diff -r 2e1c32a9c97b -r baf58e621363 mercurial/context.py
--- a/mercurial/context.py	Thu Dec 07 16:07:06 2017 -0800
+++ b/mercurial/context.py	Thu Dec 07 16:07:06 2017 -0800
@@ -2217,6 +2217,9 @@
     def remove(self, ignoremissing=False):
         return self._parent.remove(self._path)
 
+    def clearunknown(self):
+        pass
+
 class workingcommitctx(workingctx):
     """A workingcommitctx object makes access to data related to
     the revision being committed convenient.