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

> 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.
>