[9.1] Fix semantic highlighting bug on flat quantized fields (#131525)

docs/changelog/131525.yaml

@@ -0,0 +1,6 @@
+pr: 131525
+summary: Fix semantic highlighting bug on flat quantized fields
+area: Highlighting
+type: bug
+issues:
+ - 131443

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/InferenceFeatures.java

@@ -41,6 +41,7 @@ public class InferenceFeatures implements FeatureSpecification {
     );
     private static final NodeFeature SEMANTIC_TEXT_MATCH_ALL_HIGHLIGHTER = new NodeFeature("semantic_text.match_all_highlighter");
     private static final NodeFeature COHERE_V2_API = new NodeFeature("inference.cohere.v2");
+    public static final NodeFeature SEMANTIC_TEXT_HIGHLIGHTING_FLAT = new NodeFeature("semantic_text.highlighter.flat_index_options");
 
     @Override
     public Set<NodeFeature> getTestFeatures() {
@@ -70,7 +71,8 @@ public Set<NodeFeature> getTestFeatures() {
             SEMANTIC_TEXT_EXCLUDE_SUB_FIELDS_FROM_FIELD_CAPS,
             SEMANTIC_TEXT_INDEX_OPTIONS,
             COHERE_V2_API,
-            SEMANTIC_QUERY_REWRITE_INTERCEPTORS_PROPAGATE_BOOST_AND_QUERY_NAME_FIX
+            SEMANTIC_QUERY_REWRITE_INTERCEPTORS_PROPAGATE_BOOST_AND_QUERY_NAME_FIX,
+            SEMANTIC_TEXT_HIGHLIGHTING_FLAT
         );
     }
 }

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/highlight/SemanticTextHighlighter.java

@@ -32,6 +32,7 @@
 import org.elasticsearch.search.fetch.subphase.highlight.HighlightField;
 import org.elasticsearch.search.fetch.subphase.highlight.HighlightUtils;
 import org.elasticsearch.search.fetch.subphase.highlight.Highlighter;
+import org.elasticsearch.search.vectors.DenseVectorQuery;
 import org.elasticsearch.search.vectors.SparseVectorQueryWrapper;
 import org.elasticsearch.search.vectors.VectorData;
 import org.elasticsearch.xcontent.Text;
@@ -273,6 +274,8 @@ public void visitLeaf(Query query) {
                     queries.add(fieldType.createExactKnnQuery(VectorData.fromBytes(knnQuery.getTargetCopy()), null));
                 } else if (query instanceof MatchAllDocsQuery) {
                     queries.add(new MatchAllDocsQuery());
+                } else if (query instanceof DenseVectorQuery.Floats floatsQuery) {
+                    queries.add(fieldType.createExactKnnQuery(VectorData.fromFloats(floatsQuery.getQuery()), null));
                 }
             }
         });