[8.16] Fix synthetic source issue with deeply nested ignored source fields (#121715) (#121790)

* Fix synthetic source issue with deeply nested ignored source fields (#121715)

* Fix synthetic source issue with deeply nested ignored source fields

* Update docs/changelog/121715.yaml

* fix tests

Author: lkts

docs/changelog/121715.yaml

@@ -0,0 +1,5 @@
+pr: 121715
+summary: Fix synthetic source issue with deeply nested ignored source fields
+area: Mapping
+type: bug
+issues: []

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

@@ -1083,7 +1083,7 @@ public boolean setIgnoredValues(Map<String, List<IgnoredSourceFieldMapper.NameVa
             for (SourceLoader.SyntheticFieldLoader loader : fields) {
                 ignoredValuesPresent |= loader.setIgnoredValues(objectsWithIgnoredFields);
             }
-            return this.ignoredValues != null;
+            return ignoredValuesPresent;
         }
 
         @Override

server/src/test/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapperTests.java

@@ -2205,6 +2205,34 @@ public void testStoredArrayWithFlatFields() throws IOException {
             {"outer":{"inner":[{"a.b":"a.b","a.c":"a.c"}]}}""", syntheticSource);
     }
 
+    public void testSingleDeepIgnoredField() throws IOException {
+        DocumentMapper documentMapper = createMapperService(syntheticSourceMapping(b -> {
+            b.startObject("top");
+            b.startObject("properties");
+            {
+                b.startObject("level1").startObject("properties");
+                {
+                    b.startObject("level2").startObject("properties");
+                    {
+                        b.startObject("n")
+                            .field("type", "integer")
+                            .field("doc_values", "false")
+                            .field("synthetic_source_keep", "all")
+                            .endObject();
+                    }
+                    b.endObject().endObject();
+                }
+                b.endObject().endObject();
+            }
+            b.endObject().endObject();
+        })).documentMapper();
+
+        var syntheticSource = syntheticSource(documentMapper, b -> {
+            b.startObject("top").startObject("level1").startObject("level2").field("n", 25).endObject().endObject().endObject();
+        });
+        assertEquals("{\"top\":{\"level1\":{\"level2\":{\"n\":25}}}}", syntheticSource);
+    }
+
     protected void validateRoundTripReader(String syntheticSource, DirectoryReader reader, DirectoryReader roundTripReader)
         throws IOException {
         // We exclude ignored source field since in some cases it contains an exact copy of a part of document source.