On Sun, Mar 31, 2024 at 3:09 PM Junio C Hamano <gitster@xxxxxxxxx> wrote:
> ... we are giving to "update-symref" is not an object name, but a
> refname (i.e. the target of the symref at <ref> points at), so
> "newvalue" -> "new-ref" or something is needed.
I kept this line just to say, I agree on all of the above ...
> Existing "update" command can be used to create (by having "zero"
> <old-oid>) and to delete (by having "zero" <new-oid>), but we still
> have "create" and "delete" separately. Given that we are teaching
> the command to also work with symrefs by adding command(s) for
> symrefs to an existing vocabulary, we should offer "create-symref"
> and "delete-symref" for consistency between refs and symrefs.
.. and on this, but:
> It probably is a good idea to allow "update-symref" to also create
> and delete a symref in similar ways with the existing "update"
> allows creation and deletion of a ref. An "zero" <old-ref> may be
> an update that can happen only when the <ref> does not exist, i.e.,
> creation, and an "zero" <new-ref> may be an update that makes <ref>
> disappear.
>
> "zero" value in the context of refs is a 0{40} object name (side
> note: we have an explicit mention of 40 in the doc, which needs to
> be updated eventually, probably outside this series). But in the
> new context of symrefs, a safe "zero" value needs to be picked
> carefully. An empty string may not work well syntactically
> especially in the `-z` format, because you cannot tell if
>
> update-symref NUL HEAD NUL refs/heads/main NUL NUL
>
> wants to say that <old-ref> is an empty string, or if it is missing.
For these reasons, I'd suggest that the all-zero hash be officially
deprecated in favor of create/delete and of course create-symref
and delete-symref. Of course, compatibility requires some sort
of support for the old system for some time. As to whether that
means something like the suggestion of ".missing" etc, I have no
particular opinion -- but since the symref options are new, they
would not *need* symmetric options, if we just say that "update-symref"
cannot create or delete a symref.
Meanwhile, for testing purposes I was curious as to what happens
if you ask `git update-ref` to delete an existing symref, so after
creating a test repository:
$ git branch
* main
symref -> main
$ git update-ref --stdin
delete refs/heads/symref
$ git branch
Whoops, this doesn't look good...
Restoring the branch name (I had saved the hash ID Just In Case):
$ echo d88ee82e6a5c29c95f712030f5efc9d43116ae79 > .git/refs/heads/main
brings things back, after which this works properly:
$ git branch -d symref
Deleted branch symref (was refs/heads/main).
$ git branch
* main
If this (deleting the target of the symref when using "delete")
is a bug, and I think it is, that's a separate topic of course...
Chris
