diff -r e5fbf9687600 -r d47d7d3bd07b mercurial/cmdutil.py
--- a/mercurial/cmdutil.py	Sat May 13 15:41:50 2017 +0900
+++ b/mercurial/cmdutil.py	Sat Jan 09 23:24:52 2016 +0900
@@ -3335,7 +3335,10 @@
         if f in copied:
             repo.dirstate.copy(copied[f], f)
 
-command = registrar.command
+class command(registrar.command):
+    def _doregister(self, func, name, *args, **kwargs):
+        func._deprecatedregistrar = True  # flag for deprecwarn in extensions.py
+        return super(command, self)._doregister(func, name, *args, **kwargs)
 
 # a list of (ui, repo, otherpeer, opts, missing) functions called by
 # commands.outgoing.  "missing" is "missing" of the result of