topic: handle ambiguous arguments to topic() revset These arguments can be interpreted as either string or a revset. The decision is made based on existence of topic with such a name. This matches the behavior of branch() revset. The code needs to know all topics that ever existed in the repo, because some commands report "disappearance" of topics after certain operations, using this revset (e.g. via stack.stack or repo.revs).

topic: handle revsets passed to topic() revset This handles cases when the argument can't be interpreted as a string at all.