diff -r 0325c0da05df -r 7f9655f37163 mercurial/localrepo.py
--- a/mercurial/localrepo.py	Mon Apr 20 17:15:50 2015 +0200
+++ b/mercurial/localrepo.py	Mon Apr 20 17:16:05 2015 +0200
@@ -1905,6 +1905,8 @@
             hookargs = {}
             if tr is not None:
                 hookargs.update(tr.hookargs)
+                pending = lambda: tr.writepending() and self.root or ""
+                hookargs['pending'] = pending
             hookargs['namespace'] = namespace
             hookargs['key'] = key
             hookargs['old'] = old