From: Patrick Steinhardt <ps@pks.im>
Date: Mon, 08 Jun 2026 09:30:44 GMT
Subject: Re: [PATCH RFC 1/2] builtin/history: abort reword on unchanged message
Message-ID: <aiaLxNwGPko5HS2G@pks.im>
In-Reply-To: <20260607-ps-history-reword-v1-1-ba43a3cbb81b@gmail.com>

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.

> 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.

Patrick