handle empty array logic in DocumentParser

Author: martijnvg

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

@@ -769,8 +769,12 @@ private static void parseNonDynamicArray(
             }
             previousToken = token;
         }
-        if (mapper != null && previousToken == XContentParser.Token.START_ARRAY) {
-            mapper.handleEmptyArray(context);
+        if (mapper != null
+            && mapper.supportStoringArrayOffsets(context)
+            && previousToken == XContentParser.Token.START_ARRAY
+            && context.isImmediateParentAnArray()
+            && context.getRecordedSource() == false) {
+            context.getOffSetContext().maybeRecordEmptyArray(mapper.getOffsetFieldName());
         }
         context.setImmediateXContentParent(token);
         if (elements <= 1 && canRemoveSingleLeafElement) {

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

@@ -1114,10 +1114,9 @@ public boolean supportStoringArrayOffsets(DocumentParserContext context) {
         }
     }
 
-    public void handleEmptyArray(DocumentParserContext context) {
-        if (offsetsFieldName != null && context.isImmediateParentAnArray() && context.getRecordedSource() == false) {
-            context.getOffSetContext().maybeRecordEmptyArray(offsetsFieldName);
-        }
+    @Override
+    public String getOffsetFieldName() {
+        return offsetsFieldName;
     }
 
     protected void parseCreateField(DocumentParserContext context) throws IOException {

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

@@ -213,9 +213,18 @@ public static FieldType freezeAndDeduplicateFieldType(FieldType fieldType) {
      */
     public abstract int getTotalFieldsCount();
 
+    /**
+     * @return whether this mapper support storing leaf array elements natively when synthetic source is enabled.
+     */
     public boolean supportStoringArrayOffsets(DocumentParserContext context) {
         return false;
     }
 
-    public void handleEmptyArray(DocumentParserContext context) {}
+    /**
+     * @return the offset field name use the store offsets iff {@link #supportStoringArrayOffsets(DocumentParserContext)} returns
+     * <code>true</code>.
+     */
+    public String getOffsetFieldName() {
+        return null;
+    }
 }