[Backport 2.19] Add highlighting for match_only_text type (#17101)

CHANGELOG.md

@@ -116,6 +116,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Fix GRPC AUX_TRANSPORT_PORT and SETTING_GRPC_PORT settings and remove lingering HTTP terminology ([#17037](https://github.com/opensearch-project/OpenSearch/pull/17037))
 - [WLM] Fix the QueryGroupTask logging bug ([#17169](https://github.com/opensearch-project/OpenSearch/pull/17169))
 - Use OpenSearch version to deserialize remote custom metadata([#16494](https://github.com/opensearch-project/OpenSearch/pull/16494))
+- Add highlighting for wildcard search on `match_only_text` field ([#17101](https://github.com/opensearch-project/OpenSearch/pull/17101))
 - Fix the failing CI's with `Failed to load eclipse jdt formatter` error ([#17172](https://github.com/opensearch-project/OpenSearch/pull/17172))
 - Fix AutoDateHistogramAggregator rounding assertion failure ([#17023](https://github.com/opensearch-project/OpenSearch/pull/17023))
 

modules/analysis-common/src/yamlRestTest/resources/rest-api-spec/test/search.query/11_match_field_match_only_text.yml

@@ -1,5 +1,5 @@
 # integration tests for queries with specific analysis chains
-
+---
 "match query with stacked stems":
   - skip:
       version: " - 2.11.99"
@@ -68,3 +68,80 @@
                 query: fox runs
                 operator: AND
   - match: {hits.total: 2}
+
+---
+"wildcard highlighting on match_only_text":
+  - skip:
+      version: " - 2.99.99"
+      reason: "wildcard highlighting on match_only_text type was added in 2.19"
+  - do:
+      indices.create:
+        index: test
+        body:
+          settings:
+            number_of_shards: 1
+            number_of_replicas: 1
+            analysis:
+              analyzer:
+                index:
+                  tokenizer: standard
+                  filter: [lowercase]
+                search:
+                  rest_total_hits_as_int: true
+                  tokenizer: standard
+                  filter: [lowercase, keyword_repeat, porter_stem, unique_stem]
+              filter:
+                unique_stem:
+                  type: unique
+                  only_on_same_position: true
+          mappings:
+            properties:
+              text:
+                type: match_only_text
+                analyzer: index
+                search_analyzer: search
+
+  - do:
+      index:
+        index: test
+        id:    1
+        body:  { "text": "the fox runs across the street" }
+        refresh: true
+
+  - do:
+      search:
+        rest_total_hits_as_int: true
+        body:
+          query:
+            match:
+              text:
+                query: fox runs
+                operator: AND
+          highlight:
+            fields:
+              - text: {}
+  - match: {hits.total: 1}
+  - match: {hits.hits.0.highlight.text.0: "the <em>fox</em> <em>runs</em> across the street"}
+
+  - do:
+      index:
+        index: test
+        id:    2
+        body:  { "text": "run fox run" }
+        refresh: true
+
+  - do:
+      search:
+        rest_total_hits_as_int: true
+        body:
+          query:
+            match:
+              text:
+                query: fox runs
+                operator: AND
+          highlight:
+            fields:
+              - text: {}
+  - match: {hits.total: 2}
+  - match: {hits.hits.0.highlight.text.0: "the <em>fox</em> <em>runs</em> across the street"}
+  - match: {hits.hits.1.highlight.text.0: "<em>run</em> <em>fox</em> <em>run</em>"}

server/src/main/java/org/opensearch/search/fetch/subphase/highlight/HighlightPhase.java

@@ -37,6 +37,7 @@
 import org.opensearch.common.regex.Regex;
 import org.opensearch.index.mapper.KeywordFieldMapper;
 import org.opensearch.index.mapper.MappedFieldType;
+import org.opensearch.index.mapper.MatchOnlyTextFieldMapper;
 import org.opensearch.index.mapper.SourceFieldMapper;
 import org.opensearch.index.mapper.TextFieldMapper;
 import org.opensearch.search.fetch.FetchContext;
@@ -152,7 +153,8 @@ private Map<String, Function<HitContext, FieldHighlightContext>> contextBuilders
                     continue;
                 }
 
-                // We should prevent highlighting if a field is anything but a text or keyword field.
+                // We should prevent highlighting if a field is anything but a text, match_only_text
+                // or keyword field.
                 // However, someone might implement a custom field type that has text and still want to
                 // highlight on that. We cannot know in advance if the highlighter will be able to
                 // highlight such a field and so we do the following:
@@ -162,7 +164,8 @@ private Map<String, Function<HitContext, FieldHighlightContext>> contextBuilders
                 // what they were doing and try to highlight anyway.
                 if (fieldNameContainsWildcards) {
                     if (fieldType.typeName().equals(TextFieldMapper.CONTENT_TYPE) == false
-                        && fieldType.typeName().equals(KeywordFieldMapper.CONTENT_TYPE) == false) {
+                        && fieldType.typeName().equals(KeywordFieldMapper.CONTENT_TYPE) == false
+                        && fieldType.typeName().equals(MatchOnlyTextFieldMapper.CONTENT_TYPE) == false) {
                         continue;
                     }
                     if (highlighter.canHighlight(fieldType) == false) {