builtin rebase: allow selecting the rebase "backend"

[thirdparty/git.git] / builtin / rebase.c

/*
 * "git rebase" builtin command
 *
 * Copyright (c) 2018 Pratik Karki
 */

#include "builtin.h"
#include "run-command.h"
#include "exec-cmd.h"
#include "argv-array.h"
#include "dir.h"
#include "packfile.h"
#include "refs.h"
#include "quote.h"
#include "config.h"
#include "cache-tree.h"
#include "unpack-trees.h"
#include "lockfile.h"
#include "parse-options.h"
#include "commit.h"
#include "diff.h"
#include "wt-status.h"
#include "revision.h"
#include "rerere.h"

static char const * const builtin_rebase_usage[] = {
	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
		"[<upstream>] [<branch>]"),
	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
		"--root [<branch>]"),
	N_("git rebase --continue | --abort | --skip | --edit-todo"),
	NULL
};

static GIT_PATH_FUNC(apply_dir, "rebase-apply")
static GIT_PATH_FUNC(merge_dir, "rebase-merge")

enum rebase_type {
	REBASE_UNSPECIFIED = -1,
	REBASE_AM,
	REBASE_MERGE,
	REBASE_INTERACTIVE,
	REBASE_PRESERVE_MERGES
};

static int use_builtin_rebase(void)
{
	struct child_process cp = CHILD_PROCESS_INIT;
	struct strbuf out = STRBUF_INIT;
	int ret;

	argv_array_pushl(&cp.args,
			 "config", "--bool", "rebase.usebuiltin", NULL);
	cp.git_cmd = 1;
	if (capture_command(&cp, &out, 6)) {
		strbuf_release(&out);
		return 0;
	}

	strbuf_trim(&out);
	ret = !strcmp("true", out.buf);
	strbuf_release(&out);
	return ret;
}

static int apply_autostash(void)
{
	warning("TODO");
	return 0;
}

struct rebase_options {
	enum rebase_type type;
	const char *state_dir;
	struct commit *upstream;
	const char *upstream_name;
	const char *upstream_arg;
	char *head_name;
	struct object_id orig_head;
	struct commit *onto;
	const char *onto_name;
	const char *revisions;
	const char *switch_to;
	int root;
	struct commit *restrict_revision;
	int dont_finish_rebase;
	enum {
		REBASE_NO_QUIET = 1<<0,
		REBASE_VERBOSE = 1<<1,
		REBASE_DIFFSTAT = 1<<2,
		REBASE_FORCE = 1<<3,
		REBASE_INTERACTIVE_EXPLICIT = 1<<4,
	} flags;
	struct strbuf git_am_opt;
	const char *action;
};

static int is_interactive(struct rebase_options *opts)
{
	return opts->type == REBASE_INTERACTIVE ||
		opts->type == REBASE_PRESERVE_MERGES;
}

/* Returns the filename prefixed by the state_dir */
static const char *state_dir_path(const char *filename, struct rebase_options *opts)
{
	static struct strbuf path = STRBUF_INIT;
	static size_t prefix_len;

	if (!prefix_len) {
		strbuf_addf(&path, "%s/", opts->state_dir);
		prefix_len = path.len;
	}

	strbuf_setlen(&path, prefix_len);
	strbuf_addstr(&path, filename);
	return path.buf;
}

/* Read one file, then strip line endings */
static int read_one(const char *path, struct strbuf *buf)
{
	if (strbuf_read_file(buf, path, 0) < 0)
		return error_errno(_("could not read '%s'"), path);
	strbuf_trim_trailing_newline(buf);
	return 0;
}

/* Initialize the rebase options from the state directory. */
static int read_basic_state(struct rebase_options *opts)
{
	struct strbuf head_name = STRBUF_INIT;
	struct strbuf buf = STRBUF_INIT;
	struct object_id oid;

	if (read_one(state_dir_path("head-name", opts), &head_name) ||
	    read_one(state_dir_path("onto", opts), &buf))
		return -1;
	opts->head_name = starts_with(head_name.buf, "refs/") ?
		xstrdup(head_name.buf) : NULL;
	strbuf_release(&head_name);
	if (get_oid(buf.buf, &oid))
		return error(_("could not get 'onto': '%s'"), buf.buf);
	opts->onto = lookup_commit_or_die(&oid, buf.buf);

	/*
	 * We always write to orig-head, but interactive rebase used to write to
	 * head. Fall back to reading from head to cover for the case that the
	 * user upgraded git with an ongoing interactive rebase.
	 */
	strbuf_reset(&buf);
	if (file_exists(state_dir_path("orig-head", opts))) {
		if (read_one(state_dir_path("orig-head", opts), &buf))
			return -1;
	} else if (read_one(state_dir_path("head", opts), &buf))
		return -1;
	if (get_oid(buf.buf, &opts->orig_head))
		return error(_("invalid orig-head: '%s'"), buf.buf);

	strbuf_reset(&buf);
	if (read_one(state_dir_path("quiet", opts), &buf))
		return -1;
	if (buf.len)
		opts->flags &= ~REBASE_NO_QUIET;
	else
		opts->flags |= REBASE_NO_QUIET;

	if (file_exists(state_dir_path("verbose", opts)))
		opts->flags |= REBASE_VERBOSE;

	strbuf_release(&buf);

	return 0;
}

static int finish_rebase(struct rebase_options *opts)
{
	struct strbuf dir = STRBUF_INIT;
	const char *argv_gc_auto[] = { "gc", "--auto", NULL };

	delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
	apply_autostash();
	close_all_packs(the_repository->objects);
	/*
	 * We ignore errors in 'gc --auto', since the
	 * user should see them.
	 */
	run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
	strbuf_addstr(&dir, opts->state_dir);
	remove_dir_recursively(&dir, 0);
	strbuf_release(&dir);

	return 0;
}

static struct commit *peel_committish(const char *name)
{
	struct object *obj;
	struct object_id oid;

	if (get_oid(name, &oid))
		return NULL;
	obj = parse_object(the_repository, &oid);
	return (struct commit *)peel_to_type(name, 0, obj, OBJ_COMMIT);
}

static void add_var(struct strbuf *buf, const char *name, const char *value)
{
	if (!value)
		strbuf_addf(buf, "unset %s; ", name);
	else {
		strbuf_addf(buf, "%s=", name);
		sq_quote_buf(buf, value);
		strbuf_addstr(buf, "; ");
	}
}

static int run_specific_rebase(struct rebase_options *opts)
{
	const char *argv[] = { NULL, NULL };
	struct strbuf script_snippet = STRBUF_INIT;
	int status;
	const char *backend, *backend_func;

	add_var(&script_snippet, "GIT_DIR", absolute_path(get_git_dir()));
	add_var(&script_snippet, "state_dir", opts->state_dir);

	add_var(&script_snippet, "upstream_name", opts->upstream_name);
	add_var(&script_snippet, "upstream", opts->upstream ?
		oid_to_hex(&opts->upstream->object.oid) : NULL);
	add_var(&script_snippet, "head_name",
		opts->head_name ? opts->head_name : "detached HEAD");
	add_var(&script_snippet, "orig_head", oid_to_hex(&opts->orig_head));
	add_var(&script_snippet, "onto", opts->onto ?
		oid_to_hex(&opts->onto->object.oid) : NULL);
	add_var(&script_snippet, "onto_name", opts->onto_name);
	add_var(&script_snippet, "revisions", opts->revisions);
	add_var(&script_snippet, "restrict_revision", opts->restrict_revision ?
		oid_to_hex(&opts->restrict_revision->object.oid) : NULL);
	add_var(&script_snippet, "GIT_QUIET",
		opts->flags & REBASE_NO_QUIET ? "" : "t");
	add_var(&script_snippet, "git_am_opt", opts->git_am_opt.buf);
	add_var(&script_snippet, "verbose",
		opts->flags & REBASE_VERBOSE ? "t" : "");
	add_var(&script_snippet, "diffstat",
		opts->flags & REBASE_DIFFSTAT ? "t" : "");
	add_var(&script_snippet, "force_rebase",
		opts->flags & REBASE_FORCE ? "t" : "");
	if (opts->switch_to)
		add_var(&script_snippet, "switch_to", opts->switch_to);
	add_var(&script_snippet, "action", opts->action ? opts->action : "");

	switch (opts->type) {
	case REBASE_AM:
		backend = "git-rebase--am";
		backend_func = "git_rebase__am";
		break;
	case REBASE_INTERACTIVE:
		backend = "git-rebase--interactive";
		backend_func = "git_rebase__interactive";
		break;
	case REBASE_MERGE:
		backend = "git-rebase--merge";
		backend_func = "git_rebase__merge";
		break;
	case REBASE_PRESERVE_MERGES:
		backend = "git-rebase--preserve-merges";
		backend_func = "git_rebase__preserve_merges";
		break;
	default:
		BUG("Unhandled rebase type %d", opts->type);
		break;
	}

	strbuf_addf(&script_snippet,
		    ". git-sh-setup && . git-rebase--common &&"
		    " . %s && %s", backend, backend_func);
	argv[0] = script_snippet.buf;

	status = run_command_v_opt(argv, RUN_USING_SHELL);
	if (opts->dont_finish_rebase)
		; /* do nothing */
	else if (status == 0) {
		if (!file_exists(state_dir_path("stopped-sha", opts)))
			finish_rebase(opts);
	} else if (status == 2) {
		struct strbuf dir = STRBUF_INIT;

		apply_autostash();
		strbuf_addstr(&dir, opts->state_dir);
		remove_dir_recursively(&dir, 0);
		strbuf_release(&dir);
		die("Nothing to do");
	}

	strbuf_release(&script_snippet);

	return status ? -1 : 0;
}

#define GIT_REFLOG_ACTION_ENVIRONMENT "GIT_REFLOG_ACTION"

static int reset_head(struct object_id *oid, const char *action,
		      const char *switch_to_branch, int detach_head)
{
	struct object_id head_oid;
	struct tree_desc desc;
	struct lock_file lock = LOCK_INIT;
	struct unpack_trees_options unpack_tree_opts;
	struct tree *tree;
	const char *reflog_action;
	struct strbuf msg = STRBUF_INIT;
	size_t prefix_len;
	struct object_id *orig = NULL, oid_orig,
		*old_orig = NULL, oid_old_orig;
	int ret = 0;

	if (switch_to_branch && !starts_with(switch_to_branch, "refs/"))
		BUG("Not a fully qualified branch: '%s'", switch_to_branch);

	if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0)
		return -1;

	if (!oid) {
		if (get_oid("HEAD", &head_oid)) {
			rollback_lock_file(&lock);
			return error(_("could not determine HEAD revision"));
		}
		oid = &head_oid;
	}

	memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
	setup_unpack_trees_porcelain(&unpack_tree_opts, action);
	unpack_tree_opts.head_idx = 1;
	unpack_tree_opts.src_index = the_repository->index;
	unpack_tree_opts.dst_index = the_repository->index;
	unpack_tree_opts.fn = oneway_merge;
	unpack_tree_opts.update = 1;
	unpack_tree_opts.merge = 1;
	if (!detach_head)
		unpack_tree_opts.reset = 1;

	if (read_index_unmerged(the_repository->index) < 0) {
		rollback_lock_file(&lock);
		return error(_("could not read index"));
	}

	if (!fill_tree_descriptor(&desc, oid)) {
		error(_("failed to find tree of %s"), oid_to_hex(oid));
		rollback_lock_file(&lock);
		free((void *)desc.buffer);
		return -1;
	}

	if (unpack_trees(1, &desc, &unpack_tree_opts)) {
		rollback_lock_file(&lock);
		free((void *)desc.buffer);
		return -1;
	}

	tree = parse_tree_indirect(oid);
	prime_cache_tree(the_repository->index, tree);

	if (write_locked_index(the_repository->index, &lock, COMMIT_LOCK) < 0)
		ret = error(_("could not write index"));
	free((void *)desc.buffer);

	if (ret)
		return ret;

	reflog_action = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
	strbuf_addf(&msg, "%s: ", reflog_action ? reflog_action : "rebase");
	prefix_len = msg.len;

	if (!get_oid("ORIG_HEAD", &oid_old_orig))
		old_orig = &oid_old_orig;
	if (!get_oid("HEAD", &oid_orig)) {
		orig = &oid_orig;
		strbuf_addstr(&msg, "updating ORIG_HEAD");
		update_ref(msg.buf, "ORIG_HEAD", orig, old_orig, 0,
			   UPDATE_REFS_MSG_ON_ERR);
	} else if (old_orig)
		delete_ref(NULL, "ORIG_HEAD", old_orig, 0);
	strbuf_setlen(&msg, prefix_len);
	strbuf_addstr(&msg, "updating HEAD");
	if (!switch_to_branch)
		ret = update_ref(msg.buf, "HEAD", oid, orig, REF_NO_DEREF,
				 UPDATE_REFS_MSG_ON_ERR);
	else {
		ret = create_symref("HEAD", switch_to_branch, msg.buf);
		if (!ret)
			ret = update_ref(msg.buf, "HEAD", oid, NULL, 0,
					 UPDATE_REFS_MSG_ON_ERR);
	}

	strbuf_release(&msg);
	return ret;
}

static int rebase_config(const char *var, const char *value, void *data)
{
	struct rebase_options *opts = data;

	if (!strcmp(var, "rebase.stat")) {
		if (git_config_bool(var, value))
			opts->flags |= REBASE_DIFFSTAT;
		else
			opts->flags &= !REBASE_DIFFSTAT;
		return 0;
	}

	return git_default_config(var, value, data);
}

/*
 * Determines whether the commits in from..to are linear, i.e. contain
 * no merge commits. This function *expects* `from` to be an ancestor of
 * `to`.
 */
static int is_linear_history(struct commit *from, struct commit *to)
{
	while (to && to != from) {
		parse_commit(to);
		if (!to->parents)
			return 1;
		if (to->parents->next)
			return 0;
		to = to->parents->item;
	}
	return 1;
}

static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
			    struct object_id *merge_base)
{
	struct commit *head = lookup_commit(the_repository, head_oid);
	struct commit_list *merge_bases;
	int res;

	if (!head)
		return 0;

	merge_bases = get_merge_bases(onto, head);
	if (merge_bases && !merge_bases->next) {
		oidcpy(merge_base, &merge_bases->item->object.oid);
		res = !oidcmp(merge_base, &onto->object.oid);
	} else {
		oidcpy(merge_base, &null_oid);
		res = 0;
	}
	free_commit_list(merge_bases);
	return res && is_linear_history(onto, head);
}

/* -i followed by -m is still -i */
static int parse_opt_merge(const struct option *opt, const char *arg, int unset)
{
	struct rebase_options *opts = opt->value;

	if (!is_interactive(opts))
		opts->type = REBASE_MERGE;

	return 0;
}

/* -i followed by -p is still explicitly interactive, but -p alone is not */
static int parse_opt_interactive(const struct option *opt, const char *arg,
				 int unset)
{
	struct rebase_options *opts = opt->value;

	opts->type = REBASE_INTERACTIVE;
	opts->flags |= REBASE_INTERACTIVE_EXPLICIT;

	return 0;
}

int cmd_rebase(int argc, const char **argv, const char *prefix)
{
	struct rebase_options options = {
		.type = REBASE_UNSPECIFIED,
		.flags = REBASE_NO_QUIET,
		.git_am_opt = STRBUF_INIT,
	};
	const char *branch_name;
	int ret, flags, total_argc, in_progress = 0;
	int ok_to_skip_pre_rebase = 0;
	struct strbuf msg = STRBUF_INIT;
	struct strbuf revisions = STRBUF_INIT;
	struct strbuf buf = STRBUF_INIT;
	struct object_id merge_base;
	enum {
		NO_ACTION,
		ACTION_CONTINUE,
		ACTION_SKIP,
		ACTION_ABORT,
		ACTION_QUIT,
		ACTION_EDIT_TODO,
		ACTION_SHOW_CURRENT_PATCH,
	} action = NO_ACTION;
	struct option builtin_rebase_options[] = {
		OPT_STRING(0, "onto", &options.onto_name,
			   N_("revision"),
			   N_("rebase onto given branch instead of upstream")),
		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
			 N_("allow pre-rebase hook to run")),
		OPT_NEGBIT('q', "quiet", &options.flags,
			   N_("be quiet. implies --no-stat"),
			   REBASE_NO_QUIET| REBASE_VERBOSE | REBASE_DIFFSTAT),
		OPT_BIT('v', "verbose", &options.flags,
			N_("display a diffstat of what changed upstream"),
			REBASE_NO_QUIET | REBASE_VERBOSE | REBASE_DIFFSTAT),
		{OPTION_NEGBIT, 'n', "no-stat", &options.flags, NULL,
			N_("do not show diffstat of what changed upstream"),
			PARSE_OPT_NOARG, NULL, REBASE_DIFFSTAT },
		OPT_BIT('f', "force-rebase", &options.flags,
			N_("cherry-pick all commits, even if unchanged"),
			REBASE_FORCE),
		OPT_BIT(0, "no-ff", &options.flags,
			N_("cherry-pick all commits, even if unchanged"),
			REBASE_FORCE),
		OPT_CMDMODE(0, "continue", &action, N_("continue"),
			    ACTION_CONTINUE),
		OPT_CMDMODE(0, "skip", &action,
			    N_("skip current patch and continue"), ACTION_SKIP),
		OPT_CMDMODE(0, "abort", &action,
			    N_("abort and check out the original branch"),
			    ACTION_ABORT),
		OPT_CMDMODE(0, "quit", &action,
			    N_("abort but keep HEAD where it is"), ACTION_QUIT),
		OPT_CMDMODE(0, "edit-todo", &action, N_("edit the todo list "
			    "during an interactive rebase"), ACTION_EDIT_TODO),
		OPT_CMDMODE(0, "show-current-patch", &action,
			    N_("show the patch file being applied or merged"),
			    ACTION_SHOW_CURRENT_PATCH),
		{ OPTION_CALLBACK, 'm', "merge", &options, NULL,
			N_("use merging strategies to rebase"),
			PARSE_OPT_NOARG | PARSE_OPT_NONEG,
			parse_opt_merge },
		{ OPTION_CALLBACK, 'i', "interactive", &options, NULL,
			N_("let the user edit the list of commits to rebase"),
			PARSE_OPT_NOARG | PARSE_OPT_NONEG,
			parse_opt_interactive },
		OPT_SET_INT('p', "preserve-merges", &options.type,
			    N_("try to recreate merges instead of ignoring "
			       "them"), REBASE_PRESERVE_MERGES),
		OPT_END(),
	};

	/*
	 * NEEDSWORK: Once the builtin rebase has been tested enough
	 * and git-legacy-rebase.sh is retired to contrib/, this preamble
	 * can be removed.
	 */

	if (!use_builtin_rebase()) {
		const char *path = mkpath("%s/git-legacy-rebase",
					  git_exec_path());

		if (sane_execvp(path, (char **)argv) < 0)
			die_errno(_("could not exec %s"), path);
		else
			BUG("sane_execvp() returned???");
	}

	if (argc == 2 && !strcmp(argv[1], "-h"))
		usage_with_options(builtin_rebase_usage,
				   builtin_rebase_options);

	prefix = setup_git_directory();
	trace_repo_setup(prefix);
	setup_work_tree();

	git_config(rebase_config, &options);

	strbuf_reset(&buf);
	strbuf_addf(&buf, "%s/applying", apply_dir());
	if(file_exists(buf.buf))
		die(_("It looks like 'git am' is in progress. Cannot rebase."));

	if (is_directory(apply_dir())) {
		options.type = REBASE_AM;
		options.state_dir = apply_dir();
	} else if (is_directory(merge_dir())) {
		strbuf_reset(&buf);
		strbuf_addf(&buf, "%s/rewritten", merge_dir());
		if (is_directory(buf.buf)) {
			options.type = REBASE_PRESERVE_MERGES;
			options.flags |= REBASE_INTERACTIVE_EXPLICIT;
		} else {
			strbuf_reset(&buf);
			strbuf_addf(&buf, "%s/interactive", merge_dir());
			if(file_exists(buf.buf)) {
				options.type = REBASE_INTERACTIVE;
				options.flags |= REBASE_INTERACTIVE_EXPLICIT;
			} else
				options.type = REBASE_MERGE;
		}
		options.state_dir = merge_dir();
	}

	if (options.type != REBASE_UNSPECIFIED)
		in_progress = 1;

	total_argc = argc;
	argc = parse_options(argc, argv, prefix,
			     builtin_rebase_options,
			     builtin_rebase_usage, 0);

	if (action != NO_ACTION && total_argc != 2) {
		usage_with_options(builtin_rebase_usage,
				   builtin_rebase_options);
	}

	if (argc > 2)
		usage_with_options(builtin_rebase_usage,
				   builtin_rebase_options);

	if (action != NO_ACTION && !in_progress)
		die(_("No rebase in progress?"));

	if (action == ACTION_EDIT_TODO && !is_interactive(&options))
		die(_("The --edit-todo action can only be used during "
		      "interactive rebase."));

	switch (action) {
	case ACTION_CONTINUE: {
		struct object_id head;
		struct lock_file lock_file = LOCK_INIT;
		int fd;

		options.action = "continue";

		/* Sanity check */
		if (get_oid("HEAD", &head))
			die(_("Cannot read HEAD"));

		fd = hold_locked_index(&lock_file, 0);
		if (read_index(the_repository->index) < 0)
			die(_("could not read index"));
		refresh_index(the_repository->index, REFRESH_QUIET, NULL, NULL,
			      NULL);
		if (0 <= fd)
			update_index_if_able(the_repository->index,
					     &lock_file);
		rollback_lock_file(&lock_file);

		if (has_unstaged_changes(1)) {
			puts(_("You must edit all merge conflicts and then\n"
			       "mark them as resolved using git add"));
			exit(1);
		}
		if (read_basic_state(&options))
			exit(1);
		goto run_rebase;
	}
	case ACTION_SKIP: {
		struct string_list merge_rr = STRING_LIST_INIT_DUP;

		options.action = "skip";

		rerere_clear(&merge_rr);
		string_list_clear(&merge_rr, 1);

		if (reset_head(NULL, "reset", NULL, 0) < 0)
			die(_("could not discard worktree changes"));
		if (read_basic_state(&options))
			exit(1);
		goto run_rebase;
	}
	case ACTION_ABORT: {
		struct string_list merge_rr = STRING_LIST_INIT_DUP;
		options.action = "abort";

		rerere_clear(&merge_rr);
		string_list_clear(&merge_rr, 1);

		if (read_basic_state(&options))
			exit(1);
		if (reset_head(&options.orig_head, "reset",
			       options.head_name, 0) < 0)
			die(_("could not move back to %s"),
			    oid_to_hex(&options.orig_head));
		ret = finish_rebase(&options);
		goto cleanup;
	}
	case ACTION_QUIT: {
		strbuf_reset(&buf);
		strbuf_addstr(&buf, options.state_dir);
		ret = !!remove_dir_recursively(&buf, 0);
		if (ret)
			die(_("could not remove '%s'"), options.state_dir);
		goto cleanup;
	}
	case ACTION_EDIT_TODO:
		options.action = "edit-todo";
		options.dont_finish_rebase = 1;
		goto run_rebase;
	case ACTION_SHOW_CURRENT_PATCH:
		options.action = "show-current-patch";
		options.dont_finish_rebase = 1;
		goto run_rebase;
	case NO_ACTION:
		break;
	default:
		BUG("action: %d", action);
	}

	/* Make sure no rebase is in progress */
	if (in_progress) {
		const char *last_slash = strrchr(options.state_dir, '/');
		const char *state_dir_base =
			last_slash ? last_slash + 1 : options.state_dir;
		const char *cmd_live_rebase =
			"git rebase (--continue | --abort | --skip)";
		strbuf_reset(&buf);
		strbuf_addf(&buf, "rm -fr \"%s\"", options.state_dir);
		die(_("It seems that there is already a %s directory, and\n"
		      "I wonder if you are in the middle of another rebase.  "
		      "If that is the\n"
		      "case, please try\n\t%s\n"
		      "If that is not the case, please\n\t%s\n"
		      "and run me again.  I am stopping in case you still "
		      "have something\n"
		      "valuable there.\n"),
		    state_dir_base, cmd_live_rebase, buf.buf);
	}

	if (!(options.flags & REBASE_NO_QUIET))
		strbuf_addstr(&options.git_am_opt, " -q");

	switch (options.type) {
	case REBASE_MERGE:
	case REBASE_INTERACTIVE:
	case REBASE_PRESERVE_MERGES:
		options.state_dir = merge_dir();
		break;
	case REBASE_AM:
		options.state_dir = apply_dir();
		break;
	default:
		/* the default rebase backend is `--am` */
		options.type = REBASE_AM;
		options.state_dir = apply_dir();
		break;
	}

	if (!options.root) {
		if (argc < 1)
			die("TODO: handle @{upstream}");
		else {
			options.upstream_name = argv[0];
			argc--;
			argv++;
			if (!strcmp(options.upstream_name, "-"))
				options.upstream_name = "@{-1}";
		}
		options.upstream = peel_committish(options.upstream_name);
		if (!options.upstream)
			die(_("invalid upstream '%s'"), options.upstream_name);
		options.upstream_arg = options.upstream_name;
	} else
		die("TODO: upstream for --root");

	/* Make sure the branch to rebase onto is valid. */
	if (!options.onto_name)
		options.onto_name = options.upstream_name;
	if (strstr(options.onto_name, "...")) {
		if (get_oid_mb(options.onto_name, &merge_base) < 0)
			die(_("'%s': need exactly one merge base"),
			    options.onto_name);
		options.onto = lookup_commit_or_die(&merge_base,
						    options.onto_name);
	} else {
		options.onto = peel_committish(options.onto_name);
		if (!options.onto)
			die(_("Does not point to a valid commit '%s'"),
				options.onto_name);
	}

	/*
	 * If the branch to rebase is given, that is the branch we will rebase
	 * branch_name -- branch/commit being rebased, or
	 * 		  HEAD (already detached)
	 * orig_head -- commit object name of tip of the branch before rebasing
	 * head_name -- refs/heads/<that-branch> or NULL (detached HEAD)
	 */
	if (argc == 1) {
		/* Is it "rebase other branchname" or "rebase other commit"? */
		branch_name = argv[0];
		options.switch_to = argv[0];

		/* Is it a local branch? */
		strbuf_reset(&buf);
		strbuf_addf(&buf, "refs/heads/%s", branch_name);
		if (!read_ref(buf.buf, &options.orig_head))
			options.head_name = xstrdup(buf.buf);
		/* If not is it a valid ref (branch or commit)? */
		else if (!get_oid(branch_name, &options.orig_head))
			options.head_name = NULL;
		else
			die(_("fatal: no such branch/commit '%s'"),
			    branch_name);
	} else if (argc == 0) {
		/* Do not need to switch branches, we are already on it. */
		options.head_name =
			xstrdup_or_null(resolve_ref_unsafe("HEAD", 0, NULL,
					 &flags));
		if (!options.head_name)
			die(_("No such ref: %s"), "HEAD");
		if (flags & REF_ISSYMREF) {
			if (!skip_prefix(options.head_name,
					 "refs/heads/", &branch_name))
				branch_name = options.head_name;

		} else {
			free(options.head_name);
			options.head_name = NULL;
			branch_name = "HEAD";
		}
		if (get_oid("HEAD", &options.orig_head))
			die(_("Could not resolve HEAD to a revision"));
	} else
		BUG("unexpected number of arguments left to parse");

	if (read_index(the_repository->index) < 0)
		die(_("could not read index"));

	if (require_clean_work_tree("rebase",
				    _("Please commit or stash them."), 1, 1)) {
		ret = 1;
		goto cleanup;
	}

	/*
	 * Now we are rebasing commits upstream..orig_head (or with --root,
	 * everything leading up to orig_head) on top of onto.
	 */

	/*
	 * Check if we are already based on onto with linear history,
	 * but this should be done only when upstream and onto are the same
	 * and if this is not an interactive rebase.
	 */
	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
	    !is_interactive(&options) && !options.restrict_revision &&
	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
		int flag;

		if (!(options.flags & REBASE_FORCE)) {
			/* Lazily switch to the target branch if needed... */
			if (options.switch_to) {
				struct object_id oid;

				if (get_oid(options.switch_to, &oid) < 0) {
					ret = !!error(_("could not parse '%s'"),
						      options.switch_to);
					goto cleanup;
				}

				strbuf_reset(&buf);
				strbuf_addf(&buf, "rebase: checkout %s",
					    options.switch_to);
				if (reset_head(&oid, "checkout",
					       options.head_name, 0) < 0) {
					ret = !!error(_("could not switch to "
							"%s"),
						      options.switch_to);
					goto cleanup;
				}
			}

			if (!(options.flags & REBASE_NO_QUIET))
				; /* be quiet */
			else if (!strcmp(branch_name, "HEAD") &&
				 resolve_ref_unsafe("HEAD", 0, NULL, &flag))
				puts(_("HEAD is up to date."));
			else
				printf(_("Current branch %s is up to date.\n"),
				       branch_name);
			ret = !!finish_rebase(&options);
			goto cleanup;
		} else if (!(options.flags & REBASE_NO_QUIET))
			; /* be quiet */
		else if (!strcmp(branch_name, "HEAD") &&
			 resolve_ref_unsafe("HEAD", 0, NULL, &flag))
			puts(_("HEAD is up to date, rebase forced."));
		else
			printf(_("Current branch %s is up to date, rebase "
				 "forced.\n"), branch_name);
	}

	/* If a hook exists, give it a chance to interrupt*/
	if (!ok_to_skip_pre_rebase &&
	    run_hook_le(NULL, "pre-rebase", options.upstream_arg,
			argc ? argv[0] : NULL, NULL))
		die(_("The pre-rebase hook refused to rebase."));

	if (options.flags & REBASE_DIFFSTAT) {
		struct diff_options opts;

		if (options.flags & REBASE_VERBOSE)
			printf(_("Changes from %s to %s:\n"),
				oid_to_hex(&merge_base),
				oid_to_hex(&options.onto->object.oid));

		/* We want color (if set), but no pager */
		diff_setup(&opts);
		opts.stat_width = -1; /* use full terminal width */
		opts.stat_graph_width = -1; /* respect statGraphWidth config */
		opts.output_format |=
			DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
		opts.detect_rename = DIFF_DETECT_RENAME;
		diff_setup_done(&opts);
		diff_tree_oid(&merge_base, &options.onto->object.oid,
			      "", &opts);
		diffcore_std(&opts);
		diff_flush(&opts);
	}

	if (is_interactive(&options))
		goto run_rebase;

	/* Detach HEAD and reset the tree */
	if (options.flags & REBASE_NO_QUIET)
		printf(_("First, rewinding head to replay your work on top of "
			 "it...\n"));

	strbuf_addf(&msg, "rebase: checkout %s", options.onto_name);
	if (reset_head(&options.onto->object.oid, "checkout", NULL, 1))
		die(_("Could not detach HEAD"));
	strbuf_release(&msg);

	strbuf_addf(&revisions, "%s..%s",
		    options.root ? oid_to_hex(&options.onto->object.oid) :
		    (options.restrict_revision ?
		     oid_to_hex(&options.restrict_revision->object.oid) :
		     oid_to_hex(&options.upstream->object.oid)),
		    oid_to_hex(&options.orig_head));

	options.revisions = revisions.buf;

run_rebase:
	ret = !!run_specific_rebase(&options);

cleanup:
	strbuf_release(&revisions);
	free(options.head_name);
	return ret;
}