Fix explanation of boost queries seeking beyond query result. (#2142)

* Make current nightly Clippy happy.

* Fix explanation of boost queries seeking beyond query result.

bitpacker/src/blocked_bitpacker.rs

@@ -64,10 +64,8 @@ fn mem_usage<T>(items: &Vec<T>) -> usize {
 
 impl BlockedBitpacker {
     pub fn new() -> Self {
-        let mut compressed_blocks = vec![];
-        compressed_blocks.resize(8, 0);
         Self {
-            compressed_blocks,
+            compressed_blocks: vec![0; 8],
             buffer: vec![],
             offset_and_bits: vec![],
         }

examples/basic_search.rs

@@ -221,5 +221,19 @@ fn main() -> tantivy::Result<()> {
         println!("{}", schema.to_json(&retrieved_doc));
     }
 
+    // We can also get an explanation to understand
+    // how a found document got its score.
+    let query = query_parser.parse_query("title:sea^20 body:whale^70")?;
+
+    let (_score, doc_address) = searcher
+        .search(&query, &TopDocs::with_limit(1))?
+        .into_iter()
+        .next()
+        .unwrap();
+
+    let explanation = query.explain(&searcher, doc_address)?;
+
+    println!("{}", explanation.to_pretty_json());
+
     Ok(())
 }

query-grammar/src/query_grammar.rs

@@ -1,3 +1,5 @@
+use std::iter::once;
+
 use nom::branch::alt;
 use nom::bytes::complete::tag;
 use nom::character::complete::{
@@ -35,11 +37,7 @@ fn field_name(i: &str) -> IResult<&str, String> {
             )),
             char(':'),
         ),
-        |(first_char, next)| {
-            std::iter::once(first_char)
-                .chain(next.into_iter())
-                .collect()
-        },
+        |(first_char, next)| once(first_char).chain(next).collect(),
     )(i)
 }
 
@@ -822,8 +820,7 @@ fn aggregate_infallible_expressions(
                 if let Some(last) = clauses.last_mut() {
                     last.push((occur.or(Some(Occur::Must)), ast.clone()));
                 } else {
-                    let mut last = Vec::new();
-                    last.push((occur.or(Some(Occur::Must)), ast.clone()));
+                    let last = vec![(occur.or(Some(Occur::Must)), ast.clone())];
                     clauses.push(last);
                 }
             }
@@ -852,8 +849,7 @@ fn aggregate_infallible_expressions(
             if let Some(last) = clauses.last_mut() {
                 last.push((last_occur.or(Some(Occur::Must)), last_ast));
             } else {
-                let mut last = Vec::new();
-                last.push((last_occur.or(Some(Occur::Must)), last_ast));
+                let last = vec![(last_occur.or(Some(Occur::Must)), last_ast)];
                 clauses.push(last);
             }
         }

src/core/json_utils.rs

@@ -60,7 +60,7 @@ impl IndexingPositionsPerPath {
     fn get_position(&mut self, term: &Term) -> &mut IndexingPosition {
         self.positions_per_path
             .entry(murmurhash2(term.serialized_term()))
-            .or_insert_with(Default::default)
+            .or_default()
     }
 }
 

src/query/boolean_query/boolean_weight.rs

@@ -98,7 +98,7 @@ impl<TScoreCombiner: ScoreCombiner> BooleanWeight<TScoreCombiner> {
             let sub_scorer: Box<dyn Scorer> = subweight.scorer(reader, boost)?;
             per_occur_scorers
                 .entry(*occur)
-                .or_insert_with(Vec::new)
+                .or_default()
                 .push(sub_scorer);
         }
         Ok(per_occur_scorers)
@@ -193,7 +193,7 @@ impl<TScoreCombiner: ScoreCombiner + Sync> Weight for BooleanWeight<TScoreCombin
             return Ok(Explanation::new("BooleanQuery with no scoring", 1.0));
         }
 
-        let mut explanation = Explanation::new("BooleanClause. Sum of ...", scorer.score());
+        let mut explanation = Explanation::new("BooleanClause. sum of ...", scorer.score());
         for (occur, subweight) in &self.weights {
             if is_positive_occur(*occur) {
                 if let Ok(child_explanation) = subweight.explain(reader, doc) {

src/query/boost_query.rs

@@ -73,13 +73,9 @@ impl Weight for BoostWeight {
     }
 
     fn explain(&self, reader: &SegmentReader, doc: u32) -> crate::Result<Explanation> {
-        let mut scorer = self.scorer(reader, 1.0)?;
-        if scorer.seek(doc) != doc {
-            return Err(does_not_match(doc));
-        }
-        let mut explanation =
-            Explanation::new(format!("Boost x{} of ...", self.boost), scorer.score());
         let underlying_explanation = self.weight.explain(reader, doc)?;
+        let score = underlying_explanation.value() * self.boost;
+        let mut explanation = Explanation::new(format!("Boost x{} of ...", self.boost), score);
         explanation.add_detail(underlying_explanation);
         Ok(explanation)
     }