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

["ZheNing Hu via GitGitGadget" <gitgitgadget@gmail.com>]

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. 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 --rebase-preserve-merges-mode for git
cherry-pick which indicates that git cherry-pick is currently called by
git-rebase--preserve-merges.sh. After `git rebase -p` completely
abolished, this option should be removed.

And then we split print_advice() into two part:
check_need_delete_cherry_pick_head() check if we set
GIT_CHERRY_PICK_HELP, if set, delete CHERRY_PICK_HEAD and return
GIT_CHERRY_PICK_HELP's value, if not set, return NULL; The parameters
of print_advice() have changed, which now accept a
`struct replay_opts *opt` and a `const char *help_msgs`. We can pass
the value of GIT_CHERRY_PICK_HELP into print_advice(), and output it.
In this way, the steps of printing advice and checking
GIT_CHERRY_PICK_HELP are decoupled.

Finally, avoid deleting CHERRY_PICK_HEAD when we are truly
cherry-picking, 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/revert.c                |  2 ++
 git-rebase--preserve-merges.sh  |  2 +-
 sequencer.c                     | 36 ++++++++++++++++++++-------------
 sequencer.h                     |  1 +
 t/t3507-cherry-pick-conflict.sh | 27 ++++++++++++++++---------
 5 files changed, 43 insertions(+), 25 deletions(-)

diff --git a/builtin/revert.c b/builtin/revert.c
index 237f2f18d4c..6165bb10143 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, "rebase-preserve-merges-mode", &opts->rebase_preserve_merges_mode,
+				   N_("use for git-rebase--preserve-merges backend"), 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..ca97d9b6539 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" --rebase-preserve-merges-mode "$@" ||
 				die_with_patch $sha1 "$(eval_gettext "Could not pick \$sha1")"
 			;;
 		esac
diff --git a/sequencer.c b/sequencer.c
index 0bec01cf38e..ceaf73a34df 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -397,13 +397,11 @@ 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 char *check_need_delete_cherry_pick_head(struct repository *r)
 {
 	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
@@ -411,18 +409,22 @@ static void print_advice(struct repository *r, int show_hint,
 		 */
 		refs_delete_ref(get_main_ref_store(r), "", "CHERRY_PICK_HEAD",
 				NULL, 0);
-		return;
+		return msg;
 	}
+	return NULL;
+}
 
-	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>'"));
-		else
-			advise(_("after resolving the conflicts, mark the corrected paths\n"
-				 "with 'git add <paths>' or 'git rm <paths>'\n"
-				 "and commit the result with 'git commit'"));
-	}
+static void print_advice(struct replay_opts *opts, const char *help_msgs)
+{
+	if (help_msgs)
+		advise("%s\n", help_msgs);
+	else if (opts->no_commit)
+		advise(_("after resolving the conflicts, mark the corrected paths\n"
+			 "with 'git add <paths>' or 'git rm <paths>'"));
+	else
+		advise(_("after resolving the conflicts, mark the corrected paths\n"
+			 "with 'git add <paths>' or 'git rm <paths>'\n"
+			 "and commit the result with 'git commit'"));
 }
 
 static int write_message(const void *buf, size_t len, const char *filename,
@@ -2261,11 +2263,17 @@ static int do_pick_commit(struct repository *r,
 		res = -1;
 
 	if (res) {
+		const char *help_msgs = NULL;
+
 		error(command == TODO_REVERT
 		      ? _("could not revert %s... %s")
 		      : _("could not apply %s... %s"),
 		      short_commit_name(commit), msg.subject);
-		print_advice(r, res == 1, opts);
+		if (((opts->action == REPLAY_PICK &&
+		      !opts->rebase_preserve_merges_mode) ||
+		      (help_msgs = check_need_delete_cherry_pick_head(r))) &&
+		      res == 1)
+			print_advice(opts, help_msgs);
 		repo_rerere(r, opts->allow_rerere_auto);
 		goto leave;
 	}
diff --git a/sequencer.h b/sequencer.h
index d57d8ea23d7..5a40b6d8bdc 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 rebase_preserve_merges_mode;
 
 	int mainline;
 
diff --git a/t/t3507-cherry-pick-conflict.sh b/t/t3507-cherry-pick-conflict.sh
index 014001b8f32..6f8035399d9 100755
--- a/t/t3507-cherry-pick-conflict.sh
+++ b/t/t3507-cherry-pick-conflict.sh
@@ -76,6 +76,23 @@ 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: after resolving the conflicts, mark the corrected paths
+		hint: with 'git add <paths>' or 'git rm <paths>'
+		hint: and commit the result with 'git commit'
+		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 +126,6 @@ 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 &&
 
-- 
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