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

[Jacob Keller <jacob.keller@gmail.com>]

On Fri, Aug 21, 2020 at 10:26 AM Jacob Keller <jacob.keller@gmail.com> wrote:
>
> On Fri, Aug 21, 2020 at 10:16 AM Jacob Keller <jacob.keller@gmail.com> wrote:
> >
> > 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.
>
> I also tried adding a test for fetch --prune, but that ultimately
> calls query_refspecs_multiple and query_refspecs. I need to figure out
> how negative refspecs need to interact with that function still.

So there's an interesting problem here... query_refspecs_multiple
takes only the destination name, which makes the "get_stale_heads" not
work properly, since for fetch we want to apply the refspec to the
remote sides "source".