updating isMetadata to return true if mapper has the correct type

Author: Samiul-TheSoccerFan

docs/changelog/121720.yaml

@@ -1,6 +1,5 @@
 pr: 121720
-summary: Fix - Requesting `_inference_fields` when using legacy format causes shard
-  failure
-area: Relevance
+summary: Skip fetching _inference_fields field in legacy semantic_text format
+area: Search
 type: bug
 issues: []

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

@@ -801,7 +801,8 @@ public static boolean isMetadataFieldStatic(String fieldName) {
      * this method considers all mapper plugins
      */
     public boolean isMetadataField(String field) {
-        return mapperRegistry.getMetadataMapperParsers(indexVersionCreated).containsKey(field);
+        var mapper = mappingLookup().getMapper(field);
+        return mapper instanceof MetadataFieldMapper;
     }
 
     /**

server/src/main/java/org/elasticsearch/search/fetch/subphase/FetchFieldsPhase.java

@@ -71,7 +71,6 @@ public FetchSubPhaseProcessor getProcessor(FetchContext fetchContext) {
                         .stream()
                         .filter(
                             fieldAndFormat -> (searchExecutionContext.isMetadataField(fieldAndFormat.field) == false
-                                || searchExecutionContext.fieldExistsInIndex(fieldAndFormat.field) == false
                                 || searchExecutionContext.getFieldType(fieldAndFormat.field).isStored() == false
                                 || IdFieldMapper.NAME.equals(fieldAndFormat.field)
                                 || SourceFieldMapper.NAME.equals(fieldAndFormat.field))
@@ -88,7 +87,6 @@ public FetchSubPhaseProcessor getProcessor(FetchContext fetchContext) {
                     continue;
                 }
                 if (searchExecutionContext.isMetadataField(fieldAndFormat.field)
-                    && searchExecutionContext.fieldExistsInIndex(fieldAndFormat.field)
                     && searchExecutionContext.getFieldType(fieldAndFormat.field).isStored()) {
                     fetchContextMetadataFields.add(fieldAndFormat);
                 }

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

@@ -36,6 +36,7 @@ public Set<NodeFeature> getTestFeatures() {
             SemanticTextFieldMapper.SEMANTIC_TEXT_DELETE_FIX,
             SemanticTextFieldMapper.SEMANTIC_TEXT_ZERO_SIZE_FIX,
             SemanticTextFieldMapper.SEMANTIC_TEXT_ALWAYS_EMIT_INFERENCE_ID_FIX,
+            SemanticTextFieldMapper.SEMANTIC_TEXT_SKIP_INFERENCE_FIELDS,
             SEMANTIC_TEXT_HIGHLIGHTER,
             SEMANTIC_MATCH_QUERY_REWRITE_INTERCEPTION_SUPPORTED,
             SEMANTIC_SPARSE_VECTOR_QUERY_REWRITE_INTERCEPTION_SUPPORTED,

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

@@ -117,6 +117,7 @@ public class SemanticTextFieldMapper extends FieldMapper implements InferenceFie
     public static final NodeFeature SEMANTIC_TEXT_ALWAYS_EMIT_INFERENCE_ID_FIX = new NodeFeature(
         "semantic_text.always_emit_inference_id_fix"
     );
+    public static final NodeFeature SEMANTIC_TEXT_SKIP_INFERENCE_FIELDS = new NodeFeature("semantic_text.skip_inference_fields");
 
     public static final String CONTENT_TYPE = "semantic_text";
     public static final String DEFAULT_ELSER_2_INFERENCE_ID = DEFAULT_ELSER_ID;

x-pack/plugin/inference/src/yamlRestTest/resources/rest-api-spec/test/inference/30_semantic_text_inference_bwc.yml

@@ -650,3 +650,42 @@ setup:
   - match: { hits.total.value: 1 }
   - match: { hits.total.relation: eq }
   - match: { hits.hits.0._source.dense_field.text: "updated text" }
+
+---
+"Skip fetching _inference_fields":
+  - requires:
+      cluster_features: semantic_text.skip_inference_fields
+      reason: Skip _inference_fields when search is performed on legacy semantic_text format.
+
+  - do:
+      indices.create:
+        index: test-skip-inference_field-index
+        body:
+          settings:
+            index:
+              mapping:
+                semantic_text:
+                  use_legacy_format: true
+          mappings:
+            properties:
+              inference_field:
+                type: semantic_text
+                inference_id: sparse-inference-id
+
+  - do:
+      index:
+        index: test-skip-inference_field-index
+        id: doc_1
+        body:
+          inference_field: "test value"
+        refresh: true
+
+  - do:
+      search:
+        index: test-skip-inference_field-index
+        body:
+          fields: [ _inference_fields ]
+          query:
+            match_all: { }
+
+  - not_exists: hits.hits.0._source._inference_fields

x-pack/plugin/inference/src/yamlRestTest/resources/rest-api-spec/test/inference/40_semantic_text_query.yml

@@ -1003,45 +1003,3 @@ setup:
   - length: { aggregations.agg_ids.buckets: 1 }
   - match: { aggregations.agg_ids.buckets.0.key: "doc_1" }
   - match: { aggregations.agg_ids.buckets.0.doc_count: 1 }
-
----
-"Querying_inference_fields with semantic_text legacy format":
-  - do:
-      indices.create:
-        index: test-index
-        body:
-          settings:
-            index:
-              mapping:
-                semantic_text:
-                  use_legacy_format: true
-          mappings:
-            properties:
-              inference_field:
-                type: semantic_text
-                inference_id: sparse-inference-id
-              source_field:
-                type: text
-                copy_to: inference_field
-
-  - do:
-      index:
-        index: test-index
-        id: doc_1
-        body:
-          inference_field: "test value"
-          source_field: "source value"
-        refresh: true
-
-  - do:
-      search:
-        index: test-index
-        body:
-          fields: [ _inference_fields ]
-          query:
-            match_all: { }
-
-  - match: { hits.total.value: 1 }
-  - match: { hits.total.relation: eq }
-  - match: { hits.hits.0._source.source_field: "source value" }
-  - match: { hits.hits.0._source.inference_field.text: "test value" }