Re: [PATCH 3/3] commit: give correct advice for empty commit during a rebase

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
> 
> In dcb500dc16c (cherry-pick/revert: advise using --skip, 2019-07-02),
> `git commit` learned to suggest to run `git cherry-pick --skip` when
> trying to cherry-pick an empty patch.
> 
> However, it was overlooked that there are more conditions than just a
> `git cherry-pick` when this advice is printed (which originally
> suggested the neutral `git reset`): the same can happen during a rebase.
> 
> Let's suggest the correct command, even during a rebase.
> 
> While at it, we adjust more places in `builtin/commit.c` that
> incorrectly assumed that the presence of a `CHERRY_PICK_HEAD` meant that
> surely this must be a `cherry-pick` in progress.
> 
> Note: we take pains to handle the situation when a user runs a `git
> cherry-pick` _during_ a rebase. This is quite valid (e.g. in an `exec`
> line in an interactive rebase). On the other hand, it is not possible to
> run a rebase during a cherry-pick, meaning: if both `rebase-merge/` and
> `sequencer/` exist, we still want to advise to use `git cherry-pick
> --skip`.

> 
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  builtin/commit.c       | 33 ++++++++++++++++++++++++---------
>  t/t3403-rebase-skip.sh |  9 +++++++++
>  2 files changed, 33 insertions(+), 9 deletions(-)
> 
> diff --git a/builtin/commit.c b/builtin/commit.c
> index e588bc6ad3..2beae13620 100644
> --- a/builtin/commit.c
> +++ b/builtin/commit.c
> @@ -59,6 +59,9 @@ N_("The previous cherry-pick is now empty, possibly due to conflict resolution.\
>  "    git commit --allow-empty\n"
>  "\n");
>  
> +static const char empty_rebase_advice[] =
> +N_("Otherwise, please use 'git rebase --skip'\n");
> +
>  static const char empty_cherry_pick_advice_single[] =
>  N_("Otherwise, please use 'git cherry-pick --skip'\n");
>  
> @@ -122,7 +125,7 @@ static enum commit_msg_cleanup_mode cleanup_mode;
>  static const char *cleanup_arg;
>  
>  static enum commit_whence whence;
> -static int sequencer_in_use;
> +static int sequencer_in_use, rebase_in_progress;
>  static int use_editor = 1, include_status = 1;
>  static int have_option_m;
>  static struct strbuf message = STRBUF_INIT;
> @@ -183,6 +186,8 @@ static void determine_whence(struct wt_status *s)
>  		whence = FROM_CHERRY_PICK;
>  		if (file_exists(git_path_seq_dir()))
>  			sequencer_in_use = 1;
> +		if (file_exists(git_path_rebase_merge_dir()))
> +			rebase_in_progress = 1;
>  	}
>  	else
>  		whence = FROM_COMMIT;
> @@ -453,8 +458,11 @@ static const char *prepare_index(int argc, const char **argv, const char *prefix
>  	if (whence != FROM_COMMIT) {
>  		if (whence == FROM_MERGE)
>  			die(_("cannot do a partial commit during a merge."));
> -		else if (whence == FROM_CHERRY_PICK)
> +		else if (whence == FROM_CHERRY_PICK) {
> +			if (rebase_in_progress && !sequencer_in_use)
> +				die(_("cannot do a partial commit during a rebase."));
>  			die(_("cannot do a partial commit during a cherry-pick."));
> +		}
>  	}
>  
>  	if (list_paths(&partial, !current_head ? NULL : "HEAD", &pathspec))
> @@ -950,10 +958,12 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
>  			fputs(_(empty_amend_advice), stderr);
>  		else if (whence == FROM_CHERRY_PICK) {
>  			fputs(_(empty_cherry_pick_advice), stderr);
> -			if (!sequencer_in_use)
> -				fputs(_(empty_cherry_pick_advice_single), stderr);
> -			else
> +			if (sequencer_in_use)
>  				fputs(_(empty_cherry_pick_advice_multi), stderr);
> +			else if (rebase_in_progress)
> +				fputs(_(empty_rebase_advice), stderr);
> +			else
> +				fputs(_(empty_cherry_pick_advice_single), stderr);
>  		}
>  		return 0;
>  	}
> @@ -1156,8 +1166,11 @@ static int parse_and_validate_options(int argc, const char *argv[],
>  	if (amend && whence != FROM_COMMIT) {
>  		if (whence == FROM_MERGE)
>  			die(_("You are in the middle of a merge -- cannot amend."));
> -		else if (whence == FROM_CHERRY_PICK)
> +		else if (whence == FROM_CHERRY_PICK) {
> +			if (rebase_in_progress && !sequencer_in_use)
> +				die(_("You are in the middle of a rebase -- cannot amend."));
>  			die(_("You are in the middle of a cherry-pick -- cannot amend."));
> +		}
>  	}
>  	if (fixup_message && squash_message)
>  		die(_("Options --squash and --fixup cannot be used together"));
> @@ -1628,9 +1641,11 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
>  			reduce_heads_replace(&parents);
>  	} else {
>  		if (!reflog_msg)
> -			reflog_msg = (whence == FROM_CHERRY_PICK)
> -					? "commit (cherry-pick)"
> -					: "commit";
> +			reflog_msg = (whence != FROM_CHERRY_PICK)
> +					? "commit"
> +					: rebase_in_progress && !sequencer_in_use
> +					? "commit (rebase)"
> +					: "commit (cherry-pick)";
>  		commit_list_insert(current_head, &parents);
>  	}
>  
> diff --git a/t/t3403-rebase-skip.sh b/t/t3403-rebase-skip.sh
> index 1f5122b632..77b03ac49f 100755
> --- a/t/t3403-rebase-skip.sh
> +++ b/t/t3403-rebase-skip.sh
> @@ -76,4 +76,13 @@ test_expect_success 'moved back to branch correctly' '
>  
>  test_debug 'gitk --all & sleep 1'
>  
> +test_expect_success 'correct advice upon empty commit' '
> +	git checkout -b rebase-skip &&
> +	test_commit a1 &&
> +	test_tick &&
> +	git commit --amend -m amended --no-edit &&
> +	test_must_fail git rebase -m --onto a1 HEAD^ 2>err &&
> +	test_i18ngrep "git rebase --skip" err
> +'
> +
>  test_done
>