diff -r d1a0a64f6e16 -r 869d660b8669 mercurial/commands.py
--- a/mercurial/commands.py	Mon Nov 14 23:17:15 2016 +0000
+++ b/mercurial/commands.py	Wed Aug 17 21:07:38 2016 -0700
@@ -1867,25 +1867,6 @@
     with repo.wlock(False):
         return cmdutil.copy(ui, repo, pats, opts)
 
-@command('debugancestor', [], _('[INDEX] REV1 REV2'), optionalrepo=True)
-def debugancestor(ui, repo, *args):
-    """find the ancestor revision of two revisions in a given index"""
-    if len(args) == 3:
-        index, rev1, rev2 = args
-        r = revlog.revlog(scmutil.opener(os.getcwd(), audit=False), index)
-        lookup = r.lookup
-    elif len(args) == 2:
-        if not repo:
-            raise error.Abort(_("there is no Mercurial repository here "
-                               "(.hg not found)"))
-        rev1, rev2 = args
-        r = repo.changelog
-        lookup = repo.lookup
-    else:
-        raise error.Abort(_('either two or three arguments required'))
-    a = r.ancestor(lookup(rev1), lookup(rev2))
-    ui.write("%d:%s\n" % (r.rev(a), hex(a)))
-
 @command('debugbuilddag',
     [('m', 'mergeable-file', None, _('add single file mergeable changes')),
     ('o', 'overwritten-file', None, _('add single file all revs overwrite')),