Collect multiple paths from XContentMapValues (#68540)

Currently, when a document source mixed json object and dotted syntax like e.g.
{ "foo" : { "bar" : 0 }, "foo.bar" : 1}, extracting the values from the source
map via XContentMapValues#extractValue returns after the first value for a path
has been found. Instead we should exhaust all possibilities and return a list of
objects of we find more than one value when extending the lookup path.

Closes #68215

server/src/main/java/org/elasticsearch/common/xcontent/support/XContentMapValues.java

@@ -154,19 +154,27 @@ private static Object extractValue(String[] pathElements,
             Map<?, ?> map = (Map<?, ?>) currentValue;
             String key = pathElements[index];
             int nextIndex = index + 1;
+            List<Object> extractedValues = new ArrayList<>();
             while (true) {
                 if (map.containsKey(key)) {
                     Object mapValue = map.get(key);
                     if (mapValue == null) {
-                        return nullValue;
-                    }
-                    Object val = extractValue(pathElements, nextIndex, mapValue, nullValue);
-                    if (val != null) {
-                        return val;
+                        extractedValues.add(nullValue);
+                    } else {
+                        Object val = extractValue(pathElements, nextIndex, mapValue, nullValue);
+                        if (val != null) {
+                            extractedValues.add(val);
+                        }
                     }
                 }
                 if (nextIndex == pathElements.length) {
-                    return null;
+                    if (extractedValues.size() == 0) {
+                        return null;
+                    } else if (extractedValues.size() == 1) {
+                        return extractedValues.get(0);
+                    } else {
+                        return extractedValues;
+                    }
                 }
                 key += "." + pathElements[nextIndex];
                 nextIndex++;

server/src/test/java/org/elasticsearch/common/xcontent/support/XContentMapValuesTests.java

@@ -33,6 +33,7 @@
 import static org.elasticsearch.common.xcontent.XContentHelper.convertToMap;
 import static org.elasticsearch.common.xcontent.XContentHelper.toXContent;
 import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.hamcrest.Matchers.hasEntry;
 import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.hasSize;
@@ -197,6 +198,17 @@ public void testExtractValueMixedObjects() throws IOException {
         }
     }
 
+    public void testExtractValueMixedDottedObjectNotation() throws IOException {
+        XContentBuilder builder = XContentFactory.jsonBuilder().startObject()
+            .startObject("foo").field("cat", "meow").endObject()
+            .field("foo.cat", "miau")
+            .endObject();
+        try (XContentParser parser = createParser(JsonXContent.jsonXContent, Strings.toString(builder))) {
+            Map<String, Object> map = parser.map();
+            assertThat((List<?>) XContentMapValues.extractValue("foo.cat", map), containsInAnyOrder("meow", "miau"));
+        }
+    }
+
     public void testExtractRawValue() throws Exception {
         XContentBuilder builder = XContentFactory.jsonBuilder().startObject()
                 .field("test", "value")

server/src/test/java/org/elasticsearch/search/fetch/subphase/FieldFetcherTests.java

@@ -98,6 +98,49 @@ public void testMixedObjectValues() throws IOException {
         DocumentField field = fields.get("foo.bar");
         assertThat(field.getValues().size(), equalTo(1));
         assertThat(field.getValue(), equalTo("baz"));
+
+        source = XContentFactory.jsonBuilder().startObject()
+            .startObject("foo").field("cat", "meow").endObject()
+            .field("foo.cat", "miau")
+            .endObject();
+
+        doc = mapperService.documentMapper().parse(source(Strings.toString(source)));
+
+        fields = fetchFields(mapperService, source, "foo.cat");
+        assertThat(fields.size(), equalTo(1));
+
+        field = fields.get("foo.cat");
+        assertThat(field.getValues().size(), equalTo(2));
+        assertThat(field.getValues(), containsInAnyOrder("meow", "miau"));
+
+        source = XContentFactory.jsonBuilder().startObject()
+            .startObject("foo").field("cat", "meow").endObject()
+            .array("foo.cat", "miau", "purr")
+            .endObject();
+
+        doc = mapperService.documentMapper().parse(source(Strings.toString(source)));
+
+        fields = fetchFields(mapperService, source, "foo.cat");
+        assertThat(fields.size(), equalTo(1));
+
+        field = fields.get("foo.cat");
+        assertThat(field.getValues().size(), equalTo(3));
+        assertThat(field.getValues(), containsInAnyOrder("meow", "miau", "purr"));
+    }
+
+    public void testMixedDottedObjectSyntax() throws IOException {
+        MapperService mapperService = createMapperService();
+        XContentBuilder source = XContentFactory.jsonBuilder().startObject()
+            .startObject("object").field("field", "value").endObject()
+            .field("object.field", "value2")
+            .endObject();
+
+        Map<String, DocumentField> fields = fetchFields(mapperService, source, "*");
+        assertThat(fields.size(), equalTo(1));
+
+        DocumentField field = fields.get("object.field");
+        assertThat(field.getValues().size(), equalTo(2));
+        assertThat(field.getValues(), containsInAnyOrder("value", "value2"));
     }
 
     public void testNonExistentField() throws IOException {