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

[Jeff King <peff@peff.net>]

On Sun, Feb 05, 2012 at 09:30:15PM -0800, Junio C Hamano wrote:

> Jeff King <peff@peff.net> 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.

I think it is only wrong at the conceptual level because you have
specified the concepts in such a way that it is so. That is how git does
it _now_, but the whole point of this is to change git's behavior to
handle a potentially useful special case. I could also say this: "git
checkout -b foo HEAD" does two things:

  1. create a new branch "foo" pointing to the current sha1 of HEAD

  2. point the HEAD symref at refs/heads/foo

And then the proposed behavior might amend the first point to say:

  1. if HEAD points to an existing ref, then create a new branch...

which is perfectly consistent and simple. It does violate your "X is a
short-hand for Y" above, but why is that a bad thing? It seems you are
arguing against a special case _because_ it is a special case, not
because it is not a reasonable thing to do or expect.

Anyway. I am still not convinced that this is even a useful thing to
want to do, so I am certainly not volunteering to write such a patch. So
perhaps there is no point arguing about it.

-Peff