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rebase -r: don't write .git/MERGE_MSG when fast-forwarding

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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 there are no changes to the fast-forward code, it is
simply moved.

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.

Reported-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Phillip Wood 2021-08-20 15:40:37 +00:00 committed by Junio C Hamano
parent 0c164ae7a6
commit baf8ec8d3a
2 changed files with 49 additions and 42 deletions
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81
sequencer.c
View file

@ -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;

10
t/lib-rebase.sh
View file

@ -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 &&