Fix match_only_text bugs if defined as multi-field

Bugs starting to occur when elastic#129126 was merged.

Closes elastic#129737

Author: martijnvg

modules/mapper-extras/src/main/java/org/elasticsearch/index/mapper/extras/MatchOnlyTextFieldMapper.java

@@ -47,6 +47,7 @@
 import org.elasticsearch.index.mapper.BlockStoredFieldsReader;
 import org.elasticsearch.index.mapper.DocumentParserContext;
 import org.elasticsearch.index.mapper.FieldMapper;
+import org.elasticsearch.index.mapper.KeywordFieldMapper;
 import org.elasticsearch.index.mapper.MapperBuilderContext;
 import org.elasticsearch.index.mapper.SourceValueFetcher;
 import org.elasticsearch.index.mapper.StringFieldType;
@@ -123,7 +124,7 @@ protected Parameter<?>[] getParameters() {
             return new Parameter<?>[] { meta };
         }
 
-        private MatchOnlyTextFieldType buildFieldType(MapperBuilderContext context) {
+        private MatchOnlyTextFieldType buildFieldType(MapperBuilderContext context, boolean storeSource) {
             NamedAnalyzer searchAnalyzer = analyzers.getSearchAnalyzer();
             NamedAnalyzer searchQuoteAnalyzer = analyzers.getSearchQuoteAnalyzer();
             NamedAnalyzer indexAnalyzer = analyzers.getIndexAnalyzer();
@@ -132,15 +133,14 @@ private MatchOnlyTextFieldType buildFieldType(MapperBuilderContext context) {
                 context.buildFullName(leafName()),
                 tsi,
                 indexAnalyzer,
-                context.isSourceSynthetic(),
+                storeSource,
                 meta.getValue()
             );
             return ft;
         }
 
         @Override
         public MatchOnlyTextFieldMapper build(MapperBuilderContext context) {
-            MatchOnlyTextFieldType tft = buildFieldType(context);
             final boolean storeSource;
             if (multiFieldsNotStoredByDefaultIndexVersionCheck(indexCreatedVersion)) {
                 storeSource = context.isSourceSynthetic()
@@ -149,6 +149,7 @@ public MatchOnlyTextFieldMapper build(MapperBuilderContext context) {
             } else {
                 storeSource = context.isSourceSynthetic();
             }
+            MatchOnlyTextFieldType tft = buildFieldType(context, storeSource);
             return new MatchOnlyTextFieldMapper(leafName(), Defaults.FIELD_TYPE, tft, builderParams(this, context), storeSource, this);
         }
     }
@@ -211,14 +212,18 @@ private IOFunction<LeafReaderContext, CheckedIntFunction<List<Object>, IOExcepti
             }
             if (searchExecutionContext.isSourceSynthetic()) {
                 String name = storedFieldNameForSyntheticSource();
-                StoredFieldLoader loader = StoredFieldLoader.create(false, Set.of(name));
-                return context -> {
-                    LeafStoredFieldLoader leafLoader = loader.getLoader(context, null);
-                    return docId -> {
-                        leafLoader.advanceTo(docId);
-                        return leafLoader.storedFields().get(name);
+                // TODO: go the parent field and load either via stored fields or doc values the values instead synthesizing complete source
+                // (in case of synthetic source and if this field is a multi field, then it will not have a stored field.)
+                if (name != null) {
+                    StoredFieldLoader loader = StoredFieldLoader.create(false, Set.of(name));
+                    return context -> {
+                        LeafStoredFieldLoader leafLoader = loader.getLoader(context, null);
+                        return docId -> {
+                            leafLoader.advanceTo(docId);
+                            return leafLoader.storedFields().get(name);
+                        };
                     };
-                };
+                }
             }
             return context -> {
                 ValueFetcher valueFetcher = valueFetcher(searchExecutionContext, null);
@@ -506,18 +511,30 @@ public MatchOnlyTextFieldType fieldType() {
 
     @Override
     protected SyntheticSourceSupport syntheticSourceSupport() {
-        return new SyntheticSourceSupport.Native(
-            () -> new StringStoredFieldFieldLoader(fieldType().storedFieldNameForSyntheticSource(), fieldType().name(), leafName()) {
-                @Override
-                protected void write(XContentBuilder b, Object value) throws IOException {
-                    if (value instanceof BytesRef valueBytes) {
-                        b.value(valueBytes.utf8ToString());
-                    } else {
-                        assert value instanceof String;
-                        b.value(value.toString());
+        if (storeSource) {
+            return new SyntheticSourceSupport.Native(
+                () -> new StringStoredFieldFieldLoader(fieldType().storedFieldNameForSyntheticSource(), fieldType().name(), leafName()) {
+                    @Override
+                    protected void write(XContentBuilder b, Object value) throws IOException {
+                        if (value instanceof BytesRef valueBytes) {
+                            b.value(valueBytes.utf8ToString());
+                        } else {
+                            assert value instanceof String;
+                            b.value(value.toString());
+                        }
+                    }
+                }
+            );
+        } else {
+            for (FieldMapper multiField : multiFields()) {
+                if (multiField instanceof KeywordFieldMapper kwd) {
+                    if (kwd.hasNormalizer() == false && (kwd.fieldType().hasDocValues() || kwd.fieldType().isStored())) {
+                        return kwd.syntheticSourceSupport();
                     }
                 }
             }
-        );
+            assert false : "there should be a suite field mapper with native synthetic source support";
+            return null;
+        }
     }
 }

modules/mapper-extras/src/yamlRestTest/resources/rest-api-spec/test/match_only_text/10_basic.yml

@@ -394,4 +394,77 @@ synthetic_source with copy_to:
   - match:
       hits.hits.0.fields.copy.0: "Apache Lucene powers Elasticsearch"
 
+---
+synthetic_source match_only_text as multi-field:
+  - do:
+      indices.create:
+        index: synthetic_source_test
+        body:
+          settings:
+            index:
+              mapping.source.mode: synthetic
+          mappings:
+            properties:
+              foo:
+                type: keyword
+                fields:
+                  text:
+                    type: match_only_text
+
+  - do:
+      index:
+        index: synthetic_source_test
+        id:    "1"
+        refresh: true
+        body:
+          foo: "Apache Lucene powers Elasticsearch"
+
+  - do:
+      search:
+        index: synthetic_source_test
+        body:
+          query:
+            match_phrase:
+              foo.text: apache lucene
+
+  - match: { "hits.total.value": 1 }
+  - match:
+      hits.hits.0._source.foo: "Apache Lucene powers Elasticsearch"
+
+---
+synthetic_source match_only_text with multi-field:
+  - do:
+      indices.create:
+        index: synthetic_source_test
+        body:
+          settings:
+            index:
+              mapping.source.mode: synthetic
+          mappings:
+            properties:
+              foo:
+                type: match_only_text
+                fields:
+                  raw:
+                    type: keyword
+
+  - do:
+      index:
+        index: synthetic_source_test
+        id:    "1"
+        refresh: true
+        body:
+          foo: "Apache Lucene powers Elasticsearch"
+
+  - do:
+      search:
+        index: synthetic_source_test
+        body:
+          query:
+            match_phrase:
+              foo: apache lucene
+
+  - match: { "hits.total.value": 1 }
+  - match:
+      hits.hits.0._source.foo: "Apache Lucene powers Elasticsearch"
 

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

@@ -1261,7 +1261,7 @@ public void doValidate(MappingLookup lookup) {
         }
     }
 
-    boolean hasNormalizer() {
+    public boolean hasNormalizer() {
         return normalizerName != null;
     }
 
@@ -1275,7 +1275,7 @@ private String originalName() {
     }
 
     @Override
-    protected SyntheticSourceSupport syntheticSourceSupport() {
+    public SyntheticSourceSupport syntheticSourceSupport() {
         if (hasNormalizer()) {
             // NOTE: no matter if we have doc values or not we use fallback synthetic source
             // to store the original value whose doc values would be altered by the normalizer