From: Pablo Sabater <pabloosabaterr@gmail.com>
Date: Mon, 08 Jun 2026 10:52:49 GMT
Subject: Re: [PATCH RFC 1/2] builtin/history: abort reword on unchanged message
Message-ID: <CAN5EUNSAOMRvmLGVfzQiwWoOn9VGNVU5rVMZizOryn_q2fbCNA@mail.gmail.com>
In-Reply-To: <aiaLxNwGPko5HS2G@pks.im>

El lun, 8 jun 2026 a las 11:30, Patrick Steinhardt (<ps@pks.im>) escribió:
>
> On Sun, Jun 07, 2026 at 10:07:20PM +0200, Pablo Sabater wrote:
> > When using `git history reword` if the new message is the same as the
> > original it continues anyway creating a new commit with the same
> > message and updates its descendants, modifying the history after this
> > 'reworded' commit even though there was no actual change.
> >
> > `git commit --amend` and `git rebase -i` + reword share this behavior,
> > however `git history reword` is different:
> > 1. Works in-memory without touching the index or the worktree [1], so
> >    there are no side effects like staged files that could justify
> >    rewriting the history when the commit message is the same.
> > 2. `git history` by default updates all the branches [2] that contain the
> >    original commit making it more costly than `git rebase -i` that only
> >    updates the current branch.
> >
> > Add a check if the original commit message is the same as the new one
> > and abort if so.
> >
> > [1]: https://lore.kernel.org/git/20260113-b4-pks-history-builtin-v11-8-e74ebfa2652d@pks.im/
> > [2]: https://git-scm.com/docs/git-history#_description
>
> Nit: I feel like both of the links don't really add much value.

I'll just drop em.

>
> > Signed-off-by: Pablo Sabater <pabloosabaterr@gmail.com>
> > ---
> >  builtin/history.c         | 10 ++++++++++
> >  t/t3451-history-reword.sh | 20 ++++++++++++++++++++
> >  2 files changed, 30 insertions(+)
> >
> > diff --git a/builtin/history.c b/builtin/history.c
> > index 0fc06fb204..51a22a9a1c 100644
> > --- a/builtin/history.c
> > +++ b/builtin/history.c
> > @@ -135,6 +135,13 @@ static int commit_tree_ext(struct repository *repo,
> >                                         original_body, action, &commit_message);
> >               if (ret < 0)
> >                       goto out;
> > +
> > +             if (!strcmp(original_body, commit_message.buf)) {
> > +                     fprintf(stderr, _("Message unchanged,"
> > +                                       " aborting reword.\n"));
> > +                     ret = 1;
> > +                     goto out;
> > +             }
> >       } else {
> >               strbuf_addstr(&commit_message, original_body);
> >       }
>
> We also execute this logic via "git history fixup --reedit-message", and
> here it wouldn't make sense to abort the commit in case the message is
> unchanged.

True I hadn't thought that, I made it here because we have both the
original and new message before creating the new commit. We could let
ret = 1 mean that the commit message is the same and then
cmd_history_fixup ignores ret = 1 and for cmd_history_reword handle
the abort.
What do you think?

>
> Patrick

--
Pablo