[GSoC][PATCH v3 2/3] cherry-pick/revert: add --skip option

[Rohit Ashiwal <rohit.ashiwal265@gmail.com>]

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 and some tests
hence finishing the process of teaching revert and cherry-pick
"how to skip commits".

Signed-off-by: Rohit Ashiwal <rohit.ashiwal265@gmail.com>
---
changes:
    - Remove `reset_merge` from last revision[1] and modified `reset_for_rollback`
      and signature of `rollback_single_pick` to handle if `--skip` flag
    - Modify test which gave "ambiguous refname" warning[2]

[1]: https://public-inbox.org/git/20190608191958.4593-1-rohit.ashiwal265@gmail.com/T/#m11a573a3b91dfd2fcfae40c6ecc2148f8c92e10c
[2]: https://public-inbox.org/git/20190608191958.4593-1-rohit.ashiwal265@gmail.com/T/#m586cb8930cfcb737e4f19662f0eef3716b1e9d35

 Documentation/git-cherry-pick.txt |   4 +-
 Documentation/git-revert.txt      |   4 +-
 Documentation/sequencer.txt       |   4 ++
 builtin/revert.c                  |   5 ++
 sequencer.c                       |  67 +++++++++++++++++---
 sequencer.h                       |   1 +
 t/t3510-cherry-pick-sequence.sh   | 102 ++++++++++++++++++++++++++++++
 7 files changed, 171 insertions(+), 16 deletions(-)

diff --git a/Documentation/git-cherry-pick.txt b/Documentation/git-cherry-pick.txt
index 754b16ce0c..955880ab88 100644
--- a/Documentation/git-cherry-pick.txt
+++ b/Documentation/git-cherry-pick.txt
@@ -10,9 +10,7 @@ SYNOPSIS
 [verse]
 'git cherry-pick' [--edit] [-n] [-m parent-number] [-s] [-x] [--ff]
 		  [-S[<keyid>]] <commit>...
-'git cherry-pick' --continue
-'git cherry-pick' --quit
-'git cherry-pick' --abort
+'git cherry-pick' --continue | --skip | --abort | --quit
 
 DESCRIPTION
 -----------
diff --git a/Documentation/git-revert.txt b/Documentation/git-revert.txt
index 0c82ca5bc0..ffce98099c 100644
--- a/Documentation/git-revert.txt
+++ b/Documentation/git-revert.txt
@@ -9,9 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git revert' [--[no-]edit] [-n] [-m parent-number] [-s] [-S[<keyid>]] <commit>...
-'git revert' --continue
-'git revert' --quit
-'git revert' --abort
+'git revert' --continue | --skip | --abort | --quit
 
 DESCRIPTION
 -----------
diff --git a/Documentation/sequencer.txt b/Documentation/sequencer.txt
index 5a57c4a407..3bceb56474 100644
--- a/Documentation/sequencer.txt
+++ b/Documentation/sequencer.txt
@@ -3,6 +3,10 @@
 	`.git/sequencer`.  Can be used to continue after resolving
 	conflicts in a failed cherry-pick or revert.
 
+--skip::
+	Skip the current commit and continue with the rest of the
+	sequence.
+
 --quit::
 	Forget about the current operation in progress.  Can be used
 	to clear the sequencer state after a failed cherry-pick or
diff --git a/builtin/revert.c b/builtin/revert.c
index d4dcedbdc6..5dc5891ea2 100644
--- a/builtin/revert.c
+++ b/builtin/revert.c
@@ -102,6 +102,7 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
 		OPT_CMDMODE(0, "quit", &cmd, N_("end revert or cherry-pick sequence"), 'q'),
 		OPT_CMDMODE(0, "continue", &cmd, N_("resume revert or cherry-pick sequence"), 'c'),
 		OPT_CMDMODE(0, "abort", &cmd, N_("cancel revert or cherry-pick sequence"), 'a'),
+		OPT_CMDMODE(0, "skip", &cmd, N_("skip current commit and continue"), 's'),
 		OPT_CLEANUP(&cleanup_arg),
 		OPT_BOOL('n', "no-commit", &opts->no_commit, N_("don't automatically commit")),
 		OPT_BOOL('e', "edit", &opts->edit, N_("edit the commit message")),
@@ -151,6 +152,8 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
 			this_operation = "--quit";
 		else if (cmd == 'c')
 			this_operation = "--continue";
+		else if (cmd == 's')
+			this_operation = "--skip";
 		else {
 			assert(cmd == 'a');
 			this_operation = "--abort";
@@ -210,6 +213,8 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
 		return sequencer_continue(the_repository, opts);
 	if (cmd == 'a')
 		return sequencer_rollback(the_repository, opts);
+	if (cmd == 's')
+		return sequencer_skip(the_repository, opts);
 	return sequencer_pick_revisions(the_repository, opts);
 }
 
diff --git a/sequencer.c b/sequencer.c
index 918cb5d761..6b78a26920 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2733,25 +2733,26 @@ static int rollback_is_safe(void)
 
 static int reset_for_rollback(const struct object_id *oid)
 {
-	const char *argv[4];	/* reset --merge <arg> + NULL */
+	struct argv_array argv = ARGV_ARRAY_INIT;	/* reset --merge <arg> + NULL */
 
-	argv[0] = "reset";
-	argv[1] = "--merge";
-	argv[2] = oid_to_hex(oid);
-	argv[3] = NULL;
-	return run_command_v_opt(argv, RUN_GIT_CMD);
+	argv_array_pushl(&argv, "reset", "--merge", NULL);
+
+	if (!is_null_oid(oid))
+		argv_array_push(&argv, oid_to_hex(oid));
+
+	return run_command_v_opt(argv.argv, RUN_GIT_CMD);
 }
 
-static int rollback_single_pick(struct repository *r)
+static int rollback_single_pick(struct repository *r, unsigned int is_skip)
 {
 	struct object_id head_oid;
 
 	if (!file_exists(git_path_cherry_pick_head(r)) &&
-	    !file_exists(git_path_revert_head(r)))
+	    !file_exists(git_path_revert_head(r)) && !is_skip)
 		return error(_("no cherry-pick or revert in progress"));
 	if (read_ref_full("HEAD", 0, &head_oid, NULL))
 		return error(_("cannot resolve HEAD"));
-	if (is_null_oid(&head_oid))
+	if (is_null_oid(&head_oid) && !is_skip)
 		return error(_("cannot abort from a branch yet to be born"));
 	return reset_for_rollback(&head_oid);
 }
@@ -2770,7 +2771,7 @@ int sequencer_rollback(struct repository *r, struct replay_opts *opts)
 		 * If CHERRY_PICK_HEAD or REVERT_HEAD indicates
 		 * a single-cherry-pick in progress, abort that.
 		 */
-		return rollback_single_pick(r);
+		return rollback_single_pick(r, 0);
 	}
 	if (!f)
 		return error_errno(_("cannot open '%s'"), git_path_head_file());
@@ -2805,6 +2806,52 @@ int sequencer_rollback(struct repository *r, struct replay_opts *opts)
 	return -1;
 }
 
+int sequencer_skip(struct repository *r, struct replay_opts *opts)
+{
+	enum replay_action action = -1;
+	sequencer_get_last_command(r, &action);
+
+	switch (opts->action) {
+	case REPLAY_REVERT:
+		if (!file_exists(git_path_revert_head(r))) {
+			if (action == REPLAY_REVERT) {
+				if (!rollback_is_safe())
+					goto give_advice;
+				else
+					break;
+			}
+			return error(_("no revert in progress"));
+		}
+		break;
+	case REPLAY_PICK:
+		if (!file_exists(git_path_cherry_pick_head(r))) {
+			if (action == REPLAY_PICK) {
+				if (!rollback_is_safe())
+					goto give_advice;
+				else
+					break;
+			}
+			return error(_("no cherry-pick in progress"));
+		}
+		break;
+	default:
+		BUG("the control must not reach here");
+	}
+
+	if (rollback_single_pick(r, 1))
+		return error(_("failed to skip the commit"));
+	if (!is_directory(git_path_seq_dir()))
+		return 0;
+
+	return sequencer_continue(r, opts);
+
+give_advice:
+	advise(_("have you committed already?\n"
+		 "try \"git %s --continue\""),
+		 action == REPLAY_REVERT ? "revert" : "cherry-pick");
+	return error(_("there is nothing to skip"));
+}
+
 static int save_todo(struct todo_list *todo_list, struct replay_opts *opts)
 {
 	struct lock_file todo_lock = LOCK_INIT;
diff --git a/sequencer.h b/sequencer.h
index 0c494b83d4..731b9853eb 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -129,6 +129,7 @@ int sequencer_pick_revisions(struct repository *repo,
 			     struct replay_opts *opts);
 int sequencer_continue(struct repository *repo, struct replay_opts *opts);
 int sequencer_rollback(struct repository *repo, struct replay_opts *opts);
+int sequencer_skip(struct repository *repo, struct replay_opts *opts);
 int sequencer_remove_state(struct replay_opts *opts);
 
 #define TODO_LIST_KEEP_EMPTY (1U << 0)
diff --git a/t/t3510-cherry-pick-sequence.sh b/t/t3510-cherry-pick-sequence.sh
index 941d5026da..f85ef51cac 100755
--- a/t/t3510-cherry-pick-sequence.sh
+++ b/t/t3510-cherry-pick-sequence.sh
@@ -93,6 +93,108 @@ test_expect_success 'cherry-pick cleans up sequencer state upon success' '
 	test_path_is_missing .git/sequencer
 '
 
+test_expect_success 'cherry-pick --skip requires cherry-pick in progress' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick --skip
+'
+
+test_expect_success 'revert --skip requires revert in progress' '
+	pristine_detach initial &&
+	test_must_fail git revert --skip
+'
+
+test_expect_success 'cherry-pick --skip to skip commit' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick anotherpick &&
+	test_must_fail git revert --skip &&
+	git cherry-pick --skip &&
+	test_cmp_rev initial HEAD &&
+	test_path_is_missing .git/CHERRY_PICK_HEAD
+'
+
+test_expect_success 'revert --skip to skip commit' '
+	pristine_detach anotherpick &&
+	test_must_fail git revert anotherpick~1 &&
+	test_must_fail git cherry-pick --skip &&
+	git revert --skip &&
+	test_cmp_rev anotherpick HEAD
+'
+
+test_expect_success 'skip "empty" commit' '
+	pristine_detach picked &&
+	test_commit dummy foo d &&
+	test_must_fail git cherry-pick anotherpick &&
+	git cherry-pick --skip &&
+	test_cmp_rev dummy HEAD
+'
+
+test_expect_success 'skip a commit and check if rest of sequence is correct' '
+	pristine_detach initial &&
+	echo e >expect &&
+	cat >expect.log <<-EOF &&
+	OBJID
+	:100644 100644 OBJID OBJID M	foo
+	OBJID
+	:100644 100644 OBJID OBJID M	foo
+	OBJID
+	:100644 100644 OBJID OBJID M	unrelated
+	OBJID
+	:000000 100644 OBJID OBJID A	foo
+	:000000 100644 OBJID OBJID A	unrelated
+	EOF
+	test_must_fail git cherry-pick base..yetanotherpick &&
+	test_must_fail git cherry-pick --skip &&
+	echo d >foo &&
+	git add foo &&
+	git cherry-pick --continue &&
+	{
+		git rev-list HEAD |
+		git diff-tree --root --stdin |
+		sed "s/$OID_REGEX/OBJID/g"
+	} >actual.log &&
+	test_cmp expect foo &&
+	test_cmp expect.log actual.log
+'
+
+test_expect_success 'check advice when we move HEAD by committing' '
+	pristine_detach initial &&
+	cat >expect <<-EOF &&
+	hint: have you committed already?
+	hint: try "git cherry-pick --continue"
+	error: there is nothing to skip
+	fatal: cherry-pick failed
+	EOF
+	test_must_fail git cherry-pick base..yetanotherpick &&
+	echo c >foo &&
+	git commit -a &&
+	test_path_is_missing .git/CHERRY_PICK_HEAD &&
+	test_must_fail git cherry-pick --skip 2>advice &&
+	test_cmp expect advice
+'
+
+test_expect_success 'allow skipping commit but not abort for a new history' '
+	pristine_detach initial &&
+	cat >expect <<-EOF &&
+	error: cannot abort from a branch yet to be born
+	fatal: cherry-pick failed
+	EOF
+	git checkout --orphan new_disconnected &&
+	git reset --hard &&
+	test_must_fail git cherry-pick anotherpick &&
+	test_must_fail git cherry-pick --abort 2>advice &&
+	git cherry-pick --skip &&
+	test_cmp expect advice
+'
+
+test_expect_success 'allow skipping stopped cherry-pick because of untracked file modifications' '
+	pristine_detach initial &&
+	git rm --cached unrelated &&
+	git commit -m "untrack unrelated" &&
+	test_must_fail git cherry-pick initial base &&
+	test_path_is_missing .git/CHERRY_PICK_HEAD &&
+	git cherry-pick --skip
+'
+
 test_expect_success '--quit does not complain when no cherry-pick is in progress' '
 	pristine_detach initial &&
 	git cherry-pick --quit
-- 
2.21.0