Re: [PATCH 1/2] [GSOC] cherry-pick: fix bug when used with GIT_CHERRY_PICK_HELP

> From: ZheNing Hu <adlternative@gmail.com>
> 
> GIT_CHERRY_PICK_HELP is an environment variable, as the
> implementation detail of some porcelain in git to help realize
> the rebasing steps. E.g. `git rebase -p` set GIT_CHERRY_PICK_HELP
> value in `git-rebase--preserve-merges.sh`, `git rebase --merge` set
> GIT_CHERRY_PICK_HELP value in run_specific_rebase(). But If we set
> the value of GIT_CHERRY_PICK_HELP when using `git cherry-pick`,
> CHERRY_PICK_HEAD will be deleted, then we will get an error when we
> try to use `git cherry-pick --continue` or other cherr-pick command.
> 
> Introduce new "hidden" option `--delete-cherry-pick-head` for git
> cherry-pick which indicates that CHERRY_PICK_HEAD will be deleted when
> conflict occurs, which provided for some porcelain commands of git like
> `git-rebase--preserve-merges.sh`. After `git rebase -p` completely
> abolished, this option should be removed. At the same time, add the flag
> `delete_cherry_pick_head` to `struct rebase_options` and
> `struct replay_opts`, We can decide whether to delete CHERRY_PICK_HEAD
> by setting, passing, and checking this flag bit.
> 
> Then we split print_advice() into two part: Firstly, print_advice()
> will only be responsible for outputting content; Secondly, check if
> we set the `delete_cherry_pick_head` flag; if set, delete CHERRY_PICK_HEAD.
> In this way, the steps of printing advice and deleting CHERRY_PICK_HEAD
> are decoupled. Finally, let `git-rebase--preserve-merges.sh` use the
> `--delete-cherry-pick-head` option when it executes git cherry-pick, and
> set the `delete_cherry_pick_head` flag in run_specific_rebase() when we
> are using `git rebase --merge`, which can fix this breakage.
> 
> Mentored-by: Christian Couder <christian.couder@gmail.com>
> Mentored-by Hariom Verma <hariom18599@gmail.com>:
> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> Hepled-by: Junio C Hamano <gitster@pobox.com>
> Signed-off-by: ZheNing Hu <adlternative@gmail.com>
> ---
>   builtin/rebase.c                |  3 +++
>   builtin/revert.c                |  2 ++
>   git-rebase--preserve-merges.sh  |  2 +-
>   sequencer.c                     | 28 +++++++++++++---------------
>   sequencer.h                     |  1 +
>   t/t3507-cherry-pick-conflict.sh | 25 +++++++++++++++----------
>   6 files changed, 35 insertions(+), 26 deletions(-)
> 
> diff --git a/builtin/rebase.c b/builtin/rebase.c
> index 12f093121d9..5983f37d531 100644
> --- a/builtin/rebase.c
> +++ b/builtin/rebase.c
> @@ -84,6 +84,7 @@ struct rebase_options {
>   		REBASE_FORCE = 1<<3,
>   		REBASE_INTERACTIVE_EXPLICIT = 1<<4,
>   	} flags;
> +	int delete_cherry_pick_head;
>   	struct strvec git_am_opts;
>   	const char *action;
>   	int signoff;
> @@ -152,6 +153,7 @@ static struct replay_opts get_replay_opts(const struct rebase_options *opts)
>   		oidcpy(&replay.squash_onto, opts->squash_onto);
>   		replay.have_squash_onto = 1;
>   	}
> +	replay.delete_cherry_pick_head = opts->delete_cherry_pick_head;

>   
>   	return replay;
>   }
> @@ -948,6 +950,7 @@ static int run_specific_rebase(struct rebase_options *opts, enum action action)
>   	if (opts->type == REBASE_MERGE) {
>   		/* Run sequencer-based rebase */
>   		setenv("GIT_CHERRY_PICK_HELP", resolvemsg, 1);
> +		opts->delete_cherry_pick_head = 1;
>   		if (!(opts->flags & REBASE_INTERACTIVE_EXPLICIT)) {
>   			setenv("GIT_SEQUENCE_EDITOR", ":", 1);
>   			opts->autosquash = 0;
> diff --git a/builtin/revert.c b/builtin/revert.c
> index 237f2f18d4c..15a4b6fe4ee 100644
> --- a/builtin/revert.c
> +++ b/builtin/revert.c
> @@ -127,6 +127,8 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
>   			OPT_BOOL(0, "allow-empty", &opts->allow_empty, N_("preserve initially empty commits")),
>   			OPT_BOOL(0, "allow-empty-message", &opts->allow_empty_message, N_("allow commits with empty messages")),
>   			OPT_BOOL(0, "keep-redundant-commits", &opts->keep_redundant_commits, N_("keep redundant, empty commits")),
> +			OPT_BOOL_F(0, "delete-cherry-pick-head", &opts->delete_cherry_pick_head,
> +				   N_("delete CHERRY_PICK_HEAD when conflict occurs"), PARSE_OPT_HIDDEN),
>   			OPT_END(),
>   		};
>   		options = parse_options_concat(options, cp_extra);
> diff --git a/git-rebase--preserve-merges.sh b/git-rebase--preserve-merges.sh
> index b9c71d2a71b..eaa8f9de2c5 100644
> --- a/git-rebase--preserve-merges.sh
> +++ b/git-rebase--preserve-merges.sh
> @@ -444,7 +444,7 @@ pick_one_preserving_merges () {
>   			output eval git cherry-pick $allow_rerere_autoupdate \
>   				$allow_empty_message \
>   				${gpg_sign_opt:+$(git rev-parse --sq-quote "$gpg_sign_opt")} \
> -				"$strategy_args" "$@" ||
> +				"$strategy_args" --delete-cherry-pick-head "$@" ||
>   				die_with_patch $sha1 "$(eval_gettext "Could not pick \$sha1")"
>   			;;
>   		esac
> diff --git a/sequencer.c b/sequencer.c
> index 0bec01cf38e..83cf6a5da3c 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -397,24 +397,13 @@ static void free_message(struct commit *commit, struct commit_message *msg)
>   	unuse_commit_buffer(commit, msg->message);
>   }
>   
> -static void print_advice(struct repository *r, int show_hint,
> -			 struct replay_opts *opts)
> +static void print_advice(struct replay_opts *opts, int show_hint)
>   {
>   	char *msg = getenv("GIT_CHERRY_PICK_HELP");
>   
>   	if (msg) {
> -		fprintf(stderr, "%s\n", msg);
> -		/*
> -		 * A conflict has occurred but the porcelain
> -		 * (typically rebase --interactive) wants to take care
> -		 * of the commit itself so remove CHERRY_PICK_HEAD
> -		 */
> -		refs_delete_ref(get_main_ref_store(r), "", "CHERRY_PICK_HEAD",
> -				NULL, 0);
> -		return;
> -	}
> -
> -	if (show_hint) {
> +		advise("%s\n", msg);

> +	} else if (show_hint) {
>   		if (opts->no_commit)
>   			advise(_("after resolving the conflicts, mark the corrected paths\n"
>   				 "with 'git add <paths>' or 'git rm <paths>'"));
> @@ -2265,7 +2254,16 @@ static int do_pick_commit(struct repository *r,
>   		      ? _("could not revert %s... %s")
>   		      : _("could not apply %s... %s"),
>   		      short_commit_name(commit), msg.subject);
> -		print_advice(r, res == 1, opts);
> +		print_advice(opts, res == 1);
> +		if (opts->delete_cherry_pick_head) {
> +			/*
> +			 * A conflict has occurred but the porcelain
> +			 * (typically rebase --interactive) wants to take care
> +			 * of the commit itself so remove CHERRY_PICK_HEAD
> +			 */
> +			refs_delete_ref(get_main_ref_store(r), "", "CHERRY_PICK_HEAD",
> +					NULL, 0);
> +		}
>   		repo_rerere(r, opts->allow_rerere_auto);
>   		goto leave;
>   	}
> diff --git a/sequencer.h b/sequencer.h
> index d57d8ea23d7..76fb4af56fd 100644
> --- a/sequencer.h
> +++ b/sequencer.h
> @@ -49,6 +49,7 @@ struct replay_opts {
>   	int reschedule_failed_exec;
>   	int committer_date_is_author_date;
>   	int ignore_date;
> +	int delete_cherry_pick_head;
>   
>   	int mainline;
>   
> diff --git a/t/t3507-cherry-pick-conflict.sh b/t/t3507-cherry-pick-conflict.sh
> index 014001b8f32..f17621d1915 100755
> --- a/t/t3507-cherry-pick-conflict.sh
> +++ b/t/t3507-cherry-pick-conflict.sh
> @@ -76,6 +76,21 @@ test_expect_success 'advice from failed cherry-pick --no-commit' "
>   	test_cmp expected actual
>   "
>   
> +test_expect_success 'advice from failed cherry-pick with GIT_CHERRY_PICK_HELP' "
> +	pristine_detach initial &&
> +	(
> +		picked=\$(git rev-parse --short picked) &&
> +		cat <<-EOF >expected &&
> +		error: could not apply \$picked... picked
> +		hint: and then do something else
> +		EOF
> +		GIT_CHERRY_PICK_HELP='and then do something else' &&
> +		export GIT_CHERRY_PICK_HELP &&
> +		test_must_fail git cherry-pick picked 2>actual &&
> +		test_cmp expected actual
> +	)
> +"
> +
>   test_expect_success 'failed cherry-pick sets CHERRY_PICK_HEAD' '
>   	pristine_detach initial &&
>   	test_must_fail git cherry-pick picked &&
> @@ -109,16 +124,6 @@ test_expect_success \
>   	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
>   '
>   
> -test_expect_success 'GIT_CHERRY_PICK_HELP suppresses CHERRY_PICK_HEAD' '
> -	pristine_detach initial &&
> -	(
> -		GIT_CHERRY_PICK_HELP="and then do something else" &&
> -		export GIT_CHERRY_PICK_HELP &&
> -		test_must_fail git cherry-pick picked
> -	) &&
> -	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
> -'
> -
>   test_expect_success 'git reset clears CHERRY_PICK_HEAD' '
>   	pristine_detach initial &&