Merge branch 'pw/rebase-i-error-message'

When the user adds to "git rebase -i" instruction to "pick" a merge
commit, the error experience is not pleasant.  Such an error is now
caught earlier in the process that parses the todo list.

* pw/rebase-i-error-message:
  rebase -i: improve error message when picking merge
  rebase -i: pass struct replay_opts to parse_insn_line()

9 files changed, 153 insertions, 30 deletions

diff --git a/Documentation/config/advice.txt b/Documentation/config/advice.txt
index 0e35ae5240..fa61241756 100644
--- a/Documentation/config/advice.txt
+++ b/Documentation/config/advice.txt
@@ -96,6 +96,8 @@ advice.*::
 		`pushNonFFCurrent`, `pushNonFFMatching`, `pushAlreadyExists`,
 		`pushFetchFirst`, `pushNeedsForce`, and `pushRefNeedsUpdate`
 		simultaneously.
+	rebaseTodoError::
+		Shown when there is an error after editing the rebase todo list.
 	refSyntax::
 		Shown when the user provides an illegal ref name, to
 		tell the user about the ref syntax documentation.
diff --git a/advice.c b/advice.c
index 0a122c2020..558a46fc0b 100644
--- a/advice.c
+++ b/advice.c
@@ -70,6 +70,7 @@ static struct {
 	[ADVICE_PUSH_UNQUALIFIED_REF_NAME]		= { "pushUnqualifiedRefName" },
 	[ADVICE_PUSH_UPDATE_REJECTED]			= { "pushUpdateRejected" },
 	[ADVICE_PUSH_UPDATE_REJECTED_ALIAS]		= { "pushNonFastForward" }, /* backwards compatibility */
+	[ADVICE_REBASE_TODO_ERROR]			= { "rebaseTodoError" },
 	[ADVICE_REF_SYNTAX]				= { "refSyntax" },
 	[ADVICE_RESET_NO_REFRESH_WARNING]		= { "resetNoRefresh" },
 	[ADVICE_RESOLVE_CONFLICT]			= { "resolveConflict" },
diff --git a/advice.h b/advice.h
index c8d29f97f3..5105d90129 100644
--- a/advice.h
+++ b/advice.h
@@ -37,6 +37,7 @@ enum advice_type {
 	ADVICE_PUSH_UNQUALIFIED_REF_NAME,
 	ADVICE_PUSH_UPDATE_REJECTED,
 	ADVICE_PUSH_UPDATE_REJECTED_ALIAS,
+	ADVICE_REBASE_TODO_ERROR,
 	ADVICE_REF_SYNTAX,
 	ADVICE_RESET_NO_REFRESH_WARNING,
 	ADVICE_RESOLVE_CONFLICT,
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 4506bae768..e3a8e74cfc 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -206,7 +206,7 @@ static struct replay_opts get_replay_opts(const struct rebase_options *opts)
 	return replay;
 }
 
-static int edit_todo_file(unsigned flags)
+static int edit_todo_file(unsigned flags, struct replay_opts *opts)
 {
 	const char *todo_file = rebase_path_todo();
 	struct todo_list todo_list = TODO_LIST_INIT,
@@ -217,7 +217,8 @@ static int edit_todo_file(unsigned flags)
 		return error_errno(_("could not read '%s'."), todo_file);
 
 	strbuf_stripspace(&todo_list.buf, comment_line_str);
-	res = edit_todo_list(the_repository, &todo_list, &new_todo, NULL, NULL, flags);
+	res = edit_todo_list(the_repository, opts, &todo_list, &new_todo,
+			     NULL, NULL, flags);
 	if (!res && todo_list_write_to_file(the_repository, &new_todo, todo_file,
 					    NULL, NULL, -1, flags & ~(TODO_LIST_SHORTEN_IDS)))
 		res = error_errno(_("could not write '%s'"), todo_file);
@@ -308,8 +309,8 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 		error(_("could not generate todo list"));
 	else {
 		discard_index(the_repository->index);
-		if (todo_list_parse_insn_buffer(the_repository, todo_list.buf.buf,
-						&todo_list))
+		if (todo_list_parse_insn_buffer(the_repository, &replay,
+						todo_list.buf.buf, &todo_list))
 			BUG("unusable todo list");
 
 		ret = complete_action(the_repository, &replay, flags,
@@ -364,9 +365,13 @@ static int run_sequencer_rebase(struct rebase_options *opts)
 		replay_opts_release(&replay_opts);
 		break;
 	}
-	case ACTION_EDIT_TODO:
-		ret = edit_todo_file(flags);
+	case ACTION_EDIT_TODO: {
+		struct replay_opts replay_opts = get_replay_opts(opts);
+
+		ret = edit_todo_file(flags, &replay_opts);
+		replay_opts_release(&replay_opts);
 		break;
+	}
 	case ACTION_SHOW_CURRENT_PATCH: {
 		struct child_process cmd = CHILD_PROCESS_INIT;
 
diff --git a/rebase-interactive.c b/rebase-interactive.c
index c343e16fcd..56fd7206a9 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -101,9 +101,10 @@ void append_todo_help(int command_count,
 	strbuf_add_commented_lines(buf, msg, strlen(msg), comment_line_str);
 }
 
-int edit_todo_list(struct repository *r, struct todo_list *todo_list,
-		   struct todo_list *new_todo, const char *shortrevisions,
-		   const char *shortonto, unsigned flags)
+int edit_todo_list(struct repository *r, struct replay_opts *opts,
+		   struct todo_list *todo_list, struct todo_list *new_todo,
+		   const char *shortrevisions, const char *shortonto,
+		   unsigned flags)
 {
 	const char *todo_file = rebase_path_todo(),
 		*todo_backup = rebase_path_todo_backup();
@@ -114,7 +115,9 @@ int edit_todo_list(struct repository *r, struct todo_list *todo_list,
 	 * it.  If there is an error, we do not return, because the user
 	 * might want to fix it in the first place. */
 	if (!initial)
-		incorrect = todo_list_parse_insn_buffer(r, todo_list->buf.buf, todo_list) |
+		incorrect = todo_list_parse_insn_buffer(r, opts,
+							todo_list->buf.buf,
+							todo_list) |
 			file_exists(rebase_path_dropped());
 
 	if (todo_list_write_to_file(r, todo_list, todo_file, shortrevisions, shortonto,
@@ -134,13 +137,13 @@ int edit_todo_list(struct repository *r, struct todo_list *todo_list,
 	if (initial && new_todo->buf.len == 0)
 		return -3;
 
-	if (todo_list_parse_insn_buffer(r, new_todo->buf.buf, new_todo)) {
+	if (todo_list_parse_insn_buffer(r, opts, new_todo->buf.buf, new_todo)) {
 		fprintf(stderr, _(edit_todo_list_advice));
 		return -4;
 	}
 
 	if (incorrect) {
-		if (todo_list_check_against_backup(r, new_todo)) {
+		if (todo_list_check_against_backup(r, opts, new_todo)) {
 			write_file(rebase_path_dropped(), "%s", "");
 			return -4;
 		}
@@ -228,13 +231,15 @@ leave_check:
 	return res;
 }
 
-int todo_list_check_against_backup(struct repository *r, struct todo_list *todo_list)
+int todo_list_check_against_backup(struct repository *r,
+				   struct replay_opts *opts,
+				   struct todo_list *todo_list)
 {
 	struct todo_list backup = TODO_LIST_INIT;
 	int res = 0;
 
 	if (strbuf_read_file(&backup.buf, rebase_path_todo_backup(), 0) > 0) {
-		todo_list_parse_insn_buffer(r, backup.buf.buf, &backup);
+		todo_list_parse_insn_buffer(r, opts, backup.buf.buf, &backup);
 		res = todo_list_check(&backup, todo_list);
 	}
 
diff --git a/rebase-interactive.h b/rebase-interactive.h
index 7239c60f79..8e5b181b33 100644
--- a/rebase-interactive.h
+++ b/rebase-interactive.h
@@ -3,17 +3,20 @@
 
 struct strbuf;
 struct repository;
+struct replay_opts;
 struct todo_list;
 
 void append_todo_help(int command_count,
 		      const char *shortrevisions, const char *shortonto,
 		      struct strbuf *buf);
-int edit_todo_list(struct repository *r, struct todo_list *todo_list,
-		   struct todo_list *new_todo, const char *shortrevisions,
-		   const char *shortonto, unsigned flags);
+int edit_todo_list(struct repository *r, struct replay_opts *opts,
+		   struct todo_list *todo_list, struct todo_list *new_todo,
+		   const char *shortrevisions, const char *shortonto,
+		   unsigned flags);
 
 int todo_list_check(struct todo_list *old_todo, struct todo_list *new_todo);
 int todo_list_check_against_backup(struct repository *r,
+				   struct replay_opts *opts,
 				   struct todo_list *todo_list);
 
 #endif
diff --git a/sequencer.c b/sequencer.c
index 30513e87bf..c6a5ccf6dd 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -2626,8 +2626,63 @@ static int check_label_or_ref_arg(enum todo_command command, const char *arg)
 	return 0;
 }
 
-static int parse_insn_line(struct repository *r, struct todo_item *item,
-			   const char *buf, const char *bol, char *eol)
+static int check_merge_commit_insn(enum todo_command command)
+{
+	switch(command) {
+	case TODO_PICK:
+		error(_("'%s' does not accept merge commits"),
+		      todo_command_info[command].str);
+		advise_if_enabled(ADVICE_REBASE_TODO_ERROR, _(
+			/*
+			 * TRANSLATORS: 'pick' and 'merge -C' should not be
+			 * translated.
+			 */
+			"'pick' does not take a merge commit. If you wanted to\n"
+			"replay the merge, use 'merge -C' on the commit."));
+		return -1;
+
+	case TODO_REWORD:
+		error(_("'%s' does not accept merge commits"),
+		      todo_command_info[command].str);
+		advise_if_enabled(ADVICE_REBASE_TODO_ERROR, _(
+			/*
+			 * TRANSLATORS: 'reword' and 'merge -c' should not be
+			 * translated.
+			 */
+			"'reword' does not take a merge commit. If you wanted to\n"
+			"replay the merge and reword the commit message, use\n"
+			"'merge -c' on the commit"));
+		return -1;
+
+	case TODO_EDIT:
+		error(_("'%s' does not accept merge commits"),
+		      todo_command_info[command].str);
+		advise_if_enabled(ADVICE_REBASE_TODO_ERROR, _(
+			/*
+			 * TRANSLATORS: 'edit', 'merge -C' and 'break' should
+			 * not be translated.
+			 */
+			"'edit' does not take a merge commit. If you wanted to\n"
+			"replay the merge, use 'merge -C' on the commit, and then\n"
+			"'break' to give the control back to you so that you can\n"
+			"do 'git commit --amend && git rebase --continue'."));
+		return -1;
+
+	case TODO_FIXUP:
+	case TODO_SQUASH:
+		return error(_("cannot squash merge commit into another commit"));
+
+	case TODO_MERGE:
+		return 0;
+
+	default:
+		BUG("unexpected todo_command");
+	}
+}
+
+static int parse_insn_line(struct repository *r, struct replay_opts *opts,
+			   struct todo_item *item, const char *buf,
+			   const char *bol, char *eol)
 {
 	struct object_id commit_oid;
 	char *end_of_object_name;
@@ -2731,7 +2786,12 @@ static int parse_insn_line(struct repository *r, struct todo_item *item,
 		return status;
 
 	item->commit = lookup_commit_reference(r, &commit_oid);
-	return item->commit ? 0 : -1;
+	if (!item->commit)
+		return -1;
+	if (is_rebase_i(opts) &&
+	    item->commit->parents && item->commit->parents->next)
+		return check_merge_commit_insn(item->command);
+	return 0;
 }
 
 int sequencer_get_last_command(struct repository *r UNUSED, enum replay_action *action)
@@ -2761,8 +2821,8 @@ int sequencer_get_last_command(struct repository *r UNUSED, enum replay_action *
 	return ret;
 }
 
-int todo_list_parse_insn_buffer(struct repository *r, char *buf,
-				struct todo_list *todo_list)
+int todo_list_parse_insn_buffer(struct repository *r, struct replay_opts *opts,
+				char *buf, struct todo_list *todo_list)
 {
 	struct todo_item *item;
 	char *p = buf, *next_p;
@@ -2780,7 +2840,7 @@ int todo_list_parse_insn_buffer(struct repository *r, char *buf,
 
 		item = append_new_todo(todo_list);
 		item->offset_in_buf = p - todo_list->buf.buf;
-		if (parse_insn_line(r, item, buf, p, eol)) {
+		if (parse_insn_line(r, opts, item, buf, p, eol)) {
 			res = error(_("invalid line %d: %.*s"),
 				i, (int)(eol - p), p);
 			item->command = TODO_COMMENT + 1;
@@ -2930,7 +2990,7 @@ static int read_populate_todo(struct repository *r,
 	if (strbuf_read_file_or_whine(&todo_list->buf, todo_file) < 0)
 		return -1;
 
-	res = todo_list_parse_insn_buffer(r, todo_list->buf.buf, todo_list);
+	res = todo_list_parse_insn_buffer(r, opts, todo_list->buf.buf, todo_list);
 	if (res) {
 		if (is_rebase_i(opts))
 			return error(_("please fix this using "
@@ -2960,7 +3020,7 @@ static int read_populate_todo(struct repository *r,
 		struct todo_list done = TODO_LIST_INIT;
 
 		if (strbuf_read_file(&done.buf, rebase_path_done(), 0) > 0 &&
-		    !todo_list_parse_insn_buffer(r, done.buf.buf, &done))
+		    !todo_list_parse_insn_buffer(r, opts, done.buf.buf, &done))
 			todo_list->done_nr = count_commands(&done);
 		else
 			todo_list->done_nr = 0;
@@ -5319,7 +5379,8 @@ int sequencer_continue(struct repository *r, struct replay_opts *opts)
 			goto release_todo_list;
 
 		if (file_exists(rebase_path_dropped())) {
-			if ((res = todo_list_check_against_backup(r, &todo_list)))
+			if ((res = todo_list_check_against_backup(r, opts,
+								  &todo_list)))
 				goto release_todo_list;
 
 			unlink(rebase_path_dropped());
@@ -6363,7 +6424,7 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 		return error(_("nothing to do"));
 	}
 
-	res = edit_todo_list(r, todo_list, &new_todo, shortrevisions,
+	res = edit_todo_list(r, opts, todo_list, &new_todo, shortrevisions,
 			     shortonto, flags);
 	if (res == -1)
 		return -1;
@@ -6391,7 +6452,7 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 	strbuf_release(&buf2);
 	/* Nothing is done yet, and we're reparsing, so let's reset the count */
 	new_todo.total_nr = 0;
-	if (todo_list_parse_insn_buffer(r, new_todo.buf.buf, &new_todo) < 0)
+	if (todo_list_parse_insn_buffer(r, opts, new_todo.buf.buf, &new_todo) < 0)
 		BUG("invalid todo list after expanding IDs:\n%s",
 		    new_todo.buf.buf);
 
diff --git a/sequencer.h b/sequencer.h
index a309ddd712..304ba4b4d3 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -136,8 +136,8 @@ struct todo_list {
 	.buf = STRBUF_INIT, \
 }
 
-int todo_list_parse_insn_buffer(struct repository *r, char *buf,
-				struct todo_list *todo_list);
+int todo_list_parse_insn_buffer(struct repository *r, struct replay_opts *opts,
+				char *buf, struct todo_list *todo_list);
 int todo_list_write_to_file(struct repository *r, struct todo_list *todo_list,
 			    const char *file, const char *shortrevisions,
 			    const char *shortonto, int num, unsigned flags);
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index d1bead61fa..f92baad138 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -2215,6 +2215,51 @@ test_expect_success 'bad labels and refs rejected when parsing todo list' '
 	test_path_is_missing execed
 '
 
+test_expect_success 'non-merge commands reject merge commits' '
+	test_when_finished "test_might_fail git rebase --abort" &&
+	git checkout E &&
+	git merge I &&
+	oid=$(git rev-parse HEAD) &&
+	cat >todo <<-EOF &&
+	pick $oid
+	reword $oid
+	edit $oid
+	fixup $oid
+	squash $oid
+	EOF
+	(
+		set_replace_editor todo &&
+		test_must_fail git rebase -i HEAD 2>actual
+	) &&
+	cat >expect <<-EOF &&
+	error: ${SQ}pick${SQ} does not accept merge commits
+	hint: ${SQ}pick${SQ} does not take a merge commit. If you wanted to
+	hint: replay the merge, use ${SQ}merge -C${SQ} on the commit.
+	hint: Disable this message with "git config advice.rebaseTodoError false"
+	error: invalid line 1: pick $oid
+	error: ${SQ}reword${SQ} does not accept merge commits
+	hint: ${SQ}reword${SQ} does not take a merge commit. If you wanted to
+	hint: replay the merge and reword the commit message, use
+	hint: ${SQ}merge -c${SQ} on the commit
+	hint: Disable this message with "git config advice.rebaseTodoError false"
+	error: invalid line 2: reword $oid
+	error: ${SQ}edit${SQ} does not accept merge commits
+	hint: ${SQ}edit${SQ} does not take a merge commit. If you wanted to
+	hint: replay the merge, use ${SQ}merge -C${SQ} on the commit, and then
+	hint: ${SQ}break${SQ} to give the control back to you so that you can
+	hint: do ${SQ}git commit --amend && git rebase --continue${SQ}.
+	hint: Disable this message with "git config advice.rebaseTodoError false"
+	error: invalid line 3: edit $oid
+	error: cannot squash merge commit into another commit
+	error: invalid line 4: fixup $oid
+	error: cannot squash merge commit into another commit
+	error: invalid line 5: squash $oid
+	You can fix this with ${SQ}git rebase --edit-todo${SQ} and then run ${SQ}git rebase --continue${SQ}.
+	Or you can abort the rebase with ${SQ}git rebase --abort${SQ}.
+	EOF
+	test_cmp expect actual
+'
+
 # This must be the last test in this file
 test_expect_success '$EDITOR and friends are unchanged' '
 	test_editor_unchanged