From: Karthik Nayak <karthik.188@gmail.com>
Date: Sat, 19 Sep 2026 20:52:22 GMT
Subject: Re: [BUG] reference-transaction hook misses destination of git branch -m
Message-ID: <CAOLa=ZTN1TU2A1sgEhiw=ymMYr6Ge11cMEubSaeKqr4WNU=2EQ@mail.gmail.com>
In-Reply-To: <CACQ=SRHCOCcmVCgHqd+sjMsZ9LCdSHuXdCo0gkwxXwYgF7iwig@mail.gmail.com>

Maciej Ciemborowicz <maciej.ciemborowicz@gmail.com> writes:

> Hello,
>
> `git branch -m old new` changes refs/heads/old into refs/heads/new,
> but the reference-transaction hook does not report both ref changes.
>

My understanding without digging too deep is that both 'copy' and
'rename' do not use a transaction, as such they don't trigger the
'reference-transaction' hook. This is definitely absurd, since we would
expect that all reference operations should use the transaction and
trigger the hook.

> Observed with Git 2.55:
>
> * files backend: the hook reports deletion of refs/heads/old, but
>   does not report creation of refs/heads/new;

Yeah, because the files backend calls `refs_delete_ref()` on the old
reference which is done within a transaction.

> * reftable backend: the hook reports no usable rename payload.

Reftable doesn't call `refs_delete_ref()` and simply writes a TOMBSTONE
entry to delete the old reference.

> The equivalent atomic operation performed with `git update-ref --stdin`
> reports both updates correctly.
>

By equivalent atomic operation do you a 'delete' and 'create' command?

> I expected the transaction to include:
>
>     <oid> <zero> refs/heads/old
>     <zero> <oid> refs/heads/new
>
> Minimal reproducer:
>
>     #!/bin/sh
>     set -eu
>
>     format=${1:-files}
>     root=$(mktemp -d)
>     trap 'rm -rf "$root"' EXIT
>
>     repo=$root/repo
>     hooks=$root/hooks
>     log=$root/transactions
>
>     git init -q --ref-format="$format" "$repo"
>     git -C "$repo" config user.name Reproducer
>     git -C "$repo" config user.email repro@example.com
>     git -C "$repo" commit --allow-empty -qm initial
>     git -C "$repo" branch old
>
>     mkdir "$hooks"
>     cat >"$hooks/reference-transaction" <<'HOOK'
>     #!/bin/sh
>     printf '%s\n' "--- $1" >>"$HOOK_LOG"
>     cat >>"$HOOK_LOG"
>     HOOK
>     chmod +x "$hooks/reference-transaction"
>
>     git -C "$repo" config core.hooksPath "$hooks"
>     export HOOK_LOG=$log
>     : >"$log"
>
>     git -C "$repo" branch -m old new
>     cat "$log"
>
> The behavior was also tested across Git 2.28–2.55:
> https://github.com/ciembor/git-hooks-ext/blob/v0.2.0/tests/compat/README.md
>
> The reference-transaction documentation says that the hook is invoked by
> Git commands performing reference updates. A branch rename changes two refs,
> but the destination update is not visible to the hook.
>

Either ways, I think we should fix this, I could have a look if you
aren't submitting a patch yourself :)

> Thanks,
> Maciej Ciemborowicz