rebase -i: run without forking rebase--interactive

When the builtin rebase starts an interactive rebase it parses the
options and then repackages them and forks
`rebase--interactive`. Separate the option parsing in
cmd_rebase__interactive() from the business logic to allow interactive
rebases can be run without forking `rebase__interactive` by calling
run_rebase_interactive() directly.

Starting interactive rebases without forking makes it easy to debug
the sequencer without worrying about attaching to child
processes. Ævar has also reported that some of the rebase perf tests
are 30% faster [1].

This patch also makes it easy to remove cmd_rebase__interactive() in
the future when git-legacy-rebase.sh and
git-rebase--preserve-merges.sh are retired.

[1] https://public-inbox.org/git/87y359cfjj.fsf@evledraar.gmail.com/

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rebase.c

@@ -316,7 +316,9 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 				&revisions, &shortrevisions))
 		return -1;
 
-	if (init_basic_state(&replay, opts->head_name, opts->onto, head_hash)) {
+	if (init_basic_state(&replay,
+			     opts->head_name ? opts->head_name : "detached HEAD",
+			     opts->onto, head_hash)) {
 		free(revisions);
 		free(shortrevisions);
 
@@ -359,6 +361,77 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 	return ret;
 }
 
+static int run_rebase_interactive(struct rebase_options *opts,
+				  enum action command)
+{
+	unsigned flags = 0;
+	int abbreviate_commands = 0, ret = 0;
+
+	git_config_get_bool("rebase.abbreviatecommands", &abbreviate_commands);
+
+	flags |= opts->keep_empty ? TODO_LIST_KEEP_EMPTY : 0;
+	flags |= abbreviate_commands ? TODO_LIST_ABBREVIATE_CMDS : 0;
+	flags |= opts->rebase_merges ? TODO_LIST_REBASE_MERGES : 0;
+	flags |= opts->rebase_cousins > 0 ? TODO_LIST_REBASE_COUSINS : 0;
+	flags |= command == ACTION_SHORTEN_OIDS ? TODO_LIST_SHORTEN_IDS : 0;
+
+	switch (command) {
+	case ACTION_NONE: {
+		if (!opts->onto && !opts->upstream)
+			die(_("a base commit must be provided with --upstream or --onto"));
+
+		ret = do_interactive_rebase(opts, flags);
+		break;
+	}
+	case ACTION_SKIP: {
+		struct string_list merge_rr = STRING_LIST_INIT_DUP;
+
+		rerere_clear(the_repository, &merge_rr);
+	}
+		/* fallthrough */
+	case ACTION_CONTINUE: {
+		struct replay_opts replay_opts = get_replay_opts(opts);
+
+		ret = sequencer_continue(the_repository, &replay_opts);
+		break;
+	}
+	case ACTION_EDIT_TODO:
+		ret = edit_todo_file(flags);
+		break;
+	case ACTION_SHOW_CURRENT_PATCH: {
+		struct child_process cmd = CHILD_PROCESS_INIT;
+
+		cmd.git_cmd = 1;
+		argv_array_pushl(&cmd.args, "show", "REBASE_HEAD", "--", NULL);
+		ret = run_command(&cmd);
+
+		break;
+	}
+	case ACTION_SHORTEN_OIDS:
+	case ACTION_EXPAND_OIDS:
+		ret = transform_todo_file(flags);
+		break;
+	case ACTION_CHECK_TODO_LIST:
+		ret = check_todo_list_from_file(the_repository);
+		break;
+	case ACTION_REARRANGE_SQUASH:
+		ret = rearrange_squash_in_todo_file();
+		break;
+	case ACTION_ADD_EXEC: {
+		struct string_list commands = STRING_LIST_INIT_DUP;
+
+		split_exec_commands(opts->cmd, &commands);
+		ret = add_exec_commands(&commands);
+		string_list_clear(&commands, 0);
+		break;
+	}
+	default:
+		BUG("invalid command '%d'", command);
+	}
+
+	return ret;
+}
+
 static const char * const builtin_rebase_interactive_usage[] = {
 	N_("git rebase--interactive [<options>]"),
 	NULL
@@ -367,8 +440,6 @@ static const char * const builtin_rebase_interactive_usage[] = {
 int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 {
 	struct rebase_options opts = REBASE_OPTIONS_INIT;
-	unsigned flags = 0;
-	int abbreviate_commands = 0, ret = 0;
 	struct object_id squash_onto = null_oid;
 	enum action command = ACTION_NONE;
 	struct option options[] = {
@@ -433,8 +504,6 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 
 	opts.rebase_cousins = -1;
 
-	git_config_get_bool("rebase.abbreviatecommands", &abbreviate_commands);
-
 	if (argc == 1)
 		usage_with_options(builtin_rebase_interactive_usage, options);
 
@@ -444,71 +513,11 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 	if (!is_null_oid(&squash_onto))
 		opts.squash_onto = &squash_onto;
 
-	flags |= opts.keep_empty ? TODO_LIST_KEEP_EMPTY : 0;
-	flags |= abbreviate_commands ? TODO_LIST_ABBREVIATE_CMDS : 0;
-	flags |= opts.rebase_merges ? TODO_LIST_REBASE_MERGES : 0;
-	flags |= opts.rebase_cousins > 0 ? TODO_LIST_REBASE_COUSINS : 0;
-	flags |= command == ACTION_SHORTEN_OIDS ? TODO_LIST_SHORTEN_IDS : 0;
-
 	if (opts.rebase_cousins >= 0 && !opts.rebase_merges)
 		warning(_("--[no-]rebase-cousins has no effect without "
 			  "--rebase-merges"));
 
-	switch (command) {
-	case ACTION_NONE: {
-		if (!opts.onto && !opts.upstream)
-			die(_("a base commit must be provided with --upstream or --onto"));
-
-		ret = do_interactive_rebase(&opts, flags);
-		break;
-	}
-	case ACTION_SKIP: {
-		struct string_list merge_rr = STRING_LIST_INIT_DUP;
-
-		rerere_clear(the_repository, &merge_rr);
-	}
-		/* fallthrough */
-	case ACTION_CONTINUE: {
-		struct replay_opts replay_opts = get_replay_opts(&opts);
-
-		ret = sequencer_continue(the_repository, &replay_opts);
-		break;
-	}
-	case ACTION_EDIT_TODO:
-		ret = edit_todo_file(flags);
-		break;
-	case ACTION_SHOW_CURRENT_PATCH: {
-		struct child_process cmd = CHILD_PROCESS_INIT;
-
-		cmd.git_cmd = 1;
-		argv_array_pushl(&cmd.args, "show", "REBASE_HEAD", "--", NULL);
-		ret = run_command(&cmd);
-
-		break;
-	}
-	case ACTION_SHORTEN_OIDS:
-	case ACTION_EXPAND_OIDS:
-		ret = transform_todo_file(flags);
-		break;
-	case ACTION_CHECK_TODO_LIST:
-		ret = check_todo_list_from_file(the_repository);
-		break;
-	case ACTION_REARRANGE_SQUASH:
-		ret = rearrange_squash_in_todo_file();
-		break;
-	case ACTION_ADD_EXEC: {
-		struct string_list commands = STRING_LIST_INIT_DUP;
-
-		split_exec_commands(opts.cmd, &commands);
-		ret = add_exec_commands(&commands);
-		string_list_clear(&commands, 0);
-		break;
-	}
-	default:
-		BUG("invalid command '%d'", command);
-	}
-
-	return !!ret;
+	return !!run_rebase_interactive(&opts, command);
 }
 
 static int use_builtin_rebase(void)
@@ -1071,7 +1080,7 @@ static int run_am(struct rebase_options *opts)
 	return status;
 }
 
-static int run_specific_rebase(struct rebase_options *opts)
+static int run_specific_rebase(struct rebase_options *opts, enum action action)
 {
 	const char *argv[] = { NULL, NULL };
 	struct strbuf script_snippet = STRBUF_INIT, buf = STRBUF_INIT;
@@ -1080,77 +1089,19 @@ static int run_specific_rebase(struct rebase_options *opts)
 
 	if (opts->type == REBASE_INTERACTIVE) {
 		/* Run builtin interactive rebase */
-		struct child_process child = CHILD_PROCESS_INIT;
-
-		argv_array_pushf(&child.env_array, "GIT_CHERRY_PICK_HELP=%s",
-				 resolvemsg);
+		setenv("GIT_CHERRY_PICK_HELP", resolvemsg, 1);
 		if (!(opts->flags & REBASE_INTERACTIVE_EXPLICIT)) {
-			argv_array_push(&child.env_array,
-					"GIT_SEQUENCE_EDITOR=:");
+			setenv("GIT_SEQUENCE_EDITOR", ":", 1);
 			opts->autosquash = 0;
 		}
+		if (opts->gpg_sign_opt) {
+			/* remove the leading "-S" */
+			char *tmp = xstrdup(opts->gpg_sign_opt + 2);
+			free(opts->gpg_sign_opt);
+			opts->gpg_sign_opt = tmp;
+		}
 
-		child.git_cmd = 1;
-		argv_array_push(&child.args, "rebase--interactive");
-
-		if (opts->action)
-			argv_array_pushf(&child.args, "--%s", opts->action);
-		if (opts->keep_empty)
-			argv_array_push(&child.args, "--keep-empty");
-		if (opts->rebase_merges)
-			argv_array_push(&child.args, "--rebase-merges");
-		if (opts->rebase_cousins)
-			argv_array_push(&child.args, "--rebase-cousins");
-		if (opts->autosquash)
-			argv_array_push(&child.args, "--autosquash");
-		if (opts->flags & REBASE_VERBOSE)
-			argv_array_push(&child.args, "--verbose");
-		if (opts->flags & REBASE_FORCE)
-			argv_array_push(&child.args, "--no-ff");
-		if (opts->restrict_revision)
-			argv_array_pushf(&child.args,
-					 "--restrict-revision=^%s",
-					 oid_to_hex(&opts->restrict_revision->object.oid));
-		if (opts->upstream)
-			argv_array_pushf(&child.args, "--upstream=%s",
-					 oid_to_hex(&opts->upstream->object.oid));
-		if (opts->onto)
-			argv_array_pushf(&child.args, "--onto=%s",
-					 oid_to_hex(&opts->onto->object.oid));
-		if (opts->squash_onto)
-			argv_array_pushf(&child.args, "--squash-onto=%s",
-					 oid_to_hex(opts->squash_onto));
-		if (opts->onto_name)
-			argv_array_pushf(&child.args, "--onto-name=%s",
-					 opts->onto_name);
-		argv_array_pushf(&child.args, "--head-name=%s",
-				 opts->head_name ?
-				 opts->head_name : "detached HEAD");
-		if (opts->strategy)
-			argv_array_pushf(&child.args, "--strategy=%s",
-					 opts->strategy);
-		if (opts->strategy_opts)
-			argv_array_pushf(&child.args, "--strategy-opts=%s",
-					 opts->strategy_opts);
-		if (opts->switch_to)
-			argv_array_pushf(&child.args, "--switch-to=%s",
-					 opts->switch_to);
-		if (opts->cmd)
-			argv_array_pushf(&child.args, "--cmd=%s", opts->cmd);
-		if (opts->allow_empty_message)
-			argv_array_push(&child.args, "--allow-empty-message");
-		if (opts->allow_rerere_autoupdate == RERERE_AUTOUPDATE)
-			argv_array_push(&child.args, "--rerere-autoupdate");
-		else if (opts->allow_rerere_autoupdate == RERERE_NOAUTOUPDATE)
-			argv_array_push(&child.args, "--no-rerere-autoupdate");
-		if (opts->gpg_sign_opt)
-			argv_array_push(&child.args, opts->gpg_sign_opt);
-		if (opts->signoff)
-			argv_array_push(&child.args, "--signoff");
-		if (opts->reschedule_failed_exec)
-			argv_array_push(&child.args, "--reschedule-failed-exec");
-
-		status = run_command(&child);
+		status = run_rebase_interactive(opts, action);
 		goto finished_rebase;
 	}
 
@@ -2211,7 +2162,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	options.revisions = revisions.buf;
 
 run_rebase:
-	ret = !!run_specific_rebase(&options);
+	ret = !!run_specific_rebase(&options, action);
 
 cleanup:
 	strbuf_release(&revisions);