non-builtin rebase: use non-builtin interactive backend

We recently converted both the `git rebase` and the `git rebase -i`
command from Unix shell scripts to builtins.

The former has a safety valve allowing to fall back to the scripted
`rebase`, just in case that there is a bug in the builtin `rebase`:
setting the config variable `rebase.useBuiltin` to `false` will
fall back to using the scripted version.

The latter did not have such a safety hatch.

Let's reinstate the scripted interactive rebase backend so that `rebase.useBuiltin=false` will not use the builtin interactive rebase,
just in case that an end user runs into a bug with the builtin version
and needs to get out of the fix really quickly.

This is necessary because Git for Windows wants to ship the builtin
rebase/interactive rebase earlier than core Git: Git for Windows
v2.19.0 will come with the option of a drastically faster (if a lot
less battle-tested) `git rebase`/`git rebase -i`.

As the file name `git-rebase--interactive` is already in use, let's
rename the scripted backend to `git-legacy-rebase--interactive`.

A couple of additional touch-ups are needed (such as teaching the
builtin `rebase--interactive`, which assumed the role of the
`rebase--helper`, to perform the two tricks to skip the unnecessary
picks and to generate a new todo list) to make things work again.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

.gitignore

@@ -83,6 +83,7 @@
 /git-interpret-trailers
 /git-instaweb
 /git-legacy-rebase
+/git-legacy-rebase--interactive
 /git-legacy-stash
 /git-log
 /git-ls-files

Makefile

@@ -639,6 +639,7 @@ SCRIPT_SH += git-request-pull.sh
 SCRIPT_SH += git-submodule.sh
 SCRIPT_SH += git-web--browse.sh
 
+SCRIPT_LIB += git-legacy-rebase--interactive
 SCRIPT_LIB += git-mergetool--lib
 SCRIPT_LIB += git-parse-remote
 SCRIPT_LIB += git-rebase--am

builtin/rebase--interactive.c

@@ -143,7 +143,8 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 	char *raw_strategies = NULL;
 	enum {
 		NONE = 0, CONTINUE, SKIP, EDIT_TODO, SHOW_CURRENT_PATCH,
-		SHORTEN_OIDS, EXPAND_OIDS, CHECK_TODO_LIST, REARRANGE_SQUASH, ADD_EXEC
+		SHORTEN_OIDS, EXPAND_OIDS, CHECK_TODO_LIST, REARRANGE_SQUASH, ADD_EXEC,
+		MAKE_SCRIPT, SKIP_UNNECESSARY_PICKS,
 	} command = 0;
 	struct option options[] = {
 		OPT_BOOL(0, "ff", &opts.allow_ff, N_("allow fast-forward")),
@@ -196,6 +197,10 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		OPT_RERERE_AUTOUPDATE(&opts.allow_rerere_auto),
 		OPT_BOOL(0, "reschedule-failed-exec", &opts.reschedule_failed_exec,
 			 N_("automatically re-schedule any `exec` that fails")),
+		OPT_CMDMODE(0, "make-script", &command,
+			N_("make rebase script"), MAKE_SCRIPT),
+		OPT_CMDMODE(0, "skip-unnecessary-picks", &command,
+			N_("skip unnecessary picks"), SKIP_UNNECESSARY_PICKS),
 		OPT_END()
 	};
 
@@ -267,6 +272,18 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 	case ADD_EXEC:
 		ret = sequencer_add_exec_commands(the_repository, cmd);
 		break;
+	case MAKE_SCRIPT:
+		ret = sequencer_make_script(the_repository,
+					    stdout, argc, argv, flags);
+		break;
+	case SKIP_UNNECESSARY_PICKS: {
+		struct object_id oid;
+
+		ret = skip_unnecessary_picks(the_repository, &oid);
+		if (!ret)
+			printf("%s\n", oid_to_hex(&oid));
+		break;
+	}
 	default:
 		BUG("invalid command '%d'", command);
 	}

git-legacy-rebase--interactive.sh

@@ -95,11 +95,11 @@ git_sequence_editor () {
 }
 
 expand_todo_ids() {
-	git rebase--helper --expand-ids
+	git rebase--interactive --expand-ids
 }
 
 collapse_todo_ids() {
-	git rebase--helper --shorten-ids
+	git rebase--interactive --shorten-ids
 }
 
 # Switch to the branch in $into and notify it in the reflog
@@ -131,12 +131,12 @@ get_missing_commit_check_level () {
 initiate_action () {
 	case "$1" in
 	continue)
-		exec git rebase--helper ${force_rebase:+--no-ff} $allow_empty_message \
+		exec git rebase--interactive ${force_rebase:+--no-ff} $allow_empty_message \
 		     --continue
 		;;
 	skip)
 		git rerere clear
-		exec git rebase--helper ${force_rebase:+--no-ff} $allow_empty_message \
+		exec git rebase--interactive ${force_rebase:+--no-ff} $allow_empty_message \
 		     --continue
 		;;
 	edit-todo)
@@ -207,8 +207,8 @@ init_revisions_and_shortrevisions () {
 
 complete_action() {
 	test -s "$todo" || echo noop >> "$todo"
-	test -z "$autosquash" || git rebase--helper --rearrange-squash || exit
-	test -n "$cmd" && git rebase--helper --add-exec-commands "$cmd"
+	test -z "$autosquash" || git rebase--interactive --rearrange-squash || exit
+	test -n "$cmd" && git rebase--interactive --add-exec-commands --cmd "$cmd"
 
 	todocount=$(git stripspace --strip-comments <"$todo" | wc -l)
 	todocount=${todocount##* }
@@ -243,7 +243,7 @@ EOF
 	has_action "$todo" ||
 		return 2
 
-	git rebase--helper --check-todo-list || {
+	git rebase--interactive --check-todo-list || {
 		ret=$?
 		checkout_onto
 		exit $ret
@@ -252,12 +252,12 @@ EOF
 	expand_todo_ids
 
 	test -n "$force_rebase" ||
-	onto="$(git rebase--helper --skip-unnecessary-picks)" ||
+	onto="$(git rebase--interactive --skip-unnecessary-picks)" ||
 	die "Could not skip unnecessary pick commands"
 
 	checkout_onto
 	require_clean_work_tree "rebase"
-	exec git rebase--helper ${force_rebase:+--no-ff} $allow_empty_message \
+	exec git rebase--interactive ${force_rebase:+--no-ff} $allow_empty_message \
 	     --continue
 }
 
@@ -273,7 +273,7 @@ git_rebase__interactive () {
 
 	init_revisions_and_shortrevisions
 
-	git rebase--helper --make-script ${keep_empty:+--keep-empty} \
+	git rebase--interactive --make-script ${keep_empty:+--keep-empty} \
 		${rebase_merges:+--rebase-merges} \
 		${rebase_cousins:+--rebase-cousins} \
 		$revisions ${restrict_revision+^$restrict_revision} >"$todo" ||

git-legacy-rebase.sh

@@ -141,38 +141,6 @@ finish_rebase () {
 	rm -rf "$state_dir"
 }
 
-run_interactive () {
-	GIT_CHERRY_PICK_HELP="$resolvemsg"
-	export GIT_CHERRY_PICK_HELP
-
-	test -n "$keep_empty" && keep_empty="--keep-empty"
-	test -n "$rebase_merges" && rebase_merges="--rebase-merges"
-	test -n "$rebase_cousins" && rebase_cousins="--rebase-cousins"
-	test -n "$autosquash" && autosquash="--autosquash"
-	test -n "$verbose" && verbose="--verbose"
-	test -n "$force_rebase" && force_rebase="--no-ff"
-	test -n "$restrict_revision" && \
-		restrict_revision="--restrict-revision=^$restrict_revision"
-	test -n "$upstream" && upstream="--upstream=$upstream"
-	test -n "$onto" && onto="--onto=$onto"
-	test -n "$squash_onto" && squash_onto="--squash-onto=$squash_onto"
-	test -n "$onto_name" && onto_name="--onto-name=$onto_name"
-	test -n "$head_name" && head_name="--head-name=$head_name"
-	test -n "$strategy" && strategy="--strategy=$strategy"
-	test -n "$strategy_opts" && strategy_opts="--strategy-opts=$strategy_opts"
-	test -n "$switch_to" && switch_to="--switch-to=$switch_to"
-	test -n "$cmd" && cmd="--cmd=$cmd"
-	test -n "$action" && action="--$action"
-
-	exec git rebase--interactive "$action" "$keep_empty" "$rebase_merges" "$rebase_cousins" \
-		"$upstream" "$onto" "$squash_onto" "$restrict_revision" \
-		"$allow_empty_message" "$autosquash" "$verbose" \
-		"$force_rebase" "$onto_name" "$head_name" "$strategy" \
-		"$strategy_opts" "$cmd" "$switch_to" \
-		"$allow_rerere_autoupdate" "$gpg_sign_opt" "$signoff" \
-		"$reschedule_failed_exec"
-}
-
 run_specific_rebase () {
 	if [ "$interactive_rebase" = implied ]; then
 		GIT_SEQUENCE_EDITOR=:
@@ -182,7 +150,9 @@ run_specific_rebase () {
 
 	if test -n "$interactive_rebase" -a -z "$preserve_merges"
 	then
-		run_interactive
+		. git-legacy-rebase--$type
+
+		git_rebase__$type
 	else
 		. git-rebase--$type
 
@@ -202,7 +172,12 @@ run_specific_rebase () {
 	then
 		apply_autostash &&
 		rm -rf "$state_dir" &&
-		die "Nothing to do"
+		if test -n "$interactive_rebase" -a -z "$preserve_merges"
+		then
+			die "error: nothing to do"
+		else
+			die "Nothing to do"
+		fi
 	fi
 	exit $ret
 }

sequencer.c

@@ -4793,7 +4793,7 @@ static int rewrite_file(const char *path, const char *buf, size_t len)
 }
 
 /* skip picking commits whose parents are unchanged */
-static int skip_unnecessary_picks(struct repository *r, struct object_id *output_oid)
+int skip_unnecessary_picks(struct repository *r, struct object_id *output_oid)
 {
 	const char *todo_file = rebase_path_todo();
 	struct strbuf buf = STRBUF_INIT;

sequencer.h

@@ -144,3 +144,5 @@ 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);
+
+int skip_unnecessary_picks(struct repository *r, struct object_id *output_oid);