[PATCH 7/7] sequencer: teach parser about CHERRY_PICK_HEAD

[Ramkumar Ramachandra <artagnon@gmail.com>]

The final step in unifying the sequencer interface involves making
sure that a single-commit pick can be concluded with a '--continue'.

  $ git cherry-pick foo
  ... conflict ...
  $ echo "resolved" >problematicfile
  $ git add problematicfile
  $ git sequencer --continue

To do this, we have to update our parser that normally reads
'.git/sequencer/todo' to read '.git/CHERRY_PICK_HEAD' as a special
case before proceeding as usual.  Add a new test in
't3510-sequencer.sh' to make sure that this works.  Although we have
added a similar test for revert in the same patch for symmetry, the
test doesn't depend on this patch to work.  A single-commit revert
operation does not create a '.git/CHERRY_PICK_HEAD' at all: it uses
the information in '.git/sequencer' as usual.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 sequencer.c          |   32 ++++++++++++++++++++++++++++----
 t/t3510-sequencer.sh |   44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 4 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 7b10b7b..84df926 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -569,12 +569,32 @@ static int parse_insn_buffer(char *buf, struct replay_insn_list **todo_list)
 	return 0;
 }
 
-static void read_populate_todo(struct replay_insn_list **todo_list)
+static void read_populate_todo(struct replay_insn_list **todo_list, int cph_flag)
 {
 	const char *todo_file = git_path(SEQ_TODO_FILE);
 	struct strbuf buf = STRBUF_INIT;
 	int fd, res;
 
+	if (cph_flag) {
+		struct replay_insn_list item = {0, NULL, NULL};
+		const char *name = "CHERRY_PICK_HEAD";
+		const char *CHERRY_PICK_HEAD = git_path(name);
+
+		fd = open(CHERRY_PICK_HEAD, O_RDONLY);
+		if (fd < 0)
+			die_errno(_("Could not open %s."), CHERRY_PICK_HEAD);
+
+		item.action = REPLAY_PICK;
+		item.operand = lookup_commit_reference_by_name(name);
+
+		if (!item.operand)
+			die(_("could not lookup commit %s"), name);
+		replay_insn_list_append(item.action, item.operand, todo_list);
+		close(fd);
+		strbuf_release(&buf);
+		return;
+	}
+
 	fd = open(todo_file, O_RDONLY);
 	if (fd < 0)
 		die_errno(_("Could not open %s."), todo_file);
@@ -792,10 +812,14 @@ int sequencer_pick_revisions(struct replay_opts *opts)
 		remove_sequencer_state(1);
 		return 0;
 	} else if (opts->subcommand == REPLAY_CONTINUE) {
-		if (!file_exists(git_path(SEQ_TODO_FILE)))
-			goto error;
+		if (!file_exists(git_path(SEQ_TODO_FILE))) {
+			if (!file_exists(git_path("CHERRY_PICK_HEAD")))
+				goto error;
+			read_populate_todo(&todo_list, 1);
+		}
+		else
+			read_populate_todo(&todo_list, 0);
 		read_populate_opts(&opts);
-		read_populate_todo(&todo_list);
 
 		if (!index_differs_from("HEAD", 0))
 			todo_list = todo_list->next;
diff --git a/t/t3510-sequencer.sh b/t/t3510-sequencer.sh
index 65f2724..f7c3a37 100755
--- a/t/t3510-sequencer.sh
+++ b/t/t3510-sequencer.sh
@@ -45,6 +45,50 @@ test_expect_success '--continue complains when there are unresolved conflicts' '
 	test_must_fail git sequencer --continue
 '
 
+test_expect_success '--continue continues single-commit cherry-pick' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick anotherpick &&
+	echo "c" >foo &&
+	git add foo &&
+	git sequencer --continue &&
+	test_path_is_missing .git/sequencer &&
+	{
+		git rev-list HEAD |
+		git diff-tree --root --stdin |
+		sed "s/$_x40/OBJID/g"
+	} >actual &&
+	cat >expect <<-\EOF &&
+	OBJID
+	:100644 100644 OBJID OBJID M	foo
+	OBJID
+	:000000 100644 OBJID OBJID A	foo
+	:000000 100644 OBJID OBJID A	unrelated
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '--continue continues single-commit revert' '
+	pristine_detach initial &&
+	test_must_fail git revert anotherpick &&
+	echo "c" >foo &&
+	git add foo &&
+	git sequencer --continue &&
+	test_path_is_missing .git/sequencer &&
+	{
+		git rev-list HEAD |
+		git diff-tree --root --stdin |
+		sed "s/$_x40/OBJID/g"
+	} >actual &&
+	cat >expect <<-\EOF &&
+	OBJID
+	:100644 100644 OBJID OBJID M	foo
+	OBJID
+	:000000 100644 OBJID OBJID A	foo
+	:000000 100644 OBJID OBJID A	unrelated
+	EOF
+	test_cmp expect actual
+'
+
 test_expect_success '--continue continues after conflicts are resolved' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick base..anotherpick &&
-- 
1.7.6.351.gb35ac.dirty