Re: [RFC 3/3] refspec: add support for negative refspecs

From: Jacob Keller <jacob.keller@gmail.com>
To: Jeff King <peff@peff.net>
Cc: Junio C Hamano <gitster@pobox.com>,
	Jacob Keller <jacob.e.keller@intel.com>,
	Git mailing list <git@vger.kernel.org>
Subject: Re: [RFC 3/3] refspec: add support for negative refspecs
Date: Fri, 21 Aug 2020 10:16:36 -0700	[thread overview]
Message-ID: <CA+P7+xrPep7caJm2uN+hAqOqZU3b2njpW95JQCzYJdKgbakp8A@mail.gmail.com> (raw)
In-Reply-To: <20200818174116.GA2473110@coredump.intra.peff.net>

On Tue, Aug 18, 2020 at 10:41 AM Jeff King <peff@peff.net> wrote:
> Hmm. I think the behavior we'd want is something like:
>
>   # make sure the other side has three refs
>   git branch prune/one HEAD
>   git branch prune/two HEAD
>   git branch prune/three HEAD
>   git push dst.git refs/heads/prune/*
>
>   # now drop two of ours, which are eligible for pruning
>   git branch -d prune/one
>   git branch -d prune/two
>
>   # push with pruning, omitting "two"
>   git push --prune dst.git refs/heads/prune/* ^refs/heads/prune/two
>
>   # we should leave "two" but still deleted "one"
>   test_write_lines one three >expect
>   git -C dst.git for-each-ref --format='%(refname:lstrip=3)' refs/heads/prune/ >actual
>   test_cmp expect actual
>
> I.e., the negative refspec shrinks the space we're considering pruning.
> And we'd probably want a similar test for "fetch --prune".
>
> I just tried that, though, and got an interesting result. The push
> actually complains:
>
>   $ git push --prune dst.git refs/heads/prune/* ^refs/heads/prune/two
>   error: src refspec refs/heads/prune/two does not match any
>   error: failed to push some refs to 'dst.git'
>
> For negative refspecs, would we want to loosen the "must-exist" check?
> Or really, is this getting into the "are we negative on the src or dst"
> thing you brought up earlier? Especially with --prune, what I really
> want to say is "do not touch the remote refs/heads/two".
>
> We can get work around it by using a wildcard:
>
>   $ git push --prune dst.git refs/heads/prune/* ^refs/heads/prune/two*
>   To dst.git
>    - [deleted]         prune/one
>
> So it works as I'd expect already with your patch. But I do wonder if
> there are corner cases around the src/dst thing that might not behave
> sensibly.
>

Hmm. So this raises a good point. I added a variation of this test
where I used separate names for the source and destination. It looks
like with the current implementation, negative refspecs always apply
to the destination.