1 files changed, 13 insertions, 1 deletions
diff --git a/src/google/protobuf/util/message_differencer.h b/src/google/protobuf/util/message_differencer.h
index b7d4de00..11d6cc03 100644
--- a/src/google/protobuf/util/message_differencer.h
+++ b/src/google/protobuf/util/message_differencer.h
@@ -64,6 +64,7 @@ class Printer;
 
 namespace util {
 
+class DefaultFieldComparator;
 class FieldContext;  // declared below MessageDifferencer
 
 // A basic differencer that can be used to determine
@@ -372,7 +373,7 @@ class LIBPROTOBUF_EXPORT MessageDifferencer {
                  // repeated fields have different numbers of elements, the
                  // unpaired elements are reported using ReportAdded() or
                  // ReportDeleted().
-    AS_SET,      // Treat all the repeated fields as sets by default.
+    AS_SET,      // Treat all the repeated fields as sets.
                  // See TreatAsSet(), as below.
   };
 
@@ -386,6 +387,11 @@ class LIBPROTOBUF_EXPORT MessageDifferencer {
   // the only differences between the compared messages is that some fields
   // have been moved, then the comparison returns true.
   //
+  // Note that despite the name of this method, this is really
+  // comparison as multisets: if one side of the comparison has a duplicate
+  // in the repeated field but the other side doesn't, this will count as
+  // a mismatch.
+  //
   // If the scope of comparison is set to PARTIAL, then in addition to what's
   // above, extra values added to repeated fields of the second message will
   // not cause the comparison to fail.
@@ -470,6 +476,10 @@ class LIBPROTOBUF_EXPORT MessageDifferencer {
       const FieldDescriptor* field,
       const MapKeyComparator* key_comparator);
 
+  // Initiates and returns a new instance of MultipleFieldsMapKeyComparator.
+  MapKeyComparator* CreateMultipleFieldsMapKeyComparator(
+      const std::vector<std::vector<const FieldDescriptor*> >& key_field_paths);
+
   // Add a custom ignore criteria that is evaluated in addition to the
   // ignored fields added with IgnoreField.
   // Takes ownership of ignore_criteria.
@@ -660,6 +670,8 @@ class LIBPROTOBUF_EXPORT MessageDifferencer {
   };
 
  private:
+  friend class DefaultFieldComparator;
+
   // A MapKeyComparator to be used in TreatAsMapUsingKeyComparator.
   // Implementation of this class needs to do field value comparison which
   // relies on some private methods of MessageDifferencer. That's why this