diff -r 66eb74f9d87d -r 79d7d715f3d0 mercurial/obsutil.py
--- a/mercurial/obsutil.py	Fri Jul 06 21:35:47 2018 +0900
+++ b/mercurial/obsutil.py	Fri Jul 06 21:38:33 2018 +0900
@@ -395,7 +395,7 @@
 
     This is a first and basic implementation, with many shortcoming.
     """
-    diffopts = diffutil.diffopts(leftctx._repo.ui, {'git': True})
+    diffopts = diffutil.diffopts(leftctx.repo().ui, {'git': True})
     # Leftctx or right ctx might be filtered, so we need to use the contexts
     # with an unfiltered repository to safely compute the diff
     leftunfi = leftctx._repo.unfiltered()[leftctx.rev()]