Use alternate approach

Author: Mikep86

server/src/main/java/org/elasticsearch/index/mapper/InferenceMetadataFieldsMapper.java

@@ -36,17 +36,16 @@ public abstract class InferenceMetadataFieldsMapper extends MetadataFieldMapper
      */
     public static final Setting<Boolean> USE_LEGACY_SEMANTIC_TEXT_FORMAT = Setting.boolSetting(
         "index.mapping.semantic_text.use_legacy_format",
-        s -> {
-            // Check index version SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP because that index version was added in the same serverless promotion
-            // where the new format was enabled by default
-            IndexVersion indexVersion = IndexMetadata.SETTING_INDEX_VERSION_CREATED.get(s);
-            return Boolean.toString(indexVersion.before(IndexVersions.SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP));
-        },
+        false,
         Setting.Property.Final,
         Setting.Property.IndexScope,
         Setting.Property.InternalIndex
     );
 
+    // Check index version SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP because that index version was added in the same serverless promotion
+    // where the new format was enabled by default
+    public static final IndexVersion USE_NEW_FORMAT_BY_DEFAULT = IndexVersions.SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP;
+
     public static final String NAME = "_inference_fields";
     public static final String CONTENT_TYPE = "_inference_fields";
 
@@ -92,10 +91,12 @@ public abstract ValueFetcher valueFetcher(
      */
     public static boolean isEnabled(Settings settings) {
         var version = IndexMetadata.SETTING_INDEX_VERSION_CREATED.get(settings);
-        if (version.before(IndexVersions.INFERENCE_METADATA_FIELDS)
-            && version.between(IndexVersions.INFERENCE_METADATA_FIELDS_BACKPORT, IndexVersions.UPGRADE_TO_LUCENE_10_0_0) == false) {
+        if ((version.before(IndexVersions.INFERENCE_METADATA_FIELDS)
+            && version.between(IndexVersions.INFERENCE_METADATA_FIELDS_BACKPORT, IndexVersions.UPGRADE_TO_LUCENE_10_0_0) == false)
+            || (version.before(USE_NEW_FORMAT_BY_DEFAULT) && USE_LEGACY_SEMANTIC_TEXT_FORMAT.exists(settings) == false)) {
             return false;
         }
+
         return USE_LEGACY_SEMANTIC_TEXT_FORMAT.get(settings) == false;
     }
 

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

@@ -56,18 +56,16 @@ public void testIsEnabled() {
     }
 
     public void testIsEnabledByDefault() {
-        // Check index version SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP because that index version was added in the same serverless promotion
-        // where the new format was enabled by default
         var settings = Settings.builder()
             .put(
                 IndexMetadata.SETTING_INDEX_VERSION_CREATED.getKey(),
-                IndexVersionUtils.getPreviousVersion(IndexVersions.SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP)
+                IndexVersionUtils.getPreviousVersion(InferenceMetadataFieldsMapper.USE_NEW_FORMAT_BY_DEFAULT)
             )
             .build();
         assertFalse(InferenceMetadataFieldsMapper.isEnabled(settings));
 
         settings = Settings.builder()
-            .put(IndexMetadata.SETTING_INDEX_VERSION_CREATED.getKey(), IndexVersions.SOURCE_MAPPER_MODE_ATTRIBUTE_NOOP)
+            .put(IndexMetadata.SETTING_INDEX_VERSION_CREATED.getKey(), InferenceMetadataFieldsMapper.USE_NEW_FORMAT_BY_DEFAULT)
             .build();
         assertTrue(InferenceMetadataFieldsMapper.isEnabled(settings));
     }