diff --git a/mercurial/context.py b/mercurial/context.py
--- a/mercurial/context.py
+++ b/mercurial/context.py
@@ -249,11 +249,18 @@ class basectx(object):
             return ''
 
     def sub(self, path):
+        '''return a subrepo for the stored revision of path, never wdir()'''
         return subrepo.subrepo(self, path)
 
     def nullsub(self, path, pctx):
         return subrepo.nullsubrepo(self, path, pctx)
 
+    def workingsub(self, path):
+        '''return a subrepo for the stored revision, or wdir if this is a wdir
+        context.
+        '''
+        return subrepo.subrepo(self, path, allowwdir=True)
+
     def match(self, pats=[], include=None, exclude=None, default='glob',
               listsubrepos=False, badfn=None):
         r = self._repo
diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -324,7 +324,7 @@ def _sanitize(ui, vfs, ignore):
                           "in '%s'\n") % vfs.join(dirname))
                 vfs.unlink(vfs.reljoin(dirname, f))
 
-def subrepo(ctx, path):
+def subrepo(ctx, path, allowwdir=False):
     """return instance of the right subrepo class for subrepo in path"""
     # subrepo inherently violates our import layering rules
     # because it wants to make repo objects from deep inside the stack
@@ -338,6 +338,8 @@ def subrepo(ctx, path):
     state = ctx.substate[path]
     if state[2] not in types:
         raise util.Abort(_('unknown subrepo type %s') % state[2])
+    if allowwdir:
+        state = (state[0], ctx.subrev(path), state[2])
     return types[state[2]](ctx, path, state[:2])
 
 def nullsubrepo(ctx, path, pctx):