Re: [PATCH 1/2] ref-filter: hacky "streaming" mode

From: Jeff King <peff@peff.net>
Date: Sep 16, 2021, 21:45 UTC
Message-ID: <YUO63qy2/5wibY4/@coredump.intra.peff.net>
In-Reply-To: <CAOLTT8SYxUbfG7YvAs03nwRdee8JfNPUYCCpKcFoAgBjB2oqLw@mail.gmail.com>

On Wed, Sep 15, 2021 at 10:23:43PM +0800, ZheNing Hu wrote:

Show 15 quoted lines

> ZheNing Hu <adlternative@gmail.com> 于2021年9月15日周三 下午8:27写道：
> >
> > > So yes, it's complicated. And it must be explained to the user that
> > > "%(refname)" behaves slightly differently with "git tag --verify", but
> > > that is unavoidable if we do not want to break scripts (it _already_
> > > behaves slightly differently, and we just never told anyone).
> > >
> 
> $ git tag --verify --format='verify: %(refname) %(symref)' annotated symref
> verify: annotated
> verify: symref
> $ git tag --verify --format='verify: %(refname) %(symref)'
> refs/tags/annotated refs/tags/symref
> error: tag 'refs/tags/annotated' not found.
> error: tag 'refs/tags/symref' not found.

This is expected. When you provide a tag name on the command line of "git tag" it is assumed to be a non-qualified name in refs/tags/ (and ditto for git-branch and refs/heads/). It is tempting to try to be friendly and accept fully-qualified refs there, but it would create ambiguities (e.g., you could really have refs/tags/refs/tags/foo as a ref).

I think we can ignore that for our purposes here, though. It's a question of input from the command-line, and we focus on just the output that we produce.

Show 13 quoted lines

> $ git verify-tag --format='verify: %(refname) %(symref)' annotated
> symref
> verify: annotated
> verify: symref
> $ git verify-tag --format='verify: %(refname) %(symref)'
> refs/tags/annotated refs/tags/symref
> verify: refs/tags/annotated
> verify: refs/tags/symref
> 
> As we can see, there is a slight difference between git tag --verify and
> git verify-tag: git tag --verify can not handle refs' fullname refs/tags/*
> (because read_ref_full() | read_ref() can't handle them). So, as a standard,
> which characteristics should we keep?

Whereas are you notice here, verify-tag takes any name (which could be fully qualified), and uses it as-is. In fact, it might not even be a ref at all! You can say "git verify-tag c06b72d02" if you want to. And as a plumbing tool, we should make sure this continues to work. For example, careful scripts may resolve a ref into an object, and want to continue talking about that object without worrying about the ref being changed simultaneously.

But it also creates a weirdness for "git verify-tag --format". We do not necessarily even have a ref to show. So IMHO the feature is somewhat mis-designed in the first place. But we should probably continue to support it as best we can.

The best I can come up with is:

  - when we resolve the name, if it was a ref, we should record that.
    I think this is hard to do now. It would probably require
    get_oid_with_context() learning to report on the results it got from
    dwim_ref().

  - if we have a refname, then feed it to pretty_print_ref() as a
    fully-qualified name. And pass whatever "default lstrip=2" magic we
    come up with for "git tag --verify". That would mean that "git
    verify-tag --format=%(refname) v2.33.0" would behave the same before
    and after.

  - if we didn't get a refname, then...I guess continue to pass the name
    the user gave us into pretty_print_ref()? That would keep "git
    verify-tag --format=%(refname) c06b72d02" working as it does today.

The alternative is to do none of those things, and just document that "verify-tag" is weird:

  - its %(refname) reports whatever you gave it, whether it is a ref or
    not

  - some advanced format placeholders like %(symref) may not work if you
    don't pass a fully-qualified ref

-Peff