[RFC PATCH v2] revert: Implement --abort processing

[Ramkumar Ramachandra <artagnon@gmail.com>]

To abort, simply reset the HEAD to the location specified by the
HEAD_FILE written earlier, without touching the worktree or index.  It
is upto the user to execute "rerere clear", "reset --hard", and "reset
--merge" as approprite.

Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 I've persisted the TODO early, and made it complain when an existing
 cherry-pick/ revert is in progress.  Further, as Junio suggested,
 I've made no attempt to touch the index or the worktree during the
 --abort operation: I simply update HEAD and leave the user to do the
 rest.  Should we print some hints about this?

 However, by making it complain everytime a cherry-pick/ revert is in
 progress, I've essentially broken the entire testsuite -- everytime a
 test or even a script (see git-rebase.sh) calls cherry-pick or
 revert, I must call '--abort' to clean up afterwards.  Fixing this
 will require me to touch many seemingly unrelated files.

 Also, note that I'm depending on the "libify reset" patch I posted a
 few minutes ago to print_new_head_line exactly the way reset does.

 In other news, I've started writing '--continue' and '--skip'
 operations, but the limiting factor is the instruction sheet's
 format: I'm still wondering if there's any way to avoid being
 verbose/ ugly and flexible (by allowing command-line options for each
 instruction) at the same time.  Will post RFC patches asking more
 directed questions soon.

 Thanks.

 builtin/revert.c                |   85 +++++++++++++++++++++++++++++++++++---
 t/t3510-cherry-pick-sequence.sh |   16 +++++++
 2 files changed, 94 insertions(+), 7 deletions(-)

diff --git a/builtin/revert.c b/builtin/revert.c
index e1a05a3..efcc01f 100644
--- a/builtin/revert.c
+++ b/builtin/revert.c
@@ -14,6 +14,7 @@
 #include "merge-recursive.h"
 #include "refs.h"
 #include "dir.h"
+#include "reset.h"
 
 /*
  * This implements the builtins revert and cherry-pick.
@@ -208,8 +209,6 @@ static void parse_args(int argc, const char **argv, struct replay_opts *opts)
 				NULL);
 
 	/* Remove these when the options are actually implemented */
-	if (opts->abort_oper)
-		die("--abort is not implemented yet");
 	if (opts->skip_oper)
 		die("--skip is not implemented yet");
 	if (opts->continue_oper)
@@ -719,6 +718,7 @@ static int pick_commits(struct replay_opts *opts)
 	struct commit *commit;
 	unsigned char sha1[20];
 	const char *head;
+	int res;
 
 	setenv(GIT_REFLOG_ACTION, me, 0);
 
@@ -730,11 +730,30 @@ static int pick_commits(struct replay_opts *opts)
 	persist_head(head);
 	prepare_revs(&revs, opts);
 
+	/* Prepare todo_list and persist it early before picking */
+	struct commit_list *todo_list = NULL;
+	struct commit_list *cur = NULL;
+	struct commit_list *new_item = NULL;
+
+	/* Insert into todo_list in the same order */
 	while ((commit = get_revision(&revs))) {
-		int res = do_pick_commit(commit, opts);
+		new_item = xmalloc(sizeof(struct commit_list));
+		new_item->item = commit;
+		if (cur)
+			cur->next = new_item;
+		else
+			todo_list = new_item;
+		cur = new_item;
+	}
+	cur->next = NULL;
+
+	persist_todo(todo_list, opts);
+
+	for (cur = todo_list; cur; cur = cur->next) {
+		res = do_pick_commit(cur->item, opts);
 		if (res) {
-			commit_list_insert(commit, &revs.commits);
-			persist_todo(revs.commits, opts);
+			commit_list_insert(cur->item, &todo_list);
+			persist_todo(todo_list, opts);
 			return res;
 		}
 	}
@@ -743,6 +762,58 @@ static int pick_commits(struct replay_opts *opts)
 	return cleanup_sequencer_dir();
 }
 
+static int process_continuation(struct replay_opts *opts)
+{
+	unsigned char sha1[20];
+	struct commit *commit;
+	char head_hex[40];
+	char msg[1024];
+	int fd;
+
+	if (opts->abort_oper) {
+		/* First, read the HEAD_FILE */
+		if (!file_exists(HEAD_FILE))
+			goto error;
+		fd = open(HEAD_FILE, O_RDONLY, 0666);
+		if (fd < 0)
+			return error(_("Could not open '%s' for reading: %s"),
+				HEAD_FILE, strerror(errno));
+		if (read_in_full(fd, head_hex, 40) < 40 || get_sha1_hex(head_hex, sha1) < 0) {
+			close(fd);
+			return error(_("Corrupt '%s': %s"), HEAD_FILE, strerror(errno));
+		}
+		close(fd);
+
+		/* Update the HEAD ref */
+		if (snprintf(msg, sizeof(msg), "%s: updating HEAD", me) >= sizeof(msg))
+			warning(_("Reflog action message too long: %.*s..."), 50, msg);
+		if (update_ref(msg, "HEAD", sha1, NULL, 0, MSG_ON_ERR))
+			return -1;
+		commit = lookup_commit_reference(sha1);
+		print_new_head_line(commit);
+
+		return cleanup_sequencer_dir();
+	}
+	else if (opts->skip_oper) {
+		if (!file_exists(TODO_FILE))
+			goto error;
+	}
+	else if (opts->continue_oper) {
+		if (!file_exists(TODO_FILE))
+			goto error;
+	}
+	else if (file_exists(HEAD_FILE)) {
+		error(_("A %s is already in progress"), me);
+		advise(_("Use %s --continue to continue the operation"), me);
+		advise(_("or %s --abort to start afresh"), me);
+		return -1;
+	}
+
+	return pick_commits(opts);
+error:
+	return error(_("No %s in progress"), me);
+}
+
 int cmd_revert(int argc, const char **argv, const char *prefix)
 {
 	int res;
@@ -755,7 +826,7 @@ int cmd_revert(int argc, const char **argv, const char *prefix)
 	git_config(git_default_config, NULL);
 	me = "revert";
 	parse_args(argc, argv, &opts);
-	res = pick_commits(&opts);
+	res = process_continuation(&opts);
 	if (res > 0)
 		/* Exit status from conflict */
 		return res;
@@ -775,7 +846,7 @@ int cmd_cherry_pick(int argc, const char **argv, const char *prefix)
 	git_config(git_default_config, NULL);
 	me = "cherry-pick";
 	parse_args(argc, argv, &opts);
-	res = pick_commits(&opts);
+	res = process_continuation(&opts);
 	if (res > 0)
 		return res;
 	if (res < 0)
diff --git a/t/t3510-cherry-pick-sequence.sh b/t/t3510-cherry-pick-sequence.sh
index a2e1888..c6ace35 100644
--- a/t/t3510-cherry-pick-sequence.sh
+++ b/t/t3510-cherry-pick-sequence.sh
@@ -36,4 +36,20 @@ test_expect_success 'cherry-pick cleans up sequencer directory upon success' '
 	test_must_fail test -d .git/sequencer
 '
 
+test_expect_success '--abort complains when no cherry-pick is in progress' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick --abort >actual 2>&1 &&
+	echo "error: No cherry-pick in progress" >expect &&
+	test_i18ncmp expect actual
+'
+
+test_expect_success '--abort restores HEAD after failed cherry-pick' '
+	pristine_detach initial &&
+	head=$(git rev-parse HEAD) &&
+	test_must_fail git cherry-pick base..picked &&
+	git cherry-pick --abort &&
+	newhead=$(git rev-parse HEAD) &&
+	test "$head" = "$newhead"
+'
+
 test_done
-- 
1.7.4.1