cherry-pick/revert: add --skip option

git am or rebase have a --skip flag to skip the current commit if the
user wishes to do so. During a cherry-pick or revert a user could
likewise skip a commit, but needs to use 'git reset' (or in the case
of conflicts 'git reset --merge'), followed by 'git (cherry-pick |
revert) --continue' to skip the commit. This is more annoying and
sometimes confusing on the users' part. Add a `--skip` option to make
skipping commits easier for the user and to make the commands more
consistent.

In the next commit, we will change the advice messages hence finishing
the process of teaching revert and cherry-pick "how to skip commits".

Signed-off-by: Rohit Ashiwal <rohit.ashiwal265@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 73 insertions, 0 deletions

diff --git a/sequencer.c b/sequencer.c
index 0b858ca8e0..dede47a21b 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2762,6 +2762,15 @@ static int rollback_single_pick(struct repository *r)
 	return reset_merge(&head_oid);
 }
 
+static int skip_single_pick(void)
+{
+	struct object_id head;
+
+	if (read_ref_full("HEAD", 0, &head, NULL))
+		return error(_("cannot resolve HEAD"));
+	return reset_merge(&head);
+}
+
 int sequencer_rollback(struct repository *r, struct replay_opts *opts)
 {
 	FILE *f;
@@ -2811,6 +2820,70 @@ fail:
 	return -1;
 }
 
+int sequencer_skip(struct repository *r, struct replay_opts *opts)
+{
+	enum replay_action action = -1;
+	sequencer_get_last_command(r, &action);
+
+	/*
+	 * Check whether the subcommand requested to skip the commit is actually
+	 * in progress and that it's safe to skip the commit.
+	 *
+	 * opts->action tells us which subcommand requested to skip the commit.
+	 * If the corresponding .git/<ACTION>_HEAD exists, we know that the
+	 * action is in progress and we can skip the commit.
+	 *
+	 * Otherwise we check that the last instruction was related to the
+	 * particular subcommand we're trying to execute and barf if that's not
+	 * the case.
+	 *
+	 * Finally we check that the rollback is "safe", i.e., has the HEAD
+	 * moved? In this case, it doesn't make sense to "reset the merge" and
+	 * "skip the commit" as the user already handled this by committing. But
+	 * we'd not want to barf here, instead give advice on how to proceed. We
+	 * only need to check that when .git/<ACTION>_HEAD doesn't exist because
+	 * it gets removed when the user commits, so if it still exists we're
+	 * sure the user can't have committed before.
+	 */
+	switch (opts->action) {
+	case REPLAY_REVERT:
+		if (!file_exists(git_path_revert_head(r))) {
+			if (action != REPLAY_REVERT)
+				return error(_("no revert in progress"));
+			if (!rollback_is_safe())
+				goto give_advice;
+		}
+		break;
+	case REPLAY_PICK:
+		if (!file_exists(git_path_cherry_pick_head(r))) {
+			if (action != REPLAY_PICK)
+				return error(_("no cherry-pick in progress"));
+			if (!rollback_is_safe())
+				goto give_advice;
+		}
+		break;
+	default:
+		BUG("unexpected action in sequencer_skip");
+	}
+
+	if (skip_single_pick())
+		return error(_("failed to skip the commit"));
+	if (!is_directory(git_path_seq_dir()))
+		return 0;
+
+	return sequencer_continue(r, opts);
+
+give_advice:
+	error(_("there is nothing to skip"));
+
+	if (advice_resolve_conflict) {
+		advise(_("have you committed already?\n"
+			 "try \"git %s --continue\""),
+			 action == REPLAY_REVERT ? "revert" : "cherry-pick");
+	}
+	return -1;
+}
+
 static int save_todo(struct todo_list *todo_list, struct replay_opts *opts)
 {
 	struct lock_file todo_lock = LOCK_INIT;