On Fri, Aug 13, 2021 at 01:07:32PM +0000, Phillip Wood via GitGitGadget wrote:
> From: Phillip Wood <phillip.wood@xxxxxxxxxxxxx>
>
> When fast-forwarding we do not create a new commit so .git/MERGE_MSG
> is not removed and can end up seeding the message of a commit made
> after the rebase has finished. Avoid writing .git/MERGE_MSG when we
> are fast-forwarding by writing the file after the fast-forward
> checks.
>
> Note that the way this change is implemented means we no longer write
> the author script when fast-forwarding either. I believe this is safe
> for the reasons below but it is a departure from what we do when
> fast-forwarding a non-merge commit. If we reword the merge then 'git
> commit --amend' will keep the authorship of the commit we're rewording
> as it ignores GIT_AUTHOR_* unless --reset-author is passed. It will
> also export the correct GIT_AUTHOR_* variables to any hooks and we
> already test the authorship of the reworded commit. If we are not
> rewording then we no longer call spilt_ident() which means we are no
> longer checking the commit author header looks sane. However this is
> what we already do when fast-forwarding non-merge commits in
> skip_unnecessary_picks() so I don't think we're breaking any promises
> by not checking the author here.
Thanks you for fixing this bug.
FWIW (not that much, I'm afraid), I think your reasoning about the
harmlessness of the behavior change concerning the author script makes
sense.
My only nit is that the movement of a ~40 lines block of code makes
out the bulk of the patch; perhaps it would be worth mentioning it
explicitly in the commit message, so future readers of this commit
won't look for changes in those hunks.
> Reported-by: SZEDER Gábor <szeder.dev@xxxxxxxxx>
> Signed-off-by: Phillip Wood <phillip.wood@xxxxxxxxxxxxx>
> ---
> sequencer.c | 81 +++++++++++++++++++++++++------------------------
> t/lib-rebase.sh | 10 ++++--
> 2 files changed, 49 insertions(+), 42 deletions(-)
>
> diff --git a/sequencer.c b/sequencer.c
> index cc8a361cceb..c2cba5ed4b1 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -983,7 +983,8 @@ static int run_git_commit(const char *defmsg,
>
> cmd.git_cmd = 1;
>
> - if (is_rebase_i(opts) && read_env_script(&cmd.env_array)) {
> + if (is_rebase_i(opts) && !(!defmsg && (flags & AMEND_MSG)) &&
> + read_env_script(&cmd.env_array)) {
> const char *gpg_opt = gpg_sign_opt_quoted(opts);
>
> return error(_(staged_changes_advice),
> @@ -3815,6 +3816,45 @@ static int do_merge(struct repository *r,
> goto leave_merge;
> }
>
> + /*
> + * If HEAD is not identical to the first parent of the original merge
> + * commit, we cannot fast-forward.
> + */
> + can_fast_forward = opts->allow_ff && commit && commit->parents &&
> + oideq(&commit->parents->item->object.oid,
> + &head_commit->object.oid);
> +
> + /*
> + * If any merge head is different from the original one, we cannot
> + * fast-forward.
> + */
> + if (can_fast_forward) {
> + struct commit_list *p = commit->parents->next;
> +
> + for (j = to_merge; j && p; j = j->next, p = p->next)
> + if (!oideq(&j->item->object.oid,
> + &p->item->object.oid)) {
> + can_fast_forward = 0;
> + break;
> + }
> + /*
> + * If the number of merge heads differs from the original merge
> + * commit, we cannot fast-forward.
> + */
> + if (j || p)
> + can_fast_forward = 0;
> + }
> +
> + if (can_fast_forward) {
> + rollback_lock_file(&lock);
> + ret = fast_forward_to(r, &commit->object.oid,
> + &head_commit->object.oid, 0, opts);
> + if (flags & TODO_EDIT_MERGE_MSG)
> + goto fast_forward_edit;
> +
> + goto leave_merge;
> + }
> +
> if (commit) {
> const char *encoding = get_commit_output_encoding();
> const char *message = logmsg_reencode(commit, NULL, encoding);
> @@ -3864,45 +3904,6 @@ static int do_merge(struct repository *r,
> }
> }
>
> - /*
> - * If HEAD is not identical to the first parent of the original merge
> - * commit, we cannot fast-forward.
> - */
> - can_fast_forward = opts->allow_ff && commit && commit->parents &&
> - oideq(&commit->parents->item->object.oid,
> - &head_commit->object.oid);
> -
> - /*
> - * If any merge head is different from the original one, we cannot
> - * fast-forward.
> - */
> - if (can_fast_forward) {
> - struct commit_list *p = commit->parents->next;
> -
> - for (j = to_merge; j && p; j = j->next, p = p->next)
> - if (!oideq(&j->item->object.oid,
> - &p->item->object.oid)) {
> - can_fast_forward = 0;
> - break;
> - }
> - /*
> - * If the number of merge heads differs from the original merge
> - * commit, we cannot fast-forward.
> - */
> - if (j || p)
> - can_fast_forward = 0;
> - }
> -
> - if (can_fast_forward) {
> - rollback_lock_file(&lock);
> - ret = fast_forward_to(r, &commit->object.oid,
> - &head_commit->object.oid, 0, opts);
> - if (flags & TODO_EDIT_MERGE_MSG)
> - goto fast_forward_edit;
> -
> - goto leave_merge;
> - }
> -
> if (strategy || to_merge->next) {
> /* Octopus merge */
> struct child_process cmd = CHILD_PROCESS_INIT;
> diff --git a/t/lib-rebase.sh b/t/lib-rebase.sh
> index 99d9e7efd2d..ec6b9b107da 100644
> --- a/t/lib-rebase.sh
> +++ b/t/lib-rebase.sh
> @@ -173,10 +173,16 @@ set_reword_editor () {
>
> write_script reword-editor.sh <<-EOF &&
> # Save the oid of the first reworded commit so we can check rebase
> - # fast-forwards to it
> + # fast-forwards to it. Also check that we do not write .git/MERGE_MSG
> + # when fast-forwarding
> if ! test -s reword-oid
> then
> - git rev-parse HEAD >reword-oid
> + git rev-parse HEAD >reword-oid &&
> + if test -f .git/MERGE_MSG
> + then
> + echo 1>&2 "error: .git/MERGE_MSG exists"
> + exit 1
> + fi
> fi &&
> # There should be no uncommited changes
> git diff --exit-code HEAD &&
> --
> gitgitgadget
>
