builtin/rebase.c - jrn/git - Git at Google

 /*
  * "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"

 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;
 	char *head_name;
 	struct object_id orig_head;
 	struct commit *onto;
 	const char *onto_name;
 	const char *revisions;
 	int root;
 	struct commit *restrict_revision;
 	int dont_finish_rebase;
 };

 /* 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;
 }

 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",
 				 oid_to_hex(&opts->upstream->object.oid));
 	add_var(&script_snippet, "head_name", opts->head_name);
 	add_var(&script_snippet, "orig_head", oid_to_hex(&opts->orig_head));
 	add_var(&script_snippet, "onto", oid_to_hex(&opts->onto->object.oid));
 	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);

 	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 (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;
 }

 int cmd_rebase(int argc, const char **argv, const char *prefix)
 {
 	struct rebase_options options = {
 		.type = REBASE_UNSPECIFIED,
 	};
 	const char *branch_name;
 	int ret, flags;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
 	struct option builtin_rebase_options[] = {
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
 		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(git_default_config, NULL);
 	argc = parse_options(argc, argv, prefix,
 			     builtin_rebase_options,
 			     builtin_rebase_usage, 0);

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

 	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);
 	} 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, "...")) {
 		die("TODO");
 	} 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 "detached HEAD"
 	 */
 	if (argc > 0)
 		 die("TODO: handle switch_to");
 	else {
 		/* 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 {
 			options.head_name = xstrdup("detached HEAD");
 			branch_name = "HEAD";
 		}
 		if (get_oid("HEAD", &options.orig_head))
 			die(_("Could not resolve HEAD to a revision"));
 	}

 	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;

 	ret = !!run_specific_rebase(&options);

 	strbuf_release(&revisions);
 	free(options.head_name);
 	return ret;
 }
	/*
	* "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"

	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;
	char *head_name;
	struct object_id orig_head;
	struct commit *onto;
	const char *onto_name;
	const char *revisions;
	int root;
	struct commit *restrict_revision;
	int dont_finish_rebase;
	};

	/* 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;
	}

	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",
	oid_to_hex(&opts->upstream->object.oid));
	add_var(&script_snippet, "head_name", opts->head_name);
	add_var(&script_snippet, "orig_head", oid_to_hex(&opts->orig_head));
	add_var(&script_snippet, "onto", oid_to_hex(&opts->onto->object.oid));
	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);

	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 (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;
	}

	int cmd_rebase(int argc, const char *argv, const char prefix)
	{
	struct rebase_options options = {
	.type = REBASE_UNSPECIFIED,
	};
	const char *branch_name;
	int ret, flags;
	struct strbuf msg = STRBUF_INIT;
	struct strbuf revisions = STRBUF_INIT;
	struct option builtin_rebase_options[] = {
	OPT_STRING(0, "onto", &options.onto_name,
	N_("revision"),
	N_("rebase onto given branch instead of upstream")),
	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(git_default_config, NULL);
	argc = parse_options(argc, argv, prefix,
	builtin_rebase_options,
	builtin_rebase_usage, 0);

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

	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);
	} 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, "...")) {
	die("TODO");
	} 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 "detached HEAD"
	*/
	if (argc > 0)
	die("TODO: handle switch_to");
	else {
	/* 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 {
	options.head_name = xstrdup("detached HEAD");
	branch_name = "HEAD";
	}
	if (get_oid("HEAD", &options.orig_head))
	die(_("Could not resolve HEAD to a revision"));
	}

	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;

	ret = !!run_specific_rebase(&options);

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