Re: [PATCH 3/4] builtin/refs: add "update" subcommand

[Patrick Steinhardt <ps@pks.im>]

On Tue, Jun 16, 2026 at 04:17:27AM -0700, Junio C Hamano wrote:
> Patrick Steinhardt <ps@pks.im> writes:
> 
> > Add a new "update" subcommand which mirrors `git update-ref <refname>
> > <oldoid> <newoid>`. This follows the same reasoning as the preceding
> > commit.
> >
> > Signed-off-by: Patrick Steinhardt <ps@pks.im>
> > ---
> >  Documentation/git-refs.adoc |   7 ++
> >  builtin/refs.c              |  50 +++++++++++++
> >  t/meson.build               |   1 +
> >  t/t1465-refs-update.sh      | 179 ++++++++++++++++++++++++++++++++++++++++++++
> >  4 files changed, 237 insertions(+)
> 
> I do not offhand know (and I am still away by 2 hours from the time
> I wake up and start functioning) if update-ref shares the same
> issue, but with "delete, update, rename" combo, lack of "create"
> feels a bit annoying.  Wouldn't we want to offer an option to users
> who want to ensure that the refs they create are truly new and they
> are not overwriting a ref somebody has created?  Either (1) drop
> "delete" and take a special value (e.g. "") as <newvalue> to signal
> deletion and make the same special value used as <oldvalue> signals
> creation, or (2) add "create" and insist that "update" takes only an
> existing ref, would make the annoyance go away, I guess.

In theory "update" can handle both updating existing references,
deleting them and creating them race-free by providing NUL object IDs
for either old or new value. But I agree that this is cumbersome, and
adding another "create" subcommand as an easy-to-understand shortcut
feels sensible.

> > +test_expect_success 'update creates a new reference' '
> > +	test_when_finished "rm -rf repo" &&
> > +	setup_repo repo &&
> > +	(
> > +		cd repo &&
> > +		A=$(git rev-parse A) &&
> > +		git refs update refs/heads/foo $A &&
> > +		test_ref_matches refs/heads/foo "$A"
> > +	)
> > +'
> 
> Here we cannot test (and I strongly suspect that "git refs update"
> and "git update-ref" lack ability to do so) a case where a creation
> is attempted on an existing ref and fails.

We can:

    $ git update-ref $NEW_OID $NULL_OID
    $ git refs update $NEW_OID $NULL_OID

This will verify that the reference doesn't exist before actually
writing it. Will add a test.

Patrick