Re: [PATCH v2 2/3] commit: refuse to amend during conflict resolution

From: Elijah Newren <redacted>

diff --git a/builtin/commit.c b/builtin/commit.c
index 0d908d72bb..4a6054aae0 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c

@@ -1326,15 +1326,30 @@ static int parse_and_validate_options(int argc, const char *argv[],
  		use_editor = 0;
  
  	/* Sanity check options */
-	if (amend && !current_head)
-		die(_("You have nothing to amend."));
-	if (amend && whence != FROM_COMMIT) {
-		if (whence == FROM_MERGE)
+	if (amend) {
+		if (!current_head)
+			die(_("You have nothing to amend."));
+		/*
+		 * Refuse to amend in the middle of any operation that is
+		 * meant to record its result as a new commit on top of HEAD
+		 * rather than by rewriting HEAD.
+		 */
+		switch (sequencer_ongoing_operation(s->repo, whence)) {
+		case ONGOING_NONE:
+			break;
+		case ONGOING_MERGE:
  			die(_("You are in the middle of a merge -- cannot amend."));
-		else if (is_from_cherry_pick(whence))
+		case ONGOING_CHERRY_PICK:
  			die(_("You are in the middle of a cherry-pick -- cannot amend."));

diff --git a/sequencer.c b/sequencer.c
index 65afd100d9..bd4a724410 100644
--- a/sequencer.c
+++ b/sequencer.c

@@ -6966,6 +6966,71 @@ int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
  	return 0;
  }
  
+enum ongoing_operation sequencer_ongoing_operation(struct repository *r,
+						   enum commit_whence whence)
+{

[...]
+	/*
+	 * In the middle of a rebase that stopped for conflict resolution?
+	 * The apply backend only ever stops for conflicts, so the presence
+	 * of its state directory is enough.  The merge backend writes
+	 * stopped-sha whenever it hands control back to the user, but omits
+	 * `amend` unless it stopped with HEAD already pointing at the commit
+	 * to be amended (a clean edit/reword stop); its absence therefore
+	 * marks a conflicted stop.
+	 */
+	path = repo_git_path(r, "rebase-apply");
+	found = file_exists(path);
+	free(path);
+	if (!found) {
+		char *stopped_sha = repo_git_path(r, "rebase-merge/stopped-sha");
+		char *amend_marker = repo_git_path(r, "rebase-merge/amend");
+
+		found = file_exists(stopped_sha) && !file_exists(amend_marker);

+		free(stopped_sha);
+		free(amend_marker);
+	}
+	if (found)
+		return ONGOING_REBASE_CONFLICT;
+
+	return ONGOING_NONE;
+}
+
  int sequencer_get_update_refs_state(const char *wt_dir,
  				    struct string_list *refs)
  {

diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..3a4bd97db1 100644
--- a/sequencer.h
+++ b/sequencer.h

@@ -277,6 +277,29 @@ int sequencer_get_last_command(struct repository* r,
  			       enum replay_action *action);
  int sequencer_determine_whence(struct repository *r, enum commit_whence *whence);
  
+/*
+ * An in-progress operation that records its result (often a conflict
+ * resolution) as a new commit on top of HEAD, during which amending
+ * HEAD via "git commit --amend" is almost always a mistake.
+ */
+enum ongoing_operation {
+	ONGOING_NONE = 0,
+	ONGOING_MERGE,
+	ONGOING_CHERRY_PICK,
+	ONGOING_REBASE_EMPTY,
+	ONGOING_REVERT,
+	ONGOING_AM,
+	ONGOING_REBASE_CONFLICT
+};
+
+/*
+ * Return which in-progress operation, if any, is underway; see enum
+ * ongoing_operation.  'whence' is the origin already computed for the
+ * pending commit.
+ */
+enum ongoing_operation sequencer_ongoing_operation(struct repository *r,
+						   enum commit_whence whence);
+
  /**
   * Append the set of ref-OID pairs that are currently stored for the 'git
   * rebase --update-refs' feature if such a rebase is currently happening.

diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 1e78dbfd90..7cf06e5f9a 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh

@@ -1884,6 +1884,93 @@ test_expect_success 'correct error message for commit --amend after empty pick'
  	test_grep "resolving a commit that became empty -- cannot amend." err
  '
  
+test_expect_success 'commit --amend is refused at a rebase conflict stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/patch &&
+	test_path_is_missing .git/rebase-merge/amend &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit --amend --no-edit 2>err &&
+	test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+'
+
+test_expect_success 'commit --amend is refused when an "edit" pick conflicts' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 edit 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/patch &&
+	test_path_is_missing .git/rebase-merge/amend &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit --amend --no-edit 2>err &&
+	test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+'
+
+test_expect_success 'commit --amend is allowed at a rebase edit stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach no-conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="edit 1 2 3 4" &&
+		export FAKE_LINES &&
+		git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/amend &&
+	echo tweak >fileJ &&
+	git add fileJ &&
+	git commit --amend --no-edit
+'
+
+test_expect_success 'commit --amend is allowed at a rebase break stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach no-conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="break 1 2 3 4" &&
+		export FAKE_LINES &&
+		git rebase -i A
+	) &&
+	test_must_fail git rev-parse --verify REBASE_HEAD &&
+	echo tweak >fileJ &&
+	git add fileJ &&
+	git commit --amend --no-edit
+'
+
+test_expect_success 'commit --amend is refused at an apply-backend conflict stop' '
+	test_when_finished "rm -rf apply-backend" &&
+	test_create_repo apply-backend &&
+	(
+		cd apply-backend &&
+		test_commit base file &&
+		git branch -M mainline &&
+		test_commit upstream file upstream &&
+		git checkout -b side mainline~1 &&
+		test_commit conflicting file side &&
+		test_commit unrelated other &&
+		test_must_fail git rebase --apply mainline &&
+		# the apply backend only ever stops for conflicts, and
+		# leaves HEAD on the previously-applied commit
+		test_path_is_dir .git/rebase-apply &&
+		test_path_is_missing .git/rebase-apply/applying &&
+		echo resolved >file &&
+		git add file &&
+		test_must_fail git commit --amend --no-edit 2>err &&
+		test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+	)
+'
+
  test_expect_success 'todo has correct onto hash' '
  	GIT_SEQUENCE_EDITOR=cat git rebase -i no-conflict-branch~4 no-conflict-branch >actual &&
  	onto=$(git rev-parse --short HEAD~4) &&

diff --git a/t/t3507-cherry-pick-conflict.sh b/t/t3507-cherry-pick-conflict.sh
index 44596cb1e8..42de398f76 100755
--- a/t/t3507-cherry-pick-conflict.sh
+++ b/t/t3507-cherry-pick-conflict.sh

@@ -364,6 +364,17 @@ test_expect_success 'failed revert sets REVERT_HEAD' '
  	test_cmp_rev picked REVERT_HEAD
  '
  
+test_expect_success 'commit --amend of revert fails' '
+	pristine_detach initial &&
+
+	test_must_fail git revert picked &&
+	echo resolved >foo &&
+	git add foo &&
+	test_must_fail git commit --amend 2>err &&
+
+	test_grep "in the middle of a revert -- cannot amend." err
+'
+
  test_expect_success 'successful revert does not set REVERT_HEAD' '
  	pristine_detach base &&
  	git revert base &&

diff --git a/t/t4151-am-abort.sh b/t/t4151-am-abort.sh
index 8e1ecf8a68..9313a074b2 100755
--- a/t/t4151-am-abort.sh
+++ b/t/t4151-am-abort.sh

@@ -63,6 +63,17 @@ do
  
  done
  
+test_expect_success 'commit --amend during a failed am fails' '
+	git reset --hard initial &&
+	cp file-2-expect file-2 &&
+	test_must_fail git am 000[1245]-*.patch &&
+	echo resolved >file-1 &&
+	git add file-1 &&
+	test_must_fail git commit --amend 2>err &&
+	test_grep "in the middle of an am session -- cannot amend." err &&
+	git am --abort
+'
+
  test_expect_success 'am -3 --skip removes otherfile-4' '
  	git reset --hard initial &&
  	test_must_fail git am -3 0003-*.patch &&