Re: Bug: "git checkout -b" should be allowed in empty repo

Jeff King [off-list ref] writes:

Sure, that's one way to do it. But I don't see any point in not allowing
"git checkout -b" to be another way of doing it. Is there some other use
case for "git checkout -b" from an unborn branch? Or is there some
harmful outcome that can come from doing so that we need to be
protecting against? Am I missing something?

Mostly because it is wrong at the conceptual level to do so.

	git checkout -b foo

is a short-hand for

	git checkout -b foo HEAD

which is a short-hand for

	git branch foo HEAD &&
        git checkout foo

But the last one has no chance of working if you think about it, because
"git branch foo $start" is a way to start a branch at $start and you need
to have something to point at with refs/heads/foo.

So we are breaking the equivalence between these three only when HEAD
points at an unborn branch.