Make sure KnnVectorQuery applies search boost (#956)

Before, the rewritten query DocAndScoreQuery ignored the boost.

lucene/CHANGES.txt

@@ -103,6 +103,8 @@ Bug Fixes
 
 * LUCENE-10605: Fix error in 32bit jvm object alignment gap calculation (Sun Wuqiang)
 
+* GITHUB#956: Make sure KnnVectorQuery applies search boost. (Julie Tibshirani)
+
 Other
 ---------------------
 

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

@@ -346,7 +346,7 @@ public class KnnVectorQuery extends Query {
           if (found < 0) {
             return Explanation.noMatch("not in top " + k);
           }
-          return Explanation.match(scores[found], "within top " + k);
+          return Explanation.match(scores[found] * boost, "within top " + k);
         }
 
         @Override
@@ -388,18 +388,18 @@ public class KnnVectorQuery extends Query {
             }
 
             @Override
-            public float getMaxScore(int docid) {
+            public float getMaxScore(int docId) {
-              docid += context.docBase;
+              docId += context.docBase;
               float maxScore = 0;
-              for (int idx = Math.max(0, upTo); idx < upper && docs[idx] <= docid; idx++) {
+              for (int idx = Math.max(0, upTo); idx < upper && docs[idx] <= docId; idx++) {
                 maxScore = Math.max(maxScore, scores[idx]);
               }
-              return maxScore;
+              return maxScore * boost;
             }
 
             @Override
             public float score() {
-              return scores[upTo];
+              return scores[upTo] * boost;
             }
 
             @Override

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

@@ -112,6 +112,29 @@ public class TestKnnVectorQuery extends LuceneTestCase {
     }
   }
 
+  public void testSearchBoost() throws IOException {
+    try (Directory indexStore =
+            getIndexStore("field", new float[] {0, 1}, new float[] {1, 2}, new float[] {0, 0});
+        IndexReader reader = DirectoryReader.open(indexStore)) {
+      IndexSearcher searcher = newSearcher(reader);
+
+      Query vectorQuery = new KnnVectorQuery("field", new float[] {0, 0}, 10);
+      ScoreDoc[] scoreDocs = searcher.search(vectorQuery, 3).scoreDocs;
+
+      Query boostQuery = new BoostQuery(vectorQuery, 3.0f);
+      ScoreDoc[] boostScoreDocs = searcher.search(boostQuery, 3).scoreDocs;
+      assertEquals(scoreDocs.length, boostScoreDocs.length);
+
+      for (int i = 0; i < scoreDocs.length; i++) {
+        ScoreDoc scoreDoc = scoreDocs[i];
+        ScoreDoc boostScoreDoc = boostScoreDocs[i];
+
+        assertEquals(scoreDoc.doc, boostScoreDoc.doc);
+        assertEquals(scoreDoc.score * 3.0f, boostScoreDoc.score, 0.001f);
+      }
+    }
+  }
+
   /** Tests that a KnnVectorQuery applies the filter query */
   public void testSimpleFilter() throws IOException {
     try (Directory indexStore =