diff -r 61b267a99fea -r fa6309c5761d mercurial/simplemerge.py
--- a/mercurial/simplemerge.py	Thu Aug 24 21:30:37 2017 -0700
+++ b/mercurial/simplemerge.py	Thu Aug 24 21:30:51 2017 -0700
@@ -419,8 +419,8 @@
 
     return [name_a, name_b, name_base]
 
-def simplemerge(ui, localfile, basefile, otherfile,
-                localctx=None, basectx=None, otherctx=None, repo=None, **opts):
+def simplemerge(ui, localctx=None, basectx=None, otherctx=None, repo=None,
+                **opts):
     """Performs the simplemerge algorithm.
 
     {local|base|other}ctx are optional. If passed, they (local/base/other) will