Updated CHANGELOG

- Pass Collector into TweakedScoreTopCollector and
  CustomScoreTopCollector.
- Add std:: qualifier to f32, i32 etc. Not sure why this was not failing
  already.
- Add unit tests for TopDocs with offset including for tweaked and
  custom score collectors.

In order to convert a TopCollector<Score> to a TopCollector<TScore> I
had to add a `into_tscore` method to `TopCollector`. This is a hack but
I don't know how to avoid it.

CHANGELOG.md

@@ -1,6 +1,23 @@
 Tantivy 0.13.0
 ======================
 - 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). 
+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 `Scorer::skip(target)` has been replaced by `Scorer::seek(target)` and returns the resulting DocId.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
+```rust
+let mut doc = docset.doc();
+while doc != TERMINATED {
+   // ...
+   doc = docset.advance();
+}
+```
+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)
+
 
 Tantivy 0.12.0
 ======================

Cargo.toml

@@ -18,7 +18,7 @@ byteorder = "1.0"
 crc32fast = "1.2.0"
 once_cell = "1.0"
 regex ={version = "1.3.0", default-features = false, features = ["std"]}
-tantivy-fst = {path="../tantivy-fst", version="0.3"}
+tantivy-fst = "0.3"
 memmap = {version = "0.7", optional=true}
 lz4 = {version="1.20", optional=true}
 snap = "1"
@@ -45,7 +45,7 @@ fnv = "1.0.6"
 owned-read = "0.4"
 failure = "0.1"
 htmlescape = "0.3.1"
-fail = "0.3"
+fail = "0.4"
 murmurhash32 = "0.2"
 chrono = "0.4"
 smallvec = "1.0"
@@ -60,7 +60,7 @@ maplit = "1"
 matches = "0.1.8"
 
 [dev-dependencies.fail]
-version = "0.3"
+version = "0.4"
 features = ["failpoints"]
 
 [profile.release]

README.md

@@ -31,12 +31,16 @@ Tantivy is, in fact, strongly inspired by Lucene's design.
 
 # Benchmark
 
-Tantivy is typically faster than Lucene, but the results depend on 
-the nature of the queries in your workload.
-
 The following [benchmark](https://tantivy-search.github.io/bench/) break downs 
 performance for different type of queries / collection.
 
+
+In general, Tantivy tends to be 
+- slower than Lucene on union with a Top-K due to Block-WAND optimization.
+- faster than Lucene on intersection and phrase queries. 
+
+Your mileage WILL vary depending on the nature of queries and their load.
+
 # Features
 
 - Full-text search

examples/faceted_search_with_tweaked_score.rs

@@ -0,0 +1,98 @@
+use std::collections::HashSet;
+use tantivy::collector::TopDocs;
+use tantivy::doc;
+use tantivy::query::BooleanQuery;
+use tantivy::schema::*;
+use tantivy::{DocId, Index, Score, SegmentReader};
+
+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 schema = schema_builder.build();
+    let index = Index::create_in_ram(schema.clone());
+
+    let mut index_writer = index.writer(30_000_000)?;
+
+    index_writer.add_document(doc!(
+        title => "Fried egg",
+        ingredient => Facet::from("/ingredient/egg"),
+        ingredient => Facet::from("/ingredient/oil"),
+    ));
+    index_writer.add_document(doc!(
+        title => "Scrambled egg",
+        ingredient => Facet::from("/ingredient/egg"),
+        ingredient => Facet::from("/ingredient/butter"),
+        ingredient => Facet::from("/ingredient/milk"),
+        ingredient => Facet::from("/ingredient/salt"),
+    ));
+    index_writer.add_document(doc!(
+        title => "Egg rolls",
+        ingredient => Facet::from("/ingredient/egg"),
+        ingredient => Facet::from("/ingredient/garlic"),
+        ingredient => Facet::from("/ingredient/salt"),
+        ingredient => Facet::from("/ingredient/oil"),
+        ingredient => Facet::from("/ingredient/tortilla-wrap"),
+        ingredient => Facet::from("/ingredient/mushroom"),
+    ));
+    index_writer.commit()?;
+
+    let reader = index.reader()?;
+    let searcher = reader.searcher();
+    {
+        let facets = vec![
+            Facet::from("/ingredient/egg"),
+            Facet::from("/ingredient/oil"),
+            Facet::from("/ingredient/garlic"),
+            Facet::from("/ingredient/mushroom"),
+        ];
+        let query = BooleanQuery::new_multiterms_query(
+            facets
+                .iter()
+                .map(|key| Term::from_facet(ingredient, &key))
+                .collect(),
+        );
+        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 facet_dict = ingredient_reader.facet_dict();
+
+                let query_ords: HashSet<u64> = facets
+                    .iter()
+                    .filter_map(|key| facet_dict.term_ord(key.encoded_str()))
+                    .collect();
+
+                let mut facet_ords_buffer: Vec<u64> = Vec::with_capacity(20);
+
+                move |doc: DocId, original_score: Score| {
+                    ingredient_reader.facet_ords(doc, &mut facet_ords_buffer);
+                    let missing_ingredients = facet_ords_buffer
+                        .iter()
+                        .filter(|ord| !query_ords.contains(ord))
+                        .count();
+                    let tweak = 1.0 / 4_f32.powi(missing_ingredients as i32);
+
+                    original_score * tweak
+                }
+            });
+        let top_docs = searcher.search(&query, &top_docs_by_custom_score)?;
+
+        let titles: Vec<String> = top_docs
+            .iter()
+            .map(|(_, doc_id)| {
+                searcher
+                    .doc(*doc_id)
+                    .unwrap()
+                    .get_first(title)
+                    .unwrap()
+                    .text()
+                    .unwrap()
+                    .to_owned()
+            })
+            .collect();
+        assert_eq!(titles, vec!["Fried egg", "Egg rolls"]);
+    }
+    Ok(())
+}

examples/iterating_docs_and_positions.rs

@@ -10,7 +10,7 @@
 // ---
 // Importing tantivy...
 use tantivy::schema::*;
-use tantivy::{doc, DocId, DocSet, Index, Postings};
+use tantivy::{doc, DocSet, Index, Postings, TERMINATED};
 
 fn main() -> tantivy::Result<()> {
     // We first create a schema for the sake of the
@@ -62,12 +62,11 @@ fn main() -> tantivy::Result<()> {
         {
             // this buffer will be used to request for positions
             let mut positions: Vec<u32> = Vec::with_capacity(100);
-            while segment_postings.advance() {
-                // the number of time the term appears in the document.
-                let doc_id: DocId = segment_postings.doc(); //< do not try to access this before calling advance once.
-
+            let mut doc_id = segment_postings.doc();
+            while doc_id != TERMINATED {
                 // This MAY contains deleted documents as well.
                 if segment_reader.is_deleted(doc_id) {
+                    doc_id = segment_postings.advance();
                     continue;
                 }
 
@@ -86,6 +85,7 @@ fn main() -> tantivy::Result<()> {
                 // Doc 2: TermFreq 1: [0]
                 // ```
                 println!("Doc {}: TermFreq {}: {:?}", doc_id, term_freq, positions);
+                doc_id = segment_postings.advance();
             }
         }
     }

src/collector/custom_score_top_collector.rs

@@ -11,13 +11,13 @@ impl<TCustomScorer, TScore> CustomScoreTopCollector<TCustomScorer, TScore>
 where
     TScore: Clone + PartialOrd,
 {
-    pub fn new(
+    pub(crate) fn new(
         custom_scorer: TCustomScorer,
-        limit: usize,
+        collector: TopCollector<TScore>,
     ) -> CustomScoreTopCollector<TCustomScorer, TScore> {
         CustomScoreTopCollector {
             custom_scorer,
-            collector: TopCollector::with_limit(limit),
+            collector,
         }
     }
 }
@@ -28,7 +28,7 @@ where
 /// It is the segment local version of the [`CustomScorer`](./trait.CustomScorer.html).
 pub trait CustomSegmentScorer<TScore>: 'static {
     /// Computes the score of a specific `doc`.
-    fn score(&self, doc: DocId) -> TScore;
+    fn score(&mut self, doc: DocId) -> TScore;
 }
 
 /// `CustomScorer` makes it possible to define any kind of score.
@@ -117,9 +117,9 @@ where
 
 impl<F, TScore> CustomSegmentScorer<TScore> for F
 where
-    F: 'static + Sync + Send + Fn(DocId) -> TScore,
+    F: 'static + FnMut(DocId) -> TScore,
 {
-    fn score(&self, doc: DocId) -> TScore {
+    fn score(&mut self, doc: DocId) -> TScore {
         (self)(doc)
     }
 }

src/collector/facet_collector.rs

@@ -1,6 +1,5 @@
 use crate::collector::Collector;
 use crate::collector::SegmentCollector;
-use crate::docset::SkipResult;
 use crate::fastfield::FacetReader;
 use crate::schema::Facet;
 use crate::schema::Field;
@@ -188,6 +187,11 @@ pub struct FacetSegmentCollector {
     collapse_facet_ords: Vec<u64>,
 }
 
+enum SkipResult {
+    Found,
+    NotFound,
+}
+
 fn skip<'a, I: Iterator<Item = &'a Facet>>(
     target: &[u8],
     collapse_it: &mut Peekable<I>,
@@ -197,14 +201,14 @@ fn skip<'a, I: Iterator<Item = &'a Facet>>(
             Some(facet_bytes) => match facet_bytes.encoded_str().as_bytes().cmp(target) {
                 Ordering::Less => {}
                 Ordering::Greater => {
-                    return SkipResult::OverStep;
+                    return SkipResult::NotFound;
                 }
                 Ordering::Equal => {
-                    return SkipResult::Reached;
+                    return SkipResult::Found;
                 }
             },
             None => {
-                return SkipResult::End;
+                return SkipResult::NotFound;
             }
         }
         collapse_it.next();
@@ -281,7 +285,7 @@ impl Collector for FacetCollector {
                     // is positionned on a term that has not been processed yet.
                     let skip_result = skip(facet_streamer.key(), &mut collapse_facet_it);
                     match skip_result {
-                        SkipResult::Reached => {
+                        SkipResult::Found => {
                             // we reach a facet we decided to collapse.
                             let collapse_depth = facet_depth(facet_streamer.key());
                             let mut collapsed_id = 0;
@@ -301,7 +305,7 @@ impl Collector for FacetCollector {
                             }
                             break;
                         }
-                        SkipResult::End | SkipResult::OverStep => {
+                        SkipResult::NotFound => {
                             collapse_mapping.push(0);
                             if !facet_streamer.advance() {
                                 break;

src/collector/mod.rs

@@ -109,6 +109,7 @@ pub use self::tweak_score_top_collector::{ScoreSegmentTweaker, ScoreTweaker};
 
 mod facet_collector;
 pub use self::facet_collector::FacetCollector;
+use crate::query::Scorer;
 
 /// `Fruit` is the type for the result of our collection.
 /// e.g. `usize` for the `Count` collector.
@@ -154,6 +155,28 @@ 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>;
+
+    /// Created a segment collector and
+    fn collect_segment(
+        &self,
+        scorer: &mut dyn Scorer,
+        segment_ord: u32,
+        segment_reader: &SegmentReader,
+    ) -> crate::Result<<Self::Child as SegmentCollector>::Fruit> {
+        let mut segment_collector = self.for_segment(segment_ord as u32, segment_reader)?;
+        if let Some(delete_bitset) = segment_reader.delete_bitset() {
+            scorer.for_each(&mut |doc, score| {
+                if delete_bitset.is_alive(doc) {
+                    segment_collector.collect(doc, score);
+                }
+            });
+        } else {
+            scorer.for_each(&mut |doc, score| {
+                segment_collector.collect(doc, score);
+            })
+        }
+        Ok(segment_collector.harvest())
+    }
 }
 
 /// The `SegmentCollector` is the trait in charge of defining the

src/collector/top_collector.rs

@@ -18,9 +18,9 @@ use std::collections::BinaryHeap;
 /// Two elements are equal if their feature is equal, and regardless of whether `doc`
 /// is equal. This should be perfectly fine for this usage, but let's make sure this
 /// struct is never public.
-struct ComparableDoc<T, D> {
-    feature: T,
-    doc: D,
+pub(crate) struct ComparableDoc<T, D> {
+    pub feature: T,
+    pub doc: D,
 }
 
 impl<T: PartialOrd, D: PartialOrd> PartialOrd for ComparableDoc<T, D> {
@@ -56,7 +56,8 @@ impl<T: PartialOrd, D: PartialOrd> PartialEq for ComparableDoc<T, D> {
 impl<T: PartialOrd, D: PartialOrd> Eq for ComparableDoc<T, D> {}
 
 pub(crate) struct TopCollector<T> {
-    limit: usize,
+    pub limit: usize,
+    pub offset: usize,
     _marker: PhantomData<T>,
 }
 
@@ -72,14 +73,20 @@ where
         if limit < 1 {
             panic!("Limit must be strictly greater than 0.");
         }
-        TopCollector {
+        Self {
             limit,
+            offset: 0,
             _marker: PhantomData,
         }
     }
 
-    pub fn limit(&self) -> usize {
-        self.limit
+    /// Skip the first "offset" documents when collecting.
+    ///
+    /// This is equivalent to `OFFSET` in MySQL or PostgreSQL and `start` in
+    /// Lucene's TopDocsCollector.
+    pub fn and_offset(mut self, offset: usize) -> TopCollector<T> {
+        self.offset = offset;
+        self
     }
 
     pub fn merge_fruits(
@@ -92,7 +99,7 @@ where
         let mut top_collector = BinaryHeap::new();
         for child_fruit in children {
             for (feature, doc) in child_fruit {
-                if top_collector.len() < self.limit {
+                if top_collector.len() < (self.limit + self.offset) {
                     top_collector.push(ComparableDoc { feature, doc });
                 } else if let Some(mut head) = top_collector.peek_mut() {
                     if head.feature < feature {
@@ -104,6 +111,7 @@ where
         Ok(top_collector
             .into_sorted_vec()
             .into_iter()
+            .skip(self.offset)
             .map(|cdoc| (cdoc.feature, cdoc.doc))
             .collect())
     }
@@ -113,7 +121,23 @@ where
         segment_id: SegmentLocalId,
         _: &SegmentReader,
     ) -> crate::Result<TopSegmentCollector<F>> {
-        Ok(TopSegmentCollector::new(segment_id, self.limit))
+        Ok(TopSegmentCollector::new(
+            segment_id,
+            self.limit + self.offset,
+        ))
+    }
+
+    /// Create a new TopCollector with the same limit and offset.
+    ///
+    /// Ideally we would use Into but the blanket implementation seems to cause the Scorer traits
+    /// to fail.
+    #[doc(hidden)]
+    pub(crate) fn into_tscore<TScore: PartialOrd + Clone>(self) -> TopCollector<TScore> {
+        TopCollector {
+            limit: self.limit,
+            offset: self.offset,
+            _marker: PhantomData,
+        }
     }
 }
 
@@ -187,7 +211,7 @@ impl<T: PartialOrd + Clone> TopSegmentCollector<T> {
 
 #[cfg(test)]
 mod tests {
-    use super::TopSegmentCollector;
+    use super::{TopCollector, TopSegmentCollector};
     use crate::DocAddress;
 
     #[test]
@@ -248,6 +272,48 @@ mod tests {
             top_collector_limit_3.harvest()[..2].to_vec(),
         );
     }
+
+    #[test]
+    fn test_top_collector_with_limit_and_offset() {
+        let collector = TopCollector::with_limit(2).and_offset(1);
+
+        let results = collector
+            .merge_fruits(vec![vec![
+                (0.9, DocAddress(0, 1)),
+                (0.8, DocAddress(0, 2)),
+                (0.7, DocAddress(0, 3)),
+                (0.6, DocAddress(0, 4)),
+                (0.5, DocAddress(0, 5)),
+            ]])
+            .unwrap();
+
+        assert_eq!(
+            results,
+            vec![(0.8, DocAddress(0, 2)), (0.7, DocAddress(0, 3)),]
+        );
+    }
+
+    #[test]
+    fn test_top_collector_with_limit_larger_than_set_and_offset() {
+        let collector = TopCollector::with_limit(2).and_offset(1);
+
+        let results = collector
+            .merge_fruits(vec![vec![(0.9, DocAddress(0, 1)), (0.8, DocAddress(0, 2))]])
+            .unwrap();
+
+        assert_eq!(results, vec![(0.8, DocAddress(0, 2)),]);
+    }
+
+    #[test]
+    fn test_top_collector_with_limit_and_offset_larger_than_set() {
+        let collector = TopCollector::with_limit(2).and_offset(20);
+
+        let results = collector
+            .merge_fruits(vec![vec![(0.9, DocAddress(0, 1)), (0.8, DocAddress(0, 2))]])
+            .unwrap();
+
+        assert_eq!(results, vec![]);
+    }
 }
 
 #[cfg(all(test, feature = "unstable"))]

src/collector/top_score_collector.rs

@@ -1,18 +1,21 @@
 use super::Collector;
 use crate::collector::custom_score_top_collector::CustomScoreTopCollector;
-use crate::collector::top_collector::TopCollector;
 use crate::collector::top_collector::TopSegmentCollector;
+use crate::collector::top_collector::{ComparableDoc, TopCollector};
 use crate::collector::tweak_score_top_collector::TweakedScoreTopCollector;
 use crate::collector::{
     CustomScorer, CustomSegmentScorer, ScoreSegmentTweaker, ScoreTweaker, SegmentCollector,
 };
+use crate::docset::TERMINATED;
 use crate::fastfield::FastFieldReader;
+use crate::query::Scorer;
 use crate::schema::Field;
 use crate::DocAddress;
 use crate::DocId;
 use crate::Score;
 use crate::SegmentLocalId;
 use crate::SegmentReader;
+use std::collections::BinaryHeap;
 use std::fmt;
 
 /// The `TopDocs` collector keeps track of the top `K` documents
@@ -57,7 +60,11 @@ pub struct TopDocs(TopCollector<Score>);
 
 impl fmt::Debug for TopDocs {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "TopDocs({})", self.0.limit())
+        write!(
+            f,
+            "TopDocs(limit={}, offset={})",
+            self.0.limit, self.0.offset
+        )
     }
 }
 
@@ -66,7 +73,7 @@ struct ScorerByFastFieldReader {
 }
 
 impl CustomSegmentScorer<u64> for ScorerByFastFieldReader {
-    fn score(&self, doc: DocId) -> u64 {
+    fn score(&mut self, doc: DocId) -> u64 {
         self.ff_reader.get_u64(u64::from(doc))
     }
 }
@@ -101,6 +108,45 @@ impl TopDocs {
         TopDocs(TopCollector::with_limit(limit))
     }
 
+    /// Skip the first "offset" documents when collecting.
+    ///
+    /// This is equivalent to `OFFSET` in MySQL or PostgreSQL and `start` in
+    /// Lucene's TopDocsCollector.
+    ///
+    /// ```rust
+    /// use tantivy::collector::TopDocs;
+    /// use tantivy::query::QueryParser;
+    /// use tantivy::schema::{Schema, TEXT};
+    /// use tantivy::{doc, DocAddress, Index};
+    ///
+    /// let mut schema_builder = Schema::builder();
+    /// 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, 3_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"));
+    /// index_writer.add_document(doc!(title => "The Diary of a Young Girl"));
+    /// index_writer.add_document(doc!(title => "The Diary of Lena Mukhina"));
+    /// 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 top_docs = searcher.search(&query, &TopDocs::with_limit(2).and_offset(1)).unwrap();
+    ///
+    /// assert_eq!(top_docs.len(), 2);
+    /// assert_eq!(&top_docs[0], &(0.5204813, DocAddress(0, 4)));
+    /// assert_eq!(&top_docs[1], &(0.4793185, DocAddress(0, 3)));
+    /// ```
+    pub fn and_offset(self, offset: usize) -> TopDocs {
+        TopDocs(self.0.and_offset(offset))
+    }
+
     /// Set top-K to rank documents by a given fast field.
     ///
     /// ```rust
@@ -281,7 +327,7 @@ impl TopDocs {
         TScoreSegmentTweaker: ScoreSegmentTweaker<TScore> + 'static,
         TScoreTweaker: ScoreTweaker<TScore, Child = TScoreSegmentTweaker>,
     {
-        TweakedScoreTopCollector::new(score_tweaker, self.0.limit())
+        TweakedScoreTopCollector::new(score_tweaker, self.0.into_tscore())
     }
 
     /// Ranks the documents using a custom score.
@@ -395,7 +441,7 @@ impl TopDocs {
         TCustomSegmentScorer: CustomSegmentScorer<TScore> + 'static,
         TCustomScorer: CustomScorer<TScore, Child = TCustomSegmentScorer>,
     {
-        CustomScoreTopCollector::new(custom_score, self.0.limit())
+        CustomScoreTopCollector::new(custom_score, self.0.into_tscore())
     }
 }
 
@@ -423,6 +469,58 @@ impl Collector for TopDocs {
     ) -> crate::Result<Self::Fruit> {
         self.0.merge_fruits(child_fruits)
     }
+
+    fn collect_segment(
+        &self,
+        scorer: &mut dyn Scorer,
+        segment_ord: u32,
+        segment_reader: &SegmentReader,
+    ) -> crate::Result<<Self::Child as SegmentCollector>::Fruit> {
+        let mut heap: BinaryHeap<ComparableDoc<Score, DocId>> =
+            BinaryHeap::with_capacity(self.0.limit + self.0.offset);
+        // first we fill the heap with the first `limit` elements.
+        let mut doc = scorer.doc();
+        while doc != TERMINATED && heap.len() < (self.0.limit + self.0.offset) {
+            if !segment_reader.is_deleted(doc) {
+                let score = scorer.score();
+                heap.push(ComparableDoc {
+                    feature: score,
+                    doc,
+                });
+            }
+            doc = scorer.advance();
+        }
+
+        let threshold = heap.peek().map(|el| el.feature).unwrap_or(std::f32::MIN);
+
+        if let Some(delete_bitset) = segment_reader.delete_bitset() {
+            scorer.for_each_pruning(threshold, &mut |doc, score| {
+                if delete_bitset.is_alive(doc) {
+                    *heap.peek_mut().unwrap() = ComparableDoc {
+                        feature: score,
+                        doc,
+                    };
+                }
+                heap.peek().map(|el| el.feature).unwrap_or(std::f32::MIN)
+            });
+        } else {
+            scorer.for_each_pruning(threshold, &mut |doc, score| {
+                *heap.peek_mut().unwrap() = ComparableDoc {
+                    feature: score,
+                    doc,
+                };
+                heap.peek().map(|el| el.feature).unwrap_or(std::f32::MIN)
+            });
+        }
+
+        let fruit = heap
+            .into_sorted_vec()
+            .into_iter()
+            .map(|cid| (cid.feature, DocAddress(segment_ord, cid.doc)))
+            .collect();
+
+        Ok(fruit)
+    }
 }
 
 /// Segment Collector associated to `TopDocs`.
@@ -432,7 +530,7 @@ impl SegmentCollector for TopScoreSegmentCollector {
     type Fruit = Vec<(Score, DocAddress)>;
 
     fn collect(&mut self, doc: DocId, score: Score) {
-        self.0.collect(doc, score)
+        self.0.collect(doc, score);
     }
 
     fn harvest(self) -> Vec<(Score, DocAddress)> {
@@ -446,10 +544,10 @@ mod tests {
     use crate::collector::Collector;
     use crate::query::{AllQuery, Query, QueryParser};
     use crate::schema::{Field, Schema, FAST, STORED, TEXT};
-    use crate::DocAddress;
     use crate::Index;
     use crate::IndexWriter;
     use crate::Score;
+    use crate::{DocAddress, DocId, SegmentReader};
 
     fn make_index() -> Index {
         let mut schema_builder = Schema::builder();
@@ -489,6 +587,21 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_top_collector_not_at_capacity_with_offset() {
+        let index = make_index();
+        let field = index.schema().get_field("text").unwrap();
+        let query_parser = QueryParser::for_index(&index, vec![field]);
+        let text_query = query_parser.parse_query("droopy tax").unwrap();
+        let score_docs: Vec<(Score, DocAddress)> = index
+            .reader()
+            .unwrap()
+            .searcher()
+            .search(&text_query, &TopDocs::with_limit(4).and_offset(2))
+            .unwrap();
+        assert_eq!(score_docs, vec![(0.48527452, DocAddress(0, 0))]);
+    }
+
     #[test]
     fn test_top_collector_at_capacity() {
         let index = make_index();
@@ -510,6 +623,27 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_top_collector_at_capacity_with_offset() {
+        let index = make_index();
+        let field = index.schema().get_field("text").unwrap();
+        let query_parser = QueryParser::for_index(&index, vec![field]);
+        let text_query = query_parser.parse_query("droopy tax").unwrap();
+        let score_docs: Vec<(Score, DocAddress)> = index
+            .reader()
+            .unwrap()
+            .searcher()
+            .search(&text_query, &TopDocs::with_limit(2).and_offset(1))
+            .unwrap();
+        assert_eq!(
+            score_docs,
+            vec![
+                (0.5376842, DocAddress(0u32, 2)),
+                (0.48527452, DocAddress(0, 0))
+            ]
+        );
+    }
+
     #[test]
     fn test_top_collector_stable_sorting() {
         let index = make_index();
@@ -623,6 +757,50 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_tweak_score_top_collector_with_offset() {
+        let index = make_index();
+        let field = index.schema().get_field("text").unwrap();
+        let query_parser = QueryParser::for_index(&index, vec![field]);
+        let text_query = query_parser.parse_query("droopy tax").unwrap();
+        let collector = TopDocs::with_limit(2).and_offset(1).tweak_score(
+            move |_segment_reader: &SegmentReader| move |doc: DocId, _original_score: Score| doc,
+        );
+        let score_docs: Vec<(u32, DocAddress)> = index
+            .reader()
+            .unwrap()
+            .searcher()
+            .search(&text_query, &collector)
+            .unwrap();
+
+        assert_eq!(
+            score_docs,
+            vec![(1, DocAddress(0, 1)), (0, DocAddress(0, 0)),]
+        );
+    }
+
+    #[test]
+    fn test_custom_score_top_collector_with_offset() {
+        let index = make_index();
+        let field = index.schema().get_field("text").unwrap();
+        let query_parser = QueryParser::for_index(&index, vec![field]);
+        let text_query = query_parser.parse_query("droopy tax").unwrap();
+        let collector = TopDocs::with_limit(2)
+            .and_offset(1)
+            .custom_score(move |_segment_reader: &SegmentReader| move |doc: DocId| doc);
+        let score_docs: Vec<(u32, DocAddress)> = index
+            .reader()
+            .unwrap()
+            .searcher()
+            .search(&text_query, &collector)
+            .unwrap();
+
+        assert_eq!(
+            score_docs,
+            vec![(1, DocAddress(0, 1)), (0, DocAddress(0, 0)),]
+        );
+    }
+
     fn index(
         query: &str,
         query_field: Field,

src/collector/tweak_score_top_collector.rs

@@ -14,11 +14,11 @@ where
 {
     pub fn new(
         score_tweaker: TScoreTweaker,
-        limit: usize,
+        collector: TopCollector<TScore>,
     ) -> TweakedScoreTopCollector<TScoreTweaker, TScore> {
         TweakedScoreTopCollector {
             score_tweaker,
-            collector: TopCollector::with_limit(limit),
+            collector,
         }
     }
 }
@@ -29,7 +29,7 @@ where
 /// It is the segment local version of the [`ScoreTweaker`](./trait.ScoreTweaker.html).
 pub trait ScoreSegmentTweaker<TScore>: 'static {
     /// Tweak the given `score` for the document `doc`.
-    fn score(&self, doc: DocId, score: Score) -> TScore;
+    fn score(&mut self, doc: DocId, score: Score) -> TScore;
 }
 
 /// `ScoreTweaker` makes it possible to tweak the score
@@ -121,9 +121,9 @@ where
 
 impl<F, TScore> ScoreSegmentTweaker<TScore> for F
 where
-    F: 'static + Sync + Send + Fn(DocId, Score) -> TScore,
+    F: 'static + FnMut(DocId, Score) -> TScore,
 {
-    fn score(&self, doc: DocId, score: Score) -> TScore {
+    fn score(&mut self, doc: DocId, score: Score) -> TScore {
         (self)(doc, score)
     }
 }

src/common/bitset.rs

@@ -33,6 +33,10 @@ impl TinySet {
         TinySet(0u64)
     }
 
+    pub fn clear(&mut self) {
+        self.0 = 0u64;
+    }
+
     /// Returns the complement of the set in `[0, 64[`.
     fn complement(self) -> TinySet {
         TinySet(!self.0)
@@ -43,6 +47,11 @@ impl TinySet {
         !self.intersect(TinySet::singleton(el)).is_empty()
     }
 
+    /// Returns the number of elements in the TinySet.
+    pub fn len(self) -> u32 {
+        self.0.count_ones()
+    }
+
     /// Returns the intersection of `self` and `other`
     pub fn intersect(self, other: TinySet) -> TinySet {
         TinySet(self.0 & other.0)
@@ -109,22 +118,12 @@ impl TinySet {
     pub fn range_greater_or_equal(from_included: u32) -> TinySet {
         TinySet::range_lower(from_included).complement()
     }
-
-    pub fn clear(&mut self) {
-        self.0 = 0u64;
-    }
-
-    pub fn len(self) -> u32 {
-        self.0.count_ones()
-    }
 }
 
 #[derive(Clone)]
 pub struct BitSet {
     tinysets: Box<[TinySet]>,
-    len: usize, //< Technically it should be u32, but we
-    // count multiple inserts.
-    // `usize` guards us from overflow.
+    len: usize,
     max_value: u32,
 }
 
@@ -204,7 +203,7 @@ mod tests {
 
     use super::BitSet;
     use super::TinySet;
-    use crate::docset::DocSet;
+    use crate::docset::{DocSet, TERMINATED};
     use crate::query::BitSetDocSet;
     use crate::tests;
     use crate::tests::generate_nonunique_unsorted;
@@ -278,11 +277,13 @@ mod tests {
         }
         assert_eq!(btreeset.len(), bitset.len());
         let mut bitset_docset = BitSetDocSet::from(bitset);
+        let mut remaining = true;
         for el in btreeset.into_iter() {
-            bitset_docset.advance();
+            assert!(remaining);
             assert_eq!(bitset_docset.doc(), el);
+            remaining = bitset_docset.advance() != TERMINATED;
         }
-        assert!(!bitset_docset.advance());
+        assert!(!remaining);
     }
 
     #[test]

src/core/index.rs

@@ -21,7 +21,6 @@ use crate::schema::FieldType;
 use crate::schema::Schema;
 use crate::tokenizer::{TextAnalyzer, TokenizerManager};
 use crate::IndexWriter;
-use num_cpus;
 use std::borrow::BorrowMut;
 use std::collections::HashSet;
 use std::fmt;

src/core/index_meta.rs

@@ -3,9 +3,7 @@ use crate::core::SegmentId;
 use crate::schema::Schema;
 use crate::Opstamp;
 use census::{Inventory, TrackedObject};
-use serde;
 use serde::{Deserialize, Serialize};
-use serde_json;
 use std::collections::HashSet;
 use std::fmt;
 use std::path::PathBuf;

src/core/searcher.rs

@@ -1,11 +1,8 @@
 use crate::collector::Collector;
-use crate::collector::SegmentCollector;
 use crate::core::Executor;
 use crate::core::InvertedIndexReader;
 use crate::core::SegmentReader;
 use crate::query::Query;
-use crate::query::Scorer;
-use crate::query::Weight;
 use crate::schema::Document;
 use crate::schema::Schema;
 use crate::schema::{Field, Term};
@@ -17,26 +14,6 @@ use crate::Index;
 use std::fmt;
 use std::sync::Arc;
 
-fn collect_segment<C: Collector>(
-    collector: &C,
-    weight: &dyn Weight,
-    segment_ord: u32,
-    segment_reader: &SegmentReader,
-) -> crate::Result<C::Fruit> {
-    let mut scorer = weight.scorer(segment_reader, 1.0f32)?;
-    let mut segment_collector = collector.for_segment(segment_ord as u32, segment_reader)?;
-    if let Some(delete_bitset) = segment_reader.delete_bitset() {
-        scorer.for_each(&mut |doc, score| {
-            if delete_bitset.is_alive(doc) {
-                segment_collector.collect(doc, score);
-            }
-        });
-    } else {
-        scorer.for_each(&mut |doc, score| segment_collector.collect(doc, score));
-    }
-    Ok(segment_collector.harvest())
-}
-
 /// Holds a list of `SegmentReader`s ready for search.
 ///
 /// It guarantees that the `Segment` will not be removed before
@@ -163,12 +140,8 @@ impl Searcher {
         let segment_readers = self.segment_readers();
         let fruits = executor.map(
             |(segment_ord, segment_reader)| {
-                collect_segment(
-                    collector,
-                    weight.as_ref(),
-                    segment_ord as u32,
-                    segment_reader,
-                )
+                let mut scorer = weight.scorer(segment_reader, 1.0f32)?;
+                collector.collect_segment(scorer.as_mut(), segment_ord as u32, segment_reader)
             },
             segment_readers.iter().enumerate(),
         )?;

src/directory/managed_directory.rs

@@ -11,7 +11,6 @@ use crate::error::DataCorruption;
 use crate::Directory;
 
 use crc32fast::Hasher;
-use serde_json;
 use std::collections::HashSet;
 use std::io;
 use std::io::Write;

src/directory/mmap_directory.rs

@@ -1,10 +1,3 @@
-use fs2;
-use notify;
-
-use self::fs2::FileExt;
-use self::notify::RawEvent;
-use self::notify::RecursiveMode;
-use self::notify::Watcher;
 use crate::core::META_FILEPATH;
 use crate::directory::error::LockError;
 use crate::directory::error::{
@@ -20,8 +13,11 @@ use crate::directory::WatchCallback;
 use crate::directory::WatchCallbackList;
 use crate::directory::WatchHandle;
 use crate::directory::{TerminatingWrite, WritePtr};
-use atomicwrites;
+use fs2::FileExt;
 use memmap::Mmap;
+use notify::RawEvent;
+use notify::RecursiveMode;
+use notify::Watcher;
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::convert::From;
@@ -224,17 +220,13 @@ struct MmapDirectoryInner {
 }
 
 impl MmapDirectoryInner {
-    fn new(
-        root_path: PathBuf,
-        temp_directory: Option<TempDir>,
-    ) -> Result<MmapDirectoryInner, OpenDirectoryError> {
-        let mmap_directory_inner = 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),
-        };
-        Ok(mmap_directory_inner)
+        }
     }
 
     fn watch(&self, watch_callback: WatchCallback) -> crate::Result<WatchHandle> {
@@ -268,14 +260,11 @@ impl fmt::Debug for MmapDirectory {
 }
 
 impl MmapDirectory {
-    fn new(
-        root_path: PathBuf,
-        temp_directory: Option<TempDir>,
-    ) -> Result<MmapDirectory, OpenDirectoryError> {
-        let inner = MmapDirectoryInner::new(root_path, temp_directory)?;
-        Ok(MmapDirectory {
+    fn new(root_path: PathBuf, temp_directory: Option<TempDir>) -> MmapDirectory {
+        let inner = MmapDirectoryInner::new(root_path, temp_directory);
+        MmapDirectory {
             inner: Arc::new(inner),
-        })
+        }
     }
 
     /// Creates a new MmapDirectory in a temporary directory.
@@ -285,7 +274,7 @@ impl MmapDirectory {
     pub fn create_from_tempdir() -> Result<MmapDirectory, OpenDirectoryError> {
         let tempdir = TempDir::new().map_err(OpenDirectoryError::IoError)?;
         let tempdir_path = PathBuf::from(tempdir.path());
-        MmapDirectory::new(tempdir_path, Some(tempdir))
+        Ok(MmapDirectory::new(tempdir_path, Some(tempdir)))
     }
 
     /// Opens a MmapDirectory in a directory.
@@ -303,7 +292,7 @@ impl MmapDirectory {
                 directory_path,
             )))
         } else {
-            Ok(MmapDirectory::new(PathBuf::from(directory_path), None)?)
+            Ok(MmapDirectory::new(PathBuf::from(directory_path), None))
         }
     }
 

src/docset.rs

@@ -1,58 +1,47 @@
-use crate::common::BitSet;
 use crate::fastfield::DeleteBitSet;
 use crate::DocId;
 use std::borrow::Borrow;
 use std::borrow::BorrowMut;
-use std::cmp::Ordering;
 
-/// Expresses the outcome of a call to `DocSet`'s `.skip_next(...)`.
-#[derive(PartialEq, Eq, Debug)]
-pub enum SkipResult {
-    /// target was in the docset
-    Reached,
-    /// target was not in the docset, skipping stopped as a greater element was found
-    OverStep,
-    /// the docset was entirely consumed without finding the target, nor any
-    /// element greater than the target.
-    End,
-}
+/// Sentinel value returned when a DocSet has been entirely consumed.
+///
+/// This is not u32::MAX as one would have expected, due to the lack of SSE2 instructions
+/// to compare [u32; 4].
+pub const TERMINATED: DocId = std::i32::MAX as u32;
 
 /// Represents an iterable set of sorted doc ids.
 pub trait DocSet {
     /// Goes to the next element.
-    /// `.advance(...)` needs to be called a first time to point to the correct
-    /// element.
-    fn advance(&mut self) -> bool;
+    ///
+    /// The DocId of the next element is returned.
+    /// In other words we should always have :
+    /// ```ignore
+    /// let doc = docset.advance();
+    /// assert_eq!(doc, docset.doc());
+    /// ```
+    ///
+    /// If we reached the end of the DocSet, TERMINATED should be returned.
+    ///
+    /// Calling `.advance()` on a terminated DocSet should be supported, and TERMINATED should
+    /// be returned.
+    /// TODO Test existing docsets.
+    fn advance(&mut self) -> DocId;
 
-    /// After skipping, position the iterator in such a way that `.doc()`
-    /// will return a value greater than or equal to target.
+    /// Advances the DocSet forward until reaching the target, or going to the
+    /// lowest DocId greater than the target.
     ///
-    /// SkipResult expresses whether the `target value` was reached, overstepped,
-    /// or if the `DocSet` was entirely consumed without finding any value
-    /// greater or equal to the `target`.
+    /// If the end of the DocSet is reached, TERMINATED is returned.
     ///
-    /// WARNING: Calling skip always advances the docset.
-    /// More specifically, if the docset is already positionned on the target
-    /// skipping will advance to the next position and return SkipResult::Overstep.
+    /// Calling `.seek(target)` on a terminated DocSet is legal. Implementation
+    /// of DocSet should support it.
     ///
-    /// If `.skip_next()` oversteps, then the docset must be positionned correctly
-    /// on an existing document. In other words, `.doc()` should return the first document
-    /// greater than `DocId`.
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        if !self.advance() {
-            return SkipResult::End;
-        }
-        loop {
-            match self.doc().cmp(&target) {
-                Ordering::Less => {
-                    if !self.advance() {
-                        return SkipResult::End;
-                    }
-                }
-                Ordering::Equal => return SkipResult::Reached,
-                Ordering::Greater => return SkipResult::OverStep,
-            }
+    /// Calling `seek(TERMINATED)` is also legal and is the normal way to consume a DocSet.
+    fn seek(&mut self, target: DocId) -> DocId {
+        let mut doc = self.doc();
+        while doc < target {
+            doc = self.advance();
         }
+        doc
     }
 
     /// Fills a given mutable buffer with the next doc ids from the
@@ -71,38 +60,38 @@ pub trait DocSet {
     /// use case where batching. The normal way to
     /// go through the `DocId`'s is to call `.advance()`.
     fn fill_buffer(&mut self, buffer: &mut [DocId]) -> usize {
+        if self.doc() == TERMINATED {
+            return 0;
+        }
         for (i, buffer_val) in buffer.iter_mut().enumerate() {
-            if self.advance() {
-                *buffer_val = self.doc();
-            } else {
-                return i;
+            *buffer_val = self.doc();
+            if self.advance() == TERMINATED {
+                return i + 1;
             }
         }
         buffer.len()
     }
 
     /// Returns the current document
+    /// Right after creating a new DocSet, the docset points to the first document.
+    ///
+    /// If the DocSet is empty, .doc() should return `TERMINATED`.
     fn doc(&self) -> DocId;
 
     /// Returns a best-effort hint of the
     /// length of the docset.
     fn size_hint(&self) -> u32;
 
-    /// Appends all docs to a `bitset`.
-    fn append_to_bitset(&mut self, bitset: &mut BitSet) {
-        while self.advance() {
-            bitset.insert(self.doc());
-        }
-    }
-
     /// Returns the number documents matching.
     /// Calling this method consumes the `DocSet`.
     fn count(&mut self, delete_bitset: &DeleteBitSet) -> u32 {
         let mut count = 0u32;
-        while self.advance() {
-            if !delete_bitset.is_deleted(self.doc()) {
+        let mut doc = self.doc();
+        while doc != TERMINATED {
+            if !delete_bitset.is_deleted(doc) {
                 count += 1u32;
             }
+            doc = self.advance();
         }
         count
     }
@@ -114,22 +103,42 @@ pub trait DocSet {
     /// given by `count()`.
     fn count_including_deleted(&mut self) -> u32 {
         let mut count = 0u32;
-        while self.advance() {
+        let mut doc = self.doc();
+        while doc != TERMINATED {
             count += 1u32;
+            doc = self.advance();
         }
         count
     }
 }
 
+impl<'a> DocSet for &'a mut dyn DocSet {
+    fn advance(&mut self) -> u32 {
+        (**self).advance()
+    }
+
+    fn seek(&mut self, target: DocId) -> DocId {
+        (**self).seek(target)
+    }
+
+    fn doc(&self) -> u32 {
+        (**self).doc()
+    }
+
+    fn size_hint(&self) -> u32 {
+        (**self).size_hint()
+    }
+}
+
 impl<TDocSet: DocSet + ?Sized> DocSet for Box<TDocSet> {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         let unboxed: &mut TDocSet = self.borrow_mut();
         unboxed.advance()
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
+    fn seek(&mut self, target: DocId) -> DocId {
         let unboxed: &mut TDocSet = self.borrow_mut();
-        unboxed.skip_next(target)
+        unboxed.seek(target)
     }
 
     fn doc(&self) -> DocId {
@@ -151,9 +160,4 @@ impl<TDocSet: DocSet + ?Sized> DocSet for Box<TDocSet> {
         let unboxed: &mut TDocSet = self.borrow_mut();
         unboxed.count_including_deleted()
     }
-
-    fn append_to_bitset(&mut self, bitset: &mut BitSet) {
-        let unboxed: &mut TDocSet = self.borrow_mut();
-        unboxed.append_to_bitset(bitset);
-    }
 }

src/error.rs

@@ -7,7 +7,6 @@ use crate::directory::error::{Incompatibility, LockError};
 use crate::fastfield::FastFieldNotAvailableError;
 use crate::query;
 use crate::schema;
-use serde_json;
 use std::fmt;
 use std::path::PathBuf;
 use std::sync::PoisonError;

src/indexer/index_writer.rs

@@ -10,7 +10,7 @@ use crate::core::SegmentMeta;
 use crate::core::SegmentReader;
 use crate::directory::TerminatingWrite;
 use crate::directory::{DirectoryLock, GarbageCollectionResult};
-use crate::docset::DocSet;
+use crate::docset::{DocSet, TERMINATED};
 use crate::error::TantivyError;
 use crate::fastfield::write_delete_bitset;
 use crate::indexer::delete_queue::{DeleteCursor, DeleteQueue};
@@ -112,15 +112,15 @@ fn compute_deleted_bitset(
         if let Some(mut docset) =
             inverted_index.read_postings(&delete_op.term, IndexRecordOption::Basic)
         {
-            while docset.advance() {
-                let deleted_doc = docset.doc();
+            let mut deleted_doc = docset.doc();
+            while deleted_doc != TERMINATED {
                 if deleted_doc < limit_doc {
                     delete_bitset.insert(deleted_doc);
                     might_have_changed = true;
                 }
+                deleted_doc = docset.advance();
             }
         }
-
         delete_cursor.advance();
     }
     Ok(might_have_changed)

src/indexer/merger.rs

@@ -2,7 +2,7 @@ use crate::common::MAX_DOC_LIMIT;
 use crate::core::Segment;
 use crate::core::SegmentReader;
 use crate::core::SerializableSegment;
-use crate::docset::DocSet;
+use crate::docset::{DocSet, TERMINATED};
 use crate::fastfield::BytesFastFieldReader;
 use crate::fastfield::DeleteBitSet;
 use crate::fastfield::FastFieldReader;
@@ -574,10 +574,12 @@ impl IndexMerger {
                     let inverted_index = segment_reader.inverted_index(indexed_field);
                     let mut segment_postings = inverted_index
                         .read_postings_from_terminfo(term_info, segment_postings_option);
-                    while segment_postings.advance() {
-                        if !segment_reader.is_deleted(segment_postings.doc()) {
+                    let mut doc = segment_postings.doc();
+                    while doc != TERMINATED {
+                        if !segment_reader.is_deleted(doc) {
                             return Some((segment_ord, segment_postings));
                         }
+                        doc = segment_postings.advance();
                     }
                     None
                 })
@@ -604,17 +606,9 @@ impl IndexMerger {
                 // postings serializer.
                 for (segment_ord, mut segment_postings) in segment_postings {
                     let old_to_new_doc_id = &merged_doc_id_map[segment_ord];
-                    loop {
-                        let doc = segment_postings.doc();
-
-                        // `.advance()` has been called once before the loop.
-                        //
-                        // It was required to make sure we only consider segments
-                        // that effectively contain at least one non-deleted document
-                        // and remove terms that do not have documents associated.
-                        //
-                        //  For this reason, we cannot use a `while segment_postings.advance()` loop.
 
+                    let mut doc = segment_postings.doc();
+                    while doc != TERMINATED {
                         // deleted doc are skipped as they do not have a `remapped_doc_id`.
                         if let Some(remapped_doc_id) = old_to_new_doc_id[doc as usize] {
                             // we make sure to only write the term iff
@@ -629,9 +623,8 @@ impl IndexMerger {
                                 delta_positions,
                             )?;
                         }
-                        if !segment_postings.advance() {
-                            break;
-                        }
+
+                        doc = segment_postings.advance();
                     }
                 }
 

src/indexer/segment_updater.rs

@@ -23,7 +23,6 @@ use futures::channel::oneshot;
 use futures::executor::{ThreadPool, ThreadPoolBuilder};
 use futures::future::Future;
 use futures::future::TryFutureExt;
-use serde_json;
 use std::borrow::BorrowMut;
 use std::collections::HashSet;
 use std::io::Write;

src/lib.rs

@@ -156,7 +156,7 @@ mod snippet;
 pub use self::snippet::{Snippet, SnippetGenerator};
 
 mod docset;
-pub use self::docset::{DocSet, SkipResult};
+pub use self::docset::{DocSet, TERMINATED};
 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};
@@ -285,7 +285,7 @@ mod tests {
 
     use crate::collector::tests::TEST_COLLECTOR_WITH_SCORE;
     use crate::core::SegmentReader;
-    use crate::docset::DocSet;
+    use crate::docset::{DocSet, TERMINATED};
     use crate::query::BooleanQuery;
     use crate::schema::*;
     use crate::DocAddress;
@@ -381,19 +381,12 @@ mod tests {
             index_writer.commit().unwrap();
         }
         {
-            {
-                let doc = doc!(text_field=>"a");
-                index_writer.add_document(doc);
-            }
-            {
-                let doc = doc!(text_field=>"a a");
-                index_writer.add_document(doc);
-            }
+            index_writer.add_document(doc!(text_field=>"a"));
+            index_writer.add_document(doc!(text_field=>"a a"));
             index_writer.commit().unwrap();
         }
         {
-            let doc = doc!(text_field=>"c");
-            index_writer.add_document(doc);
+            index_writer.add_document(doc!(text_field=>"c"));
             index_writer.commit().unwrap();
         }
         {
@@ -472,10 +465,12 @@ mod tests {
     }
 
     fn advance_undeleted(docset: &mut dyn DocSet, reader: &SegmentReader) -> bool {
-        while docset.advance() {
-            if !reader.is_deleted(docset.doc()) {
+        let mut doc = docset.advance();
+        while doc != TERMINATED {
+            if !reader.is_deleted(doc) {
                 return true;
             }
+            doc = docset.advance();
         }
         false
     }
@@ -641,9 +636,8 @@ mod tests {
             .inverted_index(term.field())
             .read_postings(&term, IndexRecordOption::Basic)
             .unwrap();
-        assert!(postings.advance());
         assert_eq!(postings.doc(), 0);
-        assert!(!postings.advance());
+        assert_eq!(postings.advance(), TERMINATED);
     }
 
     #[test]
@@ -665,9 +659,8 @@ mod tests {
             .inverted_index(term.field())
             .read_postings(&term, IndexRecordOption::Basic)
             .unwrap();
-        assert!(postings.advance());
         assert_eq!(postings.doc(), 0);
-        assert!(!postings.advance());
+        assert_eq!(postings.advance(), TERMINATED);
     }
 
     #[test]
@@ -689,9 +682,8 @@ mod tests {
             .inverted_index(term.field())
             .read_postings(&term, IndexRecordOption::Basic)
             .unwrap();
-        assert!(postings.advance());
         assert_eq!(postings.doc(), 0);
-        assert!(!postings.advance());
+        assert_eq!(postings.advance(), TERMINATED);
     }
 
     #[test]
@@ -760,10 +752,8 @@ mod tests {
         {
             // 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);
-            }
+            let doc = doc!(text_field=>"af af af bc bc");
+            index_writer.add_document(doc);
             index_writer.commit().unwrap();
         }
         {
@@ -779,10 +769,9 @@ mod tests {
             let mut postings = inverted_index
                 .read_postings(&term_af, IndexRecordOption::WithFreqsAndPositions)
                 .unwrap();
-            assert!(postings.advance());
             assert_eq!(postings.doc(), 0);
             assert_eq!(postings.term_freq(), 3);
-            assert!(!postings.advance());
+            assert_eq!(postings.advance(), TERMINATED);
         }
     }
 

src/postings/block_search.rs

@@ -129,23 +129,23 @@ impl BlockSearcher {
     ///
     /// If SSE2 instructions are available in the `(platform, running CPU)`,
     /// then we use a different implementation that does an exhaustive linear search over
-    /// the full block whenever the block is full (`len == 128`). It is surprisingly faster, most likely because of the lack
-    /// of branch.
+    /// the block regardless of whether the block is full or not.
+    ///
+    /// Indeed, if the block is not full, the remaining items are TERMINATED.
+    /// It is surprisingly faster, most likely because of the lack of branch misprediction.
     pub(crate) fn search_in_block(
         self,
         block_docs: &AlignedBuffer,
-        len: usize,
         start: usize,
         target: u32,
     ) -> usize {
         #[cfg(target_arch = "x86_64")]
         {
-            use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
-            if self == BlockSearcher::SSE2 && len == COMPRESSION_BLOCK_SIZE {
+            if self == BlockSearcher::SSE2 {
                 return sse2::linear_search_sse2_128(block_docs, target);
             }
         }
-        start + galloping(&block_docs.0[start..len], target)
+        start + galloping(&block_docs.0[start..], target)
     }
 }
 
@@ -166,6 +166,7 @@ mod tests {
     use super::exponential_search;
     use super::linear_search;
     use super::BlockSearcher;
+    use crate::docset::TERMINATED;
     use crate::postings::compression::{AlignedBuffer, COMPRESSION_BLOCK_SIZE};
 
     #[test]
@@ -196,16 +197,11 @@ mod tests {
     fn util_test_search_in_block(block_searcher: BlockSearcher, block: &[u32], target: u32) {
         let cursor = search_in_block_trivial_but_slow(block, target);
         assert!(block.len() < COMPRESSION_BLOCK_SIZE);
-        let mut output_buffer = [u32::max_value(); COMPRESSION_BLOCK_SIZE];
+        let mut output_buffer = [TERMINATED; COMPRESSION_BLOCK_SIZE];
         output_buffer[..block.len()].copy_from_slice(block);
         for i in 0..cursor {
             assert_eq!(
-                block_searcher.search_in_block(
-                    &AlignedBuffer(output_buffer),
-                    block.len(),
-                    i,
-                    target
-                ),
+                block_searcher.search_in_block(&AlignedBuffer(output_buffer), i, target),
                 cursor
             );
         }

src/postings/compression/mod.rs

@@ -1,4 +1,5 @@
 use crate::common::FixedSize;
+use crate::docset::TERMINATED;
 use bitpacking::{BitPacker, BitPacker4x};
 
 pub const COMPRESSION_BLOCK_SIZE: usize = BitPacker4x::BLOCK_LEN;
@@ -90,14 +91,18 @@ impl BlockDecoder {
     }
 
     #[inline]
-    pub(crate) fn output_aligned(&self) -> (&AlignedBuffer, usize) {
-        (&self.output, self.output_len)
+    pub(crate) fn output_aligned(&self) -> &AlignedBuffer {
+        &self.output
     }
 
     #[inline]
     pub fn output(&self, idx: usize) -> u32 {
         self.output.0[idx]
     }
+
+    pub fn clear(&mut self) {
+        self.output.0.iter_mut().for_each(|el| *el = TERMINATED);
+    }
 }
 
 pub trait VIntEncoder {
@@ -134,9 +139,9 @@ pub trait VIntDecoder {
     /// For instance, if delta encoded are `1, 3, 9`, and the
     /// `offset` is 5, then the output will be:
     /// `5 + 1 = 6, 6 + 3= 9, 9 + 9 = 18`
-    fn uncompress_vint_sorted<'a>(
+    fn uncompress_vint_sorted(
         &mut self,
-        compressed_data: &'a [u8],
+        compressed_data: &[u8],
         offset: u32,
         num_els: usize,
     ) -> usize;
@@ -146,7 +151,7 @@ pub trait VIntDecoder {
     ///
     /// The method takes a number of int to decompress, and returns
     /// the amount of bytes that were read to decompress them.
-    fn uncompress_vint_unsorted<'a>(&mut self, compressed_data: &'a [u8], num_els: usize) -> usize;
+    fn uncompress_vint_unsorted(&mut self, compressed_data: &[u8], num_els: usize) -> usize;
 }
 
 impl VIntEncoder for BlockEncoder {
@@ -160,9 +165,9 @@ impl VIntEncoder for BlockEncoder {
 }
 
 impl VIntDecoder for BlockDecoder {
-    fn uncompress_vint_sorted<'a>(
+    fn uncompress_vint_sorted(
         &mut self,
-        compressed_data: &'a [u8],
+        compressed_data: &[u8],
         offset: u32,
         num_els: usize,
     ) -> usize {

src/postings/compression/vint.rs

@@ -42,7 +42,7 @@ pub(crate) fn compress_unsorted<'a>(input: &[u32], output: &'a mut [u8]) -> &'a
 }
 
 #[inline(always)]
-pub fn uncompress_sorted<'a>(compressed_data: &'a [u8], output: &mut [u32], offset: u32) -> usize {
+pub fn uncompress_sorted(compressed_data: &[u8], output: &mut [u32], offset: u32) -> usize {
     let mut read_byte = 0;
     let mut result = offset;
     for output_mut in output.iter_mut() {

src/postings/mod.rs

@@ -51,7 +51,7 @@ pub mod tests {
     use crate::core::Index;
     use crate::core::SegmentComponent;
     use crate::core::SegmentReader;
-    use crate::docset::{DocSet, SkipResult};
+    use crate::docset::{DocSet, TERMINATED};
     use crate::fieldnorm::FieldNormReader;
     use crate::indexer::operation::AddOperation;
     use crate::indexer::SegmentWriter;
@@ -115,29 +115,12 @@ pub mod tests {
             let mut postings = inverted_index
                 .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
                 .unwrap();
-            postings.advance();
+            assert_eq!(postings.doc(), 0);
             postings.positions(&mut positions);
             assert_eq!(&[0, 1, 2], &positions[..]);
             postings.positions(&mut positions);
             assert_eq!(&[0, 1, 2], &positions[..]);
-            postings.advance();
-            postings.positions(&mut positions);
-            assert_eq!(&[0, 5], &positions[..]);
-        }
-        {
-            let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
-                .unwrap();
-            postings.advance();
-            postings.advance();
-            postings.positions(&mut positions);
-            assert_eq!(&[0, 5], &positions[..]);
-        }
-        {
-            let mut postings = inverted_index
-                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
-                .unwrap();
-            assert_eq!(postings.skip_next(1), SkipResult::Reached);
+            assert_eq!(postings.advance(), 1);
             assert_eq!(postings.doc(), 1);
             postings.positions(&mut positions);
             assert_eq!(&[0, 5], &positions[..]);
@@ -146,7 +129,25 @@ pub mod tests {
             let mut postings = inverted_index
                 .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
                 .unwrap();
-            assert_eq!(postings.skip_next(1002), SkipResult::Reached);
+            assert_eq!(postings.doc(), 0);
+            assert_eq!(postings.advance(), 1);
+            postings.positions(&mut positions);
+            assert_eq!(&[0, 5], &positions[..]);
+        }
+        {
+            let mut postings = inverted_index
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .unwrap();
+            assert_eq!(postings.seek(1), 1);
+            assert_eq!(postings.doc(), 1);
+            postings.positions(&mut positions);
+            assert_eq!(&[0, 5], &positions[..]);
+        }
+        {
+            let mut postings = inverted_index
+                .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
+                .unwrap();
+            assert_eq!(postings.seek(1002), 1002);
             assert_eq!(postings.doc(), 1002);
             postings.positions(&mut positions);
             assert_eq!(&[0, 5], &positions[..]);
@@ -155,8 +156,8 @@ pub mod tests {
             let mut postings = inverted_index
                 .read_postings(&term, IndexRecordOption::WithFreqsAndPositions)
                 .unwrap();
-            assert_eq!(postings.skip_next(100), SkipResult::Reached);
-            assert_eq!(postings.skip_next(1002), SkipResult::Reached);
+            assert_eq!(postings.seek(100), 100);
+            assert_eq!(postings.seek(1002), 1002);
             assert_eq!(postings.doc(), 1002);
             postings.positions(&mut positions);
             assert_eq!(&[0, 5], &positions[..]);
@@ -281,22 +282,21 @@ pub mod tests {
                     .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
                     .unwrap();
                 assert_eq!(postings_a.len(), 1000);
-                assert!(postings_a.advance());
                 assert_eq!(postings_a.doc(), 0);
                 assert_eq!(postings_a.term_freq(), 6);
                 postings_a.positions(&mut positions);
                 assert_eq!(&positions[..], [0, 2, 4, 6, 7, 13]);
-                assert!(postings_a.advance());
+                assert_eq!(postings_a.advance(), 1u32);
                 assert_eq!(postings_a.doc(), 1u32);
                 assert_eq!(postings_a.term_freq(), 1);
                 for i in 2u32..1000u32 {
-                    assert!(postings_a.advance());
+                    assert_eq!(postings_a.advance(), i);
                     assert_eq!(postings_a.term_freq(), 1);
                     postings_a.positions(&mut positions);
                     assert_eq!(&positions[..], [i]);
                     assert_eq!(postings_a.doc(), i);
                 }
-                assert!(!postings_a.advance());
+                assert_eq!(postings_a.advance(), TERMINATED);
             }
             {
                 let term_e = Term::from_field_text(text_field, "e");
@@ -306,7 +306,6 @@ pub mod tests {
                     .unwrap();
                 assert_eq!(postings_e.len(), 1000 - 2);
                 for i in 2u32..1000u32 {
-                    assert!(postings_e.advance());
                     assert_eq!(postings_e.term_freq(), i);
                     postings_e.positions(&mut positions);
                     assert_eq!(positions.len(), i as usize);
@@ -314,8 +313,9 @@ pub mod tests {
                         assert_eq!(positions[j], (j as u32));
                     }
                     assert_eq!(postings_e.doc(), i);
+                    postings_e.advance();
                 }
-                assert!(!postings_e.advance());
+                assert_eq!(postings_e.doc(), TERMINATED);
             }
         }
     }
@@ -329,16 +329,8 @@ pub 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 doc = Document::default();
-                doc.add_text(text_field, "g b b d c g c");
-                index_writer.add_document(doc);
-            }
-            {
-                let mut doc = Document::default();
-                doc.add_text(text_field, "g a b b a d c g c");
-                index_writer.add_document(doc);
-            }
+            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());
         }
         let term_a = Term::from_field_text(text_field, "a");
@@ -348,7 +340,6 @@ pub mod tests {
             .inverted_index(text_field)
             .read_postings(&term_a, IndexRecordOption::WithFreqsAndPositions)
             .unwrap();
-        assert!(postings.advance());
         assert_eq!(postings.doc(), 1u32);
         postings.positions(&mut positions);
         assert_eq!(&positions[..], &[1u32, 4]);
@@ -370,11 +361,8 @@ pub mod tests {
             let index = Index::create_in_ram(schema);
             {
                 let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-                for i in 0..num_docs {
-                    let mut doc = Document::default();
-                    doc.add_u64(value_field, 2);
-                    doc.add_u64(value_field, (i % 2) as u64);
-
+                for i in 0u64..num_docs as u64 {
+                    let doc = doc!(value_field => 2u64, value_field => i % 2u64);
                     index_writer.add_document(doc);
                 }
                 assert!(index_writer.commit().is_ok());
@@ -391,11 +379,10 @@ pub mod tests {
                     .inverted_index(term_2.field())
                     .read_postings(&term_2, IndexRecordOption::Basic)
                     .unwrap();
-
-                assert_eq!(segment_postings.skip_next(i), SkipResult::Reached);
+                assert_eq!(segment_postings.seek(i), i);
                 assert_eq!(segment_postings.doc(), i);
 
-                assert_eq!(segment_postings.skip_next(j), SkipResult::Reached);
+                assert_eq!(segment_postings.seek(j), j);
                 assert_eq!(segment_postings.doc(), j);
             }
         }
@@ -407,17 +394,16 @@ pub mod tests {
                 .unwrap();
 
             // check that `skip_next` advances the iterator
-            assert!(segment_postings.advance());
             assert_eq!(segment_postings.doc(), 0);
 
-            assert_eq!(segment_postings.skip_next(1), SkipResult::Reached);
+            assert_eq!(segment_postings.seek(1), 1);
             assert_eq!(segment_postings.doc(), 1);
 
-            assert_eq!(segment_postings.skip_next(1), SkipResult::OverStep);
-            assert_eq!(segment_postings.doc(), 2);
+            assert_eq!(segment_postings.seek(1), 1);
+            assert_eq!(segment_postings.doc(), 1);
 
             // check that going beyond the end is handled
-            assert_eq!(segment_postings.skip_next(num_docs), SkipResult::End);
+            assert_eq!(segment_postings.seek(num_docs), TERMINATED);
         }
 
         // check that filtering works
@@ -428,7 +414,7 @@ pub mod tests {
                 .unwrap();
 
             for i in 0..num_docs / 2 {
-                assert_eq!(segment_postings.skip_next(i * 2), SkipResult::Reached);
+                assert_eq!(segment_postings.seek(i * 2), i * 2);
                 assert_eq!(segment_postings.doc(), i * 2);
             }
 
@@ -438,7 +424,7 @@ pub mod tests {
                 .unwrap();
 
             for i in 0..num_docs / 2 - 1 {
-                assert_eq!(segment_postings.skip_next(i * 2 + 1), SkipResult::OverStep);
+                assert!(segment_postings.seek(i * 2 + 1) > (i * 1) * 2);
                 assert_eq!(segment_postings.doc(), (i + 1) * 2);
             }
         }
@@ -450,6 +436,7 @@ pub mod tests {
             assert!(index_writer.commit().is_ok());
         }
         let searcher = index.reader().unwrap().searcher();
+        assert_eq!(searcher.segment_readers().len(), 1);
         let segment_reader = searcher.segment_reader(0);
 
         // make sure seeking still works
@@ -460,11 +447,11 @@ pub mod tests {
                 .unwrap();
 
             if i % 2 == 0 {
-                assert_eq!(segment_postings.skip_next(i), SkipResult::Reached);
+                assert_eq!(segment_postings.seek(i), i);
                 assert_eq!(segment_postings.doc(), i);
                 assert!(segment_reader.is_deleted(i));
             } else {
-                assert_eq!(segment_postings.skip_next(i), SkipResult::Reached);
+                assert_eq!(segment_postings.seek(i), i);
                 assert_eq!(segment_postings.doc(), i);
             }
         }
@@ -479,12 +466,16 @@ pub mod tests {
             let mut last = 2; // start from 5 to avoid seeking to 3 twice
             let mut cur = 3;
             loop {
-                match segment_postings.skip_next(cur) {
-                    SkipResult::End => break,
-                    SkipResult::Reached => assert_eq!(segment_postings.doc(), cur),
-                    SkipResult::OverStep => assert_eq!(segment_postings.doc(), cur + 1),
+                let seek = segment_postings.seek(cur);
+                if seek == TERMINATED {
+                    break;
+                }
+                assert_eq!(seek, segment_postings.doc());
+                if seek == cur {
+                    assert_eq!(segment_postings.doc(), cur);
+                } else {
+                    assert_eq!(segment_postings.doc(), cur + 1);
                 }
-
                 let next = cur + last;
                 last = cur;
                 cur = next;
@@ -570,7 +561,7 @@ pub mod tests {
     }
 
     impl<TDocSet: DocSet> DocSet for UnoptimizedDocSet<TDocSet> {
-        fn advance(&mut self) -> bool {
+        fn advance(&mut self) -> DocId {
             self.0.advance()
         }
 
@@ -596,30 +587,22 @@ pub mod tests {
         for target in targets {
             let mut postings_opt = postings_factory();
             let mut postings_unopt = UnoptimizedDocSet::wrap(postings_factory());
-            let skip_result_opt = postings_opt.skip_next(target);
-            let skip_result_unopt = postings_unopt.skip_next(target);
+            let skip_result_opt = postings_opt.seek(target);
+            let skip_result_unopt = postings_unopt.seek(target);
             assert_eq!(
                 skip_result_unopt, skip_result_opt,
                 "Failed while skipping to {}",
                 target
             );
-            match skip_result_opt {
-                SkipResult::Reached => assert_eq!(postings_opt.doc(), target),
-                SkipResult::OverStep => assert!(postings_opt.doc() > target),
-                SkipResult::End => {
-                    return;
-                }
+            assert!(skip_result_opt >= target);
+            assert_eq!(skip_result_opt, postings_opt.doc());
+            if skip_result_opt == TERMINATED {
+                return;
             }
-            while postings_opt.advance() {
-                assert!(postings_unopt.advance());
-                assert_eq!(
-                    postings_opt.doc(),
-                    postings_unopt.doc(),
-                    "Failed while skipping to {}",
-                    target
-                );
+            while postings_opt.doc() != TERMINATED {
+                assert_eq!(postings_opt.doc(), postings_unopt.doc());
+                assert_eq!(postings_opt.advance(), postings_unopt.advance());
             }
-            assert!(!postings_unopt.advance());
         }
     }
 }
@@ -628,7 +611,7 @@ pub mod tests {
 mod bench {
 
     use super::tests::*;
-    use crate::docset::SkipResult;
+    use crate::docset::TERMINATED;
     use crate::query::Intersection;
     use crate::schema::IndexRecordOption;
     use crate::tests;
@@ -646,7 +629,7 @@ mod bench {
                 .inverted_index(TERM_A.field())
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
                 .unwrap();
-            while segment_postings.advance() {}
+            while segment_postings.advance() != TERMINATED {}
         });
     }
 
@@ -678,7 +661,7 @@ mod bench {
                 segment_postings_c,
                 segment_postings_d,
             ]);
-            while intersection.advance() {}
+            while intersection.advance() != TERMINATED {}
         });
     }
 
@@ -694,11 +677,10 @@ mod bench {
             .unwrap();
 
         let mut existing_docs = Vec::new();
-        segment_postings.advance();
         for doc in &docs {
             if *doc >= segment_postings.doc() {
                 existing_docs.push(*doc);
-                if segment_postings.skip_next(*doc) == SkipResult::End {
+                if segment_postings.seek(*doc) == TERMINATED {
                     break;
                 }
             }
@@ -710,7 +692,7 @@ mod bench {
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
                 .unwrap();
             for doc in &existing_docs {
-                if segment_postings.skip_next(*doc) == SkipResult::End {
+                if segment_postings.seek(*doc) == TERMINATED {
                     break;
                 }
             }
@@ -749,8 +731,9 @@ mod bench {
                 .read_postings(&*TERM_A, IndexRecordOption::Basic)
                 .unwrap();
             let mut s = 0u32;
-            while segment_postings.advance() {
+            while segment_postings.doc() != TERMINATED {
                 s += (segment_postings.doc() & n) % 1024;
+                segment_postings.advance()
             }
             s
         });

src/postings/segment_postings.rs

@@ -1,7 +1,6 @@
-use crate::common::BitSet;
 use crate::common::HasLen;
 use crate::common::{BinarySerializable, VInt};
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::{DocSet, TERMINATED};
 use crate::positions::PositionReader;
 use crate::postings::compression::{compressed_block_size, AlignedBuffer};
 use crate::postings::compression::{BlockDecoder, VIntDecoder, COMPRESSION_BLOCK_SIZE};
@@ -14,7 +13,6 @@ use crate::postings::USE_SKIP_INFO_LIMIT;
 use crate::schema::IndexRecordOption;
 use crate::DocId;
 use owned_read::OwnedRead;
-use std::cmp::Ordering;
 use tantivy_fst::Streamer;
 
 struct PositionComputer {
@@ -68,12 +66,14 @@ impl SegmentPostings {
     /// Returns an empty segment postings object
     pub fn empty() -> Self {
         let empty_block_cursor = BlockSegmentPostings::empty();
-        SegmentPostings {
+        let mut segment_postings = SegmentPostings {
             block_cursor: empty_block_cursor,
             cur: COMPRESSION_BLOCK_SIZE,
             position_computer: None,
             block_searcher: BlockSearcher::default(),
-        }
+        };
+        segment_postings.advance();
+        segment_postings
     }
 
     /// Creates a segment postings object with the given documents
@@ -116,12 +116,14 @@ impl SegmentPostings {
         segment_block_postings: BlockSegmentPostings,
         positions_stream_opt: Option<PositionReader>,
     ) -> SegmentPostings {
-        SegmentPostings {
+        let mut postings = SegmentPostings {
             block_cursor: segment_block_postings,
             cur: COMPRESSION_BLOCK_SIZE, // cursor within the block
             position_computer: positions_stream_opt.map(PositionComputer::new),
             block_searcher: BlockSearcher::default(),
-        }
+        };
+        postings.advance();
+        postings
     }
 }
 
@@ -129,7 +131,7 @@ impl DocSet for SegmentPostings {
     // goes to the next element.
     // next needs to be called a first time to point to the correct element.
     #[inline]
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         if self.position_computer.is_some() && self.cur < COMPRESSION_BLOCK_SIZE {
             let term_freq = self.term_freq() as usize;
             if let Some(position_computer) = self.position_computer.as_mut() {
@@ -138,29 +140,19 @@ impl DocSet for SegmentPostings {
         }
         self.cur += 1;
         if self.cur >= self.block_cursor.block_len() {
-            self.cur = 0;
-            if !self.block_cursor.advance() {
-                self.cur = COMPRESSION_BLOCK_SIZE;
-                return false;
+            if self.block_cursor.advance() {
+                self.cur = 0;
+            } else {
+                self.cur = COMPRESSION_BLOCK_SIZE - 1;
+                return TERMINATED;
             }
         }
-        true
+        self.doc()
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        if !self.advance() {
-            return SkipResult::End;
-        }
-        match self.doc().cmp(&target) {
-            Ordering::Equal => {
-                return SkipResult::Reached;
-            }
-            Ordering::Greater => {
-                return SkipResult::OverStep;
-            }
-            _ => {
-                // ...
-            }
+    fn seek(&mut self, target: DocId) -> DocId {
+        if self.doc() >= target {
+            return self.doc();
         }
 
         // In the following, thanks to the call to advance above,
@@ -170,44 +162,44 @@ impl DocSet for SegmentPostings {
         // skip blocks until one that might contain the target
         // check if we need to go to the next block
         let mut sum_freqs_skipped: u32 = 0;
-        if !self
+        if self
             .block_cursor
             .docs()
             .last()
-            .map(|doc| *doc >= target)
-            .unwrap_or(false)
-        // there should always be at least a document in the block
-        // since advance returned.
+            .map(|&doc| doc < target)
+            .unwrap_or(true)
         {
-            // we are not in the right block.
-            //
-            // First compute all of the freqs skipped from the current block.
+            // We are not in the right block.
             if self.position_computer.is_some() {
-                sum_freqs_skipped = self.block_cursor.freqs()[self.cur..].iter().sum();
+                // First compute all of the freqs skipped from the current block.
+                sum_freqs_skipped = self.block_cursor.freqs()[self.cur..].iter().sum::<u32>();
                 match self.block_cursor.skip_to(target) {
                     BlockSegmentPostingsSkipResult::Success(block_skip_freqs) => {
                         sum_freqs_skipped += block_skip_freqs;
                     }
                     BlockSegmentPostingsSkipResult::Terminated => {
-                        return SkipResult::End;
+                        self.block_cursor.doc_decoder.clear();
+                        self.cur = 0;
+                        return TERMINATED;
                     }
                 }
             } else if self.block_cursor.skip_to(target)
                 == BlockSegmentPostingsSkipResult::Terminated
             {
                 // no positions needed. no need to sum freqs.
-                return SkipResult::End;
+                self.block_cursor.doc_decoder.clear();
+                self.cur = 0;
+                return TERMINATED;
             }
             self.cur = 0;
         }
 
+        // At this point we are on the block, that might contain our document.
+
         let cur = self.cur;
 
-        // we're in the right block now, start with an exponential search
-        let (output, len) = self.block_cursor.docs_aligned();
-        let new_cur = self
-            .block_searcher
-            .search_in_block(&output, len, cur, target);
+        let output = self.block_cursor.docs_aligned();
+        let new_cur = self.block_searcher.search_in_block(&output, cur, target);
         if let Some(position_computer) = self.position_computer.as_mut() {
             sum_freqs_skipped += self.block_cursor.freqs()[cur..new_cur].iter().sum::<u32>();
             position_computer.add_skip(sum_freqs_skipped as usize);
@@ -217,11 +209,7 @@ impl DocSet for SegmentPostings {
         // `doc` is now the first element >= `target`
         let doc = output.0[new_cur];
         debug_assert!(doc >= target);
-        if doc == target {
-            SkipResult::Reached
-        } else {
-            SkipResult::OverStep
-        }
+        doc
     }
 
     /// Return the current document's `DocId`.
@@ -231,18 +219,14 @@ impl DocSet for SegmentPostings {
     /// Will panics if called without having called advance before.
     #[inline]
     fn doc(&self) -> DocId {
-        let docs = self.block_cursor.docs();
-        debug_assert!(
-            self.cur < docs.len(),
-            "Have you forgotten to call `.advance()` at least once before calling `.doc()`                                      ."
-        );
-        docs[self.cur]
+        self.block_cursor.doc(self.cur)
     }
 
     fn size_hint(&self) -> u32 {
         self.len() as u32
     }
 
+    /*
     fn append_to_bitset(&mut self, bitset: &mut BitSet) {
         // finish the current block
         if self.advance() {
@@ -257,6 +241,7 @@ impl DocSet for SegmentPostings {
             }
         }
     }
+     */
 }
 
 impl HasLen for SegmentPostings {
@@ -324,15 +309,14 @@ fn split_into_skips_and_postings(
     doc_freq: u32,
     mut data: OwnedRead,
 ) -> (Option<OwnedRead>, OwnedRead) {
-    if doc_freq >= USE_SKIP_INFO_LIMIT {
-        let skip_len = VInt::deserialize(&mut data).expect("Data corrupted").0 as usize;
-        let mut postings_data = data.clone();
-        postings_data.advance(skip_len);
-        data.clip(skip_len);
-        (Some(data), postings_data)
-    } else {
-        (None, data)
+    if doc_freq < USE_SKIP_INFO_LIMIT {
+        return (None, data);
     }
+    let skip_len = VInt::deserialize(&mut data).expect("Data corrupted").0 as usize;
+    let mut postings_data = data.clone();
+    postings_data.advance(skip_len);
+    data.clip(skip_len);
+    (Some(data), postings_data)
 }
 
 #[derive(Debug, Eq, PartialEq)]
@@ -414,7 +398,7 @@ impl BlockSegmentPostings {
         self.doc_decoder.output_array()
     }
 
-    pub(crate) fn docs_aligned(&self) -> (&AlignedBuffer, usize) {
+    pub(crate) fn docs_aligned(&self) -> &AlignedBuffer {
         self.doc_decoder.output_aligned()
     }
 
@@ -495,35 +479,36 @@ impl BlockSegmentPostings {
             }
         }
 
-        // we are now on the last, incomplete, variable encoded block.
-        if self.num_vint_docs > 0 {
-            let num_compressed_bytes = self.doc_decoder.uncompress_vint_sorted(
-                self.remaining_data.as_ref(),
-                self.doc_offset,
-                self.num_vint_docs,
-            );
-            self.remaining_data.advance(num_compressed_bytes);
-            match self.freq_reading_option {
-                FreqReadingOption::NoFreq | FreqReadingOption::SkipFreq => {}
-                FreqReadingOption::ReadFreq => {
-                    self.freq_decoder
-                        .uncompress_vint_unsorted(self.remaining_data.as_ref(), self.num_vint_docs);
-                }
-            }
-            self.num_vint_docs = 0;
-            return self
-                .docs()
-                .last()
-                .map(|last_doc| {
-                    if *last_doc >= target_doc {
-                        BlockSegmentPostingsSkipResult::Success(skip_freqs)
-                    } else {
-                        BlockSegmentPostingsSkipResult::Terminated
-                    }
-                })
-                .unwrap_or(BlockSegmentPostingsSkipResult::Terminated);
+        self.doc_decoder.clear();
+
+        if self.num_vint_docs == 0 {
+            return BlockSegmentPostingsSkipResult::Terminated;
         }
-        BlockSegmentPostingsSkipResult::Terminated
+        // we are now on the last, incomplete, variable encoded block.
+        let num_compressed_bytes = self.doc_decoder.uncompress_vint_sorted(
+            self.remaining_data.as_ref(),
+            self.doc_offset,
+            self.num_vint_docs,
+        );
+        self.remaining_data.advance(num_compressed_bytes);
+        match self.freq_reading_option {
+            FreqReadingOption::NoFreq | FreqReadingOption::SkipFreq => {}
+            FreqReadingOption::ReadFreq => {
+                self.freq_decoder
+                    .uncompress_vint_unsorted(self.remaining_data.as_ref(), self.num_vint_docs);
+            }
+        }
+        self.num_vint_docs = 0;
+        self.docs()
+            .last()
+            .map(|last_doc| {
+                if *last_doc >= target_doc {
+                    BlockSegmentPostingsSkipResult::Success(skip_freqs)
+                } else {
+                    BlockSegmentPostingsSkipResult::Terminated
+                }
+            })
+            .unwrap_or(BlockSegmentPostingsSkipResult::Terminated)
     }
 
     /// Advance to the next block.
@@ -554,26 +539,27 @@ impl BlockSegmentPostings {
             }
             // it will be used as the next offset.
             self.doc_offset = self.doc_decoder.output(COMPRESSION_BLOCK_SIZE - 1);
-            true
-        } else if self.num_vint_docs > 0 {
-            let num_compressed_bytes = self.doc_decoder.uncompress_vint_sorted(
-                self.remaining_data.as_ref(),
-                self.doc_offset,
-                self.num_vint_docs,
-            );
-            self.remaining_data.advance(num_compressed_bytes);
-            match self.freq_reading_option {
-                FreqReadingOption::NoFreq | FreqReadingOption::SkipFreq => {}
-                FreqReadingOption::ReadFreq => {
-                    self.freq_decoder
-                        .uncompress_vint_unsorted(self.remaining_data.as_ref(), self.num_vint_docs);
-                }
-            }
-            self.num_vint_docs = 0;
-            true
-        } else {
-            false
+            return true;
         }
+        self.doc_decoder.clear();
+        if self.num_vint_docs == 0 {
+            return false;
+        }
+        let num_compressed_bytes = self.doc_decoder.uncompress_vint_sorted(
+            self.remaining_data.as_ref(),
+            self.doc_offset,
+            self.num_vint_docs,
+        );
+        self.remaining_data.advance(num_compressed_bytes);
+        match self.freq_reading_option {
+            FreqReadingOption::NoFreq | FreqReadingOption::SkipFreq => {}
+            FreqReadingOption::ReadFreq => {
+                self.freq_decoder
+                    .uncompress_vint_unsorted(self.remaining_data.as_ref(), self.num_vint_docs);
+            }
+        }
+        self.num_vint_docs = 0;
+        true
     }
 
     /// Returns an empty segment postings object
@@ -613,34 +599,34 @@ mod tests {
     use super::SegmentPostings;
     use crate::common::HasLen;
     use crate::core::Index;
-    use crate::docset::DocSet;
+    use crate::docset::{DocSet, TERMINATED};
     use crate::postings::postings::Postings;
     use crate::schema::IndexRecordOption;
     use crate::schema::Schema;
     use crate::schema::Term;
     use crate::schema::INDEXED;
     use crate::DocId;
-    use crate::SkipResult;
     use tantivy_fst::Streamer;
 
     #[test]
     fn test_empty_segment_postings() {
         let mut postings = SegmentPostings::empty();
-        assert!(!postings.advance());
-        assert!(!postings.advance());
+        assert_eq!(postings.advance(), TERMINATED);
+        assert_eq!(postings.advance(), TERMINATED);
         assert_eq!(postings.len(), 0);
     }
 
     #[test]
-    #[should_panic(expected = "Have you forgotten to call `.advance()`")]
-    fn test_panic_if_doc_called_before_advance() {
-        SegmentPostings::empty().doc();
+    fn test_empty_postings_doc_returns_terminated() {
+        let mut postings = SegmentPostings::empty();
+        assert_eq!(postings.doc(), TERMINATED);
+        assert_eq!(postings.advance(), TERMINATED);
     }
 
     #[test]
-    #[should_panic(expected = "Have you forgotten to call `.advance()`")]
-    fn test_panic_if_freq_called_before_advance() {
-        SegmentPostings::empty().term_freq();
+    fn test_empty_postings_doc_term_freq_returns_0() {
+        let postings = SegmentPostings::empty();
+        assert_eq!(postings.term_freq(), 1);
     }
 
     #[test]
@@ -674,25 +660,27 @@ mod tests {
         {
             let block_segments = build_block_postings(&doc_ids);
             let mut docset = SegmentPostings::from_block_postings(block_segments, None);
-            assert_eq!(docset.skip_next(128), SkipResult::OverStep);
+            assert_eq!(docset.seek(128), 129);
             assert_eq!(docset.doc(), 129);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 130);
             assert_eq!(docset.doc(), 130);
-            assert!(!docset.advance());
+            assert_eq!(docset.advance(), TERMINATED);
         }
         {
             let block_segments = build_block_postings(&doc_ids);
             let mut docset = SegmentPostings::from_block_postings(block_segments, None);
-            assert_eq!(docset.skip_next(129), SkipResult::Reached);
+            assert_eq!(docset.seek(129), 129);
             assert_eq!(docset.doc(), 129);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 130);
             assert_eq!(docset.doc(), 130);
-            assert!(!docset.advance());
+            assert_eq!(docset.advance(), TERMINATED);
         }
         {
             let block_segments = build_block_postings(&doc_ids);
             let mut docset = SegmentPostings::from_block_postings(block_segments, None);
-            assert_eq!(docset.skip_next(131), SkipResult::End);
+            assert_eq!(docset.doc(), 0);
+            assert_eq!(docset.seek(131), TERMINATED);
+            assert_eq!(docset.doc(), TERMINATED);
         }
     }
 

src/postings/stacker/term_hashmap.rs

@@ -1,6 +1,4 @@
-use murmurhash32;
-
-use self::murmurhash32::murmurhash2;
+use murmurhash32::murmurhash2;
 
 use super::{Addr, MemoryArena};
 use crate::postings::stacker::memory_arena::store;

src/query/all_query.rs

@@ -1,6 +1,6 @@
 use crate::core::Searcher;
 use crate::core::SegmentReader;
-use crate::docset::DocSet;
+use crate::docset::{DocSet, TERMINATED};
 use crate::query::boost_query::BoostScorer;
 use crate::query::explanation::does_not_match;
 use crate::query::{Explanation, Query, Scorer, Weight};
@@ -25,7 +25,6 @@ pub struct AllWeight;
 impl Weight for AllWeight {
     fn scorer(&self, reader: &SegmentReader, boost: f32) -> crate::Result<Box<dyn Scorer>> {
         let all_scorer = AllScorer {
-            state: State::NotStarted,
             doc: 0u32,
             max_doc: reader.max_doc(),
         };
@@ -40,39 +39,20 @@ impl Weight for AllWeight {
     }
 }
 
-enum State {
-    NotStarted,
-    Started,
-    Finished,
-}
-
 /// Scorer associated to the `AllQuery` query.
 pub struct AllScorer {
-    state: State,
     doc: DocId,
     max_doc: DocId,
 }
 
 impl DocSet for AllScorer {
-    fn advance(&mut self) -> bool {
-        match self.state {
-            State::NotStarted => {
-                self.state = State::Started;
-                self.doc = 0;
-            }
-            State::Started => {
-                self.doc += 1u32;
-            }
-            State::Finished => {
-                return false;
-            }
-        }
-        if self.doc < self.max_doc {
-            true
-        } else {
-            self.state = State::Finished;
-            false
+    fn advance(&mut self) -> DocId {
+        if self.doc + 1 >= self.max_doc {
+            self.doc = TERMINATED;
+            return TERMINATED;
         }
+        self.doc += 1;
+        self.doc
     }
 
     fn doc(&self) -> DocId {
@@ -93,6 +73,7 @@ impl Scorer for AllScorer {
 #[cfg(test)]
 mod tests {
     use super::AllQuery;
+    use crate::docset::TERMINATED;
     use crate::query::Query;
     use crate::schema::{Schema, TEXT};
     use crate::Index;
@@ -120,18 +101,16 @@ mod tests {
         {
             let reader = searcher.segment_reader(0);
             let mut scorer = weight.scorer(reader, 1.0f32).unwrap();
-            assert!(scorer.advance());
             assert_eq!(scorer.doc(), 0u32);
-            assert!(scorer.advance());
+            assert_eq!(scorer.advance(), 1u32);
             assert_eq!(scorer.doc(), 1u32);
-            assert!(!scorer.advance());
+            assert_eq!(scorer.advance(), TERMINATED);
         }
         {
             let reader = searcher.segment_reader(1);
             let mut scorer = weight.scorer(reader, 1.0f32).unwrap();
-            assert!(scorer.advance());
             assert_eq!(scorer.doc(), 0u32);
-            assert!(!scorer.advance());
+            assert_eq!(scorer.advance(), TERMINATED);
         }
     }
 
@@ -144,13 +123,11 @@ mod tests {
         let reader = searcher.segment_reader(0);
         {
             let mut scorer = weight.scorer(reader, 2.0f32).unwrap();
-            assert!(scorer.advance());
             assert_eq!(scorer.doc(), 0u32);
             assert_eq!(scorer.score(), 2.0f32);
         }
         {
             let mut scorer = weight.scorer(reader, 1.5f32).unwrap();
-            assert!(scorer.advance());
             assert_eq!(scorer.doc(), 0u32);
             assert_eq!(scorer.score(), 1.5f32);
         }

src/query/automaton_weight.rs

@@ -6,8 +6,8 @@ use crate::query::{Scorer, Weight};
 use crate::schema::{Field, IndexRecordOption};
 use crate::termdict::{TermDictionary, TermStreamer};
 use crate::DocId;
+use crate::Result;
 use crate::TantivyError;
-use crate::{Result, SkipResult};
 use std::sync::Arc;
 use tantivy_fst::Automaton;
 
@@ -64,7 +64,7 @@ where
 
     fn explain(&self, reader: &SegmentReader, doc: DocId) -> Result<Explanation> {
         let mut scorer = self.scorer(reader, 1.0f32)?;
-        if scorer.skip_next(doc) == SkipResult::Reached {
+        if scorer.seek(doc) == doc {
             Ok(Explanation::new("AutomatonScorer", 1.0f32))
         } else {
             Err(TantivyError::InvalidArgument(
@@ -77,6 +77,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::AutomatonWeight;
+    use crate::docset::TERMINATED;
     use crate::query::Weight;
     use crate::schema::{Schema, STRING};
     use crate::Index;
@@ -141,13 +142,12 @@ mod tests {
         let mut scorer = automaton_weight
             .scorer(searcher.segment_reader(0u32), 1.0f32)
             .unwrap();
-        assert!(scorer.advance());
         assert_eq!(scorer.doc(), 0u32);
         assert_eq!(scorer.score(), 1.0f32);
-        assert!(scorer.advance());
+        assert_eq!(scorer.advance(), 2u32);
         assert_eq!(scorer.doc(), 2u32);
         assert_eq!(scorer.score(), 1.0f32);
-        assert!(!scorer.advance());
+        assert_eq!(scorer.advance(), TERMINATED);
     }
 
     #[test]
@@ -160,7 +160,6 @@ mod tests {
         let mut scorer = automaton_weight
             .scorer(searcher.segment_reader(0u32), 1.32f32)
             .unwrap();
-        assert!(scorer.advance());
         assert_eq!(scorer.doc(), 0u32);
         assert_eq!(scorer.score(), 1.32f32);
     }

src/query/bitset/mod.rs

@@ -1,7 +1,6 @@
 use crate::common::{BitSet, TinySet};
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::{DocSet, TERMINATED};
 use crate::DocId;
-use std::cmp::Ordering;
 
 /// A `BitSetDocSet` makes it possible to iterate through a bitset as if it was a `DocSet`.
 ///
@@ -33,75 +32,50 @@ impl From<BitSet> for BitSetDocSet {
         } else {
             docs.tinyset(0)
         };
-        BitSetDocSet {
+        let mut docset = BitSetDocSet {
             docs,
             cursor_bucket: 0,
             cursor_tinybitset: first_tiny_bitset,
             doc: 0u32,
-        }
+        };
+        docset.advance();
+        docset
     }
 }
 
 impl DocSet for BitSetDocSet {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         if let Some(lower) = self.cursor_tinybitset.pop_lowest() {
             self.doc = (self.cursor_bucket as u32 * 64u32) | lower;
-            return true;
+            return self.doc;
         }
         if let Some(cursor_bucket) = self.docs.first_non_empty_bucket(self.cursor_bucket + 1) {
             self.go_to_bucket(cursor_bucket);
             let lower = self.cursor_tinybitset.pop_lowest().unwrap();
             self.doc = (cursor_bucket * 64u32) | lower;
-            true
+            self.doc
         } else {
-            false
+            self.doc = TERMINATED;
+            TERMINATED
         }
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        // skip is required to advance.
-        if !self.advance() {
-            return SkipResult::End;
-        }
+    fn seek(&mut self, target: DocId) -> DocId {
         let target_bucket = target / 64u32;
 
         // Mask for all of the bits greater or equal
         // to our target document.
-        match target_bucket.cmp(&self.cursor_bucket) {
-            Ordering::Greater => {
-                self.go_to_bucket(target_bucket);
-                let greater_filter: TinySet = TinySet::range_greater_or_equal(target);
-                self.cursor_tinybitset = self.cursor_tinybitset.intersect(greater_filter);
-                if !self.advance() {
-                    SkipResult::End
-                } else if self.doc() == target {
-                    SkipResult::Reached
-                } else {
-                    debug_assert!(self.doc() > target);
-                    SkipResult::OverStep
-                }
-            }
-            Ordering::Equal => loop {
-                match self.doc().cmp(&target) {
-                    Ordering::Less => {
-                        if !self.advance() {
-                            return SkipResult::End;
-                        }
-                    }
-                    Ordering::Equal => {
-                        return SkipResult::Reached;
-                    }
-                    Ordering::Greater => {
-                        debug_assert!(self.doc() > target);
-                        return SkipResult::OverStep;
-                    }
-                }
-            },
-            Ordering::Less => {
-                debug_assert!(self.doc() > target);
-                SkipResult::OverStep
-            }
+        if target_bucket > self.cursor_bucket {
+            self.go_to_bucket(target_bucket);
+            let greater_filter: TinySet = TinySet::range_greater_or_equal(target);
+            self.cursor_tinybitset = self.cursor_tinybitset.intersect(greater_filter);
+            self.advance();
         }
+        let mut doc = self.doc();
+        while doc < target {
+            doc = self.advance();
+        }
+        doc
     }
 
     /// Returns the current document
@@ -122,7 +96,7 @@ impl DocSet for BitSetDocSet {
 mod tests {
     use super::BitSetDocSet;
     use crate::common::BitSet;
-    use crate::docset::{DocSet, SkipResult};
+    use crate::docset::{DocSet, TERMINATED};
     use crate::DocId;
 
     fn create_docbitset(docs: &[DocId], max_doc: DocId) -> BitSetDocSet {
@@ -133,19 +107,24 @@ mod tests {
         BitSetDocSet::from(docset)
     }
 
+    #[test]
+    fn test_empty() {
+        let bitset = BitSet::with_max_value(1000);
+        let mut empty = BitSetDocSet::from(bitset);
+        assert_eq!(empty.advance(), TERMINATED)
+    }
+
     fn test_go_through_sequential(docs: &[DocId]) {
         let mut docset = create_docbitset(docs, 1_000u32);
         for &doc in docs {
-            assert!(docset.advance());
             assert_eq!(doc, docset.doc());
+            docset.advance();
         }
-        assert!(!docset.advance());
-        assert!(!docset.advance());
+        assert_eq!(docset.advance(), TERMINATED);
     }
 
     #[test]
     fn test_docbitset_sequential() {
-        test_go_through_sequential(&[]);
         test_go_through_sequential(&[1, 2, 3]);
         test_go_through_sequential(&[1, 2, 3, 4, 5, 63, 64, 65]);
         test_go_through_sequential(&[63, 64, 65]);
@@ -156,64 +135,64 @@ mod tests {
     fn test_docbitset_skip() {
         {
             let mut docset = create_docbitset(&[1, 5, 6, 7, 5112], 10_000);
-            assert_eq!(docset.skip_next(7), SkipResult::Reached);
+            assert_eq!(docset.seek(7), 7);
             assert_eq!(docset.doc(), 7);
-            assert!(docset.advance(), 7);
+            assert_eq!(docset.advance(), 5112);
             assert_eq!(docset.doc(), 5112);
-            assert!(!docset.advance());
+            assert_eq!(docset.advance(), TERMINATED);
         }
         {
             let mut docset = create_docbitset(&[1, 5, 6, 7, 5112], 10_000);
-            assert_eq!(docset.skip_next(3), SkipResult::OverStep);
+            assert_eq!(docset.seek(3), 5);
             assert_eq!(docset.doc(), 5);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 6);
         }
         {
             let mut docset = create_docbitset(&[5112], 10_000);
-            assert_eq!(docset.skip_next(5112), SkipResult::Reached);
+            assert_eq!(docset.seek(5112), 5112);
             assert_eq!(docset.doc(), 5112);
-            assert!(!docset.advance());
+            assert_eq!(docset.advance(), TERMINATED);
         }
         {
             let mut docset = create_docbitset(&[5112], 10_000);
-            assert_eq!(docset.skip_next(5113), SkipResult::End);
-            assert!(!docset.advance());
+            assert_eq!(docset.seek(5113), TERMINATED);
+            assert_eq!(docset.advance(), TERMINATED);
         }
         {
             let mut docset = create_docbitset(&[5112], 10_000);
-            assert_eq!(docset.skip_next(5111), SkipResult::OverStep);
+            assert_eq!(docset.seek(5111), 5112);
             assert_eq!(docset.doc(), 5112);
-            assert!(!docset.advance());
+            assert_eq!(docset.advance(), TERMINATED);
         }
         {
             let mut docset = create_docbitset(&[1, 5, 6, 7, 5112, 5500, 6666], 10_000);
-            assert_eq!(docset.skip_next(5112), SkipResult::Reached);
+            assert_eq!(docset.seek(5112), 5112);
             assert_eq!(docset.doc(), 5112);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 5500);
             assert_eq!(docset.doc(), 5500);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 6666);
             assert_eq!(docset.doc(), 6666);
-            assert!(!docset.advance());
+            assert_eq!(docset.advance(), TERMINATED);
         }
         {
             let mut docset = create_docbitset(&[1, 5, 6, 7, 5112, 5500, 6666], 10_000);
-            assert_eq!(docset.skip_next(5111), SkipResult::OverStep);
+            assert_eq!(docset.seek(5111), 5112);
             assert_eq!(docset.doc(), 5112);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 5500);
             assert_eq!(docset.doc(), 5500);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 6666);
             assert_eq!(docset.doc(), 6666);
-            assert!(!docset.advance());
+            assert_eq!(docset.advance(), TERMINATED);
         }
         {
             let mut docset = create_docbitset(&[1, 5, 6, 7, 5112, 5513, 6666], 10_000);
-            assert_eq!(docset.skip_next(5111), SkipResult::OverStep);
+            assert_eq!(docset.seek(5111), 5112);
             assert_eq!(docset.doc(), 5112);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 5513);
             assert_eq!(docset.doc(), 5513);
-            assert!(docset.advance());
+            assert_eq!(docset.advance(), 6666);
             assert_eq!(docset.doc(), 6666);
-            assert!(!docset.advance());
+            assert_eq!(docset.advance(), TERMINATED);
         }
     }
 }
@@ -223,6 +202,7 @@ mod bench {
 
     use super::BitSet;
     use super::BitSetDocSet;
+    use crate::docset::TERMINATED;
     use crate::test;
     use crate::tests;
     use crate::DocSet;
@@ -257,7 +237,7 @@ mod bench {
         }
         b.iter(|| {
             let mut docset = BitSetDocSet::from(bitset.clone());
-            while docset.advance() {}
+            while docset.advance() != TERMINATED {}
         });
     }
 }

src/query/boolean_query/boolean_weight.rs

@@ -10,7 +10,7 @@ use crate::query::Scorer;
 use crate::query::Union;
 use crate::query::Weight;
 use crate::query::{intersect_scorers, Explanation};
-use crate::{DocId, SkipResult};
+use crate::DocId;
 use std::collections::HashMap;
 
 fn scorer_union<TScoreCombiner>(scorers: Vec<Box<dyn Scorer>>) -> Box<dyn Scorer>
@@ -133,7 +133,7 @@ impl Weight for BooleanWeight {
 
     fn explain(&self, reader: &SegmentReader, doc: DocId) -> crate::Result<Explanation> {
         let mut scorer = self.scorer(reader, 1.0f32)?;
-        if scorer.skip_next(doc) != SkipResult::Reached {
+        if scorer.seek(doc) != doc {
             return Err(does_not_match(doc));
         }
         if !self.scoring_enabled {

src/query/boolean_query/mod.rs

@@ -207,7 +207,6 @@ mod tests {
             let mut boolean_scorer = boolean_weight
                 .scorer(searcher.segment_reader(0u32), 1.0f32)
                 .unwrap();
-            assert!(boolean_scorer.advance());
             assert_eq!(boolean_scorer.doc(), 0u32);
             assert_nearly_equals(boolean_scorer.score(), 0.84163445f32);
         }
@@ -215,7 +214,6 @@ mod tests {
             let mut boolean_scorer = boolean_weight
                 .scorer(searcher.segment_reader(0u32), 2.0f32)
                 .unwrap();
-            assert!(boolean_scorer.advance());
             assert_eq!(boolean_scorer.doc(), 0u32);
             assert_nearly_equals(boolean_scorer.score(), 1.6832689f32);
         }

src/query/boost_query.rs

@@ -1,8 +1,7 @@
-use crate::common::BitSet;
 use crate::fastfield::DeleteBitSet;
 use crate::query::explanation::does_not_match;
 use crate::query::{Explanation, Query, Scorer, Weight};
-use crate::{DocId, DocSet, Searcher, SegmentReader, SkipResult, Term};
+use crate::{DocId, DocSet, Searcher, SegmentReader, Term};
 use std::collections::BTreeSet;
 use std::fmt;
 
@@ -72,7 +71,7 @@ impl Weight for BoostWeight {
 
     fn explain(&self, reader: &SegmentReader, doc: u32) -> crate::Result<Explanation> {
         let mut scorer = self.scorer(reader, 1.0f32)?;
-        if scorer.skip_next(doc) != SkipResult::Reached {
+        if scorer.seek(doc) != doc {
             return Err(does_not_match(doc));
         }
         let mut explanation =
@@ -99,12 +98,12 @@ impl<S: Scorer> BoostScorer<S> {
 }
 
 impl<S: Scorer> DocSet for BoostScorer<S> {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         self.underlying.advance()
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        self.underlying.skip_next(target)
+    fn seek(&mut self, target: DocId) -> DocId {
+        self.underlying.seek(target)
     }
 
     fn fill_buffer(&mut self, buffer: &mut [DocId]) -> usize {
@@ -119,10 +118,6 @@ impl<S: Scorer> DocSet for BoostScorer<S> {
         self.underlying.size_hint()
     }
 
-    fn append_to_bitset(&mut self, bitset: &mut BitSet) {
-        self.underlying.append_to_bitset(bitset)
-    }
-
     fn count(&mut self, delete_bitset: &DeleteBitSet) -> u32 {
         self.underlying.count(delete_bitset)
     }

src/query/empty_query.rs

@@ -1,4 +1,5 @@
 use super::Scorer;
+use crate::docset::TERMINATED;
 use crate::query::explanation::does_not_match;
 use crate::query::Weight;
 use crate::query::{Explanation, Query};
@@ -48,15 +49,12 @@ impl Weight for EmptyWeight {
 pub struct EmptyScorer;
 
 impl DocSet for EmptyScorer {
-    fn advance(&mut self) -> bool {
-        false
+    fn advance(&mut self) -> DocId {
+        TERMINATED
     }
 
     fn doc(&self) -> DocId {
-        panic!(
-            "You may not call .doc() on a scorer \
-             where the last call to advance() did not return true."
-        );
+        TERMINATED
     }
 
     fn size_hint(&self) -> u32 {
@@ -72,18 +70,15 @@ impl Scorer for EmptyScorer {
 
 #[cfg(test)]
 mod tests {
+    use crate::docset::TERMINATED;
     use crate::query::EmptyScorer;
     use crate::DocSet;
 
     #[test]
     fn test_empty_scorer() {
         let mut empty_scorer = EmptyScorer;
-        assert!(!empty_scorer.advance());
-    }
-
-    #[test]
-    #[should_panic]
-    fn test_empty_scorer_panic_on_doc_call() {
-        EmptyScorer.doc();
+        assert_eq!(empty_scorer.doc(), TERMINATED);
+        assert_eq!(empty_scorer.advance(), TERMINATED);
+        assert_eq!(empty_scorer.doc(), TERMINATED);
     }
 }

src/query/exclude.rs

@@ -1,41 +1,37 @@
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::{DocSet, TERMINATED};
 use crate::query::Scorer;
 use crate::DocId;
 use crate::Score;
 
-#[derive(Clone, Copy, Debug)]
-enum State {
-    ExcludeOne(DocId),
-    Finished,
-}
-
 /// Filters a given `DocSet` by removing the docs from a given `DocSet`.
 ///
 /// The excluding docset has no impact on scoring.
 pub struct Exclude<TDocSet, TDocSetExclude> {
     underlying_docset: TDocSet,
     excluding_docset: TDocSetExclude,
-    excluding_state: State,
 }
 
 impl<TDocSet, TDocSetExclude> Exclude<TDocSet, TDocSetExclude>
 where
+    TDocSet: DocSet,
     TDocSetExclude: DocSet,
 {
     /// Creates a new `ExcludeScorer`
     pub fn new(
-        underlying_docset: TDocSet,
+        mut underlying_docset: TDocSet,
         mut excluding_docset: TDocSetExclude,
     ) -> Exclude<TDocSet, TDocSetExclude> {
-        let state = if excluding_docset.advance() {
-            State::ExcludeOne(excluding_docset.doc())
-        } else {
-            State::Finished
-        };
+        while underlying_docset.doc() != TERMINATED {
+            let target = underlying_docset.doc();
+            if excluding_docset.seek(target) != target {
+                // this document is not excluded.
+                break;
+            }
+            underlying_docset.advance();
+        }
         Exclude {
             underlying_docset,
             excluding_docset,
-            excluding_state: state,
         }
     }
 }
@@ -51,28 +47,7 @@ where
     /// increasing `doc`.
     fn accept(&mut self) -> bool {
         let doc = self.underlying_docset.doc();
-        match self.excluding_state {
-            State::ExcludeOne(excluded_doc) => {
-                if doc == excluded_doc {
-                    return false;
-                }
-                if excluded_doc > doc {
-                    return true;
-                }
-                match self.excluding_docset.skip_next(doc) {
-                    SkipResult::OverStep => {
-                        self.excluding_state = State::ExcludeOne(self.excluding_docset.doc());
-                        true
-                    }
-                    SkipResult::End => {
-                        self.excluding_state = State::Finished;
-                        true
-                    }
-                    SkipResult::Reached => false,
-                }
-            }
-            State::Finished => true,
-        }
+        self.excluding_docset.seek(doc) != doc
     }
 }
 
@@ -81,27 +56,24 @@ where
     TDocSet: DocSet,
     TDocSetExclude: DocSet,
 {
-    fn advance(&mut self) -> bool {
-        while self.underlying_docset.advance() {
+    fn advance(&mut self) -> DocId {
+        while self.underlying_docset.advance() != TERMINATED {
             if self.accept() {
-                return true;
+                return self.doc();
             }
         }
-        false
+        TERMINATED
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        let underlying_skip_result = self.underlying_docset.skip_next(target);
-        if underlying_skip_result == SkipResult::End {
-            return SkipResult::End;
+    fn seek(&mut self, target: DocId) -> DocId {
+        let underlying_seek_result = self.underlying_docset.seek(target);
+        if underlying_seek_result == TERMINATED {
+            return TERMINATED;
         }
         if self.accept() {
-            underlying_skip_result
-        } else if self.advance() {
-            SkipResult::OverStep
-        } else {
-            SkipResult::End
+            return underlying_seek_result;
         }
+        self.advance()
     }
 
     fn doc(&self) -> DocId {
@@ -141,8 +113,9 @@ mod tests {
             VecDocSet::from(vec![1, 2, 3, 10, 16, 24]),
         );
         let mut els = vec![];
-        while exclude_scorer.advance() {
+        while exclude_scorer.doc() != TERMINATED {
             els.push(exclude_scorer.doc());
+            exclude_scorer.advance();
         }
         assert_eq!(els, vec![5, 8, 15]);
     }

src/query/fuzzy_query.rs

@@ -117,7 +117,7 @@ impl FuzzyTermQuery {
         }
     }
 
-    /// Creates a new Fuzzy Query that treats transpositions as cost one rather than two
+    /// Creates a new Fuzzy Query of the Term prefix
     pub fn new_prefix(term: Term, distance: u8, transposition_cost_one: bool) -> FuzzyTermQuery {
         FuzzyTermQuery {
             term,
@@ -188,6 +188,8 @@ mod test {
         }
         let reader = index.reader().unwrap();
         let searcher = reader.searcher();
+
+        // passes because Levenshtein distance is 1 (substitute 'o' with 'a')
         {
             let term = Term::from_field_text(country_field, "japon");
 
@@ -200,6 +202,18 @@ mod test {
             assert_nearly_equals(1f32, score);
         }
 
+        // fails because non-prefix Levenshtein distance is more than 1 (add 'a' and 'n')
+        {
+            let term = Term::from_field_text(country_field, "jap");
+
+            let fuzzy_query = FuzzyTermQuery::new(term, 1, true);
+            let top_docs = searcher
+                .search(&fuzzy_query, &TopDocs::with_limit(2))
+                .unwrap();
+            assert_eq!(top_docs.len(), 0, "Expected no document");
+        }
+
+        // passes because prefix Levenshtein distance is 0
         {
             let term = Term::from_field_text(country_field, "jap");
 

src/query/intersection.rs

@@ -1,4 +1,4 @@
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::{DocSet, TERMINATED};
 use crate::query::term_query::TermScorer;
 use crate::query::EmptyScorer;
 use crate::query::Scorer;
@@ -20,12 +20,14 @@ pub fn intersect_scorers(mut scorers: Vec<Box<dyn Scorer>>) -> Box<dyn Scorer> {
     if scorers.len() == 1 {
         return scorers.pop().unwrap();
     }
+    scorers.sort_by_key(|scorer| scorer.size_hint());
+    let doc = go_to_first_doc(&mut scorers[..]);
+    if doc == TERMINATED {
+        return Box::new(EmptyScorer);
+    }
     // We know that we have at least 2 elements.
-    let num_docsets = scorers.len();
-    scorers.sort_by(|left, right| right.size_hint().cmp(&left.size_hint()));
-    let left = scorers.pop().unwrap();
-    let right = scorers.pop().unwrap();
-    scorers.reverse();
+    let left = scorers.remove(0);
+    let right = scorers.remove(0);
     let all_term_scorers = [&left, &right]
         .iter()
         .all(|&scorer| scorer.is::<TermScorer>());
@@ -34,14 +36,12 @@ pub fn intersect_scorers(mut scorers: Vec<Box<dyn Scorer>>) -> Box<dyn Scorer> {
             left: *(left.downcast::<TermScorer>().map_err(|_| ()).unwrap()),
             right: *(right.downcast::<TermScorer>().map_err(|_| ()).unwrap()),
             others: scorers,
-            num_docsets,
         });
     }
     Box::new(Intersection {
         left,
         right,
         others: scorers,
-        num_docsets,
     })
 }
 
@@ -50,22 +50,34 @@ pub struct Intersection<TDocSet: DocSet, TOtherDocSet: DocSet = Box<dyn Scorer>>
     left: TDocSet,
     right: TDocSet,
     others: Vec<TOtherDocSet>,
-    num_docsets: usize,
+}
+
+fn go_to_first_doc<TDocSet: DocSet>(docsets: &mut [TDocSet]) -> DocId {
+    let mut candidate = 0;
+    'outer: loop {
+        for docset in docsets.iter_mut() {
+            let seek_doc = docset.seek(candidate);
+            if seek_doc > candidate {
+                candidate = docset.doc();
+                continue 'outer;
+            }
+        }
+        return candidate;
+    }
 }
 
 impl<TDocSet: DocSet> Intersection<TDocSet, TDocSet> {
     pub(crate) fn new(mut docsets: Vec<TDocSet>) -> Intersection<TDocSet, TDocSet> {
         let num_docsets = docsets.len();
         assert!(num_docsets >= 2);
-        docsets.sort_by(|left, right| right.size_hint().cmp(&left.size_hint()));
-        let left = docsets.pop().unwrap();
-        let right = docsets.pop().unwrap();
-        docsets.reverse();
+        docsets.sort_by_key(|docset| docset.size_hint());
+        go_to_first_doc(&mut docsets);
+        let left = docsets.remove(0);
+        let right = docsets.remove(0);
         Intersection {
             left,
             right,
             others: docsets,
-            num_docsets,
         }
     }
 }
@@ -80,128 +92,49 @@ impl<TDocSet: DocSet> Intersection<TDocSet, TDocSet> {
     }
 }
 
-impl<TDocSet: DocSet, TOtherDocSet: DocSet> Intersection<TDocSet, TOtherDocSet> {
-    pub(crate) fn docset_mut(&mut self, ord: usize) -> &mut dyn DocSet {
-        match ord {
-            0 => &mut self.left,
-            1 => &mut self.right,
-            n => &mut self.others[n - 2],
-        }
-    }
-}
-
 impl<TDocSet: DocSet, TOtherDocSet: DocSet> DocSet for Intersection<TDocSet, TOtherDocSet> {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         let (left, right) = (&mut self.left, &mut self.right);
-
-        if !left.advance() {
-            return false;
-        }
-
-        let mut candidate = left.doc();
-        let mut other_candidate_ord: usize = usize::max_value();
+        let mut candidate = left.advance();
 
         'outer: loop {
             // In the first part we look for a document in the intersection
             // of the two rarest `DocSet` in the intersection.
+
             loop {
-                match right.skip_next(candidate) {
-                    SkipResult::Reached => {
-                        break;
-                    }
-                    SkipResult::OverStep => {
-                        candidate = right.doc();
-                        other_candidate_ord = usize::max_value();
-                    }
-                    SkipResult::End => {
-                        return false;
-                    }
-                }
-                match left.skip_next(candidate) {
-                    SkipResult::Reached => {
-                        break;
-                    }
-                    SkipResult::OverStep => {
-                        candidate = left.doc();
-                        other_candidate_ord = usize::max_value();
-                    }
-                    SkipResult::End => {
-                        return false;
-                    }
+                let right_doc = right.seek(candidate);
+                candidate = left.seek(right_doc);
+                if candidate == right_doc {
+                    break;
                 }
             }
+
+            debug_assert_eq!(left.doc(), right.doc());
             // test the remaining scorers;
-            for (ord, docset) in self.others.iter_mut().enumerate() {
-                if ord == other_candidate_ord {
-                    continue;
-                }
+            for docset in self.others.iter_mut() {
                 // `candidate_ord` is already at the
                 // right position.
                 //
                 // Calling `skip_next` would advance this docset
                 // and miss it.
-                match docset.skip_next(candidate) {
-                    SkipResult::Reached => {}
-                    SkipResult::OverStep => {
-                        // this is not in the intersection,
-                        // let's update our candidate.
-                        candidate = docset.doc();
-                        match left.skip_next(candidate) {
-                            SkipResult::Reached => {
-                                other_candidate_ord = ord;
-                            }
-                            SkipResult::OverStep => {
-                                candidate = left.doc();
-                                other_candidate_ord = usize::max_value();
-                            }
-                            SkipResult::End => {
-                                return false;
-                            }
-                        }
-                        continue 'outer;
-                    }
-                    SkipResult::End => {
-                        return false;
-                    }
+                let seek_doc = docset.seek(candidate);
+                if seek_doc > candidate {
+                    candidate = left.seek(seek_doc);
+                    continue 'outer;
                 }
             }
-            return true;
+
+            return candidate;
         }
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        // We optimize skipping by skipping every single member
-        // of the intersection to target.
-        let mut current_target: DocId = target;
-        let mut current_ord = self.num_docsets;
-
-        'outer: loop {
-            for ord in 0..self.num_docsets {
-                let docset = self.docset_mut(ord);
-                if ord == current_ord {
-                    continue;
-                }
-                match docset.skip_next(current_target) {
-                    SkipResult::End => {
-                        return SkipResult::End;
-                    }
-                    SkipResult::OverStep => {
-                        // update the target
-                        // for the remaining members of the intersection.
-                        current_target = docset.doc();
-                        current_ord = ord;
-                        continue 'outer;
-                    }
-                    SkipResult::Reached => {}
-                }
-            }
-            if target == current_target {
-                return SkipResult::Reached;
-            } else {
-                assert!(current_target > target);
-                return SkipResult::OverStep;
-            }
+    fn seek(&mut self, target: DocId) -> DocId {
+        self.left.seek(target);
+        let mut docsets: Vec<&mut dyn DocSet> = vec![&mut self.left, &mut self.right];
+        for docset in &mut self.others {
+            docsets.push(docset);
         }
+        go_to_first_doc(&mut docsets[..])
     }
 
     fn doc(&self) -> DocId {
@@ -228,7 +161,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::Intersection;
-    use crate::docset::{DocSet, SkipResult};
+    use crate::docset::{DocSet, TERMINATED};
     use crate::postings::tests::test_skip_against_unoptimized;
     use crate::query::VecDocSet;
 
@@ -238,20 +171,18 @@ mod tests {
             let left = VecDocSet::from(vec![1, 3, 9]);
             let right = VecDocSet::from(vec![3, 4, 9, 18]);
             let mut intersection = Intersection::new(vec![left, right]);
-            assert!(intersection.advance());
             assert_eq!(intersection.doc(), 3);
-            assert!(intersection.advance());
+            assert_eq!(intersection.advance(), 9);
             assert_eq!(intersection.doc(), 9);
-            assert!(!intersection.advance());
+            assert_eq!(intersection.advance(), TERMINATED);
         }
         {
             let a = VecDocSet::from(vec![1, 3, 9]);
             let b = VecDocSet::from(vec![3, 4, 9, 18]);
             let c = VecDocSet::from(vec![1, 5, 9, 111]);
             let mut intersection = Intersection::new(vec![a, b, c]);
-            assert!(intersection.advance());
             assert_eq!(intersection.doc(), 9);
-            assert!(!intersection.advance());
+            assert_eq!(intersection.advance(), TERMINATED);
         }
     }
 
@@ -260,8 +191,8 @@ mod tests {
         let left = VecDocSet::from(vec![0]);
         let right = VecDocSet::from(vec![0]);
         let mut intersection = Intersection::new(vec![left, right]);
-        assert!(intersection.advance());
         assert_eq!(intersection.doc(), 0);
+        assert_eq!(intersection.advance(), TERMINATED);
     }
 
     #[test]
@@ -269,7 +200,7 @@ mod tests {
         let left = VecDocSet::from(vec![0, 1, 2, 4]);
         let right = VecDocSet::from(vec![2, 5]);
         let mut intersection = Intersection::new(vec![left, right]);
-        assert_eq!(intersection.skip_next(2), SkipResult::Reached);
+        assert_eq!(intersection.seek(2), 2);
         assert_eq!(intersection.doc(), 2);
     }
 
@@ -312,7 +243,7 @@ mod tests {
         let a = VecDocSet::from(vec![1, 3]);
         let b = VecDocSet::from(vec![1, 4]);
         let c = VecDocSet::from(vec![3, 9]);
-        let mut intersection = Intersection::new(vec![a, b, c]);
-        assert!(!intersection.advance());
+        let intersection = Intersection::new(vec![a, b, c]);
+        assert_eq!(intersection.doc(), TERMINATED);
     }
 }

src/query/mod.rs

@@ -1,6 +1,4 @@
-/*!
-Query
-*/
+/*! Query Module */
 
 mod all_query;
 mod automaton_weight;
@@ -24,7 +22,6 @@ mod term_query;
 mod union;
 mod weight;
 
-
 #[cfg(test)]
 mod vec_docset;
 
@@ -43,8 +40,9 @@ pub use self::boost_query::BoostQuery;
 pub use self::empty_query::{EmptyQuery, EmptyScorer, EmptyWeight};
 pub use self::exclude::Exclude;
 pub use self::explanation::Explanation;
-pub use self::fuzzy_query::FuzzyTermQuery;
+#[cfg(test)]
 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;

src/query/phrase_query/mod.rs

@@ -60,8 +60,8 @@ pub mod tests {
                 .map(|docaddr| docaddr.1)
                 .collect::<Vec<_>>()
         };
-        assert_eq!(test_query(vec!["a", "b", "c"]), vec![2, 4]);
         assert_eq!(test_query(vec!["a", "b"]), vec![1, 2, 3, 4]);
+        assert_eq!(test_query(vec!["a", "b", "c"]), vec![2, 4]);
         assert_eq!(test_query(vec!["b", "b"]), vec![0, 1]);
         assert!(test_query(vec!["g", "ewrwer"]).is_empty());
         assert!(test_query(vec!["g", "a"]).is_empty());

src/query/phrase_query/phrase_scorer.rs

@@ -1,4 +1,4 @@
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::{DocSet, TERMINATED};
 use crate::fieldnorm::FieldNormReader;
 use crate::postings::Postings;
 use crate::query::bm25::BM25Weight;
@@ -25,12 +25,12 @@ impl<TPostings: Postings> PostingsWithOffset<TPostings> {
 }
 
 impl<TPostings: Postings> DocSet for PostingsWithOffset<TPostings> {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         self.postings.advance()
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        self.postings.skip_next(target)
+    fn seek(&mut self, target: DocId) -> DocId {
+        self.postings.seek(target)
     }
 
     fn doc(&self) -> DocId {
@@ -149,7 +149,7 @@ impl<TPostings: Postings> PhraseScorer<TPostings> {
                 PostingsWithOffset::new(postings, (max_offset - offset) as u32)
             })
             .collect::<Vec<_>>();
-        PhraseScorer {
+        let mut scorer = PhraseScorer {
             intersection_docset: Intersection::new(postings_with_offsets),
             num_terms: num_docsets,
             left: Vec::with_capacity(100),
@@ -158,7 +158,11 @@ impl<TPostings: Postings> PhraseScorer<TPostings> {
             similarity_weight,
             fieldnorm_reader,
             score_needed,
+        };
+        if scorer.doc() != TERMINATED && !scorer.phrase_match() {
+            scorer.advance();
         }
+        scorer
     }
 
     pub fn phrase_count(&self) -> u32 {
@@ -225,31 +229,21 @@ impl<TPostings: Postings> PhraseScorer<TPostings> {
 }
 
 impl<TPostings: Postings> DocSet for PhraseScorer<TPostings> {
-    fn advance(&mut self) -> bool {
-        while self.intersection_docset.advance() {
-            if self.phrase_match() {
-                return true;
+    fn advance(&mut self) -> DocId {
+        loop {
+            let doc = self.intersection_docset.advance();
+            if doc == TERMINATED || self.phrase_match() {
+                return doc;
             }
         }
-        false
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        if self.intersection_docset.skip_next(target) == SkipResult::End {
-            return SkipResult::End;
-        }
-        if self.phrase_match() {
-            if self.doc() == target {
-                return SkipResult::Reached;
-            } else {
-                return SkipResult::OverStep;
-            }
-        }
-        if self.advance() {
-            SkipResult::OverStep
-        } else {
-            SkipResult::End
+    fn seek(&mut self, target: DocId) -> DocId {
+        let doc = self.intersection_docset.seek(target);
+        if doc == TERMINATED || self.phrase_match() {
+            return doc;
         }
+        self.advance()
     }
 
     fn doc(&self) -> DocId {

src/query/phrase_query/phrase_weight.rs

@@ -9,8 +9,8 @@ use crate::query::Weight;
 use crate::query::{EmptyScorer, Explanation};
 use crate::schema::IndexRecordOption;
 use crate::schema::Term;
+use crate::Result;
 use crate::{DocId, DocSet};
-use crate::{Result, SkipResult};
 
 pub struct PhraseWeight {
     phrase_terms: Vec<(usize, Term)>,
@@ -99,7 +99,7 @@ impl Weight for PhraseWeight {
             return Err(does_not_match(doc));
         }
         let mut scorer = scorer_opt.unwrap();
-        if scorer.skip_next(doc) != SkipResult::Reached {
+        if scorer.seek(doc) != doc {
             return Err(does_not_match(doc));
         }
         let fieldnorm_reader = self.fieldnorm_reader(reader);
@@ -114,6 +114,7 @@ impl Weight for PhraseWeight {
 #[cfg(test)]
 mod tests {
     use super::super::tests::create_index;
+    use crate::docset::TERMINATED;
     use crate::query::PhraseQuery;
     use crate::{DocSet, Term};
 
@@ -132,12 +133,11 @@ mod tests {
             .phrase_scorer(searcher.segment_reader(0u32), 1.0f32)
             .unwrap()
             .unwrap();
-        assert!(phrase_scorer.advance());
         assert_eq!(phrase_scorer.doc(), 1);
         assert_eq!(phrase_scorer.phrase_count(), 2);
-        assert!(phrase_scorer.advance());
+        assert_eq!(phrase_scorer.advance(), 2);
         assert_eq!(phrase_scorer.doc(), 2);
         assert_eq!(phrase_scorer.phrase_count(), 1);
-        assert!(!phrase_scorer.advance());
+        assert_eq!(phrase_scorer.advance(), TERMINATED);
     }
 }

src/query/query_parser/query_parser.rs

@@ -113,8 +113,9 @@ fn trim_ast(logical_ast: LogicalAST) -> Option<LogicalAST> {
 /// The language covered by the current parser is extremely simple.
 ///
 /// * simple terms: "e.g.: `Barack Obama` are simply tokenized using
-///   tantivy's `StandardTokenizer`, hence becoming `["barack", "obama"]`.
-///   The terms are then searched within the default terms of the query parser.
+///   tantivy's [`SimpleTokenizer`](tantivy::tokenizer::SimpleTokenizer), hence
+///   becoming `["barack", "obama"]`. The terms are then searched within
+///   the default terms of the query parser.
 ///
 ///   e.g. If `body` and `title` are default fields, our example terms are
 ///   `["title:barack", "body:barack", "title:obama", "body:obama"]`.

src/query/range_query.rs

@@ -10,7 +10,7 @@ use crate::schema::Type;
 use crate::schema::{Field, IndexRecordOption, Term};
 use crate::termdict::{TermDictionary, TermStreamer};
 use crate::DocId;
-use crate::{Result, SkipResult};
+use crate::Result;
 use std::collections::Bound;
 use std::ops::Range;
 
@@ -312,7 +312,7 @@ impl Weight for RangeWeight {
 
     fn explain(&self, reader: &SegmentReader, doc: DocId) -> Result<Explanation> {
         let mut scorer = self.scorer(reader, 1.0f32)?;
-        if scorer.skip_next(doc) != SkipResult::Reached {
+        if scorer.seek(doc) != doc {
             return Err(does_not_match(doc));
         }
         Ok(Explanation::new("RangeQuery", 1.0f32))

src/query/reqopt_scorer.rs

@@ -1,9 +1,8 @@
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::DocSet;
 use crate::query::score_combiner::ScoreCombiner;
 use crate::query::Scorer;
 use crate::DocId;
 use crate::Score;
-use std::cmp::Ordering;
 use std::marker::PhantomData;
 
 /// Given a required scorer and an optional scorer
@@ -17,7 +16,6 @@ pub struct RequiredOptionalScorer<TReqScorer, TOptScorer, TScoreCombiner> {
     req_scorer: TReqScorer,
     opt_scorer: TOptScorer,
     score_cache: Option<Score>,
-    opt_finished: bool,
     _phantom: PhantomData<TScoreCombiner>,
 }
 
@@ -29,14 +27,12 @@ where
     /// Creates a new `RequiredOptionalScorer`.
     pub fn new(
         req_scorer: TReqScorer,
-        mut opt_scorer: TOptScorer,
+        opt_scorer: TOptScorer,
     ) -> RequiredOptionalScorer<TReqScorer, TOptScorer, TScoreCombiner> {
-        let opt_finished = !opt_scorer.advance();
         RequiredOptionalScorer {
             req_scorer,
             opt_scorer,
             score_cache: None,
-            opt_finished,
             _phantom: PhantomData,
         }
     }
@@ -48,7 +44,7 @@ where
     TReqScorer: DocSet,
     TOptScorer: DocSet,
 {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         self.score_cache = None;
         self.req_scorer.advance()
     }
@@ -76,22 +72,8 @@ where
         let doc = self.doc();
         let mut score_combiner = TScoreCombiner::default();
         score_combiner.update(&mut self.req_scorer);
-        if !self.opt_finished {
-            match self.opt_scorer.doc().cmp(&doc) {
-                Ordering::Greater => {}
-                Ordering::Equal => {
-                    score_combiner.update(&mut self.opt_scorer);
-                }
-                Ordering::Less => match self.opt_scorer.skip_next(doc) {
-                    SkipResult::Reached => {
-                        score_combiner.update(&mut self.opt_scorer);
-                    }
-                    SkipResult::End => {
-                        self.opt_finished = true;
-                    }
-                    SkipResult::OverStep => {}
-                },
-            }
+        if self.opt_scorer.seek(doc) == doc {
+            score_combiner.update(&mut self.opt_scorer);
         }
         let score = score_combiner.score();
         self.score_cache = Some(score);
@@ -102,7 +84,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::RequiredOptionalScorer;
-    use crate::docset::DocSet;
+    use crate::docset::{DocSet, TERMINATED};
     use crate::postings::tests::test_skip_against_unoptimized;
     use crate::query::score_combiner::{DoNothingCombiner, SumCombiner};
     use crate::query::ConstScorer;
@@ -119,9 +101,7 @@ mod tests {
                 ConstScorer::from(VecDocSet::from(vec![])),
             );
         let mut docs = vec![];
-        while reqoptscorer.advance() {
-            docs.push(reqoptscorer.doc());
-        }
+        reqoptscorer.for_each(&mut |doc, _| docs.push(doc));
         assert_eq!(docs, req);
     }
 
@@ -133,46 +113,45 @@ mod tests {
                 ConstScorer::new(VecDocSet::from(vec![1, 2, 7, 11, 12, 15]), 1.0f32),
             );
         {
-            assert!(reqoptscorer.advance());
             assert_eq!(reqoptscorer.doc(), 1);
             assert_eq!(reqoptscorer.score(), 2f32);
         }
         {
-            assert!(reqoptscorer.advance());
+            assert_eq!(reqoptscorer.advance(), 3);
             assert_eq!(reqoptscorer.doc(), 3);
             assert_eq!(reqoptscorer.score(), 1f32);
         }
         {
-            assert!(reqoptscorer.advance());
+            assert_eq!(reqoptscorer.advance(), 7);
             assert_eq!(reqoptscorer.doc(), 7);
             assert_eq!(reqoptscorer.score(), 2f32);
         }
         {
-            assert!(reqoptscorer.advance());
+            assert_eq!(reqoptscorer.advance(), 8);
             assert_eq!(reqoptscorer.doc(), 8);
             assert_eq!(reqoptscorer.score(), 1f32);
         }
         {
-            assert!(reqoptscorer.advance());
+            assert_eq!(reqoptscorer.advance(), 9);
             assert_eq!(reqoptscorer.doc(), 9);
             assert_eq!(reqoptscorer.score(), 1f32);
         }
         {
-            assert!(reqoptscorer.advance());
+            assert_eq!(reqoptscorer.advance(), 10);
             assert_eq!(reqoptscorer.doc(), 10);
             assert_eq!(reqoptscorer.score(), 1f32);
         }
         {
-            assert!(reqoptscorer.advance());
+            assert_eq!(reqoptscorer.advance(), 13);
             assert_eq!(reqoptscorer.doc(), 13);
             assert_eq!(reqoptscorer.score(), 1f32);
         }
         {
-            assert!(reqoptscorer.advance());
+            assert_eq!(reqoptscorer.advance(), 15);
             assert_eq!(reqoptscorer.doc(), 15);
             assert_eq!(reqoptscorer.score(), 2f32);
         }
-        assert!(!reqoptscorer.advance());
+        assert_eq!(reqoptscorer.advance(), TERMINATED);
     }
 
     #[test]

src/query/scorer.rs

@@ -1,5 +1,4 @@
-use crate::common::BitSet;
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::{DocSet, TERMINATED};
 use crate::DocId;
 use crate::Score;
 use downcast_rs::impl_downcast;
@@ -17,8 +16,35 @@ pub trait Scorer: downcast_rs::Downcast + DocSet + 'static {
     /// Iterates through all of the document matched by the DocSet
     /// `DocSet` and push the scored documents to the collector.
     fn for_each(&mut self, callback: &mut dyn FnMut(DocId, Score)) {
-        while self.advance() {
-            callback(self.doc(), self.score());
+        let mut doc = self.doc();
+        while doc != TERMINATED {
+            callback(doc, self.score());
+            doc = self.advance();
+        }
+    }
+
+    /// Calls `callback` with all of the `(doc, score)` for which score
+    /// is exceeding a given threshold.
+    ///
+    /// This method is useful for the TopDocs collector.
+    /// For all docsets, the blanket implementation has the benefit
+    /// of prefiltering (doc, score) pairs, avoiding the
+    /// virtual dispatch cost.
+    ///
+    /// More importantly, it makes it possible for scorers to implement
+    /// important optimization (e.g. BlockWAND for union).
+    fn for_each_pruning(
+        &mut self,
+        mut threshold: f32,
+        callback: &mut dyn FnMut(DocId, Score) -> Score,
+    ) {
+        let mut doc = self.doc();
+        while doc != TERMINATED {
+            let score = self.score();
+            if score > threshold {
+                threshold = callback(doc, score);
+            }
+            doc = self.advance();
         }
     }
 }
@@ -61,12 +87,12 @@ impl<TDocSet: DocSet> From<TDocSet> for ConstScorer<TDocSet> {
 }
 
 impl<TDocSet: DocSet> DocSet for ConstScorer<TDocSet> {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         self.docset.advance()
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        self.docset.skip_next(target)
+    fn seek(&mut self, target: DocId) -> DocId {
+        self.docset.seek(target)
     }
 
     fn fill_buffer(&mut self, buffer: &mut [DocId]) -> usize {
@@ -80,10 +106,6 @@ impl<TDocSet: DocSet> DocSet for ConstScorer<TDocSet> {
     fn size_hint(&self) -> u32 {
         self.docset.size_hint()
     }
-
-    fn append_to_bitset(&mut self, bitset: &mut BitSet) {
-        self.docset.append_to_bitset(bitset);
-    }
 }
 
 impl<TDocSet: DocSet + 'static> Scorer for ConstScorer<TDocSet> {

src/query/term_query/mod.rs

@@ -26,10 +26,8 @@ mod tests {
         {
             // writing the segment
             let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
-            {
-                let doc = doc!(text_field => "a");
-                index_writer.add_document(doc);
-            }
+            let doc = doc!(text_field => "a");
+            index_writer.add_document(doc);
             assert!(index_writer.commit().is_ok());
         }
         let searcher = index.reader().unwrap().searcher();
@@ -40,7 +38,6 @@ mod tests {
         let term_weight = term_query.weight(&searcher, true).unwrap();
         let segment_reader = searcher.segment_reader(0);
         let mut term_scorer = term_weight.scorer(segment_reader, 1.0f32).unwrap();
-        assert!(term_scorer.advance());
         assert_eq!(term_scorer.doc(), 0);
         assert_eq!(term_scorer.score(), 0.28768212);
     }

src/query/term_query/term_scorer.rs

@@ -1,4 +1,4 @@
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::DocSet;
 use crate::query::{Explanation, Scorer};
 use crate::DocId;
 use crate::Score;
@@ -45,12 +45,12 @@ impl TermScorer {
 }
 
 impl DocSet for TermScorer {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         self.postings.advance()
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        self.postings.skip_next(target)
+    fn seek(&mut self, target: DocId) -> DocId {
+        self.postings.seek(target)
     }
 
     fn doc(&self) -> DocId {

src/query/term_query/term_weight.rs

@@ -8,8 +8,8 @@ use crate::query::Weight;
 use crate::query::{Explanation, Scorer};
 use crate::schema::IndexRecordOption;
 use crate::DocId;
+use crate::Result;
 use crate::Term;
-use crate::{Result, SkipResult};
 
 pub struct TermWeight {
     term: Term,
@@ -25,7 +25,7 @@ impl Weight for TermWeight {
 
     fn explain(&self, reader: &SegmentReader, doc: DocId) -> Result<Explanation> {
         let mut scorer = self.scorer_specialized(reader, 1.0f32)?;
-        if scorer.skip_next(doc) != SkipResult::Reached {
+        if scorer.seek(doc) != doc {
             return Err(does_not_match(doc));
         }
         Ok(scorer.explain())

src/query/union.rs

@@ -1,10 +1,9 @@
 use crate::common::TinySet;
-use crate::docset::{DocSet, SkipResult};
+use crate::docset::{DocSet, TERMINATED};
 use crate::query::score_combiner::{DoNothingCombiner, ScoreCombiner};
 use crate::query::Scorer;
 use crate::DocId;
 use crate::Score;
-use std::cmp::Ordering;
 
 const HORIZON_NUM_TINYBITSETS: usize = 64;
 const HORIZON: u32 = 64u32 * HORIZON_NUM_TINYBITSETS as u32;
@@ -47,17 +46,9 @@ where
     fn from(docsets: Vec<TScorer>) -> Union<TScorer, TScoreCombiner> {
         let non_empty_docsets: Vec<TScorer> = docsets
             .into_iter()
-            .flat_map(
-                |mut docset| {
-                    if docset.advance() {
-                        Some(docset)
-                    } else {
-                        None
-                    }
-                },
-            )
+            .filter(|docset| docset.doc() != TERMINATED)
             .collect();
-        Union {
+        let mut union = Union {
             docsets: non_empty_docsets,
             bitsets: Box::new([TinySet::empty(); HORIZON_NUM_TINYBITSETS]),
             scores: Box::new([TScoreCombiner::default(); HORIZON as usize]),
@@ -65,7 +56,13 @@ where
             offset: 0,
             doc: 0,
             score: 0f32,
+        };
+        if union.refill() {
+            union.advance();
+        } else {
+            union.doc = TERMINATED;
         }
+        union
     }
 }
 
@@ -86,7 +83,7 @@ fn refill<TScorer: Scorer, TScoreCombiner: ScoreCombiner>(
             let delta = doc - min_doc;
             bitsets[(delta / 64) as usize].insert_mut(delta % 64u32);
             score_combiner[delta as usize].update(scorer);
-            if !scorer.advance() {
+            if scorer.advance() == TERMINATED {
                 // remove the docset, it has been entirely consumed.
                 return true;
             }
@@ -99,6 +96,7 @@ impl<TScorer: Scorer, TScoreCombiner: ScoreCombiner> Union<TScorer, TScoreCombin
         if let Some(min_doc) = self.docsets.iter().map(DocSet::doc).min() {
             self.offset = min_doc;
             self.cursor = 0;
+            self.doc = min_doc;
             refill(
                 &mut self.docsets,
                 &mut *self.bitsets,
@@ -133,30 +131,23 @@ where
     TScorer: Scorer,
     TScoreCombiner: ScoreCombiner,
 {
-    fn advance(&mut self) -> bool {
+    fn advance(&mut self) -> DocId {
         if self.advance_buffered() {
-            return true;
+            return self.doc;
         }
-        if self.refill() {
-            self.advance();
-            true
-        } else {
-            false
+        if !self.refill() {
+            self.doc = TERMINATED;
+            return TERMINATED;
         }
+        if !self.advance_buffered() {
+            return TERMINATED;
+        }
+        self.doc
     }
 
-    fn skip_next(&mut self, target: DocId) -> SkipResult {
-        if !self.advance() {
-            return SkipResult::End;
-        }
-        match self.doc.cmp(&target) {
-            Ordering::Equal => {
-                return SkipResult::Reached;
-            }
-            Ordering::Greater => {
-                return SkipResult::OverStep;
-            }
-            Ordering::Less => {}
+    fn seek(&mut self, target: DocId) -> DocId {
+        if self.doc >= target {
+            return self.doc;
         }
         let gap = target - self.offset;
         if gap < HORIZON {
@@ -174,18 +165,11 @@ where
 
             // Advancing until we reach the end of the bucket
             // or we reach a doc greater or equal to the target.
-            while self.advance() {
-                match self.doc().cmp(&target) {
-                    Ordering::Equal => {
-                        return SkipResult::Reached;
-                    }
-                    Ordering::Greater => {
-                        return SkipResult::OverStep;
-                    }
-                    Ordering::Less => {}
-                }
+            let mut doc = self.doc();
+            while doc < target {
+                doc = self.advance();
             }
-            SkipResult::End
+            doc
         } else {
             // clear the buffered info.
             for obsolete_tinyset in self.bitsets.iter_mut() {
@@ -199,45 +183,30 @@ where
             // advance all docsets to a doc >= to the target.
             #[cfg_attr(feature = "cargo-clippy", allow(clippy::clippy::collapsible_if))]
             unordered_drain_filter(&mut self.docsets, |docset| {
-                if docset.doc() < target {
-                    if docset.skip_next(target) == SkipResult::End {
-                        return true;
-                    }
-                }
-                false
+                docset.seek(target) == TERMINATED
             });
 
             // at this point all of the docsets
             // are positionned on a doc >= to the target.
-            if self.refill() {
-                self.advance();
-                if self.doc() == target {
-                    SkipResult::Reached
-                } else {
-                    debug_assert!(self.doc() > target);
-                    SkipResult::OverStep
-                }
-            } else {
-                SkipResult::End
+            if !self.refill() {
+                self.doc = TERMINATED;
+                return TERMINATED;
             }
+            self.advance()
         }
     }
 
-    // TODO implement `count` efficiently.
-
-    fn doc(&self) -> DocId {
-        self.doc
-    }
-
-    fn size_hint(&self) -> u32 {
-        0u32
-    }
+    // TODO Also implement `count` with deletes efficiently.
 
     fn count_including_deleted(&mut self) -> u32 {
+        if self.doc == TERMINATED {
+            return 0;
+        }
         let mut count = self.bitsets[self.cursor..HORIZON_NUM_TINYBITSETS]
             .iter()
             .map(|bitset| bitset.len())
-            .sum::<u32>();
+            .sum::<u32>()
+            + 1;
         for bitset in self.bitsets.iter_mut() {
             bitset.clear();
         }
@@ -250,6 +219,18 @@ where
         self.cursor = HORIZON_NUM_TINYBITSETS;
         count
     }
+
+    fn doc(&self) -> DocId {
+        self.doc
+    }
+
+    fn size_hint(&self) -> u32 {
+        self.docsets
+            .iter()
+            .map(|docset| docset.size_hint())
+            .max()
+            .unwrap_or(0u32)
+    }
 }
 
 impl<TScorer, TScoreCombiner> Scorer for Union<TScorer, TScoreCombiner>
@@ -267,7 +248,7 @@ mod tests {
 
     use super::Union;
     use super::HORIZON;
-    use crate::docset::{DocSet, SkipResult};
+    use crate::docset::{DocSet, TERMINATED};
     use crate::postings::tests::test_skip_against_unoptimized;
     use crate::query::score_combiner::DoNothingCombiner;
     use crate::query::ConstScorer;
@@ -296,12 +277,12 @@ mod tests {
         };
         let mut union: Union<_, DoNothingCombiner> = make_union();
         let mut count = 0;
-        while union.advance() {
-            assert!(union_expected.advance());
+        while union.doc() != TERMINATED {
             assert_eq!(union_expected.doc(), union.doc());
+            assert_eq!(union_expected.advance(), union.advance());
             count += 1;
         }
-        assert!(!union_expected.advance());
+        assert_eq!(union_expected.advance(), TERMINATED);
         assert_eq!(count, make_union().count_including_deleted());
     }
 
@@ -329,9 +310,7 @@ mod tests {
     fn test_aux_union_skip(docs_list: &[Vec<DocId>], skip_targets: Vec<DocId>) {
         let mut btree_set = BTreeSet::new();
         for docs in docs_list {
-            for &doc in docs.iter() {
-                btree_set.insert(doc);
-            }
+            btree_set.extend(docs.iter().cloned());
         }
         let docset_factory = || {
             let res: Box<dyn DocSet> = Box::new(Union::<_, DoNothingCombiner>::from(
@@ -346,10 +325,10 @@ mod tests {
         };
         let mut docset = docset_factory();
         for el in btree_set {
-            assert!(docset.advance());
             assert_eq!(el, docset.doc());
+            docset.advance();
         }
-        assert!(!docset.advance());
+        assert_eq!(docset.doc(), TERMINATED);
         test_skip_against_unoptimized(docset_factory, skip_targets);
     }
 
@@ -372,10 +351,10 @@ mod tests {
             ConstScorer::from(VecDocSet::from(vec![0u32, 5u32])),
             ConstScorer::from(VecDocSet::from(vec![1u32, 4u32])),
         ]);
-        assert!(docset.advance());
         assert_eq!(docset.doc(), 0u32);
-        assert_eq!(docset.skip_next(0u32), SkipResult::OverStep);
-        assert_eq!(docset.doc(), 1u32)
+        assert_eq!(docset.seek(0u32), 0u32);
+        assert_eq!(docset.seek(0u32), 0u32);
+        assert_eq!(docset.doc(), 0u32)
     }
 
     #[test]

src/query/vec_docset.rs

@@ -1,9 +1,8 @@
 #![allow(dead_code)]
 
 use crate::common::HasLen;
-use crate::docset::DocSet;
+use crate::docset::{DocSet, TERMINATED};
 use crate::DocId;
-use std::num::Wrapping;
 
 /// Simulate a `Postings` objects from a `VecPostings`.
 /// `VecPostings` only exist for testing purposes.
@@ -12,26 +11,30 @@ use std::num::Wrapping;
 /// No positions are returned.
 pub struct VecDocSet {
     doc_ids: Vec<DocId>,
-    cursor: Wrapping<usize>,
+    cursor: usize,
 }
 
 impl From<Vec<DocId>> for VecDocSet {
     fn from(doc_ids: Vec<DocId>) -> VecDocSet {
-        VecDocSet {
-            doc_ids,
-            cursor: Wrapping(usize::max_value()),
-        }
+        VecDocSet { doc_ids, cursor: 0 }
     }
 }
 
 impl DocSet for VecDocSet {
-    fn advance(&mut self) -> bool {
-        self.cursor += Wrapping(1);
-        self.doc_ids.len() > self.cursor.0
+    fn advance(&mut self) -> DocId {
+        self.cursor += 1;
+        if self.cursor >= self.doc_ids.len() {
+            self.cursor = self.doc_ids.len();
+            return TERMINATED;
+        }
+        self.doc()
     }
 
     fn doc(&self) -> DocId {
-        self.doc_ids[self.cursor.0]
+        if self.cursor == self.doc_ids.len() {
+            return TERMINATED;
+        }
+        self.doc_ids[self.cursor]
     }
 
     fn size_hint(&self) -> u32 {
@@ -49,22 +52,21 @@ impl HasLen for VecDocSet {
 pub mod tests {
 
     use super::*;
-    use crate::docset::{DocSet, SkipResult};
+    use crate::docset::DocSet;
     use crate::DocId;
 
     #[test]
     pub fn test_vec_postings() {
         let doc_ids: Vec<DocId> = (0u32..1024u32).map(|e| e * 3).collect();
         let mut postings = VecDocSet::from(doc_ids);
-        assert!(postings.advance());
         assert_eq!(postings.doc(), 0u32);
-        assert!(postings.advance());
+        assert_eq!(postings.advance(), 3u32);
         assert_eq!(postings.doc(), 3u32);
-        assert_eq!(postings.skip_next(14u32), SkipResult::OverStep);
+        assert_eq!(postings.seek(14u32), 15u32);
         assert_eq!(postings.doc(), 15u32);
-        assert_eq!(postings.skip_next(300u32), SkipResult::Reached);
+        assert_eq!(postings.seek(300u32), 300u32);
         assert_eq!(postings.doc(), 300u32);
-        assert_eq!(postings.skip_next(6000u32), SkipResult::End);
+        assert_eq!(postings.seek(6000u32), TERMINATED);
     }
 
     #[test]

src/reader/mod.rs

@@ -9,6 +9,7 @@ use crate::directory::META_LOCK;
 use crate::Index;
 use crate::Searcher;
 use crate::SegmentReader;
+use std::convert::TryInto;
 use std::sync::Arc;
 
 /// Defines when a new version of the index should be reloaded.
@@ -60,7 +61,6 @@ impl IndexReaderBuilder {
     /// Building the reader is a non-trivial operation that requires
     /// to open different segment readers. It may take hundreds of milliseconds
     /// of time and it may return an error.
-    /// TODO(pmasurel) Use the `TryInto` trait once it is available in stable.
     pub fn try_into(self) -> crate::Result<IndexReader> {
         let inner_reader = InnerIndexReader {
             index: self.index,
@@ -113,6 +113,14 @@ impl IndexReaderBuilder {
     }
 }
 
+impl TryInto<IndexReader> for IndexReaderBuilder {
+    type Error = crate::TantivyError;
+
+    fn try_into(self) -> crate::Result<IndexReader> {
+        IndexReaderBuilder::try_into(self)
+    }
+}
+
 struct InnerIndexReader {
     num_searchers: usize,
     searcher_pool: Pool<Searcher>,

src/schema/document.rs

@@ -3,7 +3,6 @@ use crate::common::BinarySerializable;
 use crate::common::VInt;
 use crate::tokenizer::PreTokenizedString;
 use crate::DateTime;
-use serde;
 use std::io::{self, Read, Write};
 use std::mem;
 

src/schema/field.rs

@@ -1,5 +1,4 @@
 use crate::common::BinarySerializable;
-use serde;
 use std::io;
 use std::io::Read;
 use std::io::Write;
@@ -13,13 +12,13 @@ pub struct Field(u32);
 
 impl Field {
     /// Create a new field object for the given FieldId.
-    pub fn from_field_id(field_id: u32) -> Field {
+    pub const fn from_field_id(field_id: u32) -> Field {
         Field(field_id)
     }
 
     /// Returns a u32 identifying uniquely a field within a schema.
     #[allow(clippy::trivially_copy_pass_by_ref)]
-    pub fn field_id(&self) -> u32 {
+    pub const fn field_id(&self) -> u32 {
         self.0
     }
 }

src/schema/field_value.rs

@@ -1,10 +1,7 @@
 use crate::common::BinarySerializable;
 use crate::schema::Field;
 use crate::schema::Value;
-use serde;
-use std::io;
-use std::io::Read;
-use std::io::Write;
+use std::io::{self, Read, Write};
 
 /// `FieldValue` holds together a `Field` and its `Value`.
 #[derive(Debug, Clone, Ord, PartialEq, Eq, PartialOrd, serde::Serialize, serde::Deserialize)]

src/store/compression_snap.rs

@@ -1,5 +1,3 @@
-use snap;
-
 use std::io::{self, Read, Write};
 
 /// Name of the compression scheme used in the doc store.

src/termdict/mod.rs

@@ -434,8 +434,8 @@ mod tests {
 
     #[test]
     fn test_automaton_search() {
-        use levenshtein_automata::LevenshteinAutomatonBuilder;
         use crate::query::DFAWrapper;
+        use levenshtein_automata::LevenshteinAutomatonBuilder;
 
         const COUNTRIES: [&'static str; 7] = [
             "San Marino",

src/termdict/termdict.rs

@@ -7,7 +7,6 @@ use crate::postings::TermInfo;
 use crate::termdict::TermOrdinal;
 use once_cell::sync::Lazy;
 use std::io::{self, Write};
-use tantivy_fst;
 use tantivy_fst::raw::Fst;
 use tantivy_fst::Automaton;