Respect index options if set over defaults

Author: kderusso

server/src/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java

@@ -1703,12 +1703,12 @@ public int doHashCode() {
         }
     }
 
-    static class Int4HnswIndexOptions extends QuantizedIndexOptions {
+    public static class Int4HnswIndexOptions extends QuantizedIndexOptions {
         private final int m;
         private final int efConstruction;
         private final float confidenceInterval;
 
-        Int4HnswIndexOptions(int m, int efConstruction, Float confidenceInterval, RescoreVector rescoreVector) {
+        public Int4HnswIndexOptions(int m, int efConstruction, Float confidenceInterval, RescoreVector rescoreVector) {
             super(VectorIndexType.INT4_HNSW, rescoreVector);
             this.m = m;
             this.efConstruction = efConstruction;

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

@@ -1123,15 +1123,16 @@ private static Mapper.Builder createEmbeddingsField(
                     DenseVectorFieldMapper.DenseVectorIndexOptions denseVectorIndexOptions =
                         (DenseVectorFieldMapper.DenseVectorIndexOptions) indexOptions.indexOptions();
                     denseVectorMapperBuilder.indexOptions(denseVectorIndexOptions);
-                }
-
-                DenseVectorFieldMapper.DenseVectorIndexOptions 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);
+                    denseVectorIndexOptions.validate(modelSettings.elementType(), modelSettings.dimensions(), true);
+                } else {
+                    DenseVectorFieldMapper.DenseVectorIndexOptions 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);
+                    }
                 }
 
                 yield denseVectorMapperBuilder;

x-pack/plugin/inference/src/test/java/org/elasticsearch/xpack/inference/mapper/SemanticTextFieldMapperTests.java

@@ -1316,14 +1316,40 @@ public void testDefaultIndexOptions() throws IOException {
             b.field("element_type", "float");
             b.endObject();
         }), useLegacyFormat, IndexVersions.SEMANTIC_TEXT_DEFAULTS_TO_BBQ);
+        assertSemanticTextField(
+            mapperService,
+            "field",
+            true,
+            null,
+            new SemanticTextIndexOptions(SemanticTextIndexOptions.SupportedIndexOptions.DENSE_VECTOR, defaultDenseVectorIndexOptions())
+        );
+
+        // If we explicitly set index options, we respect those over the defaults
+        mapperService = createMapperService(fieldMapping(b -> {
+            b.field("type", "semantic_text");
+            b.field("inference_id", "another_inference_id");
+            b.startObject("model_settings");
+            b.field("task_type", "text_embedding");
+            b.field("dimensions", 100);
+            b.field("similarity", "cosine");
+            b.field("element_type", "float");
+            b.endObject();
+            b.startObject("index_options");
+            b.startObject("dense_vector");
+            b.field("type", "int4_hnsw");
+            b.field("m", 25);
+            b.field("ef_construction", 100);
+            b.endObject();
+            b.endObject();
+        }), useLegacyFormat, IndexVersions.SEMANTIC_TEXT_DEFAULTS_TO_BBQ);
         assertSemanticTextField(
             mapperService,
             "field",
             true,
             null,
             new SemanticTextIndexOptions(
                 SemanticTextIndexOptions.SupportedIndexOptions.DENSE_VECTOR,
-                SemanticTextFieldMapper.defaultSemanticDenseIndexOptions()
+                new DenseVectorFieldMapper.Int4HnswIndexOptions(25, 100, null, null)
             )
         );
 
@@ -1348,10 +1374,7 @@ public void testDefaultIndexOptions() throws IOException {
             "field",
             true,
             null,
-            new SemanticTextIndexOptions(
-                SemanticTextIndexOptions.SupportedIndexOptions.DENSE_VECTOR,
-                SemanticTextFieldMapper.defaultSemanticDenseIndexOptions()
-            )
+            new SemanticTextIndexOptions(SemanticTextIndexOptions.SupportedIndexOptions.DENSE_VECTOR, defaultDenseVectorIndexOptions())
         );
 
     }