Add count() to BayesianScoreQuery.BayesianScoreWeight (#16110)

* Add count() to BayesianScoreQuery.BayesianScoreWeight

* moved to 10.5 version

Author: iprithv

lucene/CHANGES.txt

@@ -324,6 +324,9 @@ New Features
 * GITHUB#15794: Add DocValuesSkipper metadata for the maximum number of values
   on any document in a field. (Prithvi S)
 
+* GITHUB#16110: Add count() to BayesianScoreQuery.BayesianScoreWeight, delegating to
+  the inner weight. (Prithvi S)
+
 Improvements
 ---------------------
 * GITHUB#15948: Improve BayesianScoreQuery and LogOddsFusionQuery with base rate prior,

lucene/core/src/java/org/apache/lucene/search/BayesianScoreQuery.java

@@ -242,6 +242,11 @@ public void setTopLevelScoringClause() {
       };
     }
 
+    @Override
+    public int count(LeafReaderContext context) throws IOException {
+      return innerWeight.count(context);
+    }
+
     @Override
     public boolean isCacheable(LeafReaderContext ctx) {
       return innerWeight.isCacheable(ctx);

lucene/core/src/test/org/apache/lucene/search/TestBayesianScoreQuery.java

@@ -238,6 +238,36 @@ public void testToString() {
     assertTrue("should contain alpha", s.contains("alpha"));
   }
 
+  public void testCountDelegatesToInner() throws Exception {
+    Query inner = new TermQuery(new Term("body", "alpha"));
+    BayesianScoreQuery bsq = new BayesianScoreQuery(inner, 0.5f, 5.0f);
+
+    Weight w = searcher.createWeight(searcher.rewrite(bsq), ScoreMode.COMPLETE, 1);
+    LeafReaderContext context = searcher.getIndexReader().leaves().get(0);
+
+    // BayesianScoreQuery only transforms scores; matching docs are unchanged.
+    // count() should delegate to the inner weight.
+    int count = w.count(context);
+    assertEquals(2, count);
+
+    // Verify it matches the inner query's count
+    Weight innerW = searcher.createWeight(inner, ScoreMode.COMPLETE, 1);
+    assertEquals(innerW.count(context), count);
+  }
+
+  public void testCountWithNoScoring() throws Exception {
+    // When scoreMode.needsScores() == false, createWeight returns innerWeight directly
+    Query inner = new TermQuery(new Term("body", "alpha"));
+    BayesianScoreQuery bsq = new BayesianScoreQuery(inner, 0.5f, 5.0f);
+
+    Weight w = searcher.createWeight(searcher.rewrite(bsq), ScoreMode.COMPLETE_NO_SCORES, 1);
+    LeafReaderContext context = searcher.getIndexReader().leaves().get(0);
+
+    // Should delegate to inner weight's count
+    int count = w.count(context);
+    assertEquals(2, count);
+  }
+
   public void testDifferentAlphaBeta() throws Exception {
     Query inner = new TermQuery(new Term("body", "alpha"));