Fix match_only_text bugs if defined as multi-field

Backporting elastic#130188 to 8.19 branch.

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

@@ -14,6 +14,7 @@
 import org.apache.lucene.document.Field;
 import org.apache.lucene.document.FieldType;
 import org.apache.lucene.document.StoredField;
+import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.Term;
@@ -41,7 +42,6 @@
 import org.elasticsearch.index.fielddata.IndexFieldData;
 import org.elasticsearch.index.fielddata.SourceValueFetcherSortedBinaryIndexFieldData;
 import org.elasticsearch.index.fielddata.StoredFieldSortedBinaryIndexFieldData;
-import org.elasticsearch.index.fieldvisitor.LeafStoredFieldLoader;
 import org.elasticsearch.index.fieldvisitor.StoredFieldLoader;
 import org.elasticsearch.index.mapper.BlockLoader;
 import org.elasticsearch.index.mapper.BlockSourceReader;
@@ -132,7 +132,9 @@ private MatchOnlyTextFieldType buildFieldType(MapperBuilderContext context) {
                 tsi,
                 indexAnalyzer,
                 context.isSourceSynthetic(),
-                meta.getValue()
+                meta.getValue(),
+                withinMultiField,
+                multiFieldsBuilder.hasSyntheticSourceCompatibleKeywordField()
             );
             return ft;
         }
@@ -162,17 +164,24 @@ public static class MatchOnlyTextFieldType extends StringFieldType {
         private final TextFieldType textFieldType;
         private final String originalName;
 
+        private final boolean withinMultiField;
+        private final boolean hasCompatibleMultiFields;
+
         public MatchOnlyTextFieldType(
             String name,
             TextSearchInfo tsi,
             Analyzer indexAnalyzer,
             boolean isSyntheticSource,
-            Map<String, String> meta
+            Map<String, String> meta,
+            boolean withinMultiField,
+            boolean hasCompatibleMultiFields
         ) {
             super(name, true, false, false, tsi, meta);
             this.indexAnalyzer = Objects.requireNonNull(indexAnalyzer);
             this.textFieldType = new TextFieldType(name, isSyntheticSource);
             this.originalName = isSyntheticSource ? name() + "._original" : null;
+            this.withinMultiField = withinMultiField;
+            this.hasCompatibleMultiFields = hasCompatibleMultiFields;
         }
 
         public MatchOnlyTextFieldType(String name) {
@@ -181,7 +190,9 @@ public MatchOnlyTextFieldType(String name) {
                 new TextSearchInfo(Defaults.FIELD_TYPE, null, Lucene.STANDARD_ANALYZER, Lucene.STANDARD_ANALYZER),
                 Lucene.STANDARD_ANALYZER,
                 false,
-                Collections.emptyMap()
+                Collections.emptyMap(),
+                false,
+                false
             );
         }
 
@@ -208,16 +219,34 @@ private IOFunction<LeafReaderContext, CheckedIntFunction<List<Object>, IOExcepti
                     "Field [" + name() + "] of type [" + CONTENT_TYPE + "] cannot run positional queries since [_source] is disabled."
                 );
             }
-            if (searchExecutionContext.isSourceSynthetic()) {
+            if (searchExecutionContext.isSourceSynthetic() && withinMultiField) {
+                String parentField = searchExecutionContext.parentPath(name());
+                var parent = searchExecutionContext.lookup().fieldType(parentField);
+                if (parent.isStored()) {
+                    return storedFieldFetcher(parentField);
+                } else if (parent.hasDocValues()) {
+                    return docValuesFieldFetcher(parentField);
+                } else {
+                    assert false : "parent field should either be stored or have doc values";
+                }
+            } else if (searchExecutionContext.isSourceSynthetic() && hasCompatibleMultiFields) {
+                var mapper = (MatchOnlyTextFieldMapper) searchExecutionContext.getMappingLookup().getMapper(name());
+                var kwd = TextFieldMapper.SyntheticSourceHelper.getKeywordFieldMapperForSyntheticSource(mapper);
+                if (kwd != null) {
+                    var fieldType = kwd.fieldType();
+                    if (fieldType.isStored()) {
+                        return storedFieldFetcher(fieldType.name());
+                    } else if (fieldType.hasDocValues()) {
+                        return docValuesFieldFetcher(fieldType.name());
+                    } else {
+                        assert false : "multi field should either be stored or have doc values";
+                    }
+                } else {
+                    assert false : "multi field of type keyword should exist";
+                }
+            } else 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);
-                    };
-                };
+                return storedFieldFetcher(name);
             }
             return context -> {
                 ValueFetcher valueFetcher = valueFetcher(searchExecutionContext, null);
@@ -233,6 +262,35 @@ private IOFunction<LeafReaderContext, CheckedIntFunction<List<Object>, IOExcepti
             };
         }
 
+        private static IOFunction<LeafReaderContext, CheckedIntFunction<List<Object>, IOException>> docValuesFieldFetcher(String name) {
+            return context -> {
+                var sortedDocValues = DocValues.getSortedSet(context.reader(), name);
+                return docId -> {
+                    if (sortedDocValues.advanceExact(docId)) {
+                        var values = new ArrayList<>(sortedDocValues.docValueCount());
+                        for (int i = 0; i < sortedDocValues.docValueCount(); i++) {
+                            long ord = sortedDocValues.nextOrd();
+                            values.add(sortedDocValues.lookupOrd(ord).utf8ToString());
+                        }
+                        return values;
+                    } else {
+                        return List.of();
+                    }
+                };
+            };
+        }
+
+        private static IOFunction<LeafReaderContext, CheckedIntFunction<List<Object>, IOException>> storedFieldFetcher(String name) {
+            var loader = StoredFieldLoader.create(false, Set.of(name));
+            return context -> {
+                var leafLoader = loader.getLoader(context, null);
+                return docId -> {
+                    leafLoader.advanceTo(docId);
+                    return leafLoader.storedFields().get(name);
+                };
+            };
+        }
+
         private Query toQuery(Query query, SearchExecutionContext searchExecutionContext) {
             return new ConstantScoreQuery(
                 new SourceConfirmedTextQuery(query, getValueFetcherProvider(searchExecutionContext), indexAnalyzer)
@@ -505,18 +563,27 @@ 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 {
+            var kwd = TextFieldMapper.SyntheticSourceHelper.getKeywordFieldMapperForSyntheticSource(this);
+            if (kwd != null) {
+                return new SyntheticSourceSupport.Native(() -> kwd.syntheticFieldLoader(fullPath(), leafName()));
             }
-        );
+            assert false : "there should be a suite field mapper with native synthetic source support";
+            return super.syntheticSourceSupport();
+        }
     }
 }

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

@@ -394,4 +394,170 @@ synthetic_source with copy_to:
   - match:
       hits.hits.0.fields.copy.0: "Apache Lucene powers Elasticsearch"
 
+---
+synthetic_source match_only_text as multi-field:
+  - requires:
+      cluster_features: [ "mapper.source.mode_from_index_setting" ]
+      reason: "Source mode configured through index setting"
+
+  - 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 as multi-field with stored keyword as parent:
+  - requires:
+      cluster_features: [ "mapper.source.mode_from_index_setting" ]
+      reason: "Source mode configured through index setting"
+
+  - do:
+      indices.create:
+        index: synthetic_source_test
+        body:
+          settings:
+            index:
+              mapping.source.mode: synthetic
+          mappings:
+            properties:
+              foo:
+                type: keyword
+                store: true
+                doc_values: false
+                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:
+  - requires:
+      cluster_features: [ "mapper.source.mode_from_index_setting" ]
+      reason: "Source mode configured through index setting"
+
+  - 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"
+
+---
+synthetic_source match_only_text with stored multi-field:
+  - requires:
+      cluster_features: [ "mapper.source.mode_from_index_setting" ]
+      reason: "Source mode configured through index setting"
+
+  - 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
+                    store: true
+                    doc_values: false
+
+  - 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"