Make a comment to MR whne milestone was changed

app/services/merge_requests/base_service.rb

@@ -16,5 +16,9 @@ module MergeRequests
         merge_request.project.execute_hooks(merge_request.to_hook_data, :merge_request_hooks)
       end
     end
+
+    def create_milestone_note(merge_request)
+      Note.create_milestone_change_note(merge_request, merge_request.project, current_user, merge_request.milestone)
+    end
   end
 end

app/services/merge_requests/update_service.rb

@@ -22,6 +22,10 @@ module MergeRequests
       if params.present? && merge_request.update_attributes(params)
         merge_request.reset_events_cache
 
+        if merge_request.previous_changes.include?('milestone_id')
+          create_milestone_note(merge_request)
+        end
+
         if merge_request.previous_changes.include?('assignee_id')
           notification_service.reassigned_merge_request(merge_request, current_user)
           create_assignee_note(merge_request)