Fixing the regression in inner hits aggregation

CHANGELOG.md

@@ -67,6 +67,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Enabled mockTelemetryPlugin for IT and fixed OOM issues ([#13054](https://github.com/opensearch-project/OpenSearch/pull/13054))
 - Fix implement mark() and markSupported() in class FilterStreamInput ([#13098](https://github.com/opensearch-project/OpenSearch/pull/13098))
 - Fix snapshot _status API to return correct status for partial snapshots ([#12812](https://github.com/opensearch-project/OpenSearch/pull/12812))
+- Fixed the regression in inner hits aggregation during fetch phase execution ([#13488](https://github.com/opensearch-project/OpenSearch/pull/13488))
 - Improve the error messages for _stats with closed indices ([#13012](https://github.com/opensearch-project/OpenSearch/pull/13012))
 - Ignore BaseRestHandler unconsumed content check as it's always consumed. ([#13290](https://github.com/opensearch-project/OpenSearch/pull/13290))
 

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/400_inner_hits.yml

@@ -0,0 +1,65 @@
+setup:
+  - do:
+      indices.create:
+        index: test_1
+        body:
+          settings:
+            number_of_replicas: 0
+          mappings:
+            properties:
+              list_id:
+                type: integer
+              names:
+                type: nested
+                properties:
+                  full_name:
+                    type: text
+
+  - do:
+      bulk:
+        refresh: true
+        body:
+          - index:
+              _index: test_1
+              _id:    1
+          - list_id: 1
+            names:
+              - full_name: John Doe
+              - full_name: John Micheal Doe
+          - index:
+              _index: test_1
+              _id:    2
+          - list_id: 2
+            names:
+              - full_name: Jane Doe
+              - full_name: Jane Michelle Doe
+
+---
+"Include inner hits in top hits":
+  - do:
+      search:
+        rest_total_hits_as_int: true
+        body:
+          query:
+            nested:
+              path: names
+              query:
+                match:
+                  names.full_name: Doe
+              inner_hits: { }
+          size: 0
+          aggs:
+            lists:
+              terms:
+                field: list_id
+              aggs:
+                top_result:
+                  top_hits:
+                    size: 10
+
+  - length: { hits.hits: 0 }
+  - length: { aggregations.lists.buckets: 2 }
+  - length: { aggregations.lists.buckets.0.top_result.hits.hits: 1 }
+  - length: { aggregations.lists.buckets.0.top_result.hits.hits.0.inner_hits.names.hits.hits: 2 }
+  - length: { aggregations.lists.buckets.1.top_result.hits.hits: 1 }
+  - length: { aggregations.lists.buckets.1.top_result.hits.hits.0.inner_hits.names.hits.hits: 2 }

server/src/main/java/org/opensearch/search/fetch/FetchContext.java

@@ -192,10 +192,6 @@ public boolean includeNamedQueriesScore() {
         return searchContext.includeNamedQueriesScore();
     }
 
-    public boolean hasInnerHits() {
-        return searchContext.hasInnerHits();
-    }
-
     /**
      * Configuration for returning inner hits
      */

server/src/main/java/org/opensearch/search/fetch/subphase/InnerHitsContext.java

@@ -119,11 +119,6 @@ public String getName() {
             return name;
         }
 
-        @Override
-        public boolean hasInnerHits() {
-            return childInnerHits != null;
-        }
-
         @Override
         public InnerHitsContext innerHits() {
             return childInnerHits;

server/src/main/java/org/opensearch/search/fetch/subphase/InnerHitsPhase.java

@@ -64,9 +64,7 @@ public InnerHitsPhase(FetchPhase fetchPhase) {
 
     @Override
     public FetchSubPhaseProcessor getProcessor(FetchContext searchContext) {
-        if (searchContext.hasInnerHits() == false) {
-            return null;
-        }
+        // InnerHits processor should always be included as the processing is lazy
         Map<String, InnerHitsContext.InnerHitSubContext> innerHits = searchContext.innerHits().getInnerHits();
         return new FetchSubPhaseProcessor() {
             @Override

server/src/main/java/org/opensearch/search/internal/SearchContext.java

@@ -194,10 +194,6 @@ public final void close() {
 
     public abstract void highlight(SearchHighlightContext highlight);
 
-    public boolean hasInnerHits() {
-        return innerHitsContext != null;
-    }
-
     public InnerHitsContext innerHits() {
         if (innerHitsContext == null) {
             innerHitsContext = new InnerHitsContext();