                        assert_eq!(score as u32, score_bytes.read_u32::<BigEndian>().unwrap());
+                    }
+                    scores
+                })
         };
 
         let empty_vec = Vec::<u64>::new();
-
         {
             // a first commit
             index_writer.add_document(doc!(
@@ -941,26 +917,26 @@ mod tests {
                 score_field => 3u64,
                 bytes_score_field => vec![0u8, 0, 0, 3],
             ));
-            index_writer.commit().expect("committed");
-            reader.reload().unwrap();
+            index_writer.commit()?;
+            reader.reload()?;
             let searcher = reader.searcher();
             assert_eq!(searcher.num_docs(), 2);
             assert_eq!(searcher.segment_readers()[0].num_docs(), 2);
             assert_eq!(searcher.segment_readers()[0].max_doc(), 3);
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "a")),
+                search_term(&searcher, Term::from_field_text(text_field, "a"))?,
                 vec![1]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "b")),
+                search_term(&searcher, Term::from_field_text(text_field, "b"))?,
                 vec![1]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "c")),
+                search_term(&searcher, Term::from_field_text(text_field, "c"))?,
                 vec![3]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "d")),
+                search_term(&searcher, Term::from_field_text(text_field, "d"))?,
                 vec![1, 3]
             );
         }
@@ -988,8 +964,8 @@ mod tests {
                 score_field => 7_000u64,
                 bytes_score_field => vec![0u8, 0, 27, 88],
             ));
-            index_writer.commit().expect("committed");
-            reader.reload().unwrap();
+            index_writer.commit()?;
+            reader.reload()?;
             let searcher = reader.searcher();
 
             assert_eq!(searcher.segment_readers().len(), 2);
@@ -999,31 +975,31 @@ mod tests {
             assert_eq!(searcher.segment_readers()[1].num_docs(), 1);
             assert_eq!(searcher.segment_readers()[1].max_doc(), 3);
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "a")),
+                search_term(&searcher, Term::from_field_text(text_field, "a"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "b")),
+                search_term(&searcher, Term::from_field_text(text_field, "b"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "c")),
+                search_term(&searcher, Term::from_field_text(text_field, "c"))?,
                 vec![3]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "d")),
+                search_term(&searcher, Term::from_field_text(text_field, "d"))?,
                 vec![3]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "e")),
+                search_term(&searcher, Term::from_field_text(text_field, "e"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "f")),
+                search_term(&searcher, Term::from_field_text(text_field, "f"))?,
                 vec![6_000]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "g")),
+                search_term(&searcher, Term::from_field_text(text_field, "g"))?,
                 vec![6_000, 7_000]
             );
 
@@ -1045,42 +1021,40 @@ mod tests {
         }
         {
             // merging the segments
-            let segment_ids = index
-                .searchable_segment_ids()
-                .expect("Searchable segments failed.");
-            block_on(index_writer.merge(&segment_ids)).expect("Merging failed");
-            reader.reload().unwrap();
+            let segment_ids = index.searchable_segment_ids()?;
+            block_on(index_writer.merge(&segment_ids))?;
+            reader.reload()?;
             let searcher = reader.searcher();
             assert_eq!(searcher.segment_readers().len(), 1);
             assert_eq!(searcher.num_docs(), 3);
             assert_eq!(searcher.segment_readers()[0].num_docs(), 3);
             assert_eq!(searcher.segment_readers()[0].max_doc(), 3);
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "a")),
+                search_term(&searcher, Term::from_field_text(text_field, "a"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "b")),
+                search_term(&searcher, Term::from_field_text(text_field, "b"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "c")),
+                search_term(&searcher, Term::from_field_text(text_field, "c"))?,
                 vec![3]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "d")),
+                search_term(&searcher, Term::from_field_text(text_field, "d"))?,
                 vec![3]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "e")),
+                search_term(&searcher, Term::from_field_text(text_field, "e"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "f")),
+                search_term(&searcher, Term::from_field_text(text_field, "f"))?,
                 vec![6_000]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "g")),
+                search_term(&searcher, Term::from_field_text(text_field, "g"))?,
                 vec![6_000, 7_000]
             );
             let score_field_reader = searcher
@@ -1094,40 +1068,40 @@ mod tests {
         {
             // test a commit with only deletes
             index_writer.delete_term(Term::from_field_text(text_field, "c"));
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
 
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             assert_eq!(searcher.segment_readers().len(), 1);
             assert_eq!(searcher.num_docs(), 2);
             assert_eq!(searcher.segment_readers()[0].num_docs(), 2);
             assert_eq!(searcher.segment_readers()[0].max_doc(), 3);
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "a")),
+                search_term(&searcher, Term::from_field_text(text_field, "a"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "b")),
+                search_term(&searcher, Term::from_field_text(text_field, "b"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "c")),
+                search_term(&searcher, Term::from_field_text(text_field, "c"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "d")),
+                search_term(&searcher, Term::from_field_text(text_field, "d"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "e")),
+                search_term(&searcher, Term::from_field_text(text_field, "e"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "f")),
+                search_term(&searcher, Term::from_field_text(text_field, "f"))?,
                 vec![6_000]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "g")),
+                search_term(&searcher, Term::from_field_text(text_field, "g"))?,
                 vec![6_000, 7_000]
             );
             let score_field_reader = searcher
@@ -1140,11 +1114,9 @@ mod tests {
         }
         {
             // Test merging a single segment in order to remove deletes.
-            let segment_ids = index
-                .searchable_segment_ids()
-                .expect("Searchable segments failed.");
-            block_on(index_writer.merge(&segment_ids)).expect("Merging failed");
-            reader.reload().unwrap();
+            let segment_ids = index.searchable_segment_ids()?;
+            block_on(index_writer.merge(&segment_ids))?;
+            reader.reload()?;
 
             let searcher = reader.searcher();
             assert_eq!(searcher.segment_readers().len(), 1);
@@ -1152,31 +1124,31 @@ mod tests {
             assert_eq!(searcher.segment_readers()[0].num_docs(), 2);
             assert_eq!(searcher.segment_readers()[0].max_doc(), 2);
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "a")),
+                search_term(&searcher, Term::from_field_text(text_field, "a"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "b")),
+                search_term(&searcher, Term::from_field_text(text_field, "b"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "c")),
+                search_term(&searcher, Term::from_field_text(text_field, "c"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "d")),
+                search_term(&searcher, Term::from_field_text(text_field, "d"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "e")),
+                search_term(&searcher, Term::from_field_text(text_field, "e"))?,
                 empty_vec
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "f")),
+                search_term(&searcher, Term::from_field_text(text_field, "f"))?,
                 vec![6_000]
             );
             assert_eq!(
-                search_term(&searcher, Term::from_field_text(text_field, "g")),
+                search_term(&searcher, Term::from_field_text(text_field, "g"))?,
                 vec![6_000, 7_000]
             );
             let score_field_reader = searcher
@@ -1191,27 +1163,26 @@ mod tests {
         {
             // Test removing all docs
             index_writer.delete_term(Term::from_field_text(text_field, "g"));
-            index_writer.commit().unwrap();
-            let segment_ids = index
-                .searchable_segment_ids()
-                .expect("Searchable segments failed.");
-            reader.reload().unwrap();
+            index_writer.commit()?;
+            let segment_ids = index.searchable_segment_ids()?;
+            reader.reload()?;
 
             let searcher = reader.searcher();
             assert!(segment_ids.is_empty());
             assert!(searcher.segment_readers().is_empty());
             assert_eq!(searcher.num_docs(), 0);
         }
+        Ok(())
     }
 
     #[test]
     fn test_merge_facets() {
         let mut schema_builder = schema::Schema::builder();
-        let facet_field = schema_builder.add_facet_field("facet");
+        let facet_field = schema_builder.add_facet_field("facet", INDEXED);
         let index = Index::create_in_ram(schema_builder.build());
         let reader = index.reader().unwrap();
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             let index_doc = |index_writer: &mut IndexWriter, doc_facets: &[&str]| {
                 let mut doc = Document::default();
                 for facet in doc_facets {
@@ -1276,7 +1247,7 @@ mod tests {
             let segment_ids = index
                 .searchable_segment_ids()
                 .expect("Searchable segments failed.");
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             block_on(index_writer.merge(&segment_ids)).expect("Merging failed");
             index_writer.wait_merging_threads().unwrap();
             reader.reload().unwrap();
@@ -1295,7 +1266,7 @@ mod tests {
 
         // Deleting one term
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             let facet = Facet::from_path(vec!["top", "a", "firstdoc"]);
             let facet_term = Term::from_facet(facet_field, &facet);
             index_writer.delete_term(facet_term);
@@ -1320,7 +1291,7 @@ mod tests {
         let mut schema_builder = schema::Schema::builder();
         let int_field = schema_builder.add_u64_field("intvals", INDEXED);
         let index = Index::create_in_ram(schema_builder.build());
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(int_field => 1u64));
         index_writer.commit().expect("commit failed");
         index_writer.add_document(doc!(int_field => 1u64));
@@ -1349,7 +1320,7 @@ mod tests {
         let index = Index::create_in_ram(schema_builder.build());
         let reader = index.reader().unwrap();
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             let mut doc = Document::default();
             doc.add_u64(int_field, 1);
             index_writer.add_document(doc.clone());
@@ -1388,7 +1359,7 @@ mod tests {
         let index = Index::create_in_ram(schema_builder.build());
 
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             let index_doc = |index_writer: &mut IndexWriter, int_vals: &[u64]| {
                 let mut doc = Document::default();
                 for &val in int_vals {
@@ -1462,7 +1433,7 @@ mod tests {
             let segment_ids = index
                 .searchable_segment_ids()
                 .expect("Searchable segments failed.");
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             assert!(block_on(index_writer.merge(&segment_ids)).is_ok());
             assert!(index_writer.wait_merging_threads().is_ok());
         }
@@ -1516,7 +1487,7 @@ mod tests {
 
         let index = Index::create_in_ram(builder.build());
 
-        let mut writer = index.writer_with_num_threads(1, 3_000_000)?;
+        let mut writer = index.writer_for_tests()?;
 
         // Make sure we'll attempt to merge every created segment
         let mut policy = crate::indexer::LogMergePolicy::default();
@@ -1548,7 +1519,7 @@ mod tests {
         let mut builder = schema::SchemaBuilder::new();
         let text = builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(builder.build());
-        let mut writer = index.writer_with_num_threads(1, 3_000_000)?;
+        let mut writer = index.writer_for_tests()?;
         let happy_term = Term::from_field_text(text, "happy");
         let term_query = TermQuery::new(happy_term, IndexRecordOption::WithFreqs);
         for _ in 0..62 {
@@ -1558,7 +1529,7 @@ mod tests {
         let reader = index.reader()?;
         let searcher = reader.searcher();
         let mut term_scorer = term_query
-            .specialized_weight(&searcher, true)
+            .specialized_weight(&searcher, true)?
             .specialized_scorer(searcher.segment_reader(0u32), 1.0)?;
         assert_eq!(term_scorer.doc(), 0);
         assert_nearly_equals!(term_scorer.block_max_score(), 0.0079681855);
@@ -1573,7 +1544,7 @@ mod tests {
         assert_eq!(searcher.segment_readers().len(), 2);
         for segment_reader in searcher.segment_readers() {
             let mut term_scorer = term_query
-                .specialized_weight(&searcher, true)
+                .specialized_weight(&searcher, true)?
                 .specialized_scorer(segment_reader, 1.0)?;
             // the difference compared to before is instrinsic to the bm25 formula. no worries there.
             for doc in segment_reader.doc_ids_alive() {
@@ -1597,7 +1568,7 @@ mod tests {
 
         let segment_reader = searcher.segment_reader(0u32);
         let mut term_scorer = term_query
-            .specialized_weight(&searcher, true)
+            .specialized_weight(&searcher, true)?
             .specialized_scorer(segment_reader, 1.0)?;
         // the difference compared to before is instrinsic to the bm25 formula. no worries there.
         for doc in segment_reader.doc_ids_alive() {

src/indexer/mod.rs

@@ -40,7 +40,7 @@ mod tests_mmap {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", schema::TEXT);
         let index = Index::create_from_tempdir(schema_builder.build()).unwrap();
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         // there must be one deleted document in the segment
         index_writer.add_document(doc!(text_field=>"b"));
         index_writer.delete_term(Term::from_field_text(text_field, "b"));

src/indexer/operation.rs

@@ -9,6 +9,15 @@ pub struct DeleteOperation {
     pub term: Term,
 }
 
+impl Default for DeleteOperation {
+    fn default() -> Self {
+        DeleteOperation {
+            opstamp: 0u64,
+            term: Term::new(),
+        }
+    }
+}
+
 /// Timestamped Add operation.
 #[derive(Eq, PartialEq, Debug)]
 pub struct AddOperation {

src/indexer/segment_updater.rs

@@ -43,7 +43,7 @@ const NUM_MERGE_THREADS: usize = 4;
 /// and flushed.
 ///
 /// This method is not part of tantivy's public API
-pub fn save_new_metas(schema: Schema, directory: &mut dyn Directory) -> crate::Result<()> {
+pub fn save_new_metas(schema: Schema, directory: &dyn Directory) -> crate::Result<()> {
     save_metas(
         &IndexMeta {
             segments: Vec::new(),
@@ -64,7 +64,7 @@ pub fn save_new_metas(schema: Schema, directory: &mut dyn Directory) -> crate::R
 /// and flushed.
 ///
 /// This method is not part of tantivy's public API
-fn save_metas(metas: &IndexMeta, directory: &mut dyn Directory) -> crate::Result<()> {
+fn save_metas(metas: &IndexMeta, directory: &dyn Directory) -> crate::Result<()> {
     info!("save metas");
     let mut buffer = serde_json::to_vec_pretty(metas)?;
     // Just adding a new line at the end of the buffer.
@@ -154,7 +154,7 @@ pub(crate) struct InnerSegmentUpdater {
 
     index: Index,
     segment_manager: SegmentManager,
-    merge_policy: RwLock<Arc<Box<dyn MergePolicy>>>,
+    merge_policy: RwLock<Arc<dyn MergePolicy>>,
     killed: AtomicBool,
     stamper: Stamper,
     merge_operations: MergeOperationInventory,
@@ -193,19 +193,19 @@ impl SegmentUpdater {
             merge_thread_pool,
             index,
             segment_manager,
-            merge_policy: RwLock::new(Arc::new(Box::new(DefaultMergePolicy::default()))),
+            merge_policy: RwLock::new(Arc::new(DefaultMergePolicy::default())),
             killed: AtomicBool::new(false),
             stamper,
             merge_operations: Default::default(),
         })))
     }
 
-    pub fn get_merge_policy(&self) -> Arc<Box<dyn MergePolicy>> {
+    pub fn get_merge_policy(&self) -> Arc<dyn MergePolicy> {
         self.merge_policy.read().unwrap().clone()
     }
 
     pub fn set_merge_policy(&self, merge_policy: Box<dyn MergePolicy>) {
-        let arc_merge_policy = Arc::new(merge_policy);
+        let arc_merge_policy = Arc::from(merge_policy);
         *self.merge_policy.write().unwrap() = arc_merge_policy;
     }
 
@@ -450,9 +450,8 @@ impl SegmentUpdater {
             .into_iter()
             .map(|merge_candidate: MergeCandidate| {
                 MergeOperation::new(&self.merge_operations, commit_opstamp, merge_candidate.0)
-            })
-            .collect::<Vec<_>>();
-        merge_candidates.extend(committed_merge_candidates.into_iter());
+            });
+        merge_candidates.extend(committed_merge_candidates);
 
         for merge_operation in merge_candidates {
             if let Err(err) = self.start_merge(merge_operation) {
@@ -555,7 +554,7 @@ mod tests {
         let index = Index::create_in_ram(schema);
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.set_merge_policy(Box::new(MergeWheneverPossible));
 
         {
@@ -608,7 +607,7 @@ mod tests {
         let index = Index::create_in_ram(schema);
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
 
         {
             for _ in 0..100 {
@@ -679,7 +678,7 @@ mod tests {
         let index = Index::create_in_ram(schema);
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
 
         {
             for _ in 0..100 {

src/indexer/segment_writer.rs

@@ -16,8 +16,6 @@ use crate::tokenizer::{FacetTokenizer, TextAnalyzer};
 use crate::tokenizer::{TokenStreamChain, Tokenizer};
 use crate::Opstamp;
 use crate::{DocId, SegmentComponent};
-use std::io;
-use std::str;
 
 /// Computes the initial size of the hash table.
 ///
@@ -48,6 +46,7 @@ pub struct SegmentWriter {
     fieldnorms_writer: FieldNormsWriter,
     doc_opstamps: Vec<Opstamp>,
     tokenizers: Vec<Option<TextAnalyzer>>,
+    term_buffer: Term,
 }
 
 impl SegmentWriter {
@@ -91,6 +90,7 @@ impl SegmentWriter {
             fast_field_writers: FastFieldsWriter::from_schema(schema),
             doc_opstamps: Vec::with_capacity(1_000),
             tokenizers,
+            term_buffer: Term::new(),
         })
     }
 
@@ -116,7 +116,11 @@ impl SegmentWriter {
     /// Indexes a new document
     ///
     /// As a user, you should rather use `IndexWriter`'s add_document.
-    pub fn add_document(&mut self, add_operation: AddOperation, schema: &Schema) -> io::Result<()> {
+    pub fn add_document(
+        &mut self,
+        add_operation: AddOperation,
+        schema: &Schema,
+    ) -> crate::Result<()> {
         let doc_id = self.max_doc;
         let mut doc = add_operation.document;
         self.doc_opstamps.push(add_operation.opstamp);
@@ -124,34 +128,45 @@ impl SegmentWriter {
         self.fast_field_writers.add_document(&doc);
 
         for (field, field_values) in doc.get_sorted_field_values() {
-            let field_options = schema.get_field_entry(field);
-            if !field_options.is_indexed() {
+            let field_entry = schema.get_field_entry(field);
+            let make_schema_error = || {
+                crate::TantivyError::SchemaError(format!(
+                    "Expected a {:?} for field {:?}",
+                    field_entry.field_type().value_type(),
+                    field_entry.name()
+                ))
+            };
+            if !field_entry.is_indexed() {
                 continue;
             }
-            match *field_options.field_type() {
-                FieldType::HierarchicalFacet => {
-                    let facets: Vec<&str> = field_values
-                        .iter()
-                        .flat_map(|field_value| match *field_value.value() {
-                            Value::Facet(ref facet) => Some(facet.encoded_str()),
-                            _ => {
-                                panic!("Expected hierarchical facet");
-                            }
-                        })
-                        .collect();
-                    let mut term = Term::for_field(field); // we set the Term
-                    for fake_str in facets {
+            let (term_buffer, multifield_postings) =
+                (&mut self.term_buffer, &mut self.multifield_postings);
+            match *field_entry.field_type() {
+                FieldType::HierarchicalFacet(_) => {
+                    term_buffer.set_field(field);
+                    let facets =
+                        field_values
+                            .iter()
+                            .flat_map(|field_value| match *field_value.value() {
+                                Value::Facet(ref facet) => Some(facet.encoded_str()),
+                                _ => {
+                                    panic!("Expected hierarchical facet");
+                                }
+                            });
+                    for facet_str in facets {
                         let mut unordered_term_id_opt = None;
-                        FacetTokenizer.token_stream(fake_str).process(&mut |token| {
-                            term.set_text(&token.text);
-                            let unordered_term_id =
-                                self.multifield_postings.subscribe(doc_id, &term);
-                            unordered_term_id_opt = Some(unordered_term_id);
-                        });
+                        FacetTokenizer
+                            .token_stream(facet_str)
+                            .process(&mut |token| {
+                                term_buffer.set_text(&token.text);
+                                let unordered_term_id =
+                                    multifield_postings.subscribe(doc_id, &term_buffer);
+                                unordered_term_id_opt = Some(unordered_term_id);
+                            });
                         if let Some(unordered_term_id) = unordered_term_id_opt {
                             self.fast_field_writers
                                 .get_multivalue_writer(field)
-                                .expect("multified writer for facet missing")
+                                .expect("writer for facet missing")
                                 .add_val(unordered_term_id);
                         }
                     }
@@ -168,7 +183,6 @@ impl SegmentWriter {
                                 if let Some(last_token) = tok_str.tokens.last() {
                                     total_offset += last_token.offset_to;
                                 }
-
                                 token_streams
                                     .push(PreTokenizedStream::from(tok_str.clone()).into());
                             }
@@ -178,7 +192,6 @@ impl SegmentWriter {
                                 {
                                     offsets.push(total_offset);
                                     total_offset += text.len();
-
                                     token_streams.push(tokenizer.token_stream(text));
                                 }
                             }
@@ -190,58 +203,70 @@ impl SegmentWriter {
                         0
                     } else {
                         let mut token_stream = TokenStreamChain::new(offsets, token_streams);
-                        self.multifield_postings
-                            .index_text(doc_id, field, &mut token_stream)
+                        multifield_postings.index_text(
+                            doc_id,
+                            field,
+                            &mut token_stream,
+                            term_buffer,
+                        )
                     };
 
                     self.fieldnorms_writer.record(doc_id, field, num_tokens);
                 }
-                FieldType::U64(ref int_option) => {
-                    if int_option.is_indexed() {
-                        for field_value in field_values {
-                            let term = Term::from_field_u64(
-                                field_value.field(),
-                                field_value.value().u64_value(),
-                            );
-                            self.multifield_postings.subscribe(doc_id, &term);
-                        }
+                FieldType::U64(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let u64_val = field_value
+                            .value()
+                            .u64_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_u64(u64_val);
+                        multifield_postings.subscribe(doc_id, &term_buffer);
                     }
                 }
-                FieldType::Date(ref int_option) => {
-                    if int_option.is_indexed() {
-                        for field_value in field_values {
-                            let term = Term::from_field_i64(
-                                field_value.field(),
-                                field_value.value().date_value().timestamp(),
-                            );
-                            self.multifield_postings.subscribe(doc_id, &term);
-                        }
+                FieldType::Date(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let date_val = field_value
+                            .value()
+                            .date_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_i64(date_val.timestamp());
+                        multifield_postings.subscribe(doc_id, &term_buffer);
                     }
                 }
-                FieldType::I64(ref int_option) => {
-                    if int_option.is_indexed() {
-                        for field_value in field_values {
-                            let term = Term::from_field_i64(
-                                field_value.field(),
-                                field_value.value().i64_value(),
-                            );
-                            self.multifield_postings.subscribe(doc_id, &term);
-                        }
+                FieldType::I64(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let i64_val = field_value
+                            .value()
+                            .i64_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_i64(i64_val);
+                        multifield_postings.subscribe(doc_id, &term_buffer);
                     }
                 }
-                FieldType::F64(ref int_option) => {
-                    if int_option.is_indexed() {
-                        for field_value in field_values {
-                            let term = Term::from_field_f64(
-                                field_value.field(),
-                                field_value.value().f64_value(),
-                            );
-                            self.multifield_postings.subscribe(doc_id, &term);
-                        }
+                FieldType::F64(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let f64_val = field_value
+                            .value()
+                            .f64_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_f64(f64_val);
+                        multifield_postings.subscribe(doc_id, &term_buffer);
                     }
                 }
-                FieldType::Bytes => {
-                    // Do nothing. Bytes only supports fast fields.
+                FieldType::Bytes(_) => {
+                    for field_value in field_values {
+                        term_buffer.set_field(field_value.field());
+                        let bytes = field_value
+                            .value()
+                            .bytes_value()
+                            .ok_or_else(make_schema_error)?;
+                        term_buffer.set_bytes(bytes);
+                        self.multifield_postings.subscribe(doc_id, &term_buffer);
+                    }
                 }
             }
         }

src/lib.rs

@@ -96,7 +96,7 @@
 //! A good place for you to get started is to check out
 //! the example code (
 //! [literate programming](https://tantivy-search.github.io/examples/basic_search.html) /
-//! [source code](https://github.com/tantivy-search/tantivy/blob/master/examples/basic_search.rs))
+//! [source code](https://github.com/tantivy-search/tantivy/blob/main/examples/basic_search.rs))
 
 #[cfg_attr(test, macro_use)]
 extern crate serde_json;
@@ -105,7 +105,7 @@ extern crate serde_json;
 extern crate log;
 
 #[macro_use]
-extern crate failure;
+extern crate thiserror;
 
 #[cfg(all(test, feature = "unstable"))]
 extern crate test;
@@ -134,7 +134,7 @@ mod core;
 mod indexer;
 
 #[allow(unused_doc_comments)]
-mod error;
+pub mod error;
 pub mod tokenizer;
 
 pub mod collector;
@@ -157,6 +157,7 @@ pub use self::snippet::{Snippet, SnippetGenerator};
 
 mod docset;
 pub use self::docset::{DocSet, TERMINATED};
+pub use crate::common::HasLen;
 pub use crate::common::{f64_to_u64, i64_to_u64, u64_to_f64, u64_to_i64};
 pub use crate::core::{Executor, SegmentComponent};
 pub use crate::core::{Index, IndexMeta, Searcher, Segment, SegmentId, SegmentMeta};
@@ -173,7 +174,7 @@ use once_cell::sync::Lazy;
 use serde::{Deserialize, Serialize};
 
 /// Index format version.
-const INDEX_FORMAT_VERSION: u32 = 2;
+const INDEX_FORMAT_VERSION: u32 = 3;
 
 /// Structure version for the index.
 #[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -233,6 +234,8 @@ pub mod merge_policy {
 /// A `u32` identifying a document within a segment.
 /// Documents have their `DocId` assigned incrementally,
 /// as they are added in the segment.
+///
+/// At most, a segment can contain 2^31 documents.
 pub type DocId = u32;
 
 /// A u64 assigned to every operation incrementally
@@ -245,18 +248,10 @@ pub type DocId = u32;
 /// with opstamp `n+1`.
 pub type Opstamp = u64;
 
-/// A Score that represents the relevance of the document to the query
-///
-/// This is modelled internally as a `f64`, because tantivy was compiled with the `scoref64`
-/// feature. The larger the number, the more relevant the document is to the search query.
-#[cfg(feature = "scoref64")]
-pub type Score = f64;
-
 /// A Score that represents the relevance of the document to the query
 ///
 /// This is modelled internally as a `f32`. The larger the number, the more relevant
 /// the document to the search query.
-#[cfg(not(feature = "scoref64"))]
 pub type Score = f32;
 
 /// A `SegmentLocalId` identifies a segment.
@@ -284,7 +279,7 @@ impl DocAddress {
 ///
 /// The id used for the segment is actually an ordinal
 /// in the list of `Segment`s held by a `Searcher`.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct DocAddress(pub SegmentLocalId, pub DocId);
 
 #[cfg(test)]
@@ -296,7 +291,6 @@ mod tests {
     use crate::schema::*;
     use crate::DocAddress;
     use crate::Index;
-    use crate::IndexWriter;
     use crate::Postings;
     use crate::ReloadPolicy;
     use rand::distributions::Bernoulli;
@@ -361,14 +355,14 @@ mod tests {
 
     #[test]
     #[cfg(feature = "mmap")]
-    fn test_indexing() {
+    fn test_indexing() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_from_tempdir(schema).unwrap();
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             {
                 let doc = doc!(text_field=>"af b");
                 index_writer.add_document(doc);
@@ -383,100 +377,76 @@ mod tests {
             }
             assert!(index_writer.commit().is_ok());
         }
+        Ok(())
     }
 
     #[test]
-    fn test_docfreq1() {
+    fn test_docfreq1() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-        {
-            index_writer.add_document(doc!(text_field=>"a b c"));
-            index_writer.commit().unwrap();
-        }
-        {
-            index_writer.add_document(doc!(text_field=>"a"));
-            index_writer.add_document(doc!(text_field=>"a a"));
-            index_writer.commit().unwrap();
-        }
-        {
-            index_writer.add_document(doc!(text_field=>"c"));
-            index_writer.commit().unwrap();
-        }
-        {
-            let reader = index.reader().unwrap();
-            let searcher = reader.searcher();
-            let term_a = Term::from_field_text(text_field, "a");
-            assert_eq!(searcher.doc_freq(&term_a), 3);
-            let term_b = Term::from_field_text(text_field, "b");
-            assert_eq!(searcher.doc_freq(&term_b), 1);
-            let term_c = Term::from_field_text(text_field, "c");
-            assert_eq!(searcher.doc_freq(&term_c), 2);
-            let term_d = Term::from_field_text(text_field, "d");
-            assert_eq!(searcher.doc_freq(&term_d), 0);
-        }
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.commit()?;
+        index_writer.add_document(doc!(text_field=>"a"));
+        index_writer.add_document(doc!(text_field=>"a a"));
+        index_writer.commit()?;
+        index_writer.add_document(doc!(text_field=>"c"));
+        index_writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let term_a = Term::from_field_text(text_field, "a");
+        assert_eq!(searcher.doc_freq(&term_a)?, 3);
+        let term_b = Term::from_field_text(text_field, "b");
+        assert_eq!(searcher.doc_freq(&term_b)?, 1);
+        let term_c = Term::from_field_text(text_field, "c");
+        assert_eq!(searcher.doc_freq(&term_c)?, 2);
+        let term_d = Term::from_field_text(text_field, "d");
+        assert_eq!(searcher.doc_freq(&term_d)?, 0);
+        Ok(())
     }
 
     #[test]
-    fn test_fieldnorm_no_docs_with_field() {
+    fn test_fieldnorm_no_docs_with_field() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let title_field = schema_builder.add_text_field("title", TEXT);
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.commit()?;
+        let index_reader = index.reader()?;
+        let searcher = index_reader.searcher();
+        let reader = searcher.segment_reader(0);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            {
-                let doc = doc!(text_field=>"a b c");
-                index_writer.add_document(doc);
-            }
-            index_writer.commit().unwrap();
+            let fieldnorm_reader = reader.get_fieldnorms_reader(text_field)?;
+            assert_eq!(fieldnorm_reader.fieldnorm(0), 3);
         }
         {
-            let index_reader = index.reader().unwrap();
-            let searcher = index_reader.searcher();
-            let reader = searcher.segment_reader(0);
-            {
-                let fieldnorm_reader = reader.get_fieldnorms_reader(text_field);
-                assert_eq!(fieldnorm_reader.fieldnorm(0), 3);
-            }
-            {
-                let fieldnorm_reader = reader.get_fieldnorms_reader(title_field);
-                assert_eq!(fieldnorm_reader.fieldnorm_id(0), 0);
-            }
+            let fieldnorm_reader = reader.get_fieldnorms_reader(title_field)?;
+            assert_eq!(fieldnorm_reader.fieldnorm_id(0), 0);
         }
+        Ok(())
     }
 
     #[test]
-    fn test_fieldnorm() {
+    fn test_fieldnorm() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let index = Index::create_in_ram(schema_builder.build());
-        {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            {
-                let doc = doc!(text_field=>"a b c");
-                index_writer.add_document(doc);
-            }
-            {
-                let doc = doc!();
-                index_writer.add_document(doc);
-            }
-            {
-                let doc = doc!(text_field=>"a b");
-                index_writer.add_document(doc);
-            }
-            index_writer.commit().unwrap();
-        }
-        {
-            let reader = index.reader().unwrap();
-            let searcher = reader.searcher();
-            let segment_reader: &SegmentReader = searcher.segment_reader(0);
-            let fieldnorms_reader = segment_reader.get_fieldnorms_reader(text_field);
-            assert_eq!(fieldnorms_reader.fieldnorm(0), 3);
-            assert_eq!(fieldnorms_reader.fieldnorm(1), 0);
-            assert_eq!(fieldnorms_reader.fieldnorm(2), 2);
-        }
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.add_document(doc!());
+        index_writer.add_document(doc!(text_field=>"a b"));
+        index_writer.commit()?;
+        let reader = index.reader()?;
+        let searcher = reader.searcher();
+        let segment_reader: &SegmentReader = searcher.segment_reader(0);
+        let fieldnorms_reader = segment_reader.get_fieldnorms_reader(text_field)?;
+        assert_eq!(fieldnorms_reader.fieldnorm(0), 3);
+        assert_eq!(fieldnorms_reader.fieldnorm(1), 0);
+        assert_eq!(fieldnorms_reader.fieldnorm(2), 2);
+        Ok(())
     }
 
     fn advance_undeleted(docset: &mut dyn DocSet, reader: &SegmentReader) -> bool {
@@ -491,7 +461,7 @@ mod tests {
     }
 
     #[test]
-    fn test_delete_postings1() {
+    fn test_delete_postings1() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let term_abcd = Term::from_field_text(text_field, "abcd");
@@ -507,7 +477,7 @@ mod tests {
             .unwrap();
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             // 0
             index_writer.add_document(doc!(text_field=>"a b"));
             // 1
@@ -523,19 +493,19 @@ mod tests {
             index_writer.add_document(doc!(text_field=>" b c"));
             // 5
             index_writer.add_document(doc!(text_field=>" a"));
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
         {
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 5);
@@ -543,7 +513,7 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 3);
@@ -554,25 +524,25 @@ mod tests {
         }
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             // 0
             index_writer.add_document(doc!(text_field=>"a b"));
             // 1
             index_writer.delete_term(Term::from_field_text(text_field, "c"));
-            index_writer.rollback().unwrap();
+            index_writer.rollback()?;
         }
         {
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             let seg_reader = searcher.segment_reader(0);
-            let inverted_index = seg_reader.inverted_index(term_abcd.field());
+            let inverted_index = seg_reader.inverted_index(term_abcd.field())?;
 
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, seg_reader));
                 assert_eq!(postings.doc(), 5);
@@ -580,7 +550,7 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, seg_reader));
                 assert_eq!(postings.doc(), 3);
@@ -591,30 +561,30 @@ mod tests {
         }
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.add_document(doc!(text_field=>"a b"));
             index_writer.delete_term(Term::from_field_text(text_field, "c"));
-            index_writer.rollback().unwrap();
+            index_writer.rollback()?;
             index_writer.delete_term(Term::from_field_text(text_field, "a"));
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
         {
-            reader.reload().unwrap();
+            reader.reload()?;
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0);
-            let inverted_index = segment_reader.inverted_index(term_abcd.field());
+            let inverted_index = segment_reader.inverted_index(term_abcd.field())?;
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(!advance_undeleted(&mut postings, segment_reader));
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_b, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 3);
@@ -624,101 +594,107 @@ mod tests {
             }
             {
                 let mut postings = inverted_index
-                    .read_postings(&term_c, IndexRecordOption::WithFreqsAndPositions)
+                    .read_postings(&term_c, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert!(advance_undeleted(&mut postings, segment_reader));
                 assert_eq!(postings.doc(), 4);
                 assert!(!advance_undeleted(&mut postings, segment_reader));
             }
         }
+        Ok(())
     }
 
     #[test]
-    fn test_indexed_u64() {
+    fn test_indexed_u64() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let field = schema_builder.add_u64_field("value", INDEXED);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.add_document(doc!(field=>1u64));
-        index_writer.commit().unwrap();
-        let reader = index.reader().unwrap();
+        index_writer.commit()?;
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let term = Term::from_field_u64(field, 1u64);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
-            .read_postings(&term, IndexRecordOption::Basic)
+            .inverted_index(term.field())?
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
+        Ok(())
     }
 
     #[test]
-    fn test_indexed_i64() {
+    fn test_indexed_i64() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let value_field = schema_builder.add_i64_field("value", INDEXED);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         let negative_val = -1i64;
         index_writer.add_document(doc!(value_field => negative_val));
-        index_writer.commit().unwrap();
-        let reader = index.reader().unwrap();
+        index_writer.commit()?;
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let term = Term::from_field_i64(value_field, negative_val);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
-            .read_postings(&term, IndexRecordOption::Basic)
+            .inverted_index(term.field())?
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
+        Ok(())
     }
 
     #[test]
-    fn test_indexed_f64() {
+    fn test_indexed_f64() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let value_field = schema_builder.add_f64_field("value", INDEXED);
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         let val = std::f64::consts::PI;
         index_writer.add_document(doc!(value_field => val));
-        index_writer.commit().unwrap();
-        let reader = index.reader().unwrap();
+        index_writer.commit()?;
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let term = Term::from_field_f64(value_field, val);
         let mut postings = searcher
             .segment_reader(0)
-            .inverted_index(term.field())
-            .read_postings(&term, IndexRecordOption::Basic)
+            .inverted_index(term.field())?
+            .read_postings(&term, IndexRecordOption::Basic)?
             .unwrap();
         assert_eq!(postings.doc(), 0);
         assert_eq!(postings.advance(), TERMINATED);
+        Ok(())
     }
 
     #[test]
-    fn test_indexedfield_not_in_documents() {
+    fn test_indexedfield_not_in_documents() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let absent_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(2, 6_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.add_document(doc!(text_field=>"a"));
         assert!(index_writer.commit().is_ok());
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let segment_reader = searcher.segment_reader(0);
-        segment_reader.inverted_index(absent_field); //< should not panic
+        let inverted_index = segment_reader.inverted_index(absent_field)?;
+        assert_eq!(inverted_index.terms().num_terms(), 0);
+        Ok(())
     }
 
     #[test]
-    fn test_delete_postings2() {
+    fn test_delete_postings2() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
@@ -726,125 +702,112 @@ mod tests {
         let reader = index
             .reader_builder()
             .reload_policy(ReloadPolicy::Manual)
-            .try_into()
-            .unwrap();
+            .try_into()?;
 
         // writing the segment
-        let mut index_writer = index.writer_with_num_threads(2, 6_000_000).unwrap();
-
-        let add_document = |index_writer: &mut IndexWriter, val: &'static str| {
-            let doc = doc!(text_field=>val);
-            index_writer.add_document(doc);
-        };
-
-        let remove_document = |index_writer: &mut IndexWriter, val: &'static str| {
-            let delterm = Term::from_field_text(text_field, val);
-            index_writer.delete_term(delterm);
-        };
-
-        add_document(&mut index_writer, "63");
-        add_document(&mut index_writer, "70");
-        add_document(&mut index_writer, "34");
-        add_document(&mut index_writer, "1");
-        add_document(&mut index_writer, "38");
-        add_document(&mut index_writer, "33");
-        add_document(&mut index_writer, "40");
-        add_document(&mut index_writer, "17");
-        remove_document(&mut index_writer, "38");
-        remove_document(&mut index_writer, "34");
-        index_writer.commit().unwrap();
-        reader.reload().unwrap();
-        let searcher = reader.searcher();
-        assert_eq!(searcher.num_docs(), 6);
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(text_field=>"63"));
+        index_writer.add_document(doc!(text_field=>"70"));
+        index_writer.add_document(doc!(text_field=>"34"));
+        index_writer.add_document(doc!(text_field=>"1"));
+        index_writer.add_document(doc!(text_field=>"38"));
+        index_writer.add_document(doc!(text_field=>"33"));
+        index_writer.add_document(doc!(text_field=>"40"));
+        index_writer.add_document(doc!(text_field=>"17"));
+        index_writer.delete_term(Term::from_field_text(text_field, "38"));
+        index_writer.delete_term(Term::from_field_text(text_field, "34"));
+        index_writer.commit()?;
+        reader.reload()?;
+        assert_eq!(reader.searcher().num_docs(), 6);
+        Ok(())
     }
 
     #[test]
-    fn test_termfreq() {
+    fn test_termfreq() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            let doc = doc!(text_field=>"af af af bc bc");
-            index_writer.add_document(doc);
-            index_writer.commit().unwrap();
+            let mut index_writer = index.writer_for_tests()?;
+            index_writer.add_document(doc!(text_field=>"af af af bc bc"));
+            index_writer.commit()?;
         }
         {
-            let index_reader = index.reader().unwrap();
+            let index_reader = index.reader()?;
             let searcher = index_reader.searcher();
             let reader = searcher.segment_reader(0);
-            let inverted_index = reader.inverted_index(text_field);
+            let inverted_index = reader.inverted_index(text_field)?;
             let term_abcd = Term::from_field_text(text_field, "abcd");
             assert!(inverted_index
-                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_abcd, IndexRecordOption::WithFreqsAndPositions)?
                 .is_none());
             let term_af = Term::from_field_text(text_field, "af");
             let mut postings = inverted_index
-                .read_postings(&term_af, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term_af, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             assert_eq!(postings.term_freq(), 3);
             assert_eq!(postings.advance(), TERMINATED);
         }
+        Ok(())
     }
 
     #[test]
-    fn test_searcher_1() {
+    fn test_searcher_1() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let reader = index.reader().unwrap();
-        {
-            // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            index_writer.add_document(doc!(text_field=>"af af af b"));
-            index_writer.add_document(doc!(text_field=>"a b c"));
-            index_writer.add_document(doc!(text_field=>"a b c d"));
-            index_writer.commit().unwrap();
-        }
-        {
-            reader.reload().unwrap();
-            let searcher = reader.searcher();
-            let get_doc_ids = |terms: Vec<Term>| {
-                let query = BooleanQuery::new_multiterms_query(terms);
-                let topdocs = searcher.search(&query, &TEST_COLLECTOR_WITH_SCORE).unwrap();
-                topdocs.docs().to_vec()
-            };
-            assert_eq!(
-                get_doc_ids(vec![Term::from_field_text(text_field, "a")]),
-                vec![DocAddress(0, 1), DocAddress(0, 2)]
-            );
-            assert_eq!(
-                get_doc_ids(vec![Term::from_field_text(text_field, "af")]),
-                vec![DocAddress(0, 0)]
-            );
-            assert_eq!(
-                get_doc_ids(vec![Term::from_field_text(text_field, "b")]),
-                vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
-            );
-            assert_eq!(
-                get_doc_ids(vec![Term::from_field_text(text_field, "c")]),
-                vec![DocAddress(0, 1), DocAddress(0, 2)]
-            );
-            assert_eq!(
-                get_doc_ids(vec![Term::from_field_text(text_field, "d")]),
-                vec![DocAddress(0, 2)]
-            );
-            assert_eq!(
-                get_doc_ids(vec![
-                    Term::from_field_text(text_field, "b"),
-                    Term::from_field_text(text_field, "a"),
-                ]),
-                vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
-            );
-        }
+        let reader = index.reader()?;
+        // writing the segment
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(text_field=>"af af af b"));
+        index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.add_document(doc!(text_field=>"a b c d"));
+        index_writer.commit()?;
+
+        reader.reload()?;
+        let searcher = reader.searcher();
+        let get_doc_ids = |terms: Vec<Term>| {
+            let query = BooleanQuery::new_multiterms_query(terms);
+            searcher
+                .search(&query, &TEST_COLLECTOR_WITH_SCORE)
+                .map(|topdocs| topdocs.docs().to_vec())
+        };
+        assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "a")])?,
+            vec![DocAddress(0, 1), DocAddress(0, 2)]
+        );
+        assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "af")])?,
+            vec![DocAddress(0, 0)]
+        );
+        assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "b")])?,
+            vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
+        );
+        assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "c")])?,
+            vec![DocAddress(0, 1), DocAddress(0, 2)]
+        );
+        assert_eq!(
+            get_doc_ids(vec![Term::from_field_text(text_field, "d")])?,
+            vec![DocAddress(0, 2)]
+        );
+        assert_eq!(
+            get_doc_ids(vec![
+                Term::from_field_text(text_field, "b"),
+                Term::from_field_text(text_field, "a"),
+            ])?,
+            vec![DocAddress(0, 0), DocAddress(0, 1), DocAddress(0, 2)]
+        );
+        Ok(())
     }
 
     #[test]
-    fn test_searcher_2() {
+    fn test_searcher_2() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
@@ -852,19 +815,17 @@ mod tests {
         let reader = index
             .reader_builder()
             .reload_policy(ReloadPolicy::Manual)
-            .try_into()
-            .unwrap();
+            .try_into()?;
         assert_eq!(reader.searcher().num_docs(), 0u64);
-        {
-            // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            index_writer.add_document(doc!(text_field=>"af b"));
-            index_writer.add_document(doc!(text_field=>"a b c"));
-            index_writer.add_document(doc!(text_field=>"a b c d"));
-            index_writer.commit().unwrap();
-        }
-        reader.reload().unwrap();
+        // writing the segment
+        let mut index_writer = index.writer_for_tests()?;
+        index_writer.add_document(doc!(text_field=>"af b"));
+        index_writer.add_document(doc!(text_field=>"a b c"));
+        index_writer.add_document(doc!(text_field=>"a b c d"));
+        index_writer.commit()?;
+        reader.reload()?;
         assert_eq!(reader.searcher().num_docs(), 3u64);
+        Ok(())
     }
 
     #[test]
@@ -876,17 +837,17 @@ mod tests {
                             text_field => "some other value",
                             other_text_field => "short");
         assert_eq!(document.len(), 3);
-        let values = document.get_all(text_field);
+        let values: Vec<&Value> = document.get_all(text_field).collect();
         assert_eq!(values.len(), 2);
         assert_eq!(values[0].text(), Some("tantivy"));
         assert_eq!(values[1].text(), Some("some other value"));
-        let values = document.get_all(other_text_field);
+        let values: Vec<&Value> = document.get_all(other_text_field).collect();
         assert_eq!(values.len(), 1);
         assert_eq!(values[0].text(), Some("short"));
     }
 
     #[test]
-    fn test_wrong_fast_field_type() {
+    fn test_wrong_fast_field_type() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let fast_field_unsigned = schema_builder.add_u64_field("unsigned", FAST);
         let fast_field_signed = schema_builder.add_i64_field("signed", FAST);
@@ -896,57 +857,58 @@ mod tests {
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 50_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         {
             let document =
                 doc!(fast_field_unsigned => 4u64, fast_field_signed=>4i64, fast_field_float=>4f64);
             index_writer.add_document(document);
-            index_writer.commit().unwrap();
+            index_writer.commit()?;
         }
-        let reader = index.reader().unwrap();
+        let reader = index.reader()?;
         let searcher = reader.searcher();
         let segment_reader: &SegmentReader = searcher.segment_reader(0);
         {
-            let fast_field_reader_opt = segment_reader.fast_fields().u64(text_field);
-            assert!(fast_field_reader_opt.is_none());
+            let fast_field_reader_res = segment_reader.fast_fields().u64(text_field);
+            assert!(fast_field_reader_res.is_err());
         }
         {
             let fast_field_reader_opt = segment_reader.fast_fields().u64(stored_int_field);
-            assert!(fast_field_reader_opt.is_none());
+            assert!(fast_field_reader_opt.is_err());
         }
         {
             let fast_field_reader_opt = segment_reader.fast_fields().u64(fast_field_signed);
-            assert!(fast_field_reader_opt.is_none());
+            assert!(fast_field_reader_opt.is_err());
         }
         {
             let fast_field_reader_opt = segment_reader.fast_fields().u64(fast_field_float);
-            assert!(fast_field_reader_opt.is_none());
+            assert!(fast_field_reader_opt.is_err());
         }
         {
             let fast_field_reader_opt = segment_reader.fast_fields().u64(fast_field_unsigned);
-            assert!(fast_field_reader_opt.is_some());
+            assert!(fast_field_reader_opt.is_ok());
             let fast_field_reader = fast_field_reader_opt.unwrap();
             assert_eq!(fast_field_reader.get(0), 4u64)
         }
 
         {
-            let fast_field_reader_opt = segment_reader.fast_fields().i64(fast_field_signed);
-            assert!(fast_field_reader_opt.is_some());
-            let fast_field_reader = fast_field_reader_opt.unwrap();
+            let fast_field_reader_res = segment_reader.fast_fields().i64(fast_field_signed);
+            assert!(fast_field_reader_res.is_ok());
+            let fast_field_reader = fast_field_reader_res.unwrap();
             assert_eq!(fast_field_reader.get(0), 4i64)
         }
 
         {
-            let fast_field_reader_opt = segment_reader.fast_fields().f64(fast_field_float);
-            assert!(fast_field_reader_opt.is_some());
-            let fast_field_reader = fast_field_reader_opt.unwrap();
+            let fast_field_reader_res = segment_reader.fast_fields().f64(fast_field_float);
+            assert!(fast_field_reader_res.is_ok());
+            let fast_field_reader = fast_field_reader_res.unwrap();
             assert_eq!(fast_field_reader.get(0), 4f64)
         }
+        Ok(())
     }
 
     // motivated by #729
     #[test]
-    fn test_update_via_delete_insert() {
+    fn test_update_via_delete_insert() -> crate::Result<()> {
         use crate::collector::Count;
         use crate::indexer::NoMergePolicy;
         use crate::query::AllQuery;
@@ -960,17 +922,17 @@ mod tests {
         let schema = schema_builder.build();
 
         let index = Index::create_in_ram(schema.clone());
-        let index_reader = index.reader().unwrap();
+        let index_reader = index.reader()?;
 
-        let mut index_writer = index.writer(3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.set_merge_policy(Box::new(NoMergePolicy));
 
         for doc_id in 0u64..DOC_COUNT {
             index_writer.add_document(doc!(id => doc_id));
         }
-        index_writer.commit().unwrap();
+        index_writer.commit()?;
 
-        index_reader.reload().unwrap();
+        index_reader.reload()?;
         let searcher = index_reader.searcher();
 
         assert_eq!(
@@ -981,12 +943,11 @@ mod tests {
         // update the 10 elements by deleting and re-adding
         for doc_id in 0u64..DOC_COUNT {
             index_writer.delete_term(Term::from_field_u64(id, doc_id));
-            index_writer.commit().unwrap();
-            index_reader.reload().unwrap();
-            let doc = doc!(id =>  doc_id);
-            index_writer.add_document(doc);
-            index_writer.commit().unwrap();
-            index_reader.reload().unwrap();
+            index_writer.commit()?;
+            index_reader.reload()?;
+            index_writer.add_document(doc!(id =>  doc_id));
+            index_writer.commit()?;
+            index_reader.reload()?;
             let searcher = index_reader.searcher();
             // The number of document should be stable.
             assert_eq!(
@@ -995,7 +956,7 @@ mod tests {
             );
         }
 
-        index_reader.reload().unwrap();
+        index_reader.reload()?;
         let searcher = index_reader.searcher();
         let segment_ids: Vec<SegmentId> = searcher
             .segment_readers()
@@ -1004,20 +965,18 @@ mod tests {
             .collect();
         block_on(index_writer.merge(&segment_ids)).unwrap();
 
-        index_reader.reload().unwrap();
+        index_reader.reload()?;
         let searcher = index_reader.searcher();
-
-        assert_eq!(
-            searcher.search(&AllQuery, &Count).unwrap(),
-            DOC_COUNT as usize
-        );
+        assert_eq!(searcher.search(&AllQuery, &Count)?, DOC_COUNT as usize);
+        Ok(())
     }
 
     #[test]
-    fn test_validate_checksum() {
+    fn test_validate_checksum() -> crate::Result<()> {
         let index_path = tempfile::tempdir().expect("dir");
         let schema = Schema::builder().build();
-        let index = Index::create_in_dir(&index_path, schema).expect("index");
-        assert!(index.validate_checksum().unwrap().is_empty());
+        let index = Index::create_in_dir(&index_path, schema)?;
+        assert!(index.validate_checksum()?.is_empty());
+        Ok(())
     }
 }

src/positions/mod.rs

@@ -38,11 +38,11 @@ const LONG_SKIP_INTERVAL: u64 = (LONG_SKIP_IN_BLOCKS * COMPRESSION_BLOCK_SIZE) a
 pub mod tests {
 
     use super::PositionSerializer;
-    use crate::directory::ReadOnlySource;
     use crate::positions::reader::PositionReader;
+    use crate::{common::HasLen, directory::FileSlice};
     use std::iter;
 
-    fn create_stream_buffer(vals: &[u32]) -> (ReadOnlySource, ReadOnlySource) {
+    fn create_stream_buffer(vals: &[u32]) -> (FileSlice, FileSlice) {
         let mut skip_buffer = vec![];
         let mut stream_buffer = vec![];
         {
@@ -53,10 +53,7 @@ pub mod tests {
             }
             serializer.close().unwrap();
         }
-        (
-            ReadOnlySource::from(stream_buffer),
-            ReadOnlySource::from(skip_buffer),
-        )
+        (FileSlice::from(stream_buffer), FileSlice::from(skip_buffer))
     }
 
     #[test]
@@ -65,7 +62,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         for &n in &[1, 10, 127, 128, 130, 312] {
             let mut v = vec![0u32; n];
             position_reader.read(0, &mut v[..]);
@@ -81,7 +78,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         for &offset in &[1u64, 10u64, 127u64, 128u64, 130u64, 312u64] {
             for &len in &[1, 10, 130, 500] {
                 let mut v = vec![0u32; len];
@@ -100,7 +97,7 @@ pub mod tests {
         assert_eq!(skip.len(), 12);
         assert_eq!(stream.len(), 1168);
 
-        let mut position_reader = PositionReader::new(stream, skip, 0u64);
+        let mut position_reader = PositionReader::new(stream, skip, 0u64).unwrap();
         let mut buf = [0u32; 7];
         let mut c = 0;
 
@@ -122,7 +119,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 4_987_872);
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0);
+        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0).unwrap();
         let mut buf = [0u32; 256];
         position_reader.read(128, &mut buf);
         for i in 0..256 {
@@ -142,7 +139,8 @@ pub mod tests {
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 4_987_872);
         let mut buf = [0u32; 1];
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 200_000);
+        let mut position_reader =
+            PositionReader::new(stream.clone(), skip.clone(), 200_000).unwrap();
         position_reader.read(230, &mut buf);
         position_reader.read(9, &mut buf);
     }
@@ -157,7 +155,7 @@ pub mod tests {
         }
         let (stream, skip) = create_stream_buffer(&v[..]);
         let mut buf = Vec::new();
-        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0);
+        let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), 0).unwrap();
         let mut offset = 0;
         for i in 1..24 {
             buf.resize(i, 0);
@@ -175,7 +173,7 @@ pub mod tests {
         let (stream, skip) = create_stream_buffer(&v[..]);
         assert_eq!(skip.len(), 15_749);
         assert_eq!(stream.len(), 1_000_000);
-        let mut position_reader = PositionReader::new(stream, skip, 128 * 1024);
+        let mut position_reader = PositionReader::new(stream, skip, 128 * 1024).unwrap();
         let mut buf = [0u32; 1];
         position_reader.read(0, &mut buf);
         assert_eq!(buf[0], CONST_VAL);
@@ -194,7 +192,8 @@ pub mod tests {
             128 * 1024 + 7,
             128 * 10 * 1024 + 10,
         ] {
-            let mut position_reader = PositionReader::new(stream.clone(), skip.clone(), offset);
+            let mut position_reader =
+                PositionReader::new(stream.clone(), skip.clone(), offset).unwrap();
             let mut buf = [0u32; 1];
             position_reader.read(0, &mut buf);
             assert_eq!(buf[0], offset as u32);

src/positions/reader.rs

@@ -1,8 +1,13 @@
+use std::io;
+
 use crate::common::{BinarySerializable, FixedSize};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::positions::COMPRESSION_BLOCK_SIZE;
 use crate::positions::LONG_SKIP_INTERVAL;
 use crate::positions::LONG_SKIP_IN_BLOCKS;
+use bitpacking::{BitPacker, BitPacker4x};
+
 /// Positions works as a long sequence of compressed block.
 /// All terms are chained one after the other.
 ///
@@ -23,28 +28,28 @@ use crate::positions::LONG_SKIP_IN_BLOCKS;
 /// A given block obviously takes `(128 x  num_bit_for_the_block / num_bits_in_a_byte)`,
 /// so skipping a block without decompressing it is just a matter of advancing that many
 /// bytes.
-use bitpacking::{BitPacker, BitPacker4x};
-use owned_read::OwnedRead;
 
 struct Positions {
     bit_packer: BitPacker4x,
-    skip_source: ReadOnlySource,
-    position_source: ReadOnlySource,
-    long_skip_source: ReadOnlySource,
+    skip_file: FileSlice,
+    position_file: FileSlice,
+    long_skip_data: OwnedBytes,
 }
 
 impl Positions {
-    pub fn new(position_source: ReadOnlySource, skip_source: ReadOnlySource) -> Positions {
-        let (body, footer) = skip_source.split_from_end(u32::SIZE_IN_BYTES);
-        let num_long_skips = u32::deserialize(&mut footer.as_slice()).expect("Index corrupted");
-        let (skip_source, long_skip_source) =
+    pub fn new(position_file: FileSlice, skip_file: FileSlice) -> io::Result<Positions> {
+        let (body, footer) = skip_file.split_from_end(u32::SIZE_IN_BYTES);
+        let footer_data = footer.read_bytes()?;
+        let num_long_skips = u32::deserialize(&mut footer_data.as_slice())?;
+        let (skip_file, long_skip_file) =
             body.split_from_end(u64::SIZE_IN_BYTES * (num_long_skips as usize));
-        Positions {
+        let long_skip_data = long_skip_file.read_bytes()?;
+        Ok(Positions {
             bit_packer: BitPacker4x::new(),
-            skip_source,
-            long_skip_source,
-            position_source,
-        }
+            skip_file,
+            long_skip_data,
+            position_file,
+        })
     }
 
     /// Returns the offset of the block associated to the given `long_skip_id`.
@@ -54,19 +59,23 @@ impl Positions {
         if long_skip_id == 0 {
             return 0;
         }
-        let long_skip_slice = self.long_skip_source.as_slice();
+        let long_skip_slice = self.long_skip_data.as_slice();
         let mut long_skip_blocks: &[u8] = &long_skip_slice[(long_skip_id - 1) * 8..][..8];
         u64::deserialize(&mut long_skip_blocks).expect("Index corrupted")
     }
 
-    fn reader(&self, offset: u64) -> PositionReader {
+    fn reader(&self, offset: u64) -> io::Result<PositionReader> {
         let long_skip_id = (offset / LONG_SKIP_INTERVAL) as usize;
         let offset_num_bytes: u64 = self.long_skip(long_skip_id);
-        let mut position_read = OwnedRead::new(self.position_source.clone());
-        position_read.advance(offset_num_bytes as usize);
-        let mut skip_read = OwnedRead::new(self.skip_source.clone());
-        skip_read.advance(long_skip_id * LONG_SKIP_IN_BLOCKS);
-        PositionReader {
+        let position_read = self
+            .position_file
+            .slice_from(offset_num_bytes as usize)
+            .read_bytes()?;
+        let skip_read = self
+            .skip_file
+            .slice_from(long_skip_id * LONG_SKIP_IN_BLOCKS)
+            .read_bytes()?;
+        Ok(PositionReader {
             bit_packer: self.bit_packer,
             skip_read,
             position_read,
@@ -74,14 +83,14 @@ impl Positions {
             block_offset: std::i64::MAX as u64,
             anchor_offset: (long_skip_id as u64) * LONG_SKIP_INTERVAL,
             abs_offset: offset,
-        }
+        })
     }
 }
 
 #[derive(Clone)]
 pub struct PositionReader {
-    skip_read: OwnedRead,
-    position_read: OwnedRead,
+    skip_read: OwnedBytes,
+    position_read: OwnedBytes,
     bit_packer: BitPacker4x,
     buffer: Box<[u32; COMPRESSION_BLOCK_SIZE]>,
 
@@ -93,11 +102,12 @@ pub struct PositionReader {
 
 impl PositionReader {
     pub fn new(
-        position_source: ReadOnlySource,
-        skip_source: ReadOnlySource,
+        position_file: FileSlice,
+        skip_file: FileSlice,
         offset: u64,
-    ) -> PositionReader {
-        Positions::new(position_source, skip_source).reader(offset)
+    ) -> io::Result<PositionReader> {
+        let positions = Positions::new(position_file, skip_file)?;
+        positions.reader(offset)
     }
 
     fn advance_num_blocks(&mut self, num_blocks: usize) {
@@ -122,7 +132,7 @@ impl PositionReader {
             "offset arguments should be increasing."
         );
         let delta_to_block_offset = offset as i64 - self.block_offset as i64;
-        if delta_to_block_offset < 0 || delta_to_block_offset >= 128 {
+        if !(0..128).contains(&delta_to_block_offset) {
             // The first position is not within the first block.
             // We need to decompress the first block.
             let delta_to_anchor_offset = offset - self.anchor_offset;
@@ -131,7 +141,7 @@ impl PositionReader {
             self.advance_num_blocks(num_blocks_to_skip);
             self.anchor_offset = offset - (offset % COMPRESSION_BLOCK_SIZE as u64);
             self.block_offset = self.anchor_offset;
-            let num_bits = self.skip_read.get(0);
+            let num_bits = self.skip_read.as_slice()[0];
             self.bit_packer
                 .decompress(self.position_read.as_ref(), self.buffer.as_mut(), num_bits);
         } else {
@@ -141,7 +151,7 @@ impl PositionReader {
             self.anchor_offset = self.block_offset;
         }
 
-        let mut num_bits = self.skip_read.get(0);
+        let mut num_bits = self.skip_read.as_slice()[0];
         let mut position_data = self.position_read.as_ref();
 
         for i in 1.. {
@@ -155,7 +165,7 @@ impl PositionReader {
             output = &mut output[remaining_in_block..];
             offset += remaining_in_block as u64;
             position_data = &position_data[(num_bits as usize * COMPRESSION_BLOCK_SIZE / 8)..];
-            num_bits = self.skip_read.get(i);
+            num_bits = self.skip_read.as_slice()[i];
             self.bit_packer
                 .decompress(position_data, self.buffer.as_mut(), num_bits);
             self.block_offset += COMPRESSION_BLOCK_SIZE as u64;

src/positions/serializer.rs

@@ -8,7 +8,7 @@ use std::io::{self, Write};
 pub struct PositionSerializer<W: io::Write> {
     bit_packer: BitPacker4x,
     write_stream: CountingWriter<W>,
-    write_skiplist: W,
+    write_skip_index: W,
     block: Vec<u32>,
     buffer: Vec<u8>,
     num_ints: u64,
@@ -16,11 +16,11 @@ pub struct PositionSerializer<W: io::Write> {
 }
 
 impl<W: io::Write> PositionSerializer<W> {
-    pub fn new(write_stream: W, write_skiplist: W) -> PositionSerializer<W> {
+    pub fn new(write_stream: W, write_skip_index: W) -> PositionSerializer<W> {
         PositionSerializer {
             bit_packer: BitPacker4x::new(),
             write_stream: CountingWriter::wrap(write_stream),
-            write_skiplist,
+            write_skip_index,
             block: Vec::with_capacity(128),
             buffer: vec![0u8; 128 * 4],
             num_ints: 0u64,
@@ -52,7 +52,7 @@ impl<W: io::Write> PositionSerializer<W> {
 
     fn flush_block(&mut self) -> io::Result<()> {
         let num_bits = self.bit_packer.num_bits(&self.block[..]);
-        self.write_skiplist.write_all(&[num_bits])?;
+        self.write_skip_index.write_all(&[num_bits])?;
         let written_len = self
             .bit_packer
             .compress(&self.block[..], &mut self.buffer, num_bits);
@@ -70,10 +70,10 @@ impl<W: io::Write> PositionSerializer<W> {
             self.flush_block()?;
         }
         for &long_skip in &self.long_skips {
-            long_skip.serialize(&mut self.write_skiplist)?;
+            long_skip.serialize(&mut self.write_skip_index)?;
         }
-        (self.long_skips.len() as u32).serialize(&mut self.write_skiplist)?;
-        self.write_skiplist.flush()?;
+        (self.long_skips.len() as u32).serialize(&mut self.write_skip_index)?;
+        self.write_skip_index.flush()?;
         self.write_stream.flush()?;
         Ok(())
     }

src/postings/block_search.rs

@@ -1,3 +1,5 @@
+use std::ops::Range;
+
 use crate::postings::compression::AlignedBuffer;
 
 /// This modules define the logic used to search for a doc in a given
@@ -72,7 +74,7 @@ fn linear_search(arr: &[u32], target: u32) -> usize {
     arr.iter().map(|&el| if el < target { 1 } else { 0 }).sum()
 }
 
-fn exponential_search(arr: &[u32], target: u32) -> (usize, usize) {
+fn exponential_search(arr: &[u32], target: u32) -> Range<usize> {
     let end = arr.len();
     let mut begin = 0;
     for &pivot in &[1, 3, 7, 15, 31, 63] {
@@ -80,17 +82,17 @@ fn exponential_search(arr: &[u32], target: u32) -> (usize, usize) {
             break;
         }
         if arr[pivot] > target {
-            return (begin, pivot);
+            return begin..pivot;
         }
         begin = pivot;
     }
-    (begin, end)
+    begin..end
 }
 
 #[inline(never)]
 fn galloping(block_docs: &[u32], target: u32) -> usize {
-    let (start, end) = exponential_search(&block_docs, target);
-    start + linear_search(&block_docs[start..end], target)
+    let range = exponential_search(&block_docs, target);
+    range.start + linear_search(&block_docs[range], target)
 }
 
 /// Tantivy may rely on SIMD instructions to search for a specific document within
@@ -182,11 +184,11 @@ mod tests {
 
     #[test]
     fn test_exponentiel_search() {
-        assert_eq!(exponential_search(&[1, 2], 0), (0, 1));
-        assert_eq!(exponential_search(&[1, 2], 1), (0, 1));
+        assert_eq!(exponential_search(&[1, 2], 0), 0..1);
+        assert_eq!(exponential_search(&[1, 2], 1), 0..1);
         assert_eq!(
             exponential_search(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11], 7),
-            (3, 7)
+            3..7
         );
     }
 

src/postings/block_segment_postings.rs

@@ -1,5 +1,8 @@
+use std::io;
+
 use crate::common::{BinarySerializable, VInt};
-use crate::directory::ReadOnlySource;
+use crate::directory::FileSlice;
+use crate::directory::OwnedBytes;
 use crate::fieldnorm::FieldNormReader;
 use crate::postings::compression::{
     AlignedBuffer, BlockDecoder, VIntDecoder, COMPRESSION_BLOCK_SIZE,
@@ -34,7 +37,7 @@ pub struct BlockSegmentPostings {
 
     doc_freq: u32,
 
-    data: ReadOnlySource,
+    data: OwnedBytes,
     pub(crate) skip_reader: SkipReader,
 }
 
@@ -72,37 +75,34 @@ fn decode_vint_block(
 
 fn split_into_skips_and_postings(
     doc_freq: u32,
-    data: ReadOnlySource,
-) -> (Option<ReadOnlySource>, ReadOnlySource) {
+    mut bytes: OwnedBytes,
+) -> (Option<OwnedBytes>, OwnedBytes) {
     if doc_freq < COMPRESSION_BLOCK_SIZE as u32 {
-        return (None, data);
+        return (None, bytes);
     }
-    let mut data_byte_arr = data.as_slice();
-    let skip_len = VInt::deserialize(&mut data_byte_arr)
-        .expect("Data corrupted")
-        .0 as usize;
-    let vint_len = data.len() - data_byte_arr.len();
-    let (skip_data, postings_data) = data.slice_from(vint_len).split(skip_len);
+    let skip_len = VInt::deserialize(&mut bytes).expect("Data corrupted").0 as usize;
+    let (skip_data, postings_data) = bytes.split(skip_len);
     (Some(skip_data), postings_data)
 }
 
 impl BlockSegmentPostings {
-    pub(crate) fn from_data(
+    pub(crate) fn open(
         doc_freq: u32,
-        data: ReadOnlySource,
+        data: FileSlice,
         record_option: IndexRecordOption,
         requested_option: IndexRecordOption,
-    ) -> BlockSegmentPostings {
+    ) -> io::Result<BlockSegmentPostings> {
         let freq_reading_option = match (record_option, requested_option) {
             (IndexRecordOption::Basic, _) => FreqReadingOption::NoFreq,
             (_, IndexRecordOption::Basic) => FreqReadingOption::SkipFreq,
             (_, _) => FreqReadingOption::ReadFreq,
         };
 
-        let (skip_data_opt, postings_data) = split_into_skips_and_postings(doc_freq, data);
+        let (skip_data_opt, postings_data) =
+            split_into_skips_and_postings(doc_freq, data.read_bytes()?);
         let skip_reader = match skip_data_opt {
             Some(skip_data) => SkipReader::new(skip_data, doc_freq, record_option),
-            None => SkipReader::new(ReadOnlySource::empty(), doc_freq, record_option),
+            None => SkipReader::new(OwnedBytes::empty(), doc_freq, record_option),
         };
 
         let mut block_segment_postings = BlockSegmentPostings {
@@ -116,7 +116,7 @@ impl BlockSegmentPostings {
             skip_reader,
         };
         block_segment_postings.load_block();
-        block_segment_postings
+        Ok(block_segment_postings)
     }
 
     /// Returns the block_max_score for the current block.
@@ -172,15 +172,15 @@ impl BlockSegmentPostings {
     // # Warning
     //
     // This does not reset the positions list.
-    pub(crate) fn reset(&mut self, doc_freq: u32, postings_data: ReadOnlySource) {
+    pub(crate) fn reset(&mut self, doc_freq: u32, postings_data: OwnedBytes) {
         let (skip_data_opt, postings_data) = split_into_skips_and_postings(doc_freq, postings_data);
-        self.data = ReadOnlySource::new(postings_data);
+        self.data = postings_data;
         self.block_max_score_cache = None;
         self.loaded_offset = std::usize::MAX;
         if let Some(skip_data) = skip_data_opt {
             self.skip_reader.reset(skip_data, doc_freq);
         } else {
-            self.skip_reader.reset(ReadOnlySource::empty(), doc_freq);
+            self.skip_reader.reset(OwnedBytes::empty(), doc_freq);
         }
         self.doc_freq = doc_freq;
         self.load_block();
@@ -344,8 +344,8 @@ impl BlockSegmentPostings {
             freq_reading_option: FreqReadingOption::NoFreq,
             block_max_score_cache: None,
             doc_freq: 0,
-            data: ReadOnlySource::new(vec![]),
-            skip_reader: SkipReader::new(ReadOnlySource::new(vec![]), 0, IndexRecordOption::Basic),
+            data: OwnedBytes::empty(),
+            skip_reader: SkipReader::new(OwnedBytes::empty(), 0, IndexRecordOption::Basic),
         }
     }
 }
@@ -455,7 +455,7 @@ mod tests {
         let int_field = schema_builder.add_u64_field("id", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         let mut last_doc = 0u32;
         for &doc in docs {
             for _ in last_doc..doc {
@@ -467,10 +467,12 @@ mod tests {
         index_writer.commit().unwrap();
         let searcher = index.reader().unwrap().searcher();
         let segment_reader = searcher.segment_reader(0);
-        let inverted_index = segment_reader.inverted_index(int_field);
+        let inverted_index = segment_reader.inverted_index(int_field).unwrap();
         let term = Term::from_field_u64(int_field, 0u64);
-        let term_info = inverted_index.get_term_info(&term).unwrap();
-        inverted_index.read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)
+        let term_info = inverted_index.get_term_info(&term).unwrap().unwrap();
+        inverted_index
+            .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)
+            .unwrap()
     }
 
     #[test]
@@ -491,37 +493,38 @@ mod tests {
     }
 
     #[test]
-    fn test_reset_block_segment_postings() {
+    fn test_reset_block_segment_postings() -> crate::Result<()> {
         let mut schema_builder = Schema::builder();
         let int_field = schema_builder.add_u64_field("id", INDEXED);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests()?;
         // create two postings list, one containg even number,
         // the other containing odd numbers.
         for i in 0..6 {
             let doc = doc!(int_field=> (i % 2) as u64);
             index_writer.add_document(doc);
         }
-        index_writer.commit().unwrap();
-        let searcher = index.reader().unwrap().searcher();
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
         let segment_reader = searcher.segment_reader(0);
 
         let mut block_segments;
         {
             let term = Term::from_field_u64(int_field, 0u64);
-            let inverted_index = segment_reader.inverted_index(int_field);
-            let term_info = inverted_index.get_term_info(&term).unwrap();
+            let inverted_index = segment_reader.inverted_index(int_field)?;
+            let term_info = inverted_index.get_term_info(&term)?.unwrap();
             block_segments = inverted_index
-                .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic);
+                .read_block_postings_from_terminfo(&term_info, IndexRecordOption::Basic)?;
         }
         assert_eq!(block_segments.docs(), &[0, 2, 4]);
         {
             let term = Term::from_field_u64(int_field, 1u64);
-            let inverted_index = segment_reader.inverted_index(int_field);
-            let term_info = inverted_index.get_term_info(&term).unwrap();
-            inverted_index.reset_block_postings_from_terminfo(&term_info, &mut block_segments);
+            let inverted_index = segment_reader.inverted_index(int_field)?;
+            let term_info = inverted_index.get_term_info(&term)?.unwrap();
+            inverted_index.reset_block_postings_from_terminfo(&term_info, &mut block_segments)?;
         }
         assert_eq!(block_segments.docs(), &[1, 3, 5]);
+        Ok(())
     }
 }

src/postings/compression/mod.rs

@@ -310,6 +310,7 @@ pub mod tests {
 mod bench {
 
     use super::*;
+    use crate::TERMINATED;
     use rand::rngs::StdRng;
     use rand::Rng;
     use rand::SeedableRng;
@@ -340,7 +341,7 @@ mod bench {
         let mut encoder = BlockEncoder::new();
         let data = generate_array(COMPRESSION_BLOCK_SIZE, 0.1);
         let (num_bits, compressed) = encoder.compress_block_sorted(&data, 0u32);
-        let mut decoder = BlockDecoder::new();
+        let mut decoder = BlockDecoder::default();
         b.iter(|| {
             decoder.uncompress_block_sorted(compressed, 0u32, num_bits);
         });
@@ -375,9 +376,9 @@ mod bench {
         let mut encoder = BlockEncoder::new();
         let data = generate_array(NUM_INTS_BENCH_VINT, 0.001);
         let compressed = encoder.compress_vint_sorted(&data, 0u32);
-        let mut decoder = BlockDecoder::new();
+        let mut decoder = BlockDecoder::default();
         b.iter(|| {
-            decoder.uncompress_vint_sorted(compressed, 0u32, NUM_INTS_BENCH_VINT);
+            decoder.uncompress_vint_sorted(compressed, 0u32, NUM_INTS_BENCH_VINT, TERMINATED);
         });
     }
 }

src/postings/mod.rs

@@ -15,20 +15,14 @@ mod stacker;
 mod term_info;
 
 pub(crate) use self::block_search::BlockSearcher;
-
-pub(crate) use self::postings_writer::MultiFieldPostingsWriter;
-pub use self::serializer::{FieldSerializer, InvertedIndexSerializer};
-
-pub use self::postings::Postings;
-pub(crate) use self::skip::{BlockInfo, SkipReader};
-pub use self::term_info::TermInfo;
-
 pub use self::block_segment_postings::BlockSegmentPostings;
+pub use self::postings::Postings;
+pub(crate) use self::postings_writer::MultiFieldPostingsWriter;
 pub use self::segment_postings::SegmentPostings;
-
+pub use self::serializer::{FieldSerializer, InvertedIndexSerializer};
+pub(crate) use self::skip::{BlockInfo, SkipReader};
 pub(crate) use self::stacker::compute_table_size;
-
-pub use crate::common::HasLen;
+pub use self::term_info::TermInfo;
 
 pub(crate) type UnorderedTermId = u64;
 
@@ -42,8 +36,8 @@ pub(crate) enum FreqReadingOption {
 
 #[cfg(test)]
 pub mod tests {
-
-    use super::*;
+    use super::InvertedIndexSerializer;
+    use super::Postings;
     use crate::core::Index;
     use crate::core::SegmentComponent;
     use crate::core::SegmentReader;
@@ -53,16 +47,14 @@ pub mod tests {
     use crate::indexer::SegmentWriter;
     use crate::merge_policy::NoMergePolicy;
     use crate::query::Scorer;
-    use crate::schema::{Document, Schema, Term, INDEXED, STRING, TEXT};
     use crate::schema::{Field, TextOptions};
     use crate::schema::{IndexRecordOption, TextFieldIndexing};
+    use crate::schema::{Schema, Term, INDEXED, TEXT};
     use crate::tokenizer::{SimpleTokenizer, MAX_TOKEN_LEN};
     use crate::DocId;
+    use crate::HasLen;
     use crate::Score;
-    use once_cell::sync::Lazy;
-    use rand::rngs::StdRng;
-    use rand::{Rng, SeedableRng};
-    use std::iter;
+    use std::{iter, mem};
 
     #[test]
     pub fn test_position_write() -> crate::Result<()> {
@@ -79,6 +71,7 @@ pub mod tests {
             field_serializer.write_doc(doc_id, 4, &delta_positions)?;
         }
         field_serializer.close_term()?;
+        mem::drop(field_serializer);
         posting_serializer.close()?;
         let read = segment.open_read(SegmentComponent::POSITIONS)?;
         assert!(read.len() <= 140);
@@ -91,7 +84,7 @@ pub mod tests {
         let title = schema_builder.add_text_field("title", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 30_000_000)?;
+        let mut index_writer = index.writer_for_tests()?;
         index_writer.add_document(doc!(title => r#"abc abc abc"#));
         index_writer.add_document(doc!(title => r#"abc be be be be abc"#));
         for _ in 0..1_000 {
@@ -101,12 +94,12 @@ pub mod tests {
         index_writer.commit()?;
 
         let searcher = index.reader()?.searcher();
-        let inverted_index = searcher.segment_reader(0u32).inverted_index(title);
+        let inverted_index = searcher.segment_reader(0u32).inverted_index(title)?;
         let term = Term::from_field_text(title, "abc");
         let mut positions = Vec::new();
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             postings.positions(&mut positions);
@@ -120,7 +113,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.doc(), 0);
             assert_eq!(postings.advance(), 1);
@@ -129,7 +122,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(1), 1);
             assert_eq!(postings.doc(), 1);
@@ -138,7 +131,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(1002), 1002);
             assert_eq!(postings.doc(), 1002);
@@ -147,7 +140,7 @@ pub mod tests {
         }
         {
             let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)?
                 .unwrap();
             assert_eq!(postings.seek(100), 100);
             assert_eq!(postings.seek(1002), 1002);
@@ -159,7 +152,7 @@ pub mod tests {
     }
 
     #[test]
-    pub fn test_drop_token_that_are_too_long() {
+    pub fn test_drop_token_that_are_too_long() -> crate::Result<()> {
         let ok_token_text: String = iter::repeat('A').take(MAX_TOKEN_LEN).collect();
         let mut exceeding_token_text: String = iter::repeat('A').take(MAX_TOKEN_LEN + 1).collect();
         exceeding_token_text.push_str(" hello");
@@ -176,7 +169,7 @@ pub mod tests {
             .tokenizers()
             .register("simple_no_truncation", SimpleTokenizer);
         let reader = index.reader().unwrap();
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.set_merge_policy(Box::new(NoMergePolicy));
         {
             index_writer.add_document(doc!(text_field=>exceeding_token_text));
@@ -184,10 +177,10 @@ pub mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(0u32);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert_eq!(inverted_index.terms().num_terms(), 1);
             let mut bytes = vec![];
-            assert!(inverted_index.terms().ord_to_term(0, &mut bytes));
+            assert!(inverted_index.terms().ord_to_term(0, &mut bytes)?);
             assert_eq!(&bytes, b"hello");
         }
         {
@@ -196,16 +189,17 @@ pub mod tests {
             reader.reload().unwrap();
             let searcher = reader.searcher();
             let segment_reader = searcher.segment_reader(1u32);
-            let inverted_index = segment_reader.inverted_index(text_field);
+            let inverted_index = segment_reader.inverted_index(text_field)?;
             assert_eq!(inverted_index.terms().num_terms(), 1);
             let mut bytes = vec![];
-            assert!(inverted_index.terms().ord_to_term(0, &mut bytes));
+            assert!(inverted_index.terms().ord_to_term(0, &mut bytes)?);
             assert_eq!(&bytes[..], ok_token_text.as_bytes());
         }
+        Ok(())
     }
 
     #[test]
-    pub fn test_position_and_fieldnorm1() {
+    pub fn test_position_and_fieldnorm1() -> crate::Result<()> {
         let mut positions = Vec::new();
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
@@ -217,42 +211,38 @@ pub mod tests {
             let mut segment_writer =
                 SegmentWriter::for_segment(3_000_000, segment.clone(), &schema).unwrap();
             {
-                let mut doc = Document::default();
                 // checking that position works if the field has two values
-                doc.add_text(text_field, "a b a c a d a a.");
-                doc.add_text(text_field, "d d d d a");
                 let op = AddOperation {
                     opstamp: 0u64,
-                    document: doc,
+                    document: doc!(
+                       text_field => "a b a c a d a a.",
+                       text_field => "d d d d a"
+                    ),
                 };
-                segment_writer.add_document(op, &schema).unwrap();
+                segment_writer.add_document(op, &schema)?;
             }
             {
-                let mut doc = Document::default();
-                doc.add_text(text_field, "b a");
                 let op = AddOperation {
                     opstamp: 1u64,
-                    document: doc,
+                    document: doc!(text_field => "b a"),
                 };
                 segment_writer.add_document(op, &schema).unwrap();
             }
             for i in 2..1000 {
-                let mut doc = Document::default();
-                let mut text = iter::repeat("e ").take(i).collect::<String>();
+                let mut text: String = iter::repeat("e ").take(i).collect();
                 text.push_str(" a");
-                doc.add_text(text_field, &text);
                 let op = AddOperation {
                     opstamp: 2u64,
-                    document: doc,
+                    document: doc!(text_field => text),
                 };
                 segment_writer.add_document(op, &schema).unwrap();
             }
-            segment_writer.finalize().unwrap();
+            segment_writer.finalize()?;
         }
         {
-            let segment_reader = SegmentReader::open(&segment).unwrap();
+            let segment_reader = SegmentReader::open(&segment)?;
             {
-                let fieldnorm_reader = segment_reader.get_fieldnorms_reader(text_field);
+                let fieldnorm_reader = segment_reader.get_fieldnorms_reader(text_field)?;
                 assert_eq!(fieldnorm_reader.fieldnorm(0), 8 + 5);
                 assert_eq!(fieldnorm_reader.fieldnorm(1), 2);
                 for i in 2..1000 {
@@ -265,15 +255,15 @@ pub mod tests {
             {
                 let term_a = Term::from_field_text(text_field, "abcdef");
                 assert!(segment_reader
-                    .inverted_index(term_a.field())
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .inverted_index(term_a.field())?
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .is_none());
             }
             {
                 let term_a = Term::from_field_text(text_field, "a");
                 let mut postings_a = segment_reader
-                    .inverted_index(term_a.field())
-                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+                    .inverted_index(term_a.field())?
+                    .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert_eq!(postings_a.len(), 1000);
                 assert_eq!(postings_a.doc(), 0);
@@ -295,8 +285,8 @@ pub mod tests {
             {
                 let term_e = Term::from_field_text(text_field, "e");
                 let mut postings_e = segment_reader
-                    .inverted_index(term_e.field())
-                    .read_postings(&term_e, IndexRecordOption::WithFreqsAndPositions)
+                    .inverted_index(term_e.field())?
+                    .read_postings(&term_e, IndexRecordOption::WithFreqsAndPositions)?
                     .unwrap();
                 assert_eq!(postings_e.len(), 1000 - 2);
                 for i in 2u32..1000u32 {
@@ -312,17 +302,18 @@ pub mod tests {
                 assert_eq!(postings_e.doc(), TERMINATED);
             }
         }
+        Ok(())
     }
 
     #[test]
-    pub fn test_position_and_fieldnorm2() {
+    pub fn test_position_and_fieldnorm2() -> crate::Result<()> {
         let mut positions: Vec<u32> = Vec::new();
         let mut schema_builder = Schema::builder();
         let text_field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text_field => "g b b d c g c"));
             index_writer.add_document(doc!(text_field => "g a b b a d c g c"));
             assert!(index_writer.commit().is_ok());
@@ -331,16 +322,17 @@ pub mod tests {
         let searcher = index.reader().unwrap().searcher();
         let segment_reader = searcher.segment_reader(0);
         let mut postings = segment_reader
-            .inverted_index(text_field)
-            .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
+            .inverted_index(text_field)?
+            .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)?
             .unwrap();
         assert_eq!(postings.doc(), 1u32);
         postings.positions(&mut positions);
         assert_eq!(&positions[..], &[1u32, 4]);
+        Ok(())
     }
 
     #[test]
-    fn test_skip_next() {
+    fn test_skip_next() -> crate::Result<()> {
         let term_0 = Term::from_field_u64(Field::from_field_id(0), 0);
         let term_1 = Term::from_field_u64(Field::from_field_id(0), 1);
         let term_2 = Term::from_field_u64(Field::from_field_id(0), 2);
@@ -351,10 +343,9 @@ pub mod tests {
             let mut schema_builder = Schema::builder();
             let value_field = schema_builder.add_u64_field("value", INDEXED);
             let schema = schema_builder.build();
-
             let index = Index::create_in_ram(schema);
             {
-                let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+                let mut index_writer = index.writer_for_tests()?;
                 for i in 0u64..num_docs as u64 {
                     let doc = doc!(value_field => 2u64, value_field => i % 2u64);
                     index_writer.add_document(doc);
@@ -363,15 +354,15 @@ pub mod tests {
             }
             index
         };
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         let segment_reader = searcher.segment_reader(0);
 
         // check that the basic usage works
         for i in 0..num_docs - 1 {
             for j in i + 1..num_docs {
                 let mut segment_postings = segment_reader
-                    .inverted_index(term_2.field())
-                    .read_postings(&term_2, IndexRecordOption::Basic)
+                    .inverted_index(term_2.field())?
+                    .read_postings(&term_2, IndexRecordOption::Basic)?
                     .unwrap();
                 assert_eq!(segment_postings.seek(i), i);
                 assert_eq!(segment_postings.doc(), i);
@@ -383,8 +374,8 @@ pub mod tests {
 
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .inverted_index(term_2.field())?
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             // check that `skip_next` advances the iterator
@@ -403,8 +394,8 @@ pub mod tests {
         // check that filtering works
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_0.field())
-                .read_postings(&term_0, IndexRecordOption::Basic)
+                .inverted_index(term_0.field())?
+                .read_postings(&term_0, IndexRecordOption::Basic)?
                 .unwrap();
 
             for i in 0..num_docs / 2 {
@@ -413,8 +404,8 @@ pub mod tests {
             }
 
             let mut segment_postings = segment_reader
-                .inverted_index(term_0.field())
-                .read_postings(&term_0, IndexRecordOption::Basic)
+                .inverted_index(term_0.field())?
+                .read_postings(&term_0, IndexRecordOption::Basic)?
                 .unwrap();
 
             for i in 0..num_docs / 2 - 1 {
@@ -425,19 +416,19 @@ pub mod tests {
 
         // delete some of the documents
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.delete_term(term_0);
             assert!(index_writer.commit().is_ok());
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
         assert_eq!(searcher.segment_readers().len(), 1);
         let segment_reader = searcher.segment_reader(0);
 
         // make sure seeking still works
         for i in 0..num_docs {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .inverted_index(term_2.field())?
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             if i % 2 == 0 {
@@ -453,8 +444,8 @@ pub mod tests {
         // now try with a longer sequence
         {
             let mut segment_postings = segment_reader
-                .inverted_index(term_2.field())
-                .read_postings(&term_2, IndexRecordOption::Basic)
+                .inverted_index(term_2.field())?
+                .read_postings(&term_2, IndexRecordOption::Basic)?
                 .unwrap();
 
             let mut last = 2; // start from 5 to avoid seeking to 3 twice
@@ -479,69 +470,21 @@ pub mod tests {
 
         // delete everything else
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests()?;
             index_writer.delete_term(term_1);
             assert!(index_writer.commit().is_ok());
         }
-        let searcher = index.reader().unwrap().searcher();
+        let searcher = index.reader()?.searcher();
 
         // finally, check that it's empty
         {
-            let searchable_segment_ids = index
-                .searchable_segment_ids()
-                .expect("could not get index segment ids");
+            let searchable_segment_ids = index.searchable_segment_ids()?;
             assert!(searchable_segment_ids.is_empty());
             assert_eq!(searcher.num_docs(), 0);
         }
+        Ok(())
     }
 
-    pub static TERM_A: Lazy<Term> = Lazy::new(|| {
-        let field = Field::from_field_id(0);
-        Term::from_field_text(field, "a")
-    });
-    pub static TERM_B: Lazy<Term> = Lazy::new(|| {
-        let field = Field::from_field_id(0);
-        Term::from_field_text(field, "b")
-    });
-    pub static TERM_C: Lazy<Term> = Lazy::new(|| {
-        let field = Field::from_field_id(0);
-        Term::from_field_text(field, "c")
-    });
-    pub static TERM_D: Lazy<Term> = Lazy::new(|| {
-        let field = Field::from_field_id(0);
-        Term::from_field_text(field, "d")
-    });
-
-    pub static INDEX: Lazy<Index> = Lazy::new(|| {
-        let mut schema_builder = Schema::builder();
-        let text_field = schema_builder.add_text_field("text", STRING);
-        let schema = schema_builder.build();
-
-        let mut rng: StdRng = StdRng::from_seed([1u8; 32]);
-
-        let index = Index::create_in_ram(schema);
-        let posting_list_size = 1_000_000;
-        {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            for _ in 0..posting_list_size {
-                let mut doc = Document::default();
-                if rng.gen_bool(1f64 / 15f64) {
-                    doc.add_text(text_field, "a");
-                }
-                if rng.gen_bool(1f64 / 10f64) {
-                    doc.add_text(text_field, "b");
-                }
-                if rng.gen_bool(1f64 / 5f64) {
-                    doc.add_text(text_field, "c");
-                }
-                doc.add_text(text_field, "d");
-                index_writer.add_document(doc);
-            }
-            assert!(index_writer.commit().is_ok());
-        }
-        index
-    });
-
     /// Wraps a given docset, and forward alls call but the
     /// `.skip_next(...)`. This is useful to test that a specialized
     /// implementation of `.skip_next(...)` is consistent
@@ -606,15 +549,65 @@ pub mod tests {
 
 #[cfg(all(test, feature = "unstable"))]
 mod bench {
-
-    use super::tests::*;
     use crate::docset::TERMINATED;
     use crate::query::Intersection;
     use crate::schema::IndexRecordOption;
+    use crate::schema::{Document, Field, Schema, Term, STRING};
     use crate::tests;
     use crate::DocSet;
+    use crate::Index;
+    use once_cell::sync::Lazy;
+    use rand::rngs::StdRng;
+    use rand::{Rng, SeedableRng};
     use test::{self, Bencher};
 
+    pub static TERM_A: Lazy<Term> = Lazy::new(|| {
+        let field = Field::from_field_id(0);
+        Term::from_field_text(field, "a")
+    });
+    pub static TERM_B: Lazy<Term> = Lazy::new(|| {
+        let field = Field::from_field_id(0);
+        Term::from_field_text(field, "b")
+    });
+    pub static TERM_C: Lazy<Term> = Lazy::new(|| {
+        let field = Field::from_field_id(0);
+        Term::from_field_text(field, "c")
+    });
+    pub static TERM_D: Lazy<Term> = Lazy::new(|| {
+        let field = Field::from_field_id(0);
+        Term::from_field_text(field, "d")
+    });
+
+    pub static INDEX: Lazy<Index> = Lazy::new(|| {
+        let mut schema_builder = Schema::builder();
+        let text_field = schema_builder.add_text_field("text", STRING);
+        let schema = schema_builder.build();
+
+        let mut rng: StdRng = StdRng::from_seed([1u8; 32]);
+
+        let index = Index::create_in_ram(schema);
+        let posting_list_size = 1_000_000;
+        {
+            let mut index_writer = index.writer_for_tests().unwrap();
+            for _ in 0..posting_list_size {
+                let mut doc = Document::default();
+                if rng.gen_bool(1f64 / 15f64) {
+                    doc.add_text(text_field, "a");
+                }
+                if rng.gen_bool(1f64 / 10f64) {
+                    doc.add_text(text_field, "b");
+                }
+                if rng.gen_bool(1f64 / 5f64) {
+                    doc.add_text(text_field, "c");
+                }
+                doc.add_text(text_field, "d");
+                index_writer.add_document(doc);
+            }
+            assert!(index_writer.commit().is_ok());
+        }
+        index
+    });
+
     #[bench]
     fn bench_segment_postings(b: &mut Bencher) {
         let reader = INDEX.reader().unwrap();
@@ -624,7 +617,9 @@ mod bench {
         b.iter(|| {
             let mut segment_postings = segment_reader
                 .inverted_index(TERM_A.field())
+                .unwrap()
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             while segment_postings.advance() != TERMINATED {}
         });
@@ -638,19 +633,27 @@ mod bench {
         b.iter(|| {
             let segment_postings_a = segment_reader
                 .inverted_index(TERM_A.field())
+                .unwrap()
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_b = segment_reader
                 .inverted_index(TERM_B.field())
+                .unwrap()
                 .read_postings(&*TERM_B, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_c = segment_reader
                 .inverted_index(TERM_C.field())
+                .unwrap()
                 .read_postings(&*TERM_C, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let segment_postings_d = segment_reader
                 .inverted_index(TERM_D.field())
+                .unwrap()
                 .read_postings(&*TERM_D, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let mut intersection = Intersection::new(vec![
                 segment_postings_a,
@@ -670,7 +673,9 @@ mod bench {
 
         let mut segment_postings = segment_reader
             .inverted_index(TERM_A.field())
+            .unwrap()
             .read_postings(&*TERM_A, IndexRecordOption::Basic)
+            .unwrap()
             .unwrap();
 
         let mut existing_docs = Vec::new();
@@ -686,7 +691,9 @@ mod bench {
         b.iter(|| {
             let mut segment_postings = segment_reader
                 .inverted_index(TERM_A.field())
+                .unwrap()
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             for doc in &existing_docs {
                 if segment_postings.seek(*doc) == TERMINATED {
@@ -725,12 +732,14 @@ mod bench {
             let n: u32 = test::black_box(17);
             let mut segment_postings = segment_reader
                 .inverted_index(TERM_A.field())
+                .unwrap()
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
+                .unwrap()
                 .unwrap();
             let mut s = 0u32;
             while segment_postings.doc() != TERMINATED {
                 s += (segment_postings.doc() & n) % 1024;
-                segment_postings.advance()
+                segment_postings.advance();
             }
             s
         });

src/postings/postings_writer.rs

@@ -16,7 +16,7 @@ use fnv::FnvHashMap;
 use std::collections::HashMap;
 use std::io;
 use std::marker::PhantomData;
-use std::ops::DerefMut;
+use std::ops::{DerefMut, Range};
 
 fn posting_from_field_entry(field_entry: &FieldEntry) -> Box<dyn PostingsWriter> {
     match *field_entry.field_type() {
@@ -38,10 +38,8 @@ fn posting_from_field_entry(field_entry: &FieldEntry) -> Box<dyn PostingsWriter>
         | FieldType::I64(_)
         | FieldType::F64(_)
         | FieldType::Date(_)
-        | FieldType::HierarchicalFacet => SpecializedPostingsWriter::<NothingRecorder>::new_boxed(),
-        FieldType::Bytes => {
-            // FieldType::Bytes cannot actually be indexed.
-            // TODO fix during the indexer refactoring described in #276
+        | FieldType::Bytes(_)
+        | FieldType::HierarchicalFacet(_) => {
             SpecializedPostingsWriter::<NothingRecorder>::new_boxed()
         }
     }
@@ -56,7 +54,7 @@ pub struct MultiFieldPostingsWriter {
 
 fn make_field_partition(
     term_offsets: &[(&[u8], Addr, UnorderedTermId)],
-) -> Vec<(Field, usize, usize)> {
+) -> Vec<(Field, Range<usize>)> {
     let term_offsets_it = term_offsets
         .iter()
         .map(|(key, _, _)| Term::wrap(key).field())
@@ -74,7 +72,7 @@ fn make_field_partition(
     offsets.push(term_offsets.len());
     let mut field_offsets = vec![];
     for i in 0..fields.len() {
-        field_offsets.push((fields[i], offsets[i], offsets[i + 1]));
+        field_offsets.push((fields[i], offsets[i]..offsets[i + 1]));
     }
     field_offsets
 }
@@ -105,6 +103,7 @@ impl MultiFieldPostingsWriter {
         doc: DocId,
         field: Field,
         token_stream: &mut dyn TokenStream,
+        term_buffer: &mut Term,
     ) -> u32 {
         let postings_writer =
             self.per_field_postings_writers[field.field_id() as usize].deref_mut();
@@ -114,6 +113,7 @@ impl MultiFieldPostingsWriter {
             field,
             token_stream,
             &mut self.heap,
+            term_buffer,
         )
     }
 
@@ -140,14 +140,14 @@ impl MultiFieldPostingsWriter {
 
         let field_offsets = make_field_partition(&term_offsets);
 
-        for (field, start, stop) in field_offsets {
+        for (field, byte_offsets) in field_offsets {
             let field_entry = self.schema.get_field_entry(field);
 
             match *field_entry.field_type() {
-                FieldType::Str(_) | FieldType::HierarchicalFacet => {
+                FieldType::Str(_) | FieldType::HierarchicalFacet(_) => {
                     // populating the (unordered term ord) -> (ordered term ord) mapping
                     // for the field.
-                    let unordered_term_ids = term_offsets[start..stop]
+                    let unordered_term_ids = term_offsets[byte_offsets.clone()]
                         .iter()
                         .map(|&(_, _, bucket)| bucket);
                     let mapping: FnvHashMap<UnorderedTermId, TermOrdinal> = unordered_term_ids
@@ -159,18 +159,19 @@ impl MultiFieldPostingsWriter {
                     unordered_term_mappings.insert(field, mapping);
                 }
                 FieldType::U64(_) | FieldType::I64(_) | FieldType::F64(_) | FieldType::Date(_) => {}
-                FieldType::Bytes => {}
+                FieldType::Bytes(_) => {}
             }
 
-            let postings_writer = &self.per_field_postings_writers[field.field_id() as usize];
-            let fieldnorm_reader = fieldnorm_readers.get_field(field);
+            let postings_writer =
+                self.per_field_postings_writers[field.field_id() as usize].as_ref();
+            let fieldnorm_reader = fieldnorm_readers.get_field(field)?;
             let mut field_serializer = serializer.new_field(
                 field,
                 postings_writer.total_num_tokens(),
                 fieldnorm_reader,
             )?;
             postings_writer.serialize(
-                &term_offsets[start..stop],
+                &term_offsets[byte_offsets],
                 &mut field_serializer,
                 &self.term_index.heap,
                 &self.heap,
@@ -220,13 +221,20 @@ pub trait PostingsWriter {
         field: Field,
         token_stream: &mut dyn TokenStream,
         heap: &mut MemoryArena,
+        term_buffer: &mut Term,
     ) -> u32 {
-        let mut term = Term::for_field(field);
+        term_buffer.set_field(field);
         let mut sink = |token: &Token| {
             // We skip all tokens with a len greater than u16.
             if token.text.len() <= MAX_TOKEN_LEN {
-                term.set_text(token.text.as_str());
-                self.subscribe(term_index, doc_id, token.position as u32, &term, heap);
+                term_buffer.set_text(token.text.as_str());
+                self.subscribe(
+                    term_index,
+                    doc_id,
+                    token.position as u32,
+                    &term_buffer,
+                    heap,
+                );
             } else {
                 info!(
                     "A token exceeding MAX_TOKEN_LEN ({}>{}) was dropped. Search for \

src/postings/segment_postings.rs

@@ -1,20 +1,12 @@
 use crate::common::HasLen;
-
 use crate::docset::DocSet;
-use crate::positions::PositionReader;
-
-use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
-use crate::postings::serializer::PostingsSerializer;
-use crate::postings::BlockSearcher;
-
-use crate::postings::Postings;
-
-use crate::schema::IndexRecordOption;
-use crate::{DocId, TERMINATED};
-
-use crate::directory::ReadOnlySource;
 use crate::fastfield::DeleteBitSet;
+use crate::positions::PositionReader;
+use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
+use crate::postings::BlockSearcher;
 use crate::postings::BlockSegmentPostings;
+use crate::postings::Postings;
+use crate::{DocId, TERMINATED};
 
 /// `SegmentPostings` represents the inverted list or postings associated to
 /// a term in a `Segment`.
@@ -73,11 +65,15 @@ impl SegmentPostings {
     /// It serializes the doc ids using tantivy's codec
     /// and returns a `SegmentPostings` object that embeds a
     /// buffer with the serialized data.
+    #[cfg(test)]
     pub fn create_from_docs(docs: &[u32]) -> SegmentPostings {
+        use crate::directory::FileSlice;
+        use crate::postings::serializer::PostingsSerializer;
+        use crate::schema::IndexRecordOption;
         let mut buffer = Vec::new();
         {
             let mut postings_serializer =
-                PostingsSerializer::new(&mut buffer, 0.0, false, false, None);
+                PostingsSerializer::new(&mut buffer, 0.0, IndexRecordOption::Basic, None);
             postings_serializer.new_term(docs.len() as u32);
             for &doc in docs {
                 postings_serializer.write_doc(doc, 1u32);
@@ -86,12 +82,13 @@ impl SegmentPostings {
                 .close_term(docs.len() as u32)
                 .expect("In memory Serialization should never fail.");
         }
-        let block_segment_postings = BlockSegmentPostings::from_data(
+        let block_segment_postings = BlockSegmentPostings::open(
             docs.len() as u32,
-            ReadOnlySource::from(buffer),
+            FileSlice::from(buffer),
             IndexRecordOption::Basic,
             IndexRecordOption::Basic,
-        );
+        )
+        .unwrap();
         SegmentPostings::from_block_postings(block_segment_postings, None)
     }
 
@@ -101,7 +98,10 @@ impl SegmentPostings {
         doc_and_tfs: &[(u32, u32)],
         fieldnorms: Option<&[u32]>,
     ) -> SegmentPostings {
+        use crate::directory::FileSlice;
         use crate::fieldnorm::FieldNormReader;
+        use crate::postings::serializer::PostingsSerializer;
+        use crate::schema::IndexRecordOption;
         use crate::Score;
         let mut buffer: Vec<u8> = Vec::new();
         let fieldnorm_reader = fieldnorms.map(FieldNormReader::for_test);
@@ -114,14 +114,13 @@ impl SegmentPostings {
                     .iter()
                     .map(|&fieldnorm| fieldnorm as u64)
                     .sum::<u64>();
-                total_num_tokens as Score / fieldnorms.len() as f32
+                total_num_tokens as Score / fieldnorms.len() as Score
             })
             .unwrap_or(0.0);
         let mut postings_serializer = PostingsSerializer::new(
             &mut buffer,
             average_field_norm,
-            true,
-            false,
+            IndexRecordOption::WithFreqs,
             fieldnorm_reader,
         );
         postings_serializer.new_term(doc_and_tfs.len() as u32);
@@ -131,12 +130,13 @@ impl SegmentPostings {
         postings_serializer
             .close_term(doc_and_tfs.len() as u32)
             .unwrap();
-        let block_segment_postings = BlockSegmentPostings::from_data(
+        let block_segment_postings = BlockSegmentPostings::open(
             doc_and_tfs.len() as u32,
-            ReadOnlySource::from(buffer),
+            FileSlice::from(buffer),
             IndexRecordOption::WithFreqs,
             IndexRecordOption::WithFreqs,
-        );
+        )
+        .unwrap();
         SegmentPostings::from_block_postings(block_segment_postings, None)
     }
 
@@ -204,7 +204,7 @@ impl DocSet for SegmentPostings {
     }
 
     /// Return the current document's `DocId`.
-    #[inline]
+    #[inline(always)]
     fn doc(&self) -> DocId {
         self.block_cursor.doc(self.cur)
     }

src/postings/serializer.rs

@@ -8,8 +8,8 @@ use crate::positions::PositionSerializer;
 use crate::postings::compression::{BlockEncoder, VIntEncoder, COMPRESSION_BLOCK_SIZE};
 use crate::postings::skip::SkipSerializer;
 use crate::query::BM25Weight;
-use crate::schema::Schema;
 use crate::schema::{Field, FieldEntry, FieldType};
+use crate::schema::{IndexRecordOption, Schema};
 use crate::termdict::{TermDictionaryBuilder, TermOrdinal};
 use crate::{DocId, Score};
 use std::cmp::Ordering;
@@ -55,33 +55,17 @@ pub struct InvertedIndexSerializer {
 }
 
 impl InvertedIndexSerializer {
-    /// Open a new `InvertedIndexSerializer` for the given segment
-    fn create(
-        terms_write: CompositeWrite<WritePtr>,
-        postings_write: CompositeWrite<WritePtr>,
-        positions_write: CompositeWrite<WritePtr>,
-        positionsidx_write: CompositeWrite<WritePtr>,
-        schema: Schema,
-    ) -> crate::Result<InvertedIndexSerializer> {
-        Ok(InvertedIndexSerializer {
-            terms_write,
-            postings_write,
-            positions_write,
-            positionsidx_write,
-            schema,
-        })
-    }
-
     /// Open a new `PostingsSerializer` for the given segment
     pub fn open(segment: &mut Segment) -> crate::Result<InvertedIndexSerializer> {
         use crate::SegmentComponent::{POSITIONS, POSITIONSSKIP, POSTINGS, TERMS};
-        InvertedIndexSerializer::create(
-            CompositeWrite::wrap(segment.open_write(TERMS)?),
-            CompositeWrite::wrap(segment.open_write(POSTINGS)?),
-            CompositeWrite::wrap(segment.open_write(POSITIONS)?),
-            CompositeWrite::wrap(segment.open_write(POSITIONSSKIP)?),
-            segment.schema(),
-        )
+        let inv_index_serializer = InvertedIndexSerializer {
+            terms_write: CompositeWrite::wrap(segment.open_write(TERMS)?),
+            postings_write: CompositeWrite::wrap(segment.open_write(POSTINGS)?),
+            positions_write: CompositeWrite::wrap(segment.open_write(POSITIONS)?),
+            positionsidx_write: CompositeWrite::wrap(segment.open_write(POSITIONSSKIP)?),
+            schema: segment.schema(),
+        };
+        Ok(inv_index_serializer)
     }
 
     /// Must be called before starting pushing terms of
@@ -143,30 +127,24 @@ impl<'a> FieldSerializer<'a> {
         fieldnorm_reader: Option<FieldNormReader>,
     ) -> io::Result<FieldSerializer<'a>> {
         total_num_tokens.serialize(postings_write)?;
-        let (term_freq_enabled, position_enabled): (bool, bool) = match field_type {
+        let mode = match field_type {
             FieldType::Str(ref text_options) => {
                 if let Some(text_indexing_options) = text_options.get_indexing_options() {
-                    let index_option = text_indexing_options.index_option();
-                    (index_option.has_freq(), index_option.has_positions())
+                    text_indexing_options.index_option()
                 } else {
-                    (false, false)
+                    IndexRecordOption::Basic
                 }
             }
-            _ => (false, false),
+            _ => IndexRecordOption::Basic,
         };
         let term_dictionary_builder = TermDictionaryBuilder::create(term_dictionary_write)?;
         let average_fieldnorm = fieldnorm_reader
             .as_ref()
             .map(|ff_reader| (total_num_tokens as Score / ff_reader.num_docs() as Score))
             .unwrap_or(0.0);
-        let postings_serializer = PostingsSerializer::new(
-            postings_write,
-            average_fieldnorm,
-            term_freq_enabled,
-            position_enabled,
-            fieldnorm_reader,
-        );
-        let positions_serializer_opt = if position_enabled {
+        let postings_serializer =
+            PostingsSerializer::new(postings_write, average_fieldnorm, mode, fieldnorm_reader);
+        let positions_serializer_opt = if mode.has_positions() {
             Some(PositionSerializer::new(positions_write, positionsidx_write))
         } else {
             None
@@ -183,14 +161,16 @@ impl<'a> FieldSerializer<'a> {
     }
 
     fn current_term_info(&self) -> TermInfo {
-        let positions_idx = self
-            .positions_serializer_opt
-            .as_ref()
-            .map(PositionSerializer::positions_idx)
-            .unwrap_or(0u64);
+        let positions_idx =
+            if let Some(positions_serializer) = self.positions_serializer_opt.as_ref() {
+                positions_serializer.positions_idx()
+            } else {
+                0u64
+            };
+        let addr = self.postings_serializer.addr() as usize;
         TermInfo {
             doc_freq: 0,
-            postings_offset: self.postings_serializer.addr(),
+            postings_range: addr..addr,
             positions_idx,
         }
     }
@@ -244,10 +224,11 @@ impl<'a> FieldSerializer<'a> {
     /// using `VInt` encoding.
     pub fn close_term(&mut self) -> io::Result<()> {
         if self.term_open {
-            self.term_dictionary_builder
-                .insert_value(&self.current_term_info)?;
             self.postings_serializer
                 .close_term(self.current_term_info.doc_freq)?;
+            self.current_term_info.postings_range.end = self.postings_serializer.addr() as usize;
+            self.term_dictionary_builder
+                .insert_value(&self.current_term_info)?;
             self.term_open = false;
         }
         Ok(())
@@ -323,8 +304,7 @@ pub struct PostingsSerializer<W: Write> {
     postings_write: Vec<u8>,
     skip_write: SkipSerializer,
 
-    termfreq_enabled: bool,
-    termfreq_sum_enabled: bool,
+    mode: IndexRecordOption,
     fieldnorm_reader: Option<FieldNormReader>,
 
     bm25_weight: Option<BM25Weight>,
@@ -338,8 +318,7 @@ impl<W: Write> PostingsSerializer<W> {
     pub fn new(
         write: W,
         avg_fieldnorm: Score,
-        termfreq_enabled: bool,
-        termfreq_sum_enabled: bool,
+        mode: IndexRecordOption,
         fieldnorm_reader: Option<FieldNormReader>,
     ) -> PostingsSerializer<W> {
         let num_docs = fieldnorm_reader
@@ -356,8 +335,7 @@ impl<W: Write> PostingsSerializer<W> {
             skip_write: SkipSerializer::new(),
 
             last_doc_id_encoded: 0u32,
-            termfreq_enabled,
-            termfreq_sum_enabled,
+            mode,
 
             fieldnorm_reader,
             bm25_weight: None,
@@ -368,7 +346,7 @@ impl<W: Write> PostingsSerializer<W> {
     }
 
     pub fn new_term(&mut self, term_doc_freq: u32) {
-        if self.termfreq_enabled && self.num_docs > 0 {
+        if self.mode.has_freq() && self.num_docs > 0 {
             let bm25_weight = BM25Weight::for_one_term(
                 term_doc_freq as u64,
                 self.num_docs as u64,
@@ -390,13 +368,15 @@ impl<W: Write> PostingsSerializer<W> {
             // last el block 0, offset block 1,
             self.postings_write.extend(block_encoded);
         }
-        if self.termfreq_enabled {
+        if self.mode.has_freq() {
             let (num_bits, block_encoded): (u8, &[u8]) = self
                 .block_encoder
                 .compress_block_unsorted(&self.block.term_freqs());
             self.postings_write.extend(block_encoded);
             self.skip_write.write_term_freq(num_bits);
-            if self.termfreq_sum_enabled {
+            if self.mode.has_positions() {
+                // We serialize the sum of term freqs within the skip information
+                // in order to navigate through positions.
                 let sum_freq = self.block.term_freqs().iter().cloned().sum();
                 self.skip_write.write_total_term_freq(sum_freq);
             }
@@ -455,7 +435,7 @@ impl<W: Write> PostingsSerializer<W> {
                 self.postings_write.write_all(block_encoded)?;
             }
             // ... Idem for term frequencies
-            if self.termfreq_enabled {
+            if self.mode.has_freq() {
                 let block_encoded = self
                     .block_encoder
                     .compress_vint_unsorted(self.block.term_freqs());

src/postings/skip.rs

@@ -1,33 +1,46 @@
-use crate::common::{read_u32_vint_no_advance, serialize_vint_u32, BinarySerializable, VInt};
-use crate::directory::ReadOnlySource;
+use std::convert::TryInto;
+
+use crate::directory::OwnedBytes;
 use crate::postings::compression::{compressed_block_size, COMPRESSION_BLOCK_SIZE};
 use crate::query::BM25Weight;
 use crate::schema::IndexRecordOption;
 use crate::{DocId, Score, TERMINATED};
-use owned_read::OwnedRead;
+
+#[inline(always)]
+fn encode_block_wand_max_tf(max_tf: u32) -> u8 {
+    max_tf.min(u8::MAX as u32) as u8
+}
+
+#[inline(always)]
+fn decode_block_wand_max_tf(max_tf_code: u8) -> u32 {
+    if max_tf_code == u8::MAX {
+        u32::MAX
+    } else {
+        max_tf_code as u32
+    }
+}
+
+#[inline(always)]
+fn read_u32(data: &[u8]) -> u32 {
+    u32::from_le_bytes(data[..4].try_into().unwrap())
+}
+
+#[inline(always)]
+fn write_u32(val: u32, buf: &mut Vec<u8>) {
+    buf.extend_from_slice(&val.to_le_bytes());
+}
 
 pub struct SkipSerializer {
     buffer: Vec<u8>,
-    prev_doc: DocId,
 }
 
 impl SkipSerializer {
     pub fn new() -> SkipSerializer {
-        SkipSerializer {
-            buffer: Vec::new(),
-            prev_doc: 0u32,
-        }
+        SkipSerializer { buffer: Vec::new() }
     }
 
     pub fn write_doc(&mut self, last_doc: DocId, doc_num_bits: u8) {
-        assert!(
-            last_doc > self.prev_doc,
-            "write_doc(...) called with non-increasing doc ids. \
-             Did you forget to call clear maybe?"
-        );
-        let delta_doc = last_doc - self.prev_doc;
-        self.prev_doc = last_doc;
-        delta_doc.serialize(&mut self.buffer).unwrap();
+        write_u32(last_doc, &mut self.buffer);
         self.buffer.push(doc_num_bits);
     }
 
@@ -36,16 +49,13 @@ impl SkipSerializer {
     }
 
     pub fn write_total_term_freq(&mut self, tf_sum: u32) {
-        tf_sum
-            .serialize(&mut self.buffer)
-            .expect("Should never fail");
+        write_u32(tf_sum, &mut self.buffer);
     }
 
     pub fn write_blockwand_max(&mut self, fieldnorm_id: u8, term_freq: u32) {
-        self.buffer.push(fieldnorm_id);
-        let mut buf = [0u8; 8];
-        let bytes = serialize_vint_u32(term_freq, &mut buf);
-        self.buffer.extend_from_slice(bytes);
+        let block_wand_tf = encode_block_wand_max_tf(term_freq);
+        self.buffer
+            .extend_from_slice(&[fieldnorm_id, block_wand_tf]);
     }
 
     pub fn data(&self) -> &[u8] {
@@ -53,7 +63,6 @@ impl SkipSerializer {
     }
 
     pub fn clear(&mut self) {
-        self.prev_doc = 0u32;
         self.buffer.clear();
     }
 }
@@ -62,7 +71,7 @@ impl SkipSerializer {
 pub(crate) struct SkipReader {
     last_doc_in_block: DocId,
     pub(crate) last_doc_in_previous_block: DocId,
-    owned_read: OwnedRead,
+    owned_read: OwnedBytes,
     skip_info: IndexRecordOption,
     byte_offset: usize,
     remaining_docs: u32, // number of docs remaining, including the
@@ -93,7 +102,7 @@ impl Default for BlockInfo {
 }
 
 impl SkipReader {
-    pub fn new(data: ReadOnlySource, doc_freq: u32, skip_info: IndexRecordOption) -> SkipReader {
+    pub fn new(data: OwnedBytes, doc_freq: u32, skip_info: IndexRecordOption) -> SkipReader {
         let mut skip_reader = SkipReader {
             last_doc_in_block: if doc_freq >= COMPRESSION_BLOCK_SIZE as u32 {
                 0
@@ -101,7 +110,7 @@ impl SkipReader {
                 TERMINATED
             },
             last_doc_in_previous_block: 0u32,
-            owned_read: OwnedRead::new(data),
+            owned_read: data,
             skip_info,
             block_info: BlockInfo::VInt { num_docs: doc_freq },
             byte_offset: 0,
@@ -114,14 +123,14 @@ impl SkipReader {
         skip_reader
     }
 
-    pub fn reset(&mut self, data: ReadOnlySource, doc_freq: u32) {
+    pub fn reset(&mut self, data: OwnedBytes, doc_freq: u32) {
         self.last_doc_in_block = if doc_freq >= COMPRESSION_BLOCK_SIZE as u32 {
             0
         } else {
             TERMINATED
         };
         self.last_doc_in_previous_block = 0u32;
-        self.owned_read = OwnedRead::new(data);
+        self.owned_read = data;
         self.block_info = BlockInfo::VInt { num_docs: doc_freq };
         self.byte_offset = 0;
         self.remaining_docs = doc_freq;
@@ -154,17 +163,19 @@ impl SkipReader {
         self.position_offset
     }
 
+    #[inline(always)]
     pub fn byte_offset(&self) -> usize {
         self.byte_offset
     }
 
     fn read_block_info(&mut self) {
-        let doc_delta = u32::deserialize(&mut self.owned_read).expect("Skip data corrupted");
-        self.last_doc_in_block += doc_delta as DocId;
-        let doc_num_bits = self.owned_read.get(0);
+        let bytes = self.owned_read.as_slice();
+        let advance_len: usize;
+        self.last_doc_in_block = read_u32(bytes);
+        let doc_num_bits = bytes[4];
         match self.skip_info {
             IndexRecordOption::Basic => {
-                self.owned_read.advance(1);
+                advance_len = 5;
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits: 0,
@@ -174,11 +185,10 @@ impl SkipReader {
                 };
             }
             IndexRecordOption::WithFreqs => {
-                let tf_num_bits = self.owned_read.get(1);
-                let block_wand_fieldnorm_id = self.owned_read.get(2);
-                let data = &self.owned_read.as_ref()[3..];
-                let (block_wand_term_freq, num_bytes) = read_u32_vint_no_advance(data);
-                self.owned_read.advance(3 + num_bytes);
+                let tf_num_bits = bytes[5];
+                let block_wand_fieldnorm_id = bytes[6];
+                let block_wand_term_freq = decode_block_wand_max_tf(bytes[7]);
+                advance_len = 8;
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits,
@@ -188,13 +198,11 @@ impl SkipReader {
                 };
             }
             IndexRecordOption::WithFreqsAndPositions => {
-                let tf_num_bits = self.owned_read.get(1);
-                self.owned_read.advance(2);
-                let tf_sum = u32::deserialize(&mut self.owned_read).expect("Failed reading tf_sum");
-                let block_wand_fieldnorm_id = self.owned_read.get(0);
-                self.owned_read.advance(1);
-                let block_wand_term_freq =
-                    VInt::deserialize_u64(&mut self.owned_read).unwrap() as u32;
+                let tf_num_bits = bytes[5];
+                let tf_sum = read_u32(&bytes[6..10]);
+                let block_wand_fieldnorm_id = bytes[10];
+                let block_wand_term_freq = decode_block_wand_max_tf(bytes[11]);
+                advance_len = 12;
                 self.block_info = BlockInfo::BitPacked {
                     doc_num_bits,
                     tf_num_bits,
@@ -204,6 +212,7 @@ impl SkipReader {
                 };
             }
         }
+        self.owned_read.advance(advance_len);
     }
 
     pub fn block_info(&self) -> BlockInfo {
@@ -262,9 +271,27 @@ mod tests {
     use super::BlockInfo;
     use super::IndexRecordOption;
     use super::{SkipReader, SkipSerializer};
-    use crate::directory::ReadOnlySource;
+    use crate::directory::OwnedBytes;
     use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
 
+    #[test]
+    fn test_encode_block_wand_max_tf() {
+        for tf in 0..255 {
+            assert_eq!(super::encode_block_wand_max_tf(tf), tf as u8);
+        }
+        for &tf in &[255, 256, 1_000_000, u32::MAX] {
+            assert_eq!(super::encode_block_wand_max_tf(tf), 255);
+        }
+    }
+
+    #[test]
+    fn test_decode_block_wand_max_tf() {
+        for tf in 0..255 {
+            assert_eq!(super::decode_block_wand_max_tf(tf), tf as u32);
+        }
+        assert_eq!(super::decode_block_wand_max_tf(255), u32::MAX);
+    }
+
     #[test]
     fn test_skip_with_freq() {
         let buf = {
@@ -278,11 +305,8 @@ mod tests {
             skip_serializer.data().to_owned()
         };
         let doc_freq = 3u32 + (COMPRESSION_BLOCK_SIZE * 2) as u32;
-        let mut skip_reader = SkipReader::new(
-            ReadOnlySource::new(buf),
-            doc_freq,
-            IndexRecordOption::WithFreqs,
-        );
+        let mut skip_reader =
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::WithFreqs);
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
             skip_reader.block_info,
@@ -323,11 +347,8 @@ mod tests {
             skip_serializer.data().to_owned()
         };
         let doc_freq = 3u32 + (COMPRESSION_BLOCK_SIZE * 2) as u32;
-        let mut skip_reader = SkipReader::new(
-            ReadOnlySource::from(buf),
-            doc_freq,
-            IndexRecordOption::Basic,
-        );
+        let mut skip_reader =
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::Basic);
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
             skip_reader.block_info(),
@@ -367,11 +388,8 @@ mod tests {
             skip_serializer.data().to_owned()
         };
         let doc_freq = COMPRESSION_BLOCK_SIZE as u32;
-        let mut skip_reader = SkipReader::new(
-            ReadOnlySource::from(buf),
-            doc_freq,
-            IndexRecordOption::Basic,
-        );
+        let mut skip_reader =
+            SkipReader::new(OwnedBytes::new(buf), doc_freq, IndexRecordOption::Basic);
         assert_eq!(skip_reader.last_doc_in_block(), 1u32);
         assert_eq!(
             skip_reader.block_info(),

src/postings/stacker/expull.rs

@@ -206,8 +206,8 @@ mod tests {
     fn test_stack_long() {
         let mut heap = MemoryArena::new();
         let mut stack = ExpUnrolledLinkedList::new();
-        let source: Vec<u32> = (0..100).collect();
-        for &el in &source {
+        let data: Vec<u32> = (0..100).collect();
+        for &el in &data {
             assert!(stack
                 .writer(&mut heap)
                 .write_u32::<LittleEndian>(el)
@@ -221,7 +221,7 @@ mod tests {
             result.push(LittleEndian::read_u32(&remaining[..4]));
             remaining = &remaining[4..];
         }
-        assert_eq!(&result[..], &source[..]);
+        assert_eq!(&result[..], &data[..]);
     }
 
     #[test]

src/postings/stacker/term_hashmap.rs

@@ -17,10 +17,6 @@ pub fn compute_table_size(num_bits: usize) -> usize {
 /// `KeyValue` is the item stored in the hash table.
 /// The key is actually a `BytesRef` object stored in an external heap.
 /// The `value_addr` also points to an address in the heap.
-///
-/// The key and the value are actually stored contiguously.
-/// For this reason, the (start, stop) information is actually redundant
-/// and can be simplified in the future
 #[derive(Copy, Clone)]
 struct KeyValue {
     key_value_addr: Addr,

src/postings/term_info.rs

@@ -1,41 +1,54 @@
 use crate::common::{BinarySerializable, FixedSize};
 use std::io;
+use std::iter::ExactSizeIterator;
+use std::ops::Range;
 
 /// `TermInfo` wraps the metadata associated to a Term.
 /// It is segment-local.
-#[derive(Debug, Default, Ord, PartialOrd, Eq, PartialEq, Clone)]
+#[derive(Debug, Default, Eq, PartialEq, Clone)]
 pub struct TermInfo {
     /// Number of documents in the segment containing the term
     pub doc_freq: u32,
-    /// Start offset within the postings (`.idx`) file.
-    pub postings_offset: u64,
+    /// Byte range of the posting list within the postings (`.idx`) file.
+    pub postings_range: Range<usize>,
     /// Start offset of the first block within the position (`.pos`) file.
     pub positions_idx: u64,
 }
 
+impl TermInfo {
+    pub(crate) fn posting_num_bytes(&self) -> u32 {
+        let num_bytes = self.postings_range.len();
+        assert!(num_bytes <= std::u32::MAX as usize);
+        num_bytes as u32
+    }
+}
+
 impl FixedSize for TermInfo {
     /// Size required for the binary serialization of a `TermInfo` object.
     /// This is large, but in practise, `TermInfo` are encoded in blocks and
     /// only the first `TermInfo` of a block is serialized uncompressed.
     /// The subsequent `TermInfo` are delta encoded and bitpacked.
-    const SIZE_IN_BYTES: usize = u32::SIZE_IN_BYTES + 2 * u64::SIZE_IN_BYTES;
+    const SIZE_IN_BYTES: usize = 2 * u32::SIZE_IN_BYTES + 2 * u64::SIZE_IN_BYTES;
 }
 
 impl BinarySerializable for TermInfo {
     fn serialize<W: io::Write>(&self, writer: &mut W) -> io::Result<()> {
         self.doc_freq.serialize(writer)?;
-        self.postings_offset.serialize(writer)?;
+        (self.postings_range.start as u64).serialize(writer)?;
+        self.posting_num_bytes().serialize(writer)?;
         self.positions_idx.serialize(writer)?;
         Ok(())
     }
 
     fn deserialize<R: io::Read>(reader: &mut R) -> io::Result<Self> {
         let doc_freq = u32::deserialize(reader)?;
-        let postings_offset = u64::deserialize(reader)?;
+        let postings_start_offset = u64::deserialize(reader)? as usize;
+        let postings_num_bytes = u32::deserialize(reader)?;
+        let postings_end_offset = postings_start_offset + u64::from(postings_num_bytes) as usize;
         let positions_idx = u64::deserialize(reader)?;
         Ok(TermInfo {
             doc_freq,
-            postings_offset,
+            postings_range: postings_start_offset..postings_end_offset,
             positions_idx,
         })
     }

src/query/all_query.rs

@@ -83,7 +83,7 @@ mod tests {
         let field = schema_builder.add_text_field("text", TEXT);
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(field=>"aaa"));
         index_writer.add_document(doc!(field=>"bbb"));
         index_writer.commit().unwrap();

src/query/automaton_weight.rs

@@ -5,9 +5,9 @@ use crate::query::{BitSetDocSet, Explanation};
 use crate::query::{Scorer, Weight};
 use crate::schema::{Field, IndexRecordOption};
 use crate::termdict::{TermDictionary, TermStreamer};
-use crate::Result;
 use crate::TantivyError;
 use crate::{DocId, Score};
+use std::io;
 use std::sync::Arc;
 use tantivy_fst::Automaton;
 
@@ -20,6 +20,7 @@ pub struct AutomatonWeight<A> {
 impl<A> AutomatonWeight<A>
 where
     A: Automaton + Send + Sync + 'static,
+    A::State: Clone,
 {
     /// Create a new AutomationWeight
     pub fn new<IntoArcA: Into<Arc<A>>>(field: Field, automaton: IntoArcA) -> AutomatonWeight<A> {
@@ -29,7 +30,10 @@ where
         }
     }
 
-    fn automaton_stream<'a>(&'a self, term_dict: &'a TermDictionary) -> TermStreamer<'a, &'a A> {
+    fn automaton_stream<'a>(
+        &'a self,
+        term_dict: &'a TermDictionary,
+    ) -> io::Result<TermStreamer<'a, &'a A>> {
         let automaton: &A = &*self.automaton;
         let term_stream_builder = term_dict.search(automaton);
         term_stream_builder.into_stream()
@@ -39,17 +43,18 @@ where
 impl<A> Weight for AutomatonWeight<A>
 where
     A: Automaton + Send + Sync + 'static,
+    A::State: Clone,
 {
-    fn scorer(&self, reader: &SegmentReader, boost: Score) -> Result<Box<dyn Scorer>> {
+    fn scorer(&self, reader: &SegmentReader, boost: Score) -> crate::Result<Box<dyn Scorer>> {
         let max_doc = reader.max_doc();
         let mut doc_bitset = BitSet::with_max_value(max_doc);
-        let inverted_index = reader.inverted_index(self.field);
+        let inverted_index = reader.inverted_index(self.field)?;
         let term_dict = inverted_index.terms();
-        let mut term_stream = self.automaton_stream(term_dict);
+        let mut term_stream = self.automaton_stream(term_dict)?;
         while term_stream.advance() {
             let term_info = term_stream.value();
             let mut block_segment_postings = inverted_index
-                .read_block_postings_from_terminfo(term_info, IndexRecordOption::Basic);
+                .read_block_postings_from_terminfo(term_info, IndexRecordOption::Basic)?;
             loop {
                 let docs = block_segment_postings.docs();
                 if docs.is_empty() {
@@ -66,7 +71,7 @@ where
         Ok(Box::new(const_scorer))
     }
 
-    fn explain(&self, reader: &SegmentReader, doc: DocId) -> Result<Explanation> {
+    fn explain(&self, reader: &SegmentReader, doc: DocId) -> crate::Result<Explanation> {
         let mut scorer = self.scorer(reader, 1.0)?;
         if scorer.seek(doc) == doc {
             Ok(Explanation::new("AutomatonScorer", 1.0))
@@ -91,7 +96,7 @@ mod tests {
         let mut schema = Schema::builder();
         let title = schema.add_text_field("title", STRING);
         let index = Index::create_in_ram(schema.build());
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(doc!(title=>"abc"));
         index_writer.add_document(doc!(title=>"bcd"));
         index_writer.add_document(doc!(title=>"abcd"));
@@ -99,6 +104,7 @@ mod tests {
         index
     }
 
+    #[derive(Clone, Copy)]
     enum State {
         Start,
         NotMatching,

src/query/bm25.rs

@@ -52,7 +52,7 @@ impl BM25Weight {
         }
     }
 
-    pub fn for_terms(searcher: &Searcher, terms: &[Term]) -> BM25Weight {
+    pub fn for_terms(searcher: &Searcher, terms: &[Term]) -> crate::Result<BM25Weight> {
         assert!(!terms.is_empty(), "BM25 requires at least one term");
         let field = terms[0].field();
         for term in &terms[1..] {
@@ -66,25 +66,27 @@ impl BM25Weight {
         let mut total_num_tokens = 0u64;
         let mut total_num_docs = 0u64;
         for segment_reader in searcher.segment_readers() {
-            let inverted_index = segment_reader.inverted_index(field);
+            let inverted_index = segment_reader.inverted_index(field)?;
             total_num_tokens += inverted_index.total_num_tokens();
             total_num_docs += u64::from(segment_reader.max_doc());
         }
         let average_fieldnorm = total_num_tokens as Score / total_num_docs as Score;
 
         if terms.len() == 1 {
-            let term_doc_freq = searcher.doc_freq(&terms[0]);
-            BM25Weight::for_one_term(term_doc_freq, total_num_docs, average_fieldnorm)
+            let term_doc_freq = searcher.doc_freq(&terms[0])?;
+            Ok(BM25Weight::for_one_term(
+                term_doc_freq,
+                total_num_docs,
+                average_fieldnorm,
+            ))
         } else {
-            let idf = terms
-                .iter()
-                .map(|term| {
-                    let term_doc_freq = searcher.doc_freq(term);
-                    idf(term_doc_freq, total_num_docs)
-                })
-                .sum::<Score>();
-            let idf_explain = Explanation::new("idf", idf);
-            BM25Weight::new(idf_explain, average_fieldnorm)
+            let mut idf_sum: Score = 0.0;
+            for term in terms {
+                let term_doc_freq = searcher.doc_freq(term)?;
+                idf_sum += idf(term_doc_freq, total_num_docs);
+            }
+            let idf_explain = Explanation::new("idf", idf_sum);
+            Ok(BM25Weight::new(idf_explain, average_fieldnorm))
         }
     }
 
@@ -104,7 +106,7 @@ impl BM25Weight {
         BM25Weight::new(idf_explain, avg_fieldnorm)
     }
 
-    fn new(idf_explain: Explanation, average_fieldnorm: Score) -> BM25Weight {
+    pub(crate) fn new(idf_explain: Explanation, average_fieldnorm: Score) -> BM25Weight {
         let weight = idf_explain.value() * (1.0 + K1);
         BM25Weight {
             idf_explain,

src/query/boolean_query/block_wand.rs

@@ -268,7 +268,7 @@ mod tests {
     }
 
     fn nearly_equals(left: Score, right: Score) -> bool {
-        (left - right).abs() < 0.000001 * (left + right).abs()
+        (left - right).abs() < 0.0001 * (left + right).abs()
     }
 
     fn compute_checkpoints_for_each_pruning(
@@ -424,9 +424,116 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_fn_reproduce_proptest() {
+        let postings_lists = &[
+            vec![
+                (0, 1),
+                (1, 1),
+                (2, 1),
+                (3, 1),
+                (4, 1),
+                (6, 1),
+                (7, 7),
+                (8, 1),
+                (10, 1),
+                (12, 1),
+                (13, 1),
+                (14, 1),
+                (15, 1),
+                (16, 1),
+                (19, 1),
+                (20, 1),
+                (21, 1),
+                (22, 1),
+                (24, 1),
+                (25, 1),
+                (26, 1),
+                (28, 1),
+                (30, 1),
+                (31, 1),
+                (33, 1),
+                (34, 1),
+                (35, 1),
+                (36, 95),
+                (37, 1),
+                (39, 1),
+                (41, 1),
+                (44, 1),
+                (46, 1),
+            ],
+            vec![
+                (0, 5),
+                (2, 1),
+                (4, 1),
+                (5, 84),
+                (6, 47),
+                (7, 26),
+                (8, 50),
+                (9, 34),
+                (11, 73),
+                (12, 11),
+                (13, 51),
+                (14, 45),
+                (15, 18),
+                (18, 60),
+                (19, 80),
+                (20, 63),
+                (23, 79),
+                (24, 69),
+                (26, 35),
+                (28, 82),
+                (29, 19),
+                (30, 2),
+                (31, 7),
+                (33, 40),
+                (34, 1),
+                (35, 33),
+                (36, 27),
+                (37, 24),
+                (38, 65),
+                (39, 32),
+                (40, 85),
+                (41, 1),
+                (42, 69),
+                (43, 11),
+                (45, 45),
+                (47, 97),
+            ],
+            vec![
+                (2, 1),
+                (4, 1),
+                (7, 94),
+                (8, 1),
+                (9, 1),
+                (10, 1),
+                (12, 1),
+                (15, 1),
+                (22, 1),
+                (23, 1),
+                (26, 1),
+                (27, 1),
+                (32, 1),
+                (33, 1),
+                (34, 1),
+                (36, 96),
+                (39, 1),
+                (41, 1),
+            ],
+        ];
+        let fieldnorms = &[
+            685, 239, 780, 564, 664, 827, 5, 56, 930, 887, 263, 665, 167, 127, 120, 919, 292, 92,
+            489, 734, 814, 724, 700, 304, 128, 779, 311, 877, 774, 15, 866, 368, 894, 371, 982,
+            502, 507, 669, 680, 76, 594, 626, 578, 331, 170, 639, 665, 186,
+        ][..];
+        test_block_wand_aux(postings_lists, fieldnorms);
+    }
+
     proptest! {
         #![proptest_config(ProptestConfig::with_cases(500))]
+        #[ignore]
         #[test]
+        #[ignore]
         fn test_block_wand_three_term_scorers((posting_lists, fieldnorms) in gen_term_scorers(3)) {
             test_block_wand_aux(&posting_lists[..], &fieldnorms[..]);
         }

src/query/boolean_query/boolean_query.rs

@@ -83,7 +83,7 @@ use std::collections::BTreeSet;
 ///    ];
 ///    // Make a BooleanQuery equivalent to
 ///    // title:+diary title:-girl
-///    let diary_must_and_girl_mustnot = BooleanQuery::from(queries_with_occurs1);
+///    let diary_must_and_girl_mustnot = BooleanQuery::new(queries_with_occurs1);
 ///    let count1 = searcher.search(&diary_must_and_girl_mustnot, &Count)?;
 ///    assert_eq!(count1, 1);
 ///
@@ -93,7 +93,7 @@ use std::collections::BTreeSet;
 ///        IndexRecordOption::Basic,
 ///    ));
 ///    // "title:diary OR title:cow"
-///    let title_diary_or_cow = BooleanQuery::from(vec![
+///    let title_diary_or_cow = BooleanQuery::new(vec![
 ///        (Occur::Should, diary_term_query.box_clone()),
 ///        (Occur::Should, cow_term_query),
 ///    ]);
@@ -108,7 +108,7 @@ use std::collections::BTreeSet;
 ///    // You can combine subqueries of different types into 1 BooleanQuery:
 ///    // `TermQuery` and `PhraseQuery`
 ///    // "title:diary OR "dairy cow"
-///    let term_of_phrase_query = BooleanQuery::from(vec![
+///    let term_of_phrase_query = BooleanQuery::new(vec![
 ///        (Occur::Should, diary_term_query.box_clone()),
 ///        (Occur::Should, phrase_query.box_clone()),
 ///    ]);
@@ -117,7 +117,7 @@ use std::collections::BTreeSet;
 ///
 ///    // You can nest one BooleanQuery inside another
 ///    // body:found AND ("title:diary OR "dairy cow")
-///    let nested_query = BooleanQuery::from(vec![
+///    let nested_query = BooleanQuery::new(vec![
 ///        (Occur::Must, body_term_query),
 ///        (Occur::Must, Box::new(term_of_phrase_query))
 ///    ]);
@@ -143,7 +143,7 @@ impl Clone for BooleanQuery {
 
 impl From<Vec<(Occur, Box<dyn Query>)>> for BooleanQuery {
     fn from(subqueries: Vec<(Occur, Box<dyn Query>)>) -> BooleanQuery {
-        BooleanQuery { subqueries }
+        BooleanQuery::new(subqueries)
     }
 }
 
@@ -167,6 +167,23 @@ impl Query for BooleanQuery {
 }
 
 impl BooleanQuery {
+    /// Creates a new boolean query.
+    pub fn new(subqueries: Vec<(Occur, Box<dyn Query>)>) -> BooleanQuery {
+        BooleanQuery { subqueries }
+    }
+
+    /// Returns the intersection of the queries.
+    pub fn intersection(queries: Vec<Box<dyn Query>>) -> BooleanQuery {
+        let subqueries = queries.into_iter().map(|s| (Occur::Must, s)).collect();
+        BooleanQuery::new(subqueries)
+    }
+
+    /// Returns the union of the queries.
+    pub fn union(queries: Vec<Box<dyn Query>>) -> BooleanQuery {
+        let subqueries = queries.into_iter().map(|s| (Occur::Should, s)).collect();
+        BooleanQuery::new(subqueries)
+    }
+
     /// Helper method to create a boolean query matching a given list of terms.
     /// The resulting query is a disjunction of the terms.
     pub fn new_multiterms_query(terms: Vec<Term>) -> BooleanQuery {
@@ -178,7 +195,7 @@ impl BooleanQuery {
                 (Occur::Should, term_query)
             })
             .collect();
-        BooleanQuery::from(occur_term_queries)
+        BooleanQuery::new(occur_term_queries)
     }
 
     /// Deconstructed view of the clauses making up this query.
@@ -186,3 +203,77 @@ impl BooleanQuery {
         &self.subqueries[..]
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::BooleanQuery;
+    use crate::collector::DocSetCollector;
+    use crate::query::{QueryClone, TermQuery};
+    use crate::schema::{IndexRecordOption, Schema, TEXT};
+    use crate::{DocAddress, Index, Term};
+
+    fn create_test_index() -> crate::Result<Index> {
+        let mut schema_builder = Schema::builder();
+        let text = schema_builder.add_text_field("text", TEXT);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut writer = index.writer_for_tests().unwrap();
+        writer.add_document(doc!(text=>"b c"));
+        writer.add_document(doc!(text=>"a c"));
+        writer.add_document(doc!(text=>"a b"));
+        writer.add_document(doc!(text=>"a d"));
+        writer.commit()?;
+        Ok(index)
+    }
+
+    #[test]
+    fn test_union() -> crate::Result<()> {
+        let index = create_test_index()?;
+        let searcher = index.reader()?.searcher();
+        let text = index.schema().get_field("text").unwrap();
+        let term_a = TermQuery::new(Term::from_field_text(text, "a"), IndexRecordOption::Basic);
+        let term_d = TermQuery::new(Term::from_field_text(text, "d"), IndexRecordOption::Basic);
+        let union_ad = BooleanQuery::union(vec![term_a.box_clone(), term_d.box_clone()]);
+        let docs = searcher.search(&union_ad, &DocSetCollector)?;
+        assert_eq!(
+            docs,
+            vec![
+                DocAddress(0u32, 1u32),
+                DocAddress(0u32, 2u32),
+                DocAddress(0u32, 3u32)
+            ]
+            .into_iter()
+            .collect()
+        );
+        Ok(())
+    }
+
+    #[test]
+    fn test_intersection() -> crate::Result<()> {
+        let index = create_test_index()?;
+        let searcher = index.reader()?.searcher();
+        let text = index.schema().get_field("text").unwrap();
+        let term_a = TermQuery::new(Term::from_field_text(text, "a"), IndexRecordOption::Basic);
+        let term_b = TermQuery::new(Term::from_field_text(text, "b"), IndexRecordOption::Basic);
+        let term_c = TermQuery::new(Term::from_field_text(text, "c"), IndexRecordOption::Basic);
+        let intersection_ab =
+            BooleanQuery::intersection(vec![term_a.box_clone(), term_b.box_clone()]);
+        let intersection_ac =
+            BooleanQuery::intersection(vec![term_a.box_clone(), term_c.box_clone()]);
+        let intersection_bc =
+            BooleanQuery::intersection(vec![term_b.box_clone(), term_c.box_clone()]);
+        {
+            let docs = searcher.search(&intersection_ab, &DocSetCollector)?;
+            assert_eq!(docs, vec![DocAddress(0u32, 2u32)].into_iter().collect());
+        }
+        {
+            let docs = searcher.search(&intersection_ac, &DocSetCollector)?;
+            assert_eq!(docs, vec![DocAddress(0u32, 1u32)].into_iter().collect());
+        }
+        {
+            let docs = searcher.search(&intersection_bc, &DocSetCollector)?;
+            assert_eq!(docs, vec![DocAddress(0u32, 0u32)].into_iter().collect());
+        }
+        Ok(())
+    }
+}

src/query/boolean_query/mod.rs

@@ -32,14 +32,12 @@ mod tests {
         let index = Index::create_in_ram(schema);
         {
             // writing the segment
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            {
-                index_writer.add_document(doc!(text_field => "a b c"));
-                index_writer.add_document(doc!(text_field => "a c"));
-                index_writer.add_document(doc!(text_field => "b c"));
-                index_writer.add_document(doc!(text_field => "a b c d"));
-                index_writer.add_document(doc!(text_field => "d"));
-            }
+            let mut index_writer = index.writer_for_tests().unwrap();
+            index_writer.add_document(doc!(text_field => "a b c"));
+            index_writer.add_document(doc!(text_field => "a c"));
+            index_writer.add_document(doc!(text_field => "b c"));
+            index_writer.add_document(doc!(text_field => "a b c d"));
+            index_writer.add_document(doc!(text_field => "d"));
             assert!(index_writer.commit().is_ok());
         }
         (index, text_field)
@@ -134,29 +132,29 @@ mod tests {
                 .collect::<Vec<DocId>>()
         };
         {
-            let boolean_query = BooleanQuery::from(vec![(Occur::Must, make_term_query("a"))]);
+            let boolean_query = BooleanQuery::new(vec![(Occur::Must, make_term_query("a"))]);
             assert_eq!(matching_docs(&boolean_query), vec![0, 1, 3]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![(Occur::Should, make_term_query("a"))]);
+            let boolean_query = BooleanQuery::new(vec![(Occur::Should, make_term_query("a"))]);
             assert_eq!(matching_docs(&boolean_query), vec![0, 1, 3]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![
+            let boolean_query = BooleanQuery::new(vec![
                 (Occur::Should, make_term_query("a")),
                 (Occur::Should, make_term_query("b")),
             ]);
             assert_eq!(matching_docs(&boolean_query), vec![0, 1, 2, 3]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![
+            let boolean_query = BooleanQuery::new(vec![
                 (Occur::Must, make_term_query("a")),
                 (Occur::Should, make_term_query("b")),
             ]);
             assert_eq!(matching_docs(&boolean_query), vec![0, 1, 3]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![
+            let boolean_query = BooleanQuery::new(vec![
                 (Occur::Must, make_term_query("a")),
                 (Occur::Should, make_term_query("b")),
                 (Occur::MustNot, make_term_query("d")),
@@ -164,7 +162,7 @@ mod tests {
             assert_eq!(matching_docs(&boolean_query), vec![0, 1]);
         }
         {
-            let boolean_query = BooleanQuery::from(vec![(Occur::MustNot, make_term_query("d"))]);
+            let boolean_query = BooleanQuery::new(vec![(Occur::MustNot, make_term_query("d"))]);
             assert_eq!(matching_docs(&boolean_query), Vec::<u32>::new());
         }
     }
@@ -194,7 +192,7 @@ mod tests {
         let score_doc_4: Score; // score of doc 4 should not be influenced by exclusion
         {
             let boolean_query_no_excluded =
-                BooleanQuery::from(vec![(Occur::Must, make_term_query("d"))]);
+                BooleanQuery::new(vec![(Occur::Must, make_term_query("d"))]);
             let topdocs_no_excluded = matching_topdocs(&boolean_query_no_excluded);
             assert_eq!(topdocs_no_excluded.len(), 2);
             let (top_score, top_doc) = topdocs_no_excluded[0];
@@ -204,7 +202,7 @@ mod tests {
         }
 
         {
-            let boolean_query_two_excluded = BooleanQuery::from(vec![
+            let boolean_query_two_excluded = BooleanQuery::new(vec![
                 (Occur::Must, make_term_query("d")),
                 (Occur::MustNot, make_term_query("a")),
                 (Occur::MustNot, make_term_query("b")),
@@ -224,7 +222,7 @@ mod tests {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(text_field => "a b c"));
             index_writer.add_document(doc!(text_field => "a c"));
             index_writer.add_document(doc!(text_field => "b c"));
@@ -241,7 +239,7 @@ mod tests {
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
         let boolean_query =
-            BooleanQuery::from(vec![(Occur::Should, term_a), (Occur::Should, term_b)]);
+            BooleanQuery::new(vec![(Occur::Should, term_a), (Occur::Should, term_b)]);
         let boolean_weight = boolean_query.weight(&searcher, true).unwrap();
         {
             let mut boolean_scorer = boolean_weight
@@ -281,7 +279,7 @@ mod tests {
         };
 
         {
-            let boolean_query = BooleanQuery::from(vec![
+            let boolean_query = BooleanQuery::new(vec![
                 (Occur::Must, make_term_query("a")),
                 (Occur::Must, make_term_query("b")),
             ]);
@@ -290,4 +288,29 @@ mod tests {
             assert_nearly_equals!(scores[1], 0.84699446);
         }
     }
+
+    #[test]
+    pub fn test_explain() -> crate::Result<()> {
+        let mut schema_builder = Schema::builder();
+        let text = schema_builder.add_text_field("text", STRING);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_with_num_threads(1, 5_000_000)?;
+        index_writer.add_document(doc!(text=>"a"));
+        index_writer.add_document(doc!(text=>"b"));
+        index_writer.commit()?;
+        let searcher = index.reader()?.searcher();
+        let term_a: Box<dyn Query> = Box::new(TermQuery::new(
+            Term::from_field_text(text, "a"),
+            IndexRecordOption::Basic,
+        ));
+        let term_b: Box<dyn Query> = Box::new(TermQuery::new(
+            Term::from_field_text(text, "b"),
+            IndexRecordOption::Basic,
+        ));
+        let query = BooleanQuery::from(vec![(Occur::Should, term_a), (Occur::Should, term_b)]);
+        let explanation = query.explain(&searcher, DocAddress(0, 0u32))?;
+        assert_nearly_equals!(explanation.value(), 0.6931472);
+        Ok(())
+    }
 }

src/query/boost_query.rs

@@ -144,7 +144,7 @@ mod tests {
     fn test_boost_query_explain() {
         let schema = Schema::builder().build();
         let index = Index::create_in_ram(schema);
-        let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
+        let mut index_writer = index.writer_for_tests().unwrap();
         index_writer.add_document(Document::new());
         assert!(index_writer.commit().is_ok());
         let reader = index.reader().unwrap();
@@ -153,7 +153,7 @@ mod tests {
         let explanation = query.explain(&searcher, DocAddress(0, 0u32)).unwrap();
         assert_eq!(
             explanation.to_pretty_json(),
-            "{\n  \"value\": 0.2,\n  \"description\": \"Boost x0.2 of ...\",\n  \"details\": [\n    {\n      \"value\": 1.0,\n      \"description\": \"AllQuery\"\n    }\n  ]\n}"
+            "{\n  \"value\": 0.2,\n  \"description\": \"Boost x0.2 of ...\",\n  \"details\": [\n    {\n      \"value\": 1.0,\n      \"description\": \"AllQuery\",\n      \"context\": []\n    }\n  ],\n  \"context\": []\n}"
         )
     }
 }

src/query/explanation.rs

@@ -17,6 +17,7 @@ pub struct Explanation {
     description: String,
     #[serde(skip_serializing_if = "Vec::is_empty")]
     details: Vec<Explanation>,
+    context: Vec<String>,
 }
 
 impl fmt::Debug for Explanation {
@@ -32,6 +33,7 @@ impl Explanation {
             value,
             description: description.to_string(),
             details: vec![],
+            context: vec![],
         }
     }
 
@@ -47,6 +49,11 @@ impl Explanation {
         self.details.push(child_explanation);
     }
 
+    /// Adds some extra context to the explanation.
+    pub fn add_context(&mut self, context: String) {
+        self.context.push(context);
+    }
+
     /// Shortcut for `self.details.push(Explanation::new(name, value));`
     pub fn add_const<T: ToString>(&mut self, name: T, value: Score) {
         self.details.push(Explanation::new(name, value));

src/query/fuzzy_query.rs

@@ -177,7 +177,7 @@ mod test {
         let schema = schema_builder.build();
         let index = Index::create_in_ram(schema);
         {
-            let mut index_writer = index.writer_with_num_threads(1, 10_000_000).unwrap();
+            let mut index_writer = index.writer_for_tests().unwrap();
             index_writer.add_document(doc!(
                 country_field => "japan",
             ));

src/query/mod.rs

@@ -46,7 +46,7 @@ pub(crate) use self::fuzzy_query::DFAWrapper;
 pub use self::fuzzy_query::FuzzyTermQuery;
 pub use self::intersection::intersect_scorers;
 pub use self::phrase_query::PhraseQuery;
-pub use self::query::Query;
+pub use self::query::{Query, QueryClone};
 pub use self::query_parser::QueryParser;
 pub use self::query_parser::QueryParserError;
 pub use self::range_query::RangeQuery;