revert: introduce --abort to cancel a failed cherry-pick

After running some ill-advised command like "git cherry-pick
HEAD..linux-next", the bewildered novice may want to return to more
familiar territory.  Introduce a "git cherry-pick --abort" command
that rolls back the entire cherry-pick sequence and places the
repository back on solid ground.

Just like "git merge --abort", this internally uses "git reset
--merge", so local changes not involved in the conflict resolution are
preserved.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-cherry-pick.txt

@@ -11,6 +11,7 @@ SYNOPSIS
 'git cherry-pick' [--edit] [-n] [-m parent-number] [-s] [-x] [--ff] <commit>...
 'git cherry-pick' --continue
 'git cherry-pick' --quit
+'git cherry-pick' --abort
 
 DESCRIPTION
 -----------

Documentation/git-revert.txt

@@ -11,6 +11,7 @@ SYNOPSIS
 'git revert' [--edit | --no-edit] [-n] [-m parent-number] [-s] <commit>...
 'git revert' --continue
 'git revert' --quit
+'git revert' --abort
 
 DESCRIPTION
 -----------

Documentation/sequencer.txt

@@ -7,3 +7,6 @@
 	Forget about the current operation in progress.  Can be used
 	to clear the sequencer state after a failed cherry-pick or
 	revert.
+
+--abort::
+	Cancel the operation and return to the pre-sequence state.

builtin/revert.c

@@ -40,7 +40,12 @@ static const char * const cherry_pick_usage[] = {
 };
 
 enum replay_action { REVERT, CHERRY_PICK };
-enum replay_subcommand { REPLAY_NONE, REPLAY_REMOVE_STATE, REPLAY_CONTINUE };
+enum replay_subcommand {
+	REPLAY_NONE,
+	REPLAY_REMOVE_STATE,
+	REPLAY_CONTINUE,
+	REPLAY_ROLLBACK
+};
 
 struct replay_opts {
 	enum replay_action action;
@@ -135,9 +140,11 @@ static void parse_args(int argc, const char **argv, struct replay_opts *opts)
 	const char *me = action_name(opts);
 	int remove_state = 0;
 	int contin = 0;
+	int rollback = 0;
 	struct option options[] = {
 		OPT_BOOLEAN(0, "quit", &remove_state, "end revert or cherry-pick sequence"),
 		OPT_BOOLEAN(0, "continue", &contin, "resume revert or cherry-pick sequence"),
+		OPT_BOOLEAN(0, "abort", &rollback, "cancel revert or cherry-pick sequence"),
 		OPT_BOOLEAN('n', "no-commit", &opts->no_commit, "don't automatically commit"),
 		OPT_BOOLEAN('e', "edit", &opts->edit, "edit the commit message"),
 		OPT_NOOP_NOARG('r', NULL),
@@ -173,6 +180,7 @@ static void parse_args(int argc, const char **argv, struct replay_opts *opts)
 	verify_opt_mutually_compatible(me,
 				"--quit", remove_state,
 				"--continue", contin,
+				"--abort", rollback,
 				NULL);
 
 	/* Set the subcommand */
@@ -180,6 +188,8 @@ static void parse_args(int argc, const char **argv, struct replay_opts *opts)
 		opts->subcommand = REPLAY_REMOVE_STATE;
 	else if (contin)
 		opts->subcommand = REPLAY_CONTINUE;
+	else if (rollback)
+		opts->subcommand = REPLAY_ROLLBACK;
 	else
 		opts->subcommand = REPLAY_NONE;
 
@@ -188,8 +198,12 @@ static void parse_args(int argc, const char **argv, struct replay_opts *opts)
 		char *this_operation;
 		if (opts->subcommand == REPLAY_REMOVE_STATE)
 			this_operation = "--quit";
-		else
+		else if (opts->subcommand == REPLAY_CONTINUE)
 			this_operation = "--continue";
+		else {
+			assert(opts->subcommand == REPLAY_ROLLBACK);
+			this_operation = "--abort";
+		}
 
 		verify_opt_compatible(me, this_operation,
 				"--no-commit", opts->no_commit,
@@ -850,7 +864,7 @@ static int create_seq_dir(void)
 
 	if (file_exists(seq_dir)) {
 		error(_("a cherry-pick or revert is already in progress"));
-		advise(_("try \"git cherry-pick (--continue | --quit)\""));
+		advise(_("try \"git cherry-pick (--continue | --quit | --abort)\""));
 		return -1;
 	}
 	else if (mkdir(seq_dir, 0777) < 0)
@@ -873,6 +887,71 @@ static void save_head(const char *head)
 		die(_("Error wrapping up %s."), head_file);
 }
 
+static int reset_for_rollback(const unsigned char *sha1)
+{
+	const char *argv[4];	/* reset --merge <arg> + NULL */
+	argv[0] = "reset";
+	argv[1] = "--merge";
+	argv[2] = sha1_to_hex(sha1);
+	argv[3] = NULL;
+	return run_command_v_opt(argv, RUN_GIT_CMD);
+}
+
+static int rollback_single_pick(void)
+{
+	unsigned char head_sha1[20];
+
+	if (!file_exists(git_path("CHERRY_PICK_HEAD")) &&
+	    !file_exists(git_path("REVERT_HEAD")))
+		return error(_("no cherry-pick or revert in progress"));
+	if (!resolve_ref("HEAD", head_sha1, 0, NULL))
+		return error(_("cannot resolve HEAD"));
+	if (is_null_sha1(head_sha1))
+		return error(_("cannot abort from a branch yet to be born"));
+	return reset_for_rollback(head_sha1);
+}
+
+static int sequencer_rollback(struct replay_opts *opts)
+{
+	const char *filename;
+	FILE *f;
+	unsigned char sha1[20];
+	struct strbuf buf = STRBUF_INIT;
+
+	filename = git_path(SEQ_HEAD_FILE);
+	f = fopen(filename, "r");
+	if (!f && errno == ENOENT) {
+		/*
+		 * There is no multiple-cherry-pick in progress.
+		 * If CHERRY_PICK_HEAD or REVERT_HEAD indicates
+		 * a single-cherry-pick in progress, abort that.
+		 */
+		return rollback_single_pick();
+	}
+	if (!f)
+		return error(_("cannot open %s: %s"), filename,
+						strerror(errno));
+	if (strbuf_getline(&buf, f, '\n')) {
+		error(_("cannot read %s: %s"), filename, ferror(f) ?
+			strerror(errno) : _("unexpected end of file"));
+		goto fail;
+	}
+	if (get_sha1_hex(buf.buf, sha1) || buf.buf[40] != '\0') {
+		error(_("stored pre-cherry-pick HEAD file '%s' is corrupt"),
+			filename);
+		goto fail;
+	}
+	if (reset_for_rollback(sha1))
+		goto fail;
+	strbuf_release(&buf);
+	fclose(f);
+	return 0;
+fail:
+	strbuf_release(&buf);
+	fclose(f);
+	return -1;
+}
+
 static void save_todo(struct commit_list *todo_list, struct replay_opts *opts)
 {
 	const char *todo_file = git_path(SEQ_TODO_FILE);
@@ -977,6 +1056,8 @@ static int pick_revisions(struct replay_opts *opts)
 		remove_sequencer_state(1);
 		return 0;
 	}
+	if (opts->subcommand == REPLAY_ROLLBACK)
+		return sequencer_rollback(opts);
 	if (opts->subcommand == REPLAY_CONTINUE) {
 		if (!file_exists(git_path(SEQ_TODO_FILE)))
 			return error(_("No %s in progress"), action_name(opts));

t/t3510-cherry-pick-sequence.sh

@@ -2,6 +2,7 @@
 
 test_description='Test cherry-pick continuation features
 
+  + yetanotherpick: rewrites foo to e
   + anotherpick: rewrites foo to d
   + picked: rewrites foo to c
   + unrelatedpick: rewrites unrelated to reallyunrelated
@@ -19,6 +20,12 @@ pristine_detach () {
 	git clean -d -f -f -q -x
 }
 
+test_cmp_rev () {
+	git rev-parse --verify "$1" >expect.rev &&
+	git rev-parse --verify "$2" >actual.rev &&
+	test_cmp expect.rev actual.rev
+}
+
 test_expect_success setup '
 	echo unrelated >unrelated &&
 	git add unrelated &&
@@ -27,6 +34,7 @@ test_expect_success setup '
 	test_commit unrelatedpick unrelated reallyunrelated &&
 	test_commit picked foo c &&
 	test_commit anotherpick foo d &&
+	test_commit yetanotherpick foo e &&
 	git config advice.detachedhead false
 
 '
@@ -75,6 +83,11 @@ test_expect_success '--quit does not complain when no cherry-pick is in progress
 	git cherry-pick --quit
 '
 
+test_expect_success '--abort requires cherry-pick in progress' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick --abort
+'
+
 test_expect_success '--quit cleans up sequencer state' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick base..picked &&
@@ -103,6 +116,79 @@ test_expect_success 'cherry-pick --reset (another name for --quit)' '
 	test_cmp expect actual
 '
 
+test_expect_success '--abort to cancel multiple cherry-pick' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick base..anotherpick &&
+	git cherry-pick --abort &&
+	test_path_is_missing .git/sequencer &&
+	test_cmp_rev initial HEAD &&
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD
+'
+
+test_expect_success '--abort to cancel single cherry-pick' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick picked &&
+	git cherry-pick --abort &&
+	test_path_is_missing .git/sequencer &&
+	test_cmp_rev initial HEAD &&
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD
+'
+
+test_expect_success 'cherry-pick --abort to cancel multiple revert' '
+	pristine_detach anotherpick &&
+	test_must_fail git revert base..picked &&
+	git cherry-pick --abort &&
+	test_path_is_missing .git/sequencer &&
+	test_cmp_rev anotherpick HEAD &&
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD
+'
+
+test_expect_success 'revert --abort works, too' '
+	pristine_detach anotherpick &&
+	test_must_fail git revert base..picked &&
+	git revert --abort &&
+	test_path_is_missing .git/sequencer &&
+	test_cmp_rev anotherpick HEAD
+'
+
+test_expect_success '--abort to cancel single revert' '
+	pristine_detach anotherpick &&
+	test_must_fail git revert picked &&
+	git revert --abort &&
+	test_path_is_missing .git/sequencer &&
+	test_cmp_rev anotherpick HEAD &&
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD
+'
+
+test_expect_success '--abort keeps unrelated change, easy case' '
+	pristine_detach unrelatedpick &&
+	echo changed >expect &&
+	test_must_fail git cherry-pick picked..yetanotherpick &&
+	echo changed >unrelated &&
+	git cherry-pick --abort &&
+	test_cmp expect unrelated
+'
+
+test_expect_success '--abort refuses to clobber unrelated change, harder case' '
+	pristine_detach initial &&
+	echo changed >expect &&
+	test_must_fail git cherry-pick base..anotherpick &&
+	echo changed >unrelated &&
+	test_must_fail git cherry-pick --abort &&
+	test_cmp expect unrelated &&
+	git rev-list HEAD >log &&
+	test_line_count = 2 log &&
+	test_must_fail git update-index --refresh &&
+
+	git checkout unrelated &&
+	git cherry-pick --abort &&
+	test_cmp_rev initial HEAD
+'
+
 test_expect_success 'cherry-pick cleans up sequencer state when one commit is left' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick base..picked &&
@@ -127,6 +213,16 @@ test_expect_success 'cherry-pick cleans up sequencer state when one commit is le
 	test_cmp expect actual
 '
 
+test_expect_failure '--abort after last commit in sequence' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick base..picked &&
+	git cherry-pick --abort &&
+	test_path_is_missing .git/sequencer &&
+	test_cmp_rev initial HEAD &&
+	git update-index --refresh &&
+	git diff-index --exit-code HEAD
+'
+
 test_expect_success 'cherry-pick does not implicitly stomp an existing operation' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick base..anotherpick &&