[PATCH v2] rebase -i: do leave commit message intact in fixup! chains

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In 6e98de72c03 (sequencer (rebase -i): add support for the 'fixup' and 'squash' commands, 2017-01-02), this developer introduced a change of behavior by mistake: when encountering a `fixup!` commit (or multiple `fixup!` commits) without any `squash!` commit thrown in, the final `git commit` was invoked with `--cleanup=strip`. Prior to that commit, the commit command had been called without that `--cleanup` option.

Since we explicitly read the original commit message from a file in that case, there is really no sense in forcing that clean-up.

We actually need to actively suppress that clean-up lest a configured `commit.cleanup` may interfere with what we want to do: leave the commit message unchanged.

Reported-by: Vojtěch Knyttl <vojtech@knyt.tl>
Helped-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
    Fix bug in interactive rebases where fixup! cleans up the commit message
    
    Original report here:
    https://lore.kernel.org/git/CANVGpwZGbzYLMeMze64e_OU9p3bjyEgzC5thmNBr6LttBt%2BYGw%40mail.gmail.com/t
    
    Changes since v1:
    
     * The fix now works even if commit.cleanup = commit

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-818%2Fdscho%2Fautosquash-without-scissors-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-818/dscho/autosquash-without-scissors-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/818

Range-diff vs v1:

 1:  bfade3b146f ! 1:  c760d6cd203 rebase -i: do leave commit message intact in fixup! chains
     @@ Commit message
          Since we explicitly read the original commit message from a file in that
          case, there is really no sense in forcing that clean-up.
      
     +    We actually need to actively suppress that clean-up lest a configured
     +    `commit.cleanup` may interfere with what we want to do: leave the commit
     +    message unchanged.
     +
          Reported-by: Vojtěch Knyttl <vojtech@knyt.tl>
     +    Helped-by: Martin Ågren <martin.agren@gmail.com>
          Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
      
       ## sequencer.c ##
     +@@ sequencer.c: N_("you have staged changes in your working tree\n"
     + #define CLEANUP_MSG (1<<3)
     + #define VERIFY_MSG  (1<<4)
     + #define CREATE_ROOT_COMMIT (1<<5)
     ++#define VERBATIM_MSG (1<<6)
     + 
     + static int run_command_silent_on_success(struct child_process *cmd)
     + {
     +@@ sequencer.c: static int run_git_commit(const char *defmsg,
     + 		strvec_pushl(&cmd.args, "-C", "HEAD", NULL);
     + 	if ((flags & CLEANUP_MSG))
     + 		strvec_push(&cmd.args, "--cleanup=strip");
     ++	if ((flags & VERBATIM_MSG))
     ++		strvec_push(&cmd.args, "--cleanup=verbatim");
     + 	if ((flags & EDIT_MSG))
     + 		strvec_push(&cmd.args, "-e");
     + 	else if (!(flags & CLEANUP_MSG) &&
     +@@ sequencer.c: static int try_to_commit(struct repository *r,
     + 
     + 	if (flags & CLEANUP_MSG)
     + 		cleanup = COMMIT_MSG_CLEANUP_ALL;
     ++	else if (flags & VERBATIM_MSG)
     ++		cleanup = COMMIT_MSG_CLEANUP_NONE;
     + 	else if ((opts->signoff || opts->record_origin) &&
     + 		 !opts->explicit_cleanup)
     + 		cleanup = COMMIT_MSG_CLEANUP_SPACE;
      @@ sequencer.c: static int do_pick_commit(struct repository *r,
     - 		flags |= AMEND_MSG;
       		if (!final_fixup)
       			msg_file = rebase_path_squash_msg();
     --		else if (file_exists(rebase_path_fixup_msg())) {
     + 		else if (file_exists(rebase_path_fixup_msg())) {
      -			flags |= CLEANUP_MSG;
     -+		else if (file_exists(rebase_path_fixup_msg()))
     ++			flags |= VERBATIM_MSG;
       			msg_file = rebase_path_fixup_msg();
     --		} else {
     -+		else {
     + 		} else {
       			const char *dest = git_path_squash_msg(r);
     - 			unlink(dest);
     - 			if (copy_file(dest, rebase_path_squash_msg(), 0666))
      
       ## t/t3415-rebase-autosquash.sh ##
      @@ t/t3415-rebase-autosquash.sh: test_expect_success 'fixup a fixup' '
     @@ t/t3415-rebase-autosquash.sh: test_expect_success 'fixup a fixup' '
      +	oneline="#818" &&
      +	git commit --allow-empty -m "$oneline" &&
      +	git commit --fixup HEAD --allow-empty &&
     -+	git rebase -ki --autosquash HEAD~2 &&
     ++	git -c commit.cleanup=strip rebase -ki --autosquash HEAD~2 &&
      +	test "$oneline" = "$(git show -s --format=%s)"
      +'
      +

 sequencer.c                  | 7 ++++++-
 t/t3415-rebase-autosquash.sh | 8 ++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)