branchmap: don't add branch entries if there are no heads We definitely don't want any empty entries to be present in repo.branchmap() just for the sake of not breaking test-notify.t. No test changes required because the previous patch made notify extension to not raise any tracebacks in case of RepoLookupErrors. Differential Revision: https://phab.mercurial-scm.org/D12135

notify: don't produce errors if a revision is not found Notify extension has a way to only subscribe to a specific revset, such as "branch(foo)". Before this patch, when there was no branch with that name, it would produce a traceback saying "unknown revision: foo". With this patch it would no longer do that, and instead it'll assume there are no revisions that match this revset. I think this patch is an improvement in general, but there's a reason I'm sending it now. test-notify.t has a test case where it obsoletes the only revision on a branch, and previously that wouldn't produce any complications, because head computation wasn't obsolescence-aware. Now if the only revision on a branch is obsolete, repo should not see that branch at all. That branch will still be present in branchcache (with an empty list of revisions) until the next patch. Differential Revision: https://phab.mercurial-scm.org/D12134