Gate default BBQ by IndexVersion

Author: kderusso

server/src/main/java/org/elasticsearch/index/IndexVersions.java

@@ -159,6 +159,7 @@ private static Version parseUnchecked(String version) {
     public static final IndexVersion SYNTHETIC_SOURCE_STORE_ARRAYS_NATIVELY_UNSIGNED_LONG = def(9_019_0_00, Version.LUCENE_10_1_0);
     public static final IndexVersion SYNTHETIC_SOURCE_STORE_ARRAYS_NATIVELY_SCALED_FLOAT = def(9_020_0_00, Version.LUCENE_10_1_0);
     public static final IndexVersion USE_LUCENE101_POSTINGS_FORMAT = def(9_021_0_00, Version.LUCENE_10_1_0);
+    public static final IndexVersion SEMANTIC_TEXT_DEFAULTS_TO_BBQ = def(9_022_0_00, Version.LUCENE_10_1_0);
     /*
      * STOP! READ THIS FIRST! No, really,
      *        ____ _____ ___  ____  _        ____  _____    _    ____    _____ _   _ ___ ____    _____ ___ ____  ____ _____ _

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

@@ -92,6 +92,7 @@
 import java.util.function.BiConsumer;
 import java.util.function.Function;
 
+import static org.elasticsearch.index.IndexVersions.SEMANTIC_TEXT_DEFAULTS_TO_BBQ;
 import static org.elasticsearch.inference.TaskType.SPARSE_EMBEDDING;
 import static org.elasticsearch.inference.TaskType.TEXT_EMBEDDING;
 import static org.elasticsearch.search.SearchService.DEFAULT_SIZE;
@@ -1010,8 +1011,12 @@ private static Mapper.Builder createEmbeddingsField(
                 denseVectorMapperBuilder.dimensions(modelSettings.dimensions());
                 denseVectorMapperBuilder.elementType(modelSettings.elementType());
 
-                DenseVectorFieldMapper.IndexOptions defaultIndexOptions = defaultSemanticDenseIndexOptions();
-                if (defaultIndexOptions.validate(modelSettings.elementType(), modelSettings.dimensions(), false)) {
+                DenseVectorFieldMapper.IndexOptions defaultIndexOptions = null;
+                if (indexVersionCreated.onOrAfter(SEMANTIC_TEXT_DEFAULTS_TO_BBQ)) {
+                    defaultIndexOptions = defaultSemanticDenseIndexOptions();
+                }
+                if (defaultIndexOptions != null
+                    && defaultIndexOptions.validate(modelSettings.elementType(), modelSettings.dimensions(), false)) {
                     denseVectorMapperBuilder.indexOptions(defaultIndexOptions);
                 }