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 Now if the only revision on a branch is
obsolete, repo should not see that branch at all.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.