diff -r 74cbbd5420ba -r 1937671105bc mercurial/scmutil.py
--- a/mercurial/scmutil.py	Wed Mar 08 16:43:16 2017 -0800
+++ b/mercurial/scmutil.py	Fri Aug 05 14:24:53 2016 +0200
@@ -881,7 +881,7 @@
         function to call the appropriate join function on 'obj' (an instance
         of the class that its member function was decorated).
         """
-        return obj.join(fname)
+        raise NotImplementedError
 
     def __call__(self, func):
         self.func = func