static void execute_commands(struct command *commands, const char *unpacker_error)
{
	struct command *cmd;
	unsigned char sha1[20];

	if (unpacker_error) {
		for (cmd = commands; cmd; cmd = cmd->next)
			cmd->error_string = "n/a (unpacker error)";
		return;
	}

	cmd = commands;
	if (check_everything_connected(iterate_receive_command_list,
				       0, &cmd))
		set_connectivity_errors(commands);

	if (run_receive_hook(commands, pre_receive_hook, 0)) {
		for (cmd = commands; cmd; cmd = cmd->next)
			cmd->error_string = "pre-receive hook declined";
		return;
	}

	check_aliased_updates(commands);

	free(head_name_to_free);
	head_name = head_name_to_free = resolve_refdup("HEAD", sha1, 0, NULL);

	for (cmd = commands; cmd; cmd = cmd->next)
		if (!cmd->skip_update)
			cmd->error_string = update(cmd);
}

static struct complete_reflogs *read_complete_reflog(const char *ref)
{
	struct complete_reflogs *reflogs =
		xcalloc(1, sizeof(struct complete_reflogs));
	reflogs->ref = xstrdup(ref);
	for_each_reflog_ent(ref, read_one_reflog, reflogs);
	if (reflogs->nr == 0) {
		struct object_id oid;
		const char *name;
		void *name_to_free;
		name = name_to_free = resolve_refdup(ref, RESOLVE_REF_READING,
						     oid.hash, NULL);
		if (name) {
			for_each_reflog_ent(name, read_one_reflog, reflogs);
			free(name_to_free);
		}
	}
	if (reflogs->nr == 0) {
		char *refname = xstrfmt("refs/%s", ref);
		for_each_reflog_ent(refname, read_one_reflog, reflogs);
		if (reflogs->nr == 0) {
			free(refname);
			refname = xstrfmt("refs/heads/%s", ref);
			for_each_reflog_ent(refname, read_one_reflog, reflogs);
		}
		free(refname);
	}
	return reflogs;
}

static int checkout(void)
{
	unsigned char sha1[20];
	char *head;
	struct lock_file *lock_file;
	struct unpack_trees_options opts;
	struct tree *tree;
	struct tree_desc t;
	int err = 0, fd;

	if (option_no_checkout)
		return 0;

	head = resolve_refdup("HEAD", sha1, 1, NULL);
	if (!head) {
		warning(_("remote HEAD refers to nonexistent ref, "
			  "unable to checkout.\n"));
		return 0;
	}
	if (!strcmp(head, "HEAD")) {
		if (advice_detached_head)
			detach_advice(sha1_to_hex(sha1));
	} else {
		if (prefixcmp(head, "refs/heads/"))
			die(_("HEAD not found below refs/heads!"));
	}
	free(head);

	/* We need to be in the new work tree for the checkout */
	setup_work_tree();

	lock_file = xcalloc(1, sizeof(struct lock_file));
	fd = hold_locked_index(lock_file, 1);

	memset(&opts, 0, sizeof opts);
	opts.update = 1;
	opts.merge = 1;
	opts.fn = oneway_merge;
	opts.verbose_update = (option_verbosity >= 0);
	opts.src_index = &the_index;
	opts.dst_index = &the_index;

	tree = parse_tree_indirect(sha1);
	parse_tree(tree);
	init_tree_desc(&t, tree->buffer, tree->size);
	if (unpack_trees(1, &t, &opts) < 0)
		die(_("unable to checkout working tree"));

	if (write_cache(fd, active_cache, active_nr) ||
	    commit_locked_index(lock_file))
		die(_("unable to write new index file"));

	err |= run_hook(NULL, "post-checkout", sha1_to_hex(null_sha1),
			sha1_to_hex(sha1), "1", NULL);

	if (!err && option_recursive)
		err = run_command_v_opt(argv_submodule, RUN_GIT_CMD);

	return err;
}

static void execute_commands(struct command *commands,
			     const char *unpacker_error,
			     struct shallow_info *si,
			     const struct string_list *push_options)
{
	struct check_connected_options opt = CHECK_CONNECTED_INIT;
	struct command *cmd;
	unsigned char sha1[20];
	struct iterate_data data;
	struct async muxer;
	int err_fd = 0;

	if (unpacker_error) {
		for (cmd = commands; cmd; cmd = cmd->next)
			cmd->error_string = "unpacker error";
		return;
	}

	if (use_sideband) {
		memset(&muxer, 0, sizeof(muxer));
		muxer.proc = copy_to_sideband;
		muxer.in = -1;
		if (!start_async(&muxer))
			err_fd = muxer.in;
		/* ...else, continue without relaying sideband */
	}

	data.cmds = commands;
	data.si = si;
	opt.err_fd = err_fd;
	opt.progress = err_fd && !quiet;
	if (check_connected(iterate_receive_command_list, &data, &opt))
		set_connectivity_errors(commands, si);

	if (use_sideband)
		finish_async(&muxer);

	reject_updates_to_hidden(commands);

	if (run_receive_hook(commands, "pre-receive", 0, push_options)) {
		for (cmd = commands; cmd; cmd = cmd->next) {
			if (!cmd->error_string)
				cmd->error_string = "pre-receive hook declined";
		}
		return;
	}

	check_aliased_updates(commands);

	free(head_name_to_free);
	head_name = head_name_to_free = resolve_refdup("HEAD", 0, sha1, NULL);

	if (use_atomic)
		execute_commands_atomic(commands, si);
	else
		execute_commands_non_atomic(commands, si);

	if (shallow_update)
		warn_if_skipped_connectivity_check(commands, si);
}

int fmt_merge_msg(struct strbuf *in, struct strbuf *out,
		  struct fmt_merge_msg_opts *opts)
{
	int i = 0, pos = 0;
	unsigned char head_sha1[20];
	const char *current_branch;
	void *current_branch_to_free;

	/* get current branch */
	current_branch = current_branch_to_free =
		resolve_refdup("HEAD", head_sha1, 1, NULL);
	if (!current_branch)
		die("No current branch");
	if (!prefixcmp(current_branch, "refs/heads/"))
		current_branch += 11;

	/* get a line */
	while (pos < in->len) {
		int len;
		char *newline, *p = in->buf + pos;

		newline = strchr(p, '\n');
		len = newline ? newline - p : strlen(p);
		pos += len + !!newline;
		i++;
		p[len] = 0;
		if (handle_line(p))
			die ("Error in line %d: %.*s", i, len, p);
	}

	if (opts->add_title && srcs.nr)
		fmt_merge_msg_title(out, current_branch);

	if (origins.nr)
		fmt_merge_msg_sigs(out);

	if (opts->shortlog_len) {
		struct commit *head;
		struct rev_info rev;

		head = lookup_commit_or_die(head_sha1, "HEAD");
		init_revisions(&rev, NULL);
		rev.commit_format = CMIT_FMT_ONELINE;
		rev.ignore_merges = 1;
		rev.limited = 1;

		if (suffixcmp(out->buf, "\n"))
			strbuf_addch(out, '\n');

		for (i = 0; i < origins.nr; i++)
			shortlog(origins.items[i].string,
				 origins.items[i].util,
				 head, &rev, opts->shortlog_len, out);
	}

	strbuf_complete_line(out);
	free(current_branch_to_free);
	return 0;
}

static int checkout_branch(struct checkout_opts *opts,
			   struct branch_info *new_branch_info)
{
	if (opts->pathspec.nr)
		die(_("paths cannot be used with switching branches"));

	if (opts->patch_mode)
		die(_("'%s' cannot be used with switching branches"),
		    "--patch");

	if (!opts->overlay_mode)
		die(_("'%s' cannot be used with switching branches"),
		    "--no-overlay");

	if (opts->writeout_stage)
		die(_("'%s' cannot be used with switching branches"),
		    "--ours/--theirs");

	if (opts->force && opts->merge)
		die(_("'%s' cannot be used with '%s'"), "-f", "-m");

	if (opts->force_detach && opts->new_branch)
		die(_("'%s' cannot be used with '%s'"),
		    "--detach", "-b/-B/--orphan");

	if (opts->new_orphan_branch) {
		if (opts->track != BRANCH_TRACK_UNSPECIFIED)
			die(_("'%s' cannot be used with '%s'"), "--orphan", "-t");
	} else if (opts->force_detach) {
		if (opts->track != BRANCH_TRACK_UNSPECIFIED)
			die(_("'%s' cannot be used with '%s'"), "--detach", "-t");
	} else if (opts->track == BRANCH_TRACK_UNSPECIFIED)
		opts->track = git_branch_track;

	if (new_branch_info->name && !new_branch_info->commit)
		die(_("Cannot switch branch to a non-commit '%s'"),
		    new_branch_info->name);

	if (new_branch_info->path && !opts->force_detach && !opts->new_branch &&
	    !opts->ignore_other_worktrees) {
		int flag;
		char *head_ref = resolve_refdup("HEAD", 0, NULL, &flag);
		if (head_ref &&
		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new_branch_info->path)))
			die_if_checked_out(new_branch_info->path, 1);
		free(head_ref);
	}

	if (!new_branch_info->commit && opts->new_branch) {
		struct object_id rev;
		int flag;

		if (!read_ref_full("HEAD", 0, &rev, &flag) &&
		    (flag & REF_ISSYMREF) && is_null_oid(&rev))
			return switch_unborn_to_new_branch(opts);
	}
	return switch_branches(opts, new_branch_info);
}

static void execute_commands(struct command *commands,
                             const char *unpacker_error,
                             struct shallow_info *si)
{
    int checked_connectivity;
    struct command *cmd;
    unsigned char sha1[20];
    struct iterate_data data;

    if (unpacker_error) {
        for (cmd = commands; cmd; cmd = cmd->next)
            cmd->error_string = "unpacker error";
        return;
    }

    data.cmds = commands;
    data.si = si;
    if (check_everything_connected(iterate_receive_command_list, 0, &data))
        set_connectivity_errors(commands, si);

    reject_updates_to_hidden(commands);

    if (run_receive_hook(commands, "pre-receive", 0)) {
        for (cmd = commands; cmd; cmd = cmd->next) {
            if (!cmd->error_string)
                cmd->error_string = "pre-receive hook declined";
        }
        return;
    }

    check_aliased_updates(commands);

    free(head_name_to_free);
    head_name = head_name_to_free = resolve_refdup("HEAD", 0, sha1, NULL);

    checked_connectivity = 1;
    for (cmd = commands; cmd; cmd = cmd->next) {
        if (cmd->error_string)
            continue;

        if (cmd->skip_update)
            continue;

        cmd->error_string = update(cmd, si);
        if (shallow_update && !cmd->error_string &&
                si->shallow_ref[cmd->index]) {
            error("BUG: connectivity check has not been run on ref %s",
                  cmd->ref_name);
            checked_connectivity = 0;
        }
    }

    if (shallow_update && !checked_connectivity)
        error("BUG: run 'git fsck' for safety.\n"
              "If there are errors, try to remove "
              "the reported refs above");
}

static int merge_commit(struct notes_merge_options *o)
{
	struct strbuf msg = STRBUF_INIT;
	unsigned char sha1[20], parent_sha1[20];
	struct notes_tree *t;
	struct commit *partial;
	struct pretty_print_context pretty_ctx;
	void *local_ref_to_free;
	int ret;

	/*
	 * Read partial merge result from .git/NOTES_MERGE_PARTIAL,
	 * and target notes ref from .git/NOTES_MERGE_REF.
	 */

	if (get_sha1("NOTES_MERGE_PARTIAL", sha1))
		die("Failed to read ref NOTES_MERGE_PARTIAL");
	else if (!(partial = lookup_commit_reference(sha1)))
		die("Could not find commit from NOTES_MERGE_PARTIAL.");
	else if (parse_commit(partial))
		die("Could not parse commit from NOTES_MERGE_PARTIAL.");

	if (partial->parents)
		hashcpy(parent_sha1, partial->parents->item->object.sha1);
	else
		hashclr(parent_sha1);

	t = xcalloc(1, sizeof(struct notes_tree));
	init_notes(t, "NOTES_MERGE_PARTIAL", combine_notes_overwrite, 0);

	o->local_ref = local_ref_to_free =
		resolve_refdup("NOTES_MERGE_REF", 0, sha1, NULL);
	if (!o->local_ref)
		die("Failed to resolve NOTES_MERGE_REF");

	if (notes_merge_commit(o, t, partial, sha1))
		die("Failed to finalize notes merge");

	/* Reuse existing commit message in reflog message */
	memset(&pretty_ctx, 0, sizeof(pretty_ctx));
	format_commit_message(partial, "%s", &msg, &pretty_ctx);
	strbuf_trim(&msg);
	strbuf_insert(&msg, 0, "notes: ", 7);
	update_ref(msg.buf, o->local_ref, sha1,
		   is_null_sha1(parent_sha1) ? NULL : parent_sha1,
		   0, UPDATE_REFS_DIE_ON_ERR);

	free_notes(t);
	strbuf_release(&msg);
	ret = merge_abort(o);
	free(local_ref_to_free);
	return ret;
}

static int switch_branches(const struct checkout_opts *opts,
			   struct branch_info *new_branch_info)
{
	int ret = 0;
	struct branch_info old_branch_info;
	void *path_to_free;
	struct object_id rev;
	int flag, writeout_error = 0;

	trace2_cmd_mode("branch");

	memset(&old_branch_info, 0, sizeof(old_branch_info));
	old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
	if (old_branch_info.path)
		old_branch_info.commit = lookup_commit_reference_gently(the_repository, &rev, 1);
	if (!(flag & REF_ISSYMREF))
		old_branch_info.path = NULL;

	if (old_branch_info.path)
		skip_prefix(old_branch_info.path, "refs/heads/", &old_branch_info.name);

	if (!new_branch_info->name) {
		new_branch_info->name = "HEAD";
		new_branch_info->commit = old_branch_info.commit;
		if (!new_branch_info->commit)
			die(_("You are on a branch yet to be born"));
		parse_commit_or_die(new_branch_info->commit);
	}

	/* optimize the "checkout -b <new_branch> path */
	if (skip_merge_working_tree(opts, &old_branch_info, new_branch_info)) {
		if (!checkout_optimize_new_branch && !opts->quiet) {
			if (read_cache_preload(NULL) < 0)
				return error(_("index file corrupt"));
			show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
		}
	} else {
		ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
		if (ret) {
			free(path_to_free);
			return ret;
		}
	}

	if (!opts->quiet && !old_branch_info.path && old_branch_info.commit && new_branch_info->commit != old_branch_info.commit)
		orphaned_commit_warning(old_branch_info.commit, new_branch_info->commit);

	update_refs_for_switch(opts, &old_branch_info, new_branch_info);

	ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
	free(path_to_free);
	return ret || writeout_error;
}

static int branch_merged(int kind, const char *name,
			 struct commit *rev, struct commit *head_rev)
{
	/*
	 * This checks whether the merge bases of branch and HEAD (or
	 * the other branch this branch builds upon) contains the
	 * branch, which means that the branch has already been merged
	 * safely to HEAD (or the other branch).
	 */
	struct commit *reference_rev = NULL;
	const char *reference_name = NULL;
	void *reference_name_to_free = NULL;
	int merged;

	if (kind == REF_LOCAL_BRANCH) {
		struct branch *branch = branch_get(name);
		unsigned char sha1[20];

		if (branch &&
		    branch->merge &&
		    branch->merge[0] &&
		    branch->merge[0]->dst &&
		    (reference_name = reference_name_to_free =
		     resolve_refdup(branch->merge[0]->dst, RESOLVE_REF_READING,
				    sha1, NULL)) != NULL)
			reference_rev = lookup_commit_reference(sha1);
	}
	if (!reference_rev)
		reference_rev = head_rev;

	merged = in_merge_bases(rev, reference_rev);

	/*
	 * After the safety valve is fully redefined to "check with
	 * upstream, if any, otherwise with HEAD", we should just
	 * return the result of the in_merge_bases() above without
	 * any of the following code, but during the transition period,
	 * a gentle reminder is in order.
	 */
	if ((head_rev != reference_rev) &&
	    in_merge_bases(rev, head_rev) != merged) {
		if (merged)
			warning(_("deleting branch '%s' that has been merged to\n"
				"         '%s', but not yet merged to HEAD."),
				name, reference_name);
		else
			warning(_("not deleting branch '%s' that is not yet merged to\n"
				"         '%s', even though it is merged to HEAD."),
				name, reference_name);
	}
	free(reference_name_to_free);
	return merged;
}

void transport_print_push_status(const char *dest, struct ref *refs,
				  int verbose, int porcelain, unsigned int *reject_reasons)
{
	struct ref *ref;
	int n = 0;
	char *head;
	int summary_width = transport_summary_width(refs);

	if (transport_color_config() < 0)
		warning(_("could not parse transport.color.* config"));

	head = resolve_refdup("HEAD", RESOLVE_REF_READING, NULL, NULL);

	if (verbose) {
		for (ref = refs; ref; ref = ref->next)
			if (ref->status == REF_STATUS_UPTODATE)
				n += print_one_push_status(ref, dest, n,
							   porcelain, summary_width);
	}

	for (ref = refs; ref; ref = ref->next)
		if (ref->status == REF_STATUS_OK)
			n += print_one_push_status(ref, dest, n,
						   porcelain, summary_width);

	*reject_reasons = 0;
	for (ref = refs; ref; ref = ref->next) {
		if (ref->status != REF_STATUS_NONE &&
		    ref->status != REF_STATUS_UPTODATE &&
		    ref->status != REF_STATUS_OK)
			n += print_one_push_status(ref, dest, n,
						   porcelain, summary_width);
		if (ref->status == REF_STATUS_REJECT_NONFASTFORWARD) {
			if (head != NULL && !strcmp(head, ref->name))
				*reject_reasons |= REJECT_NON_FF_HEAD;
			else
				*reject_reasons |= REJECT_NON_FF_OTHER;
		} else if (ref->status == REF_STATUS_REJECT_ALREADY_EXISTS) {
			*reject_reasons |= REJECT_ALREADY_EXISTS;
		} else if (ref->status == REF_STATUS_REJECT_FETCH_FIRST) {
			*reject_reasons |= REJECT_FETCH_FIRST;
		} else if (ref->status == REF_STATUS_REJECT_NEEDS_FORCE) {
			*reject_reasons |= REJECT_NEEDS_FORCE;
		}
	}
	free(head);
}

void wt_status_prepare(struct wt_status *s)
{
	unsigned char sha1[20];

	memset(s, 0, sizeof(*s));
	memcpy(s->color_palette, default_wt_status_colors,
	       sizeof(default_wt_status_colors));
	s->show_untracked_files = SHOW_NORMAL_UNTRACKED_FILES;
	s->use_color = -1;
	s->relative_paths = 1;
	s->branch = resolve_refdup("HEAD", sha1, 0, NULL);
	s->reference = "HEAD";
	s->fp = stdout;
	s->index_file = get_index_file();
	s->change.strdup_strings = 1;
	s->untracked.strdup_strings = 1;
	s->ignored.strdup_strings = 1;
}

static void execute_commands(struct command *commands,
			     const char *unpacker_error,
			     struct shallow_info *si)
{
	struct command *cmd;
	unsigned char sha1[20];
	struct iterate_data data;

	if (unpacker_error) {
		for (cmd = commands; cmd; cmd = cmd->next)
			cmd->error_string = "unpacker error";
		return;
	}

	data.cmds = commands;
	data.si = si;
	if (check_everything_connected(iterate_receive_command_list, 0, &data))
		set_connectivity_errors(commands, si);

	reject_updates_to_hidden(commands);

	if (run_receive_hook(commands, "pre-receive", 0)) {
		for (cmd = commands; cmd; cmd = cmd->next) {
			if (!cmd->error_string)
				cmd->error_string = "pre-receive hook declined";
		}
		return;
	}

	check_aliased_updates(commands);

	free(head_name_to_free);
	head_name = head_name_to_free = resolve_refdup("HEAD", 0, sha1, NULL);

	if (use_atomic)
		execute_commands_atomic(commands, si);
	else
		execute_commands_non_atomic(commands, si);

	if (shallow_update)
		warn_if_skipped_connectivity_check(commands, si);
}

static int switch_branches(const struct checkout_opts *opts,
			   struct branch_info *new_branch_info)
{
	int ret = 0;
	struct branch_info old_branch_info;
	void *path_to_free;
	struct object_id rev;
	int flag, writeout_error = 0;
	memset(&old_branch_info, 0, sizeof(old_branch_info));
	old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
	if (old_branch_info.path)
		old_branch_info.commit = lookup_commit_reference_gently(&rev, 1);
	if (!(flag & REF_ISSYMREF))
		old_branch_info.path = NULL;

	if (old_branch_info.path)
		skip_prefix(old_branch_info.path, "refs/heads/", &old_branch_info.name);

	if (!new_branch_info->name) {
		new_branch_info->name = "HEAD";
		new_branch_info->commit = old_branch_info.commit;
		if (!new_branch_info->commit)
			die(_("You are on a branch yet to be born"));
		parse_commit_or_die(new_branch_info->commit);
	}

	ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
	if (ret) {
		free(path_to_free);
		return ret;
	}

	if (!opts->quiet && !old_branch_info.path && old_branch_info.commit && new_branch_info->commit != old_branch_info.commit)
		orphaned_commit_warning(old_branch_info.commit, new_branch_info->commit);

	update_refs_for_switch(opts, &old_branch_info, new_branch_info);

	ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
	free(path_to_free);
	return ret || writeout_error;
}

void transport_print_push_status(const char *dest, struct ref *refs,
				  int verbose, int porcelain, unsigned int *reject_reasons)
{
	struct ref *ref;
	int n = 0;
	unsigned char head_sha1[20];
	char *head;

	head = resolve_refdup("HEAD", RESOLVE_REF_READING, head_sha1, NULL);

	if (verbose) {
		for (ref = refs; ref; ref = ref->next)
			if (ref->status == REF_STATUS_UPTODATE)
				n += print_one_push_status(ref, dest, n, porcelain);
	}

	for (ref = refs; ref; ref = ref->next)
		if (ref->status == REF_STATUS_OK)
			n += print_one_push_status(ref, dest, n, porcelain);

	*reject_reasons = 0;
	for (ref = refs; ref; ref = ref->next) {
		if (ref->status != REF_STATUS_NONE &&
		    ref->status != REF_STATUS_UPTODATE &&
		    ref->status != REF_STATUS_OK)
			n += print_one_push_status(ref, dest, n, porcelain);
		if (ref->status == REF_STATUS_REJECT_NONFASTFORWARD) {
			if (head != NULL && !strcmp(head, ref->name))
				*reject_reasons |= REJECT_NON_FF_HEAD;
			else
				*reject_reasons |= REJECT_NON_FF_OTHER;
		} else if (ref->status == REF_STATUS_REJECT_ALREADY_EXISTS) {
			*reject_reasons |= REJECT_ALREADY_EXISTS;
		} else if (ref->status == REF_STATUS_REJECT_FETCH_FIRST) {
			*reject_reasons |= REJECT_FETCH_FIRST;
		} else if (ref->status == REF_STATUS_REJECT_NEEDS_FORCE) {
			*reject_reasons |= REJECT_NEEDS_FORCE;
		}
	}
	free(head);
}

int cmd_merge(int argc, const char **argv, const char *prefix)
{
	unsigned char result_tree[20];
	unsigned char stash[20];
	unsigned char head_sha1[20];
	struct commit *head_commit;
	struct strbuf buf = STRBUF_INIT;
	const char *head_arg;
	int flag, i, ret = 0, head_subsumed;
	int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
	struct commit_list *common = NULL;
	const char *best_strategy = NULL, *wt_strategy = NULL;
	struct commit_list *remoteheads, *p;
	void *branch_to_free;

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

	/*
	 * Check if we are _not_ on a detached HEAD, i.e. if there is a
	 * current branch.
	 */
	branch = branch_to_free = resolve_refdup("HEAD", head_sha1, 0, &flag);
	if (branch && !prefixcmp(branch, "refs/heads/"))
		branch += 11;
	if (!branch || is_null_sha1(head_sha1))
		head_commit = NULL;
	else
		head_commit = lookup_commit_or_die(head_sha1, "HEAD");

	git_config(git_merge_config, NULL);

	if (branch_mergeoptions)
		parse_branch_merge_options(branch_mergeoptions);
	argc = parse_options(argc, argv, prefix, builtin_merge_options,
			builtin_merge_usage, 0);
	if (shortlog_len < 0)
		shortlog_len = (merge_log_config > 0) ? merge_log_config : 0;

	if (verbosity < 0 && show_progress == -1)
		show_progress = 0;

	if (abort_current_merge) {
		int nargc = 2;
		const char *nargv[] = {"reset", "--merge", NULL};

		if (!file_exists(git_path("MERGE_HEAD")))
			die(_("There is no merge to abort (MERGE_HEAD missing)."));

		/* Invoke 'git reset --merge' */
		ret = cmd_reset(nargc, nargv, prefix);
		goto done;
	}

	if (read_cache_unmerged())
		die_resolve_conflict("merge");

	if (file_exists(git_path("MERGE_HEAD"))) {
		/*
		 * There is no unmerged entry, don't advise 'git
		 * add/rm <file>', just 'git commit'.
		 */
		if (advice_resolve_conflict)
			die(_("You have not concluded your merge (MERGE_HEAD exists).\n"
				  "Please, commit your changes before you can merge."));
		else
			die(_("You have not concluded your merge (MERGE_HEAD exists)."));
	}
	if (file_exists(git_path("CHERRY_PICK_HEAD"))) {
		if (advice_resolve_conflict)
			die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists).\n"
			    "Please, commit your changes before you can merge."));
		else
			die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists)."));
	}
	resolve_undo_clear();

	if (verbosity < 0)
		show_diffstat = 0;

	if (squash) {
		if (!allow_fast_forward)
			die(_("You cannot combine --squash with --no-ff."));
		option_commit = 0;
	}

	if (!allow_fast_forward && fast_forward_only)
		die(_("You cannot combine --no-ff with --ff-only."));

	if (!abort_current_merge) {
		if (!argc) {
			if (default_to_upstream)
				argc = setup_with_upstream(&argv);
			else
				die(_("No commit specified and merge.defaultToUpstream not set."));
		} else if (argc == 1 && !strcmp(argv[0], "-"))
			argv[0] = "@{-1}";
	}
	if (!argc)
		usage_with_options(builtin_merge_usage,
//.........这里部分代码省略.........

int add_reflog_for_walk(struct reflog_walk_info *info,
		struct commit *commit, const char *name)
{
	timestamp_t timestamp = 0;
	int recno = -1;
	struct string_list_item *item;
	struct complete_reflogs *reflogs;
	char *branch, *at = strchr(name, '@');
	struct commit_reflog *commit_reflog;
	enum selector_type selector = SELECTOR_NONE;

	if (commit->object.flags & UNINTERESTING)
		die ("Cannot walk reflogs for %s", name);

	branch = xstrdup(name);
	if (at && at[1] == '{') {
		char *ep;
		branch[at - name] = '\0';
		recno = strtoul(at + 2, &ep, 10);
		if (*ep != '}') {
			recno = -1;
			timestamp = approxidate(at + 2);
			selector = SELECTOR_DATE;
		}
		else
			selector = SELECTOR_INDEX;
	} else
		recno = 0;

	item = string_list_lookup(&info->complete_reflogs, branch);
	if (item)
		reflogs = item->util;
	else {
		if (*branch == '\0') {
			struct object_id oid;
			free(branch);
			branch = resolve_refdup("HEAD", 0, oid.hash, NULL);
			if (!branch)
				die ("No current branch");

		}
		reflogs = read_complete_reflog(branch);
		if (!reflogs || reflogs->nr == 0) {
			struct object_id oid;
			char *b;
			int ret = dwim_log(branch, strlen(branch),
					   oid.hash, &b);
			if (ret > 1)
				free(b);
			else if (ret == 1) {
				if (reflogs) {
					free(reflogs->ref);
					free(reflogs);
				}
				free(branch);
				branch = b;
				reflogs = read_complete_reflog(branch);
			}
		}
		if (!reflogs || reflogs->nr == 0) {
			if (reflogs) {
				free(reflogs->ref);
				free(reflogs);
			}
			free(branch);
			return -1;
		}
		string_list_insert(&info->complete_reflogs, branch)->util
			= reflogs;
	}
	free(branch);

	commit_reflog = xcalloc(1, sizeof(struct commit_reflog));
	if (recno < 0) {
		commit_reflog->recno = get_reflog_recno_by_time(reflogs, timestamp);
		if (commit_reflog->recno < 0) {
			if (reflogs) {
				free(reflogs->ref);
				free(reflogs);
			}
			free(commit_reflog);
			return -1;
		}
	} else
		commit_reflog->recno = reflogs->nr - recno - 1;
	commit_reflog->selector = selector;
	commit_reflog->reflogs = reflogs;

	add_commit_info(commit, commit_reflog, &info->reflogs);
	return 0;
}

static int checkout(int submodule_progress)
{
	unsigned char sha1[20];
	char *head;
	struct lock_file *lock_file;
	struct unpack_trees_options opts;
	struct tree *tree;
	struct tree_desc t;
	int err = 0;

	if (option_no_checkout)
		return 0;

	head = resolve_refdup("HEAD", RESOLVE_REF_READING, sha1, NULL);
	if (!head) {
		warning(_("remote HEAD refers to nonexistent ref, "
			  "unable to checkout.\n"));
		return 0;
	}
	if (!strcmp(head, "HEAD")) {
		if (advice_detached_head)
			detach_advice(sha1_to_hex(sha1));
	} else {
		if (!starts_with(head, "refs/heads/"))
			die(_("HEAD not found below refs/heads!"));
	}
	free(head);

	/* We need to be in the new work tree for the checkout */
	setup_work_tree();

	lock_file = xcalloc(1, sizeof(struct lock_file));
	hold_locked_index(lock_file, LOCK_DIE_ON_ERROR);

	memset(&opts, 0, sizeof opts);
	opts.update = 1;
	opts.merge = 1;
	opts.fn = oneway_merge;
	opts.verbose_update = (option_verbosity >= 0);
	opts.src_index = &the_index;
	opts.dst_index = &the_index;

	tree = parse_tree_indirect(sha1);
	parse_tree(tree);
	init_tree_desc(&t, tree->buffer, tree->size);
	if (unpack_trees(1, &t, &opts) < 0)
		die(_("unable to checkout working tree"));

	if (write_locked_index(&the_index, lock_file, COMMIT_LOCK))
		die(_("unable to write new index file"));

	err |= run_hook_le(NULL, "post-checkout", sha1_to_hex(null_sha1),
			   sha1_to_hex(sha1), "1", NULL);

	if (!err && option_recursive) {
		struct argv_array args = ARGV_ARRAY_INIT;
		argv_array_pushl(&args, "submodule", "update", "--init", "--recursive", NULL);

		if (option_shallow_submodules == 1)
			argv_array_push(&args, "--depth=1");

		if (max_jobs != -1)
			argv_array_pushf(&args, "--jobs=%d", max_jobs);

		if (submodule_progress)
			argv_array_push(&args, "--progress");

		err = run_command_v_opt(args.argv, RUN_GIT_CMD);
		argv_array_clear(&args);
	}

	return err;
}

//.........这里部分代码省略.........

	if (extra || reflog) {
		/* "listing" mode is incompatible with
		 * independent nor merge-base modes.
		 */
		if (independent || merge_base)
			usage_with_options(show_branch_usage,
					   builtin_show_branch_options);
		if (reflog && ((0 < extra) || all_heads || all_remotes))
			/*
			 * Asking for --more in reflog mode does not
			 * make sense.  --list is Ok.
			 *
			 * Also --all and --remotes do not make sense either.
			 */
			die("--reflog is incompatible with --all, --remotes, "
			    "--independent or --merge-base");
	}

	/* If nothing is specified, show all branches by default */
	if (ac <= topics && all_heads + all_remotes == 0)
		all_heads = 1;

	if (reflog) {
		struct object_id oid;
		char nth_desc[256];
		char *ref;
		int base = 0;
		unsigned int flags = 0;

		if (ac == 0) {
			static const char *fake_av[2];

			fake_av[0] = resolve_refdup("HEAD",
						    RESOLVE_REF_READING,
						    oid.hash, NULL);
			fake_av[1] = NULL;
			av = fake_av;
			ac = 1;
		}
		if (ac != 1)
			die("--reflog option needs one branch name");

		if (MAX_REVS < reflog)
			die("Only %d entries can be shown at one time.",
			    MAX_REVS);
		if (!dwim_ref(*av, strlen(*av), oid.hash, &ref))
			die("No such ref %s", *av);

		/* Has the base been specified? */
		if (reflog_base) {
			char *ep;
			base = strtoul(reflog_base, &ep, 10);
			if (*ep) {
				/* Ah, that is a date spec... */
				unsigned long at;
				at = approxidate(reflog_base);
				read_ref_at(ref, flags, at, -1, oid.hash, NULL,
					    NULL, NULL, &base);
			}
		}

		for (i = 0; i < reflog; i++) {
			char *logmsg;
			const char *msg;
			unsigned long timestamp;

static int delete_branches(int argc, const char **argv, int force, int kinds,
			   int quiet)
{
	struct commit *head_rev = NULL;
	unsigned char sha1[20];
	char *name = NULL;
	const char *fmt;
	int i;
	int ret = 0;
	int remote_branch = 0;
	struct strbuf bname = STRBUF_INIT;

	switch (kinds) {
	case FILTER_REFS_REMOTES:
		fmt = "refs/remotes/%s";
		/* For subsequent UI messages */
		remote_branch = 1;

		force = 1;
		break;
	case FILTER_REFS_BRANCHES:
		fmt = "refs/heads/%s";
		break;
	default:
		die(_("cannot use -a with -d"));
	}

	if (!force) {
		head_rev = lookup_commit_reference(head_sha1);
		if (!head_rev)
			die(_("Couldn't look up commit object for HEAD"));
	}
	for (i = 0; i < argc; i++, strbuf_release(&bname)) {
		char *target = NULL;
		int flags = 0;

		strbuf_branchname(&bname, argv[i]);
		free(name);
		name = mkpathdup(fmt, bname.buf);

		if (kinds == FILTER_REFS_BRANCHES) {
			const struct worktree *wt =
				find_shared_symref("HEAD", name);
			if (wt) {
				error(_("Cannot delete branch '%s' "
					"checked out at '%s'"),
				      bname.buf, wt->path);
				ret = 1;
				continue;
			}
		}

		target = resolve_refdup(name,
					RESOLVE_REF_READING
					| RESOLVE_REF_NO_RECURSE
					| RESOLVE_REF_ALLOW_BAD_NAME,
					sha1, &flags);
		if (!target) {
			error(remote_branch
			      ? _("remote-tracking branch '%s' not found.")
			      : _("branch '%s' not found."), bname.buf);
			ret = 1;
			continue;
		}

		if (!(flags & (REF_ISSYMREF|REF_ISBROKEN)) &&
		    check_branch_commit(bname.buf, name, sha1, head_rev, kinds,
					force)) {
			ret = 1;
			goto next;
		}

		if (delete_ref(name, is_null_sha1(sha1) ? NULL : sha1,
			       REF_NODEREF)) {
			error(remote_branch
			      ? _("Error deleting remote-tracking branch '%s'")
			      : _("Error deleting branch '%s'"),
			      bname.buf);
			ret = 1;
			goto next;
		}
		if (!quiet) {
			printf(remote_branch
			       ? _("Deleted remote-tracking branch %s (was %s).\n")
			       : _("Deleted branch %s (was %s).\n"),
			       bname.buf,
			       (flags & REF_ISBROKEN) ? "broken"
			       : (flags & REF_ISSYMREF) ? target
			       : find_unique_abbrev(sha1, DEFAULT_ABBREV));
		}
		delete_branch_config(bname.buf);

	next:
		free(target);
	}

	free(name);

	return(ret);
}