branchmap: display filtername when `updatebranch` fails to do its jobs We have a very handy assert at the ends of `branchmap.updatecache` that check the resulting branchmap is actually valid. I know we do not like assert in mercurial but this one is very handy for debugging. There is really not reason for `branchmap.updatecache` to have this kind of issue but this happened and handful of time during the development of this or introduction of other related feature. I advice to keep it around until we are a bit more confident with the new code.

--- a/mercurial/branchmap.py	Fri Jan 18 01:24:29 2013 +0100
+++ b/mercurial/branchmap.py	Sat Jan 19 02:29:56 2013 +0100
@@ -79,7 +79,7 @@
     if revs:
         partial.update(repo, revs)
         partial.write(repo)
-    assert partial.validfor(repo)
+    assert partial.validfor(repo), filtername
     repo._branchcaches[repo.filtername] = partial
 
 class branchcache(dict):