mercurial/branchmap.py

--- a/mercurial/branchmap.py	Mon Dec 24 03:06:03 2012 +0100
+++ b/mercurial/branchmap.py	Tue Jan 01 21:27:13 2013 +0100
@@ -48,7 +48,11 @@
         raise
     except Exception, inst:
         if repo.ui.debugflag:
-            repo.ui.warn(('invalid branchheads cache: %s\n') % inst)
+            msg = 'invalid branchheads cache'
+            if repo.filtername is not None:
+                msg += ' (%s)' % repo.filtername
+            msg += ': %s\n'
+            repo.ui.warn(msg % inst)
         partial = branchcache()
     return partial