Merge branch 'en/no-amend-during-conflicts' into jch

Teach 'am', 'revert', and 'rebase' that running 'commit --amend' or a
partial 'commit <paths>' makes no sense during operations that stop
and return control to the user to resolve conflicts left in the
working tree, just like 'cherry-pick' and 'merge' do.

* en/no-amend-during-conflicts:
  commit: refuse partial commits during conflict resolution
  commit: refuse to amend during conflict resolution
  commit: reword the empty-commit rebase amend error
  commit: allow a partial commit when a rebase pick becomes empty
  commit: clarify FROM_REBASE_PICK and is_from_rebase() names

builtin/commit.c

@@ -515,13 +515,25 @@ static const char *prepare_index(const char **argv, const char *prefix,
 	 */
 	commit_style = COMMIT_PARTIAL;
 
-	if (whence != FROM_COMMIT) {
+	switch (sequencer_ongoing_operation(the_repository, whence)) {
-		if (whence == FROM_MERGE)
+	case ONGOING_NONE:
-			die(_("cannot do a partial commit during a merge."));
+		break;
-		else if (is_from_cherry_pick(whence))
+	case ONGOING_MERGE:
-			die(_("cannot do a partial commit during a cherry-pick."));
+		die(_("cannot do a partial commit during a merge."));
-		else if (is_from_rebase(whence))
+	case ONGOING_CHERRY_PICK:
-			die(_("cannot do a partial commit during a rebase."));
+		die(_("cannot do a partial commit during a cherry-pick."));
+	case ONGOING_REBASE_EMPTY:
+		/*
+		 * A pick that became empty is not a conflict, and creating
+		 * a new commit (partial or not) poses no problem.
+		 */
+		break;
+	case ONGOING_REVERT:
+		die(_("cannot do a partial commit during a revert."));
+	case ONGOING_AM:
+		die(_("cannot do a partial commit during an am session."));
+	case ONGOING_REBASE_CONFLICT:
+		die(_("cannot do a partial commit while resolving conflicts during a rebase."));
 	}
 
 	if (list_paths(&partial, !current_head ? NULL : "HEAD", &pathspec))
@@ -893,7 +905,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	 */
 	else if (whence == FROM_MERGE)
 		hook_arg1 = "merge";
-	else if (is_from_cherry_pick(whence) || whence == FROM_REBASE_PICK) {
+	else if (is_from_cherry_pick(whence) || is_from_rebase_empty(whence)) {
 		hook_arg1 = "commit";
 		hook_arg2 = "CHERRY_PICK_HEAD";
 	}
@@ -1086,7 +1098,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		if (amend)
 			fputs(_(empty_amend_advice), stderr);
 		else if (is_from_cherry_pick(whence) ||
-			 whence == FROM_REBASE_PICK) {
+			 is_from_rebase_empty(whence)) {
 			fputs(_(empty_cherry_pick_advice), stderr);
 			if (whence == FROM_CHERRY_PICK_SINGLE)
 				fputs(_(empty_cherry_pick_advice_single), stderr);
@@ -1326,15 +1338,30 @@ static int parse_and_validate_options(int argc, const char *argv[],
 		use_editor = 0;
 
 	/* Sanity check options */
-	if (amend && !current_head)
+	if (amend) {
-		die(_("You have nothing to amend."));
+		if (!current_head)
-	if (amend && whence != FROM_COMMIT) {
+			die(_("You have nothing to amend."));
-		if (whence == FROM_MERGE)
+		/*
+		 * 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."));
-		else if (whence == FROM_REBASE_PICK)
+		case ONGOING_REBASE_EMPTY:
-			die(_("You are in the middle of a rebase -- cannot amend."));
+			die(_("The now-empty commit has been dropped -- cannot amend."));
+		case ONGOING_REVERT:
+			die(_("You are in the middle of a revert -- cannot amend."));
+		case ONGOING_AM:
+			die(_("You are in the middle of an am session -- cannot amend."));
+		case ONGOING_REBASE_CONFLICT:
+			die(_("You are resolving conflicts during a rebase -- cannot amend."));
+		}
 	}
 	if (fixup_message && squash_message)
 		die(_("options '%s' and '%s' cannot be used together"), "--squash", "--fixup");
@@ -1353,7 +1380,7 @@ static int parse_and_validate_options(int argc, const char *argv[],
 	if (amend && !use_message && !fixup_message)
 		use_message = "HEAD";
 	if (!use_message && !is_from_cherry_pick(whence) &&
-	    !is_from_rebase(whence) && renew_authorship)
+	    !is_from_rebase_empty(whence) && renew_authorship)
 		die(_("--reset-author can be used only with -C, -c or --amend."));
 	if (use_message) {
 		use_message_buffer = read_commit_message(use_message);
@@ -1362,7 +1389,7 @@ static int parse_and_validate_options(int argc, const char *argv[],
 			author_message_buffer = use_message_buffer;
 		}
 	}
-	if ((is_from_cherry_pick(whence) || whence == FROM_REBASE_PICK) &&
+	if ((is_from_cherry_pick(whence) || is_from_rebase_empty(whence)) &&
 	    !renew_authorship) {
 		author_message = "CHERRY_PICK_HEAD";
 		author_message_buffer = read_commit_message(author_message);
@@ -1887,7 +1914,7 @@ int cmd_commit(int argc,
 		if (!reflog_msg)
 			reflog_msg = is_from_cherry_pick(whence)
 					? "commit (cherry-pick)"
-					: is_from_rebase(whence)
+					: is_from_rebase_empty(whence)
 					? "commit (rebase)"
 					: "commit";
 		commit_list_insert(current_head, &parents);

sequencer.c

@@ -142,6 +142,13 @@ static GIT_PATH_FUNC(rebase_path_author_script, "rebase-merge/author-script")
  * command is processed, this file is deleted.
  */
 static GIT_PATH_FUNC(rebase_path_amend, "rebase-merge/amend")
+/*
+ * The apply ("am") backend keeps its state in the rebase-apply directory;
+ * the "applying" file within it marks a plain `git am` (as opposed to an
+ * apply-based rebase).
+ */
+static GIT_PATH_FUNC(apply_dir, "rebase-apply")
+static GIT_PATH_FUNC(apply_path_applying, "rebase-apply/applying")
 /*
  * When we stop at a given patch via the "edit" command, this file contains
  * the commit object name of the corresponding patch.
@@ -6957,7 +6964,7 @@ int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
 		    !repo_get_oid(r, "REBASE_HEAD", &rebase_head) &&
 		    !repo_get_oid(r, "CHERRY_PICK_HEAD", &cherry_pick_head) &&
 		    oideq(&rebase_head, &cherry_pick_head))
-			*whence = FROM_REBASE_PICK;
+			*whence = FROM_REBASE_EMPTY;
 		else
 			*whence = FROM_CHERRY_PICK_SINGLE;
 
@@ -6967,6 +6974,56 @@ 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)
+{
+	/*
+	 * The merge, cherry-pick, and (empty) rebase-pick stops are already
+	 * distinguished by 'whence'.
+	 */
+	switch (whence) {
+	case FROM_MERGE:
+		return ONGOING_MERGE;
+	case FROM_CHERRY_PICK_SINGLE:
+	case FROM_CHERRY_PICK_MULTI:
+		return ONGOING_CHERRY_PICK;
+	case FROM_REBASE_EMPTY:
+		return ONGOING_REBASE_EMPTY;
+	case FROM_COMMIT:
+		break;
+	}
+
+	/*
+	 * 'whence' is FROM_COMMIT, but we may still be in the middle of an
+	 * operation that records its result on top of HEAD; detect those
+	 * from their on-disk state.
+	 */
+
+	/* In the middle of a revert? */
+	if (refs_ref_exists(get_main_ref_store(r), "REVERT_HEAD"))
+		return ONGOING_REVERT;
+
+	/* In the middle of an `am`? */
+	if (file_exists(apply_path_applying()))
+		return ONGOING_AM;
+
+	/*
+	 * 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.
+	 */
+	if (file_exists(apply_dir()) ||
+	    (file_exists(rebase_path_stopped_sha()) &&
+	     !file_exists(rebase_path_amend())))
+		return ONGOING_REBASE_CONFLICT;
+
+	return ONGOING_NONE;
+}
+
 int sequencer_get_update_refs_state(const char *wt_dir,
 				    struct string_list *refs)
 {

sequencer.h

@@ -277,6 +277,30 @@ 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.  Some ways of invoking
+ * "git commit" -- amending HEAD, or a partial commit -- are almost
+ * always a mistake during such an operation.
+ */
+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.

t/t3404-rebase-interactive.sh

@@ -1858,7 +1858,7 @@ test_expect_success 'post-commit hook is called' '
 	test_cmp expect actual
 '
 
-test_expect_success 'correct error message for partial commit after empty pick' '
+test_expect_success 'partial commit is allowed when a rebase pick becomes empty' '
 	test_when_finished "git rebase --abort" &&
 	(
 		set_fake_editor &&
@@ -1867,8 +1867,7 @@ test_expect_success 'correct error message for partial commit after empty pick'
 		test_must_fail git rebase -i A D
 	) &&
 	echo x >file1 &&
-	test_must_fail git commit file1 2>err &&
+	git commit file1
-	test_grep "cannot do a partial commit during a rebase." err
 '
 
 test_expect_success 'correct error message for commit --amend after empty pick' '
@@ -1881,7 +1880,128 @@ test_expect_success 'correct error message for commit --amend after empty pick'
 	) &&
 	echo x>file1 &&
 	test_must_fail git commit -a --amend 2>err &&
-	test_grep "middle of a rebase -- cannot amend." err
+	test_grep "now-empty commit has been dropped -- 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 'partial commit 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
+	) &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit conflict 2>err &&
+	test_grep "cannot do a partial commit while resolving conflicts during a rebase." err
+'
+
+test_expect_success 'partial commit 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 &&
+		echo resolved >file &&
+		git add file &&
+		test_must_fail git commit file 2>err &&
+		test_grep "cannot do a partial commit while resolving conflicts during a rebase." err
+	)
 '
 
 test_expect_success 'todo has correct onto hash' '

t/t3507-cherry-pick-conflict.sh

@@ -364,6 +364,28 @@ 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 'partial commit during a revert fails' '
+	pristine_detach initial &&
+
+	test_must_fail git revert picked &&
+	echo resolved >foo &&
+	git add foo &&
+	test_must_fail git commit foo 2>err &&
+
+	test_grep "cannot do a partial commit during a revert." err
+'
+
 test_expect_success 'successful revert does not set REVERT_HEAD' '
 	pristine_detach base &&
 	git revert base &&

t/t4151-am-abort.sh

@@ -63,6 +63,28 @@ 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 'partial commit 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 file-1 2>err &&
+	test_grep "cannot do a partial commit during an am session." 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 &&

wt-status.h

@@ -41,7 +41,7 @@ enum commit_whence {
 	FROM_MERGE,      /* commit came from merge */
 	FROM_CHERRY_PICK_SINGLE, /* commit came from cherry-pick */
 	FROM_CHERRY_PICK_MULTI, /* commit came from a sequence of cherry-picks */
-	FROM_REBASE_PICK /* commit came from a pick/reword/edit */
+	FROM_REBASE_EMPTY /* rebase applied a pick that became empty */
 };
 
 static inline int is_from_cherry_pick(enum commit_whence whence)
@@ -50,9 +50,9 @@ static inline int is_from_cherry_pick(enum commit_whence whence)
 		whence == FROM_CHERRY_PICK_MULTI;
 }
 
-static inline int is_from_rebase(enum commit_whence whence)
+static inline int is_from_rebase_empty(enum commit_whence whence)
 {
-	return whence == FROM_REBASE_PICK;
+	return whence == FROM_REBASE_EMPTY;
 }
 
 struct wt_status_change_data {