commit/reset: try to clean up sequencer state

When cherry-picking or reverting a sequence of commits and if the final
pick/revert has conflicts and the user uses `git commit` to commit the
conflict resolution and does not run `git cherry-pick --continue` then
the sequencer state is left behind. This can cause problems later. In my
case I cherry-picked a sequence of commits the last one of which I
committed with `git commit` after resolving some conflicts, then a while
later, on a different branch I aborted a revert which rewound my HEAD to
the end of the cherry-pick sequence on the previous branch. Avoid this
potential problem by removing the sequencer state if we're committing or
resetting the final pick in a sequence.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

branch.c

@@ -5,6 +5,7 @@
 #include "refs.h"
 #include "refspec.h"
 #include "remote.h"
+#include "sequencer.h"
 #include "commit.h"
 #include "worktree.h"
 
@@ -339,8 +340,7 @@ void create_branch(struct repository *r,
 
 void remove_branch_state(struct repository *r)
 {
-	unlink(git_path_cherry_pick_head(r));
-	unlink(git_path_revert_head(r));
+	sequencer_post_commit_cleanup(r);
 	unlink(git_path_merge_head(r));
 	unlink(git_path_merge_rr(r));
 	unlink(git_path_merge_msg(r));

builtin/commit.c

@@ -1657,8 +1657,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		die("%s", err.buf);
 	}
 
-	unlink(git_path_cherry_pick_head(the_repository));
-	unlink(git_path_revert_head(the_repository));
+	sequencer_post_commit_cleanup(the_repository);
 	unlink(git_path_merge_head(the_repository));
 	unlink(git_path_merge_msg(the_repository));
 	unlink(git_path_merge_mode(the_repository));

sequencer.c

@@ -2220,6 +2220,57 @@ static ssize_t strbuf_read_file_or_whine(struct strbuf *sb, const char *path)
 	return len;
 }
 
+static int have_finished_the_last_pick(void)
+{
+	struct strbuf buf = STRBUF_INIT;
+	const char *eol;
+	const char *todo_path = git_path_todo_file();
+	int ret = 0;
+
+	if (strbuf_read_file(&buf, todo_path, 0) < 0) {
+		if (errno == ENOENT) {
+			return 0;
+		} else {
+			error_errno("unable to open '%s'", todo_path);
+			return 0;
+		}
+	}
+	/* If there is only one line then we are done */
+	eol = strchr(buf.buf, '\n');
+	if (!eol || !eol[1])
+		ret = 1;
+
+	strbuf_release(&buf);
+
+	return ret;
+}
+
+void sequencer_post_commit_cleanup(struct repository *r)
+{
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int need_cleanup = 0;
+
+	if (file_exists(git_path_cherry_pick_head(r))) {
+		unlink(git_path_cherry_pick_head(r));
+		opts.action = REPLAY_PICK;
+		need_cleanup = 1;
+	}
+
+	if (file_exists(git_path_revert_head(r))) {
+		unlink(git_path_revert_head(r));
+		opts.action = REPLAY_REVERT;
+		need_cleanup = 1;
+	}
+
+	if (!need_cleanup)
+		return;
+
+	if (!have_finished_the_last_pick())
+		return;
+
+	sequencer_remove_state(&opts);
+}
+
 static int read_populate_todo(struct repository *r,
 			      struct todo_list *todo_list,
 			      struct replay_opts *opts)

sequencer.h

@@ -144,3 +144,4 @@ int read_author_script(const char *path, char **name, char **email, char **date,
 void parse_strategy_opts(struct replay_opts *opts, char *raw_opts);
 int write_basic_state(struct replay_opts *opts, const char *head_name,
 		      const char *onto, const char *orig_head);
+void sequencer_post_commit_cleanup(struct repository *r);

t/t3507-cherry-pick-conflict.sh

@@ -156,6 +156,25 @@ test_expect_success 'successful commit clears CHERRY_PICK_HEAD' '
 
 	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
 '
+test_expect_success 'successful final commit clears cherry-pick state' '
+	pristine_detach initial &&
+
+	test_must_fail git cherry-pick base picked-signed &&
+	echo resolved >foo &&
+	test_path_is_file .git/sequencer/todo &&
+	git commit -a &&
+	test_must_fail test_path_exists .git/sequencer
+'
+
+test_expect_success 'reset after final pick clears cherry-pick state' '
+	pristine_detach initial &&
+
+	test_must_fail git cherry-pick base picked-signed &&
+	echo resolved >foo &&
+	test_path_is_file .git/sequencer/todo &&
+	git reset &&
+	test_must_fail test_path_exists .git/sequencer
+'
 
 test_expect_success 'failed cherry-pick produces dirty index' '
 	pristine_detach initial &&
@@ -316,6 +335,26 @@ test_expect_success 'failed commit does not clear REVERT_HEAD' '
 	test_cmp_rev picked REVERT_HEAD
 '
 
+test_expect_success 'successful final commit clears revert state' '
+       pristine_detach picked-signed &&
+
+       test_must_fail git revert picked-signed base &&
+       echo resolved >foo &&
+       test_path_is_file .git/sequencer/todo &&
+       git commit -a &&
+       test_must_fail test_path_exists .git/sequencer
+'
+
+test_expect_success 'reset after final pick clears revert state' '
+       pristine_detach picked-signed &&
+
+       test_must_fail git revert picked-signed base &&
+       echo resolved >foo &&
+       test_path_is_file .git/sequencer/todo &&
+       git reset &&
+       test_must_fail test_path_exists .git/sequencer
+'
+
 test_expect_success 'revert conflict, diff3 -m style' '
 	pristine_detach initial &&
 	git config merge.conflictstyle diff3 &&