revert: allow cherry-pick --continue to commit before resuming

When "git cherry-pick ..bar" encounters conflicts, permit the operator
to use cherry-pick --continue after resolving them as a shortcut for
"git commit && git cherry-pick --continue" to record the resolution
and carry on with the rest of the sequence.

This improves the analogy with "git rebase" (in olden days --continue
was the way to preserve authorship when a rebase encountered
conflicts) and fits well with a general UI goal of making "git cmd
--continue" save humans the trouble of deciding what to do next.

Example: after encountering a conflict from running "git cherry-pick
foo bar baz":

	CONFLICT (content): Merge conflict in main.c
	error: could not apply f78a8d98c... bar!
	hint: after resolving the conflicts, mark the corrected paths
	hint: with 'git add <paths>' or 'git rm <paths>'
	hint: and commit the result with 'git commit'

We edit main.c to resolve the conflict, mark it acceptable with "git
add main.c", and can run "cherry-pick --continue" to resume the
sequence.

	$ git cherry-pick --continue
	[editor opens to confirm commit message]
	[master 78c8a8c98] bar!
	 1 files changed, 1 insertions(+), 1 deletions(-)
	[master 87ca8798c] baz!
	 1 files changed, 1 insertions(+), 1 deletions(-)

This is done for both codepaths to pick multiple commits and a single
commit.

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

2 files changed, 156 insertions, 6 deletions

diff --git a/builtin/revert.c b/builtin/revert.c
index 9f6c85c1a7..a43b4d85fb 100644
--- a/builtin/revert.c
+++ b/builtin/revert.c
@@ -1038,18 +1038,35 @@ static int pick_commits(struct commit_list *todo_list, struct replay_opts *opts)
 	return 0;
 }
 
+static int continue_single_pick(void)
+{
+	const char *argv[] = { "commit", NULL };
+
+	if (!file_exists(git_path("CHERRY_PICK_HEAD")) &&
+	    !file_exists(git_path("REVERT_HEAD")))
+		return error(_("no cherry-pick or revert in progress"));
+	return run_command_v_opt(argv, RUN_GIT_CMD);
+}
+
 static int sequencer_continue(struct replay_opts *opts)
 {
 	struct commit_list *todo_list = NULL;
 
 	if (!file_exists(git_path(SEQ_TODO_FILE)))
-		return error(_("No %s in progress"), action_name(opts));
+		return continue_single_pick();
 	read_populate_opts(&opts);
 	read_populate_todo(&todo_list, opts);
 
 	/* Verify that the conflict has been resolved */
-	if (!index_differs_from("HEAD", 0))
-		todo_list = todo_list->next;
+	if (file_exists(git_path("CHERRY_PICK_HEAD")) ||
+	    file_exists(git_path("REVERT_HEAD"))) {
+		int ret = continue_single_pick();
+		if (ret)
+			return ret;
+	}
+	if (index_differs_from("HEAD", 0))
+		return error_dirty_index(opts);
+	todo_list = todo_list->next;
 	return pick_commits(todo_list, opts);
 }
 
diff --git a/t/t3510-cherry-pick-sequence.sh b/t/t3510-cherry-pick-sequence.sh
index 2c4c1c851d..4d1883b734 100755
--- a/t/t3510-cherry-pick-sequence.sh
+++ b/t/t3510-cherry-pick-sequence.sh
@@ -2,6 +2,7 @@
 
 test_description='Test cherry-pick continuation features
 
+ +  conflicting: rewrites unrelated to conflicting
   + yetanotherpick: rewrites foo to e
   + anotherpick: rewrites foo to d
   + picked: rewrites foo to c
@@ -27,6 +28,7 @@ test_cmp_rev () {
 }
 
 test_expect_success setup '
+	git config advice.detachedhead false
 	echo unrelated >unrelated &&
 	git add unrelated &&
 	test_commit initial foo a &&
@@ -35,8 +37,8 @@ test_expect_success setup '
 	test_commit picked foo c &&
 	test_commit anotherpick foo d &&
 	test_commit yetanotherpick foo e &&
-	git config advice.detachedhead false
-
+	pristine_detach initial &&
+	test_commit conflicting unrelated
 '
 
 test_expect_success 'cherry-pick persists data on failure' '
@@ -243,7 +245,66 @@ test_expect_success '--continue complains when there are unresolved conflicts' '
 	test_must_fail git cherry-pick --continue
 '
 
-test_expect_success '--continue continues after conflicts are resolved' '
+test_expect_success '--continue of single cherry-pick' '
+	pristine_detach initial &&
+	echo c >expect &&
+	test_must_fail git cherry-pick picked &&
+	echo c >foo &&
+	git add foo &&
+	git cherry-pick --continue &&
+
+	test_cmp expect foo &&
+	test_cmp_rev initial HEAD^ &&
+	git diff --exit-code HEAD &&
+	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
+'
+
+test_expect_success '--continue of single revert' '
+	pristine_detach initial &&
+	echo resolved >expect &&
+	echo "Revert \"picked\"" >expect.msg &&
+	test_must_fail git revert picked &&
+	echo resolved >foo &&
+	git add foo &&
+	git cherry-pick --continue &&
+
+	git diff --exit-code HEAD &&
+	test_cmp expect foo &&
+	test_cmp_rev initial HEAD^ &&
+	git diff-tree -s --pretty=tformat:%s HEAD >msg &&
+	test_cmp expect.msg msg &&
+	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD &&
+	test_must_fail git rev-parse --verify REVERT_HEAD
+'
+
+test_expect_success '--continue after resolving conflicts' '
+	pristine_detach initial &&
+	echo d >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..anotherpick &&
+	echo c >foo &&
+	git add foo &&
+	git cherry-pick --continue &&
+	{
+		git rev-list HEAD |
+		git diff-tree --root --stdin |
+		sed "s/$_x40/OBJID/g"
+	} >actual.log &&
+	test_cmp expect foo &&
+	test_cmp expect.log actual.log
+'
+
+test_expect_success '--continue after resolving conflicts and committing' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick base..anotherpick &&
 	echo "c" >foo &&
@@ -270,6 +331,29 @@ test_expect_success '--continue continues after conflicts are resolved' '
 	test_cmp expect actual
 '
 
+test_expect_success '--continue asks for help after resolving patch to nil' '
+	pristine_detach conflicting &&
+	test_must_fail git cherry-pick initial..picked &&
+
+	test_cmp_rev unrelatedpick CHERRY_PICK_HEAD &&
+	git checkout HEAD -- unrelated &&
+	test_must_fail git cherry-pick --continue 2>msg &&
+	test_i18ngrep "The previous cherry-pick is now empty" msg
+'
+
+test_expect_failure 'follow advice and skip nil patch' '
+	pristine_detach conflicting &&
+	test_must_fail git cherry-pick initial..picked &&
+
+	git checkout HEAD -- unrelated &&
+	test_must_fail git cherry-pick --continue &&
+	git reset &&
+	git cherry-pick --continue &&
+
+	git rev-list initial..HEAD >commits &&
+	test_line_count = 3 commits
+'
+
 test_expect_success '--continue respects opts' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick -x base..anotherpick &&
@@ -288,6 +372,29 @@ test_expect_success '--continue respects opts' '
 	grep "cherry picked from" anotherpick_msg
 '
 
+test_expect_success '--continue of single-pick respects -x' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick -x picked &&
+	echo c >foo &&
+	git add foo &&
+	git cherry-pick --continue &&
+	test_path_is_missing .git/sequencer &&
+	git cat-file commit HEAD >msg &&
+	grep "cherry picked from" msg
+'
+
+test_expect_success '--continue respects -x in first commit in multi-pick' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick -x picked anotherpick &&
+	echo c >foo &&
+	git add foo &&
+	git cherry-pick --continue &&
+	test_path_is_missing .git/sequencer &&
+	git cat-file commit HEAD^ >msg &&
+	picked=$(git rev-parse --verify picked) &&
+	grep "cherry picked from.*$picked" msg
+'
+
 test_expect_success '--signoff is not automatically propagated to resolved conflict' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick --signoff base..anotherpick &&
@@ -306,6 +413,32 @@ test_expect_success '--signoff is not automatically propagated to resolved confl
 	grep "Signed-off-by:" anotherpick_msg
 '
 
+test_expect_success '--signoff dropped for implicit commit of resolution, multi-pick case' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick -s picked anotherpick &&
+	echo c >foo &&
+	git add foo &&
+	git cherry-pick --continue &&
+
+	git diff --exit-code HEAD &&
+	test_cmp_rev initial HEAD^^ &&
+	git cat-file commit HEAD^ >msg &&
+	! grep Signed-off-by: msg
+'
+
+test_expect_success 'sign-off needs to be reaffirmed after conflict resolution, single-pick case' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick -s picked &&
+	echo c >foo &&
+	git add foo &&
+	git cherry-pick --continue &&
+
+	git diff --exit-code HEAD &&
+	test_cmp_rev initial HEAD^ &&
+	git cat-file commit HEAD >msg &&
+	! grep Signed-off-by: msg
+'
+
 test_expect_success 'malformed instruction sheet 1' '
 	pristine_detach initial &&
 	test_must_fail git cherry-pick base..anotherpick &&