On Thu, May 30, 2024 at 03:09:40PM +0300, Karthik Nayak wrote:

From: Karthik Nayak <redacted>

Add 'symref-update' command to the '--stdin' mode of 'git-update-ref' to
allow updates of symbolic refs. The 'symref-update' command takes in a
<new-target>, which the <ref> will be updated to. If the <ref> doesn't
exist it will be created.

It also optionally takes either an `ref <old-target>` or `oid
<old-oid>`. If the <old-target> is provided, it checks to see if the
<ref> targets the <old-target> before the update. If <old-oid> is provided
it checks <ref> to ensure that it is a regular ref and <old-oid> is the
OID before the update. This by extension also means that this when a
zero <old-oid> is provided, it ensures that the ref didn't exist before.

The divergence in syntax from the regular `update` command is because if
we don't use a `(ref | oid)` prefix for the old_value, then there is
ambiguity around if the value provided should be treated as an oid or a
reference. This is more so the reason, because we allow anything
committish to be provided as an oid.

It would be nice to explain why this isn't needed for symref-delete and
symref-create, which also both have an old value.

Patrick