static void parse_one_symref_info(struct string_list *symref, const char *val, int len)
{
	char *sym, *target;
	struct string_list_item *item;

	if (!len)
		return; /* just "symref" */
	/* e.g. "symref=HEAD:refs/heads/master" */
	sym = xmalloc(len + 1);
	memcpy(sym, val, len);
	sym[len] = '\0';
	target = strchr(sym, ':');
	if (!target)
		/* just "symref=something" */
		goto reject;
	*(target++) = '\0';
	if (check_refname_format(sym, REFNAME_ALLOW_ONELEVEL) ||
	    check_refname_format(target, REFNAME_ALLOW_ONELEVEL))
		/* "symref=bogus:pair */
		goto reject;
	item = string_list_append(symref, sym);
	item->util = target;
	return;
reject:
	free(sym);
	return;
}

int ref_transaction_update(struct ref_transaction *transaction,
			   const char *refname,
			   const unsigned char *new_sha1,
			   const unsigned char *old_sha1,
			   unsigned int flags, const char *msg,
			   struct strbuf *err)
{
	struct ref_update *update;

	assert(err);

	if (transaction->state != REF_TRANSACTION_OPEN)
		die("BUG: update called for transaction that is not open");

	if (new_sha1 && !is_null_sha1(new_sha1) &&
	    check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
		strbuf_addf(err, "refusing to update ref with bad name %s",
			    refname);
		return -1;
	}

	update = add_update(transaction, refname);
	if (new_sha1) {
		hashcpy(update->new_sha1, new_sha1);
		flags |= REF_HAVE_NEW;
	}
	if (old_sha1) {
		hashcpy(update->old_sha1, old_sha1);
		flags |= REF_HAVE_OLD;
	}
	update->flags = flags;
	if (msg)
		update->msg = xstrdup(msg);
	return 0;
}

static int check_term_format(const char *term, const char *orig_term)
{
	int res;
	char *new_term = xstrfmt("refs/bisect/%s", term);

	res = check_refname_format(new_term, 0);
	free(new_term);

	if (res)
		return error(_("'%s' is not a valid term"), term);

	if (one_of(term, "help", "start", "skip", "next", "reset",
			"visualize", "view", "replay", "log", "run", "terms", NULL))
		return error(_("can't use the builtin command '%s' as a term"), term);

	/*
	 * In theory, nothing prevents swapping completely good and bad,
	 * but this situation could be confusing and hasn't been tested
	 * enough. Forbid it for now.
	 */

	if ((strcmp(orig_term, "bad") && one_of(term, "bad", "new", NULL)) ||
		 (strcmp(orig_term, "good") && one_of(term, "good", "old", NULL)))
		return error(_("can't change the meaning of the term '%s'"), term);

	return 0;
}

static int check_ref(const char *name, int len, unsigned int flags)
{
	if (!flags)
		return 1;

	if (len < 5 || memcmp(name, "refs/", 5))
		return 0;

	/* Skip the "refs/" part */
	name += 5;
	len -= 5;

	/* REF_NORMAL means that we don't want the magic fake tag refs */
	if ((flags & REF_NORMAL) && check_refname_format(name, 0))
		return 0;

	/* REF_HEADS means that we want regular branch heads */
	if ((flags & REF_HEADS) && !memcmp(name, "heads/", 6))
		return 1;

	/* REF_TAGS means that we want tags */
	if ((flags & REF_TAGS) && !memcmp(name, "tags/", 5))
		return 1;

	/* All type bits clear means that we are ok with anything */
	return !(flags & ~REF_NORMAL);
}

static int cmd_reflog_exists(int argc, const char **argv, const char *prefix)
{
	int i, start = 0;

	for (i = 1; i < argc; i++) {
		const char *arg = argv[i];
		if (!strcmp(arg, "--")) {
			i++;
			break;
		}
		else if (arg[0] == '-')
			usage(_(reflog_exists_usage));
		else
			break;
	}

	start = i;

	if (argc - start != 1)
		usage(_(reflog_exists_usage));

	if (check_refname_format(argv[start], REFNAME_ALLOW_ONELEVEL))
		die(_("invalid ref format: %s"), argv[start]);
	return !reflog_exists(argv[start]);
}

static void filter_refs(struct fetch_pack_args *args,
			struct ref **refs,
			struct ref **sought, int nr_sought)
{
	struct ref *newlist = NULL;
	struct ref **newtail = &newlist;
	struct ref *ref, *next;
	int i;

	i = 0;
	for (ref = *refs; ref; ref = next) {
		int keep = 0;
		next = ref->next;

		if (starts_with(ref->name, "refs/") &&
		    check_refname_format(ref->name, 0))
			; /* trash */
		else {
			while (i < nr_sought) {
				int cmp = strcmp(ref->name, sought[i]->name);
				if (cmp < 0)
					break; /* definitely do not have it */
				else if (cmp == 0) {
					keep = 1; /* definitely have it */
					sought[i]->matched = 1;
				}
				i++;
			}
		}

		if (!keep && args->fetch_all &&
		    (!args->depth || !starts_with(ref->name, "refs/tags/")))
			keep = 1;

		if (keep) {
			*newtail = ref;
			ref->next = NULL;
			newtail = &ref->next;
		} else {
			free(ref);
		}
	}

	/* Append unmatched requests to the list */
	if (allow_tip_sha1_in_want) {
		for (i = 0; i < nr_sought; i++) {
			ref = sought[i];
			if (ref->matched)
				continue;
			if (get_sha1_hex(ref->name, ref->old_sha1))
				continue;

			ref->matched = 1;
			*newtail = ref;
			ref->next = NULL;
			newtail = &ref->next;
		}
	}
	*refs = newlist;
}

static int strbuf_check_tag_ref(struct strbuf *sb, const char *name)
{
	if (name[0] == '-')
		return -1;

	strbuf_reset(sb);
	strbuf_addf(sb, "refs/tags/%s", name);

	return check_refname_format(sb->buf, 0);
}

/*
 * read 'path_to_ref' into 'ref'.  Also if is_detached is not NULL,
 * set is_detached to 1 (0) if the ref is detached (is not detached).
 *
 * $GIT_COMMON_DIR/$symref (e.g. HEAD) is practically outside $GIT_DIR so
 * for linked worktrees, `resolve_ref_unsafe()` won't work (it uses
 * git_path). Parse the ref ourselves.
 *
 * return -1 if the ref is not a proper ref, 0 otherwise (success)
 */
static int parse_ref(char *path_to_ref, struct strbuf *ref, int *is_detached)
{
	if (is_detached)
		*is_detached = 0;
	if (!strbuf_readlink(ref, path_to_ref, 0)) {
		/* HEAD is symbolic link */
		if (!starts_with(ref->buf, "refs/") ||
				check_refname_format(ref->buf, 0))
			return -1;
	} else if (strbuf_read_file(ref, path_to_ref, 0) >= 0) {
		/* textual symref or detached */
		if (!starts_with(ref->buf, "ref:")) {
			if (is_detached)
				*is_detached = 1;
		} else {
			strbuf_remove(ref, 0, strlen("ref:"));
			strbuf_trim(ref);
			if (check_refname_format(ref->buf, 0))
				return -1;
		}
	} else
		return -1;
	return 0;
}

static int interpret_target(struct walker *walker, char *target, unsigned char *sha1)
{
	if (!get_sha1_hex(target, sha1))
		return 0;
	if (!check_refname_format(target, 0)) {
		struct ref *ref = alloc_ref(target);
		if (!walker->fetch_ref(walker, ref)) {
			hashcpy(sha1, ref->old_sha1);
			free(ref);
			return 0;
		}
		free(ref);
	}
	return -1;
}

static char *find_linked_symref(const char *symref, const char *branch,
				const char *id)
{
	struct strbuf sb = STRBUF_INIT;
	struct strbuf path = STRBUF_INIT;
	struct strbuf gitdir = STRBUF_INIT;
	char *existing = NULL;

	/*
	 * $GIT_COMMON_DIR/$symref (e.g. HEAD) is practically outside
	 * $GIT_DIR so resolve_ref_unsafe() won't work (it uses
	 * git_path). Parse the ref ourselves.
	 */
	if (id)
		strbuf_addf(&path, "%s/worktrees/%s/%s", get_git_common_dir(), id, symref);
	else
		strbuf_addf(&path, "%s/%s", get_git_common_dir(), symref);

	if (!strbuf_readlink(&sb, path.buf, 0)) {
		if (!starts_with(sb.buf, "refs/") ||
		    check_refname_format(sb.buf, 0))
			goto done;
	} else if (strbuf_read_file(&sb, path.buf, 0) >= 0 &&
	    starts_with(sb.buf, "ref:")) {
		strbuf_remove(&sb, 0, strlen("ref:"));
		strbuf_trim(&sb);
	} else
		goto done;
	if (strcmp(sb.buf, branch))
		goto done;
	if (id) {
		strbuf_reset(&path);
		strbuf_addf(&path, "%s/worktrees/%s/gitdir", get_git_common_dir(), id);
		if (strbuf_read_file(&gitdir, path.buf, 0) <= 0)
			goto done;
		strbuf_rtrim(&gitdir);
	} else
		strbuf_addstr(&gitdir, get_git_common_dir());
	strbuf_strip_suffix(&gitdir, ".git");

	existing = strbuf_detach(&gitdir, NULL);
done:
	strbuf_release(&path);
	strbuf_release(&sb);
	strbuf_release(&gitdir);

	return existing;
}

static int check_ref_valid(struct object_id *object,
			    struct object_id *prev,
			    struct strbuf *ref,
			    int force)
{
	strbuf_reset(ref);
	strbuf_addf(ref, "%s%s", git_replace_ref_base, oid_to_hex(object));
	if (check_refname_format(ref->buf, 0))
		return error("'%s' is not a valid ref name.", ref->buf);

	if (read_ref(ref->buf, prev))
		oidclr(prev);
	else if (!force)
		return error("replace ref '%s' already exists", ref->buf);
	return 0;
}

static void filter_refs(struct fetch_pack_args *args,
			struct ref **refs, struct string_list *sought)
{
	struct ref *newlist = NULL;
	struct ref **newtail = &newlist;
	struct ref *ref, *next;
	int sought_pos;

	sought_pos = 0;
	for (ref = *refs; ref; ref = next) {
		int keep = 0;
		next = ref->next;
		if (!memcmp(ref->name, "refs/", 5) &&
		    check_refname_format(ref->name + 5, 0))
			; /* trash */
		else {
			while (sought_pos < sought->nr) {
				int cmp = strcmp(ref->name, sought->items[sought_pos].string);
				if (cmp < 0)
					break; /* definitely do not have it */
				else if (cmp == 0) {
					keep = 1; /* definitely have it */
					sought->items[sought_pos++].util = "matched";
					break;
				}
				else
					sought_pos++; /* might have it; keep looking */
			}
		}

		if (! keep && args->fetch_all &&
		    (!args->depth || prefixcmp(ref->name, "refs/tags/")))
			keep = 1;

		if (keep) {
			*newtail = ref;
			ref->next = NULL;
			newtail = &ref->next;
		} else {
			free(ref);
		}
	}

	filter_string_list(sought, 0, non_matching_ref, NULL);
	*refs = newlist;
}

void transport_verify_remote_names(int nr_heads, const char **heads)
{
	int i;

	for (i = 0; i < nr_heads; i++) {
		const char *local = heads[i];
		const char *remote = strrchr(heads[i], ':');

		if (*local == '+')
			local++;

		/* A matching refspec is okay.  */
		if (remote == local && remote[1] == '\0')
			continue;

		remote = remote ? (remote + 1) : local;
		if (check_refname_format(remote,
				REFNAME_ALLOW_ONELEVEL|REFNAME_REFSPEC_PATTERN))
			die("remote part of refspec is not a valid name in %s",
				heads[i]);
	}
}

int cmd_check_ref_format(int argc, const char **argv, const char *prefix)
{
	int i;
	int normalize = 0;
	int flags = 0;
	const char *refname;

	if (argc == 2 && !strcmp(argv[1], "-h"))
		usage(builtin_check_ref_format_usage);

	if (argc == 3 && !strcmp(argv[1], "--branch"))
		return check_ref_format_branch(argv[2]);

	for (i = 1; i < argc && argv[i][0] == '-'; i++) {
		if (!strcmp(argv[i], "--normalize") || !strcmp(argv[i], "--print"))
			normalize = 1;
		else if (!strcmp(argv[i], "--allow-onelevel"))
			flags |= REFNAME_ALLOW_ONELEVEL;
		else if (!strcmp(argv[i], "--no-allow-onelevel"))
			flags &= ~REFNAME_ALLOW_ONELEVEL;
		else if (!strcmp(argv[i], "--refspec-pattern"))
			flags |= REFNAME_REFSPEC_PATTERN;
		else
			usage(builtin_check_ref_format_usage);
	}
	if (! (i == argc - 1))
		usage(builtin_check_ref_format_usage);

	refname = argv[i];
	if (normalize)
		refname = collapse_slashes(refname);
	if (check_refname_format(refname, flags))
		return 1;
	if (normalize)
		printf("%s\n", refname);

	return 0;
}

static int check_ref(const char *name, unsigned int flags)
{
	if (!flags)
		return 1;

	if (!skip_prefix(name, "refs/", &name))
		return 0;

	/* REF_NORMAL means that we don't want the magic fake tag refs */
	if ((flags & REF_NORMAL) && check_refname_format(name, 0))
		return 0;

	/* REF_HEADS means that we want regular branch heads */
	if ((flags & REF_HEADS) && starts_with(name, "heads/"))
		return 1;

	/* REF_TAGS means that we want tags */
	if ((flags & REF_TAGS) && starts_with(name, "tags/"))
		return 1;

	/* All type bits clear means that we are ok with anything */
	return !(flags & ~REF_NORMAL);
}

int ref_transaction_update(struct ref_transaction *transaction,
			   const char *refname,
			   const unsigned char *new_sha1,
			   const unsigned char *old_sha1,
			   unsigned int flags, const char *msg,
			   struct strbuf *err)
{
	assert(err);

	if ((new_sha1 && !is_null_sha1(new_sha1)) ?
	    check_refname_format(refname, REFNAME_ALLOW_ONELEVEL) :
	    !refname_is_safe(refname)) {
		strbuf_addf(err, "refusing to update ref with bad name '%s'",
			    refname);
		return -1;
	}

	flags |= (new_sha1 ? REF_HAVE_NEW : 0) | (old_sha1 ? REF_HAVE_OLD : 0);

	ref_transaction_add_update(transaction, refname, flags,
				   new_sha1, old_sha1, msg);
	return 0;
}

/*
 * read "^(?:<anything>\s)?<refname>(?:\^\{\})?$" from the standard input,
 * and
 * (1) strip "^{}" at the end of line if any;
 * (2) ignore if match is provided and does not head-match refname;
 * (3) warn if refname is not a well-formed refname and skip;
 * (4) ignore if refname is a ref that exists in the local repository;
 * (5) otherwise output the line.
 */
static int exclude_existing(const char *match)
{
	static struct string_list existing_refs = STRING_LIST_INIT_DUP;
	char buf[1024];
	int matchlen = match ? strlen(match) : 0;

	for_each_ref(add_existing, &existing_refs);
	while (fgets(buf, sizeof(buf), stdin)) {
		char *ref;
		int len = strlen(buf);

		if (len > 0 && buf[len - 1] == '\n')
			buf[--len] = '\0';
		if (3 <= len && !strcmp(buf + len - 3, "^{}")) {
			len -= 3;
			buf[len] = '\0';
		}
		for (ref = buf + len; buf < ref; ref--)
			if (isspace(ref[-1]))
				break;
		if (match) {
			int reflen = buf + len - ref;
			if (reflen < matchlen)
				continue;
			if (strncmp(ref, match, matchlen))
				continue;
		}
		if (check_refname_format(ref, 0)) {
			warning("ref '%s' ignored", ref);
			continue;
		}
		if (!string_list_has_string(&existing_refs, ref)) {
			printf("%s\n", buf);
		}
	}
	return 0;
}

static void filter_refs(struct ref **refs, int nr_match, char **match)
{
	struct ref **return_refs;
	struct ref *newlist = NULL;
	struct ref **newtail = &newlist;
	struct ref *ref, *next;
	struct ref *fastarray[32];

	if (nr_match && !args.fetch_all) {
		if (ARRAY_SIZE(fastarray) < nr_match)
			return_refs = xcalloc(nr_match, sizeof(struct ref *));
		else {
			return_refs = fastarray;
			memset(return_refs, 0, sizeof(struct ref *) * nr_match);
		}
	}
	else
		return_refs = NULL;

	for (ref = *refs; ref; ref = next) {
		next = ref->next;
		if (!memcmp(ref->name, "refs/", 5) &&
		    check_refname_format(ref->name + 5, 0))
			; /* trash */
		else if (args.fetch_all &&
			 (!args.depth || prefixcmp(ref->name, "refs/tags/") )) {
			*newtail = ref;
			ref->next = NULL;
			newtail = &ref->next;
			continue;
		}
		else {
			int i;
			for (i = 0; i < nr_match; i++) {
				if (!strcmp(ref->name, match[i])) {
					match[i][0] = '\0';
					return_refs[i] = ref;
					break;
				}
			}
			if (i < nr_match)
				continue; /* we will link it later */
		}
		free(ref);
	}

	if (!args.fetch_all) {
		int i;
		for (i = 0; i < nr_match; i++) {
			ref = return_refs[i];
			if (ref) {
				*newtail = ref;
				ref->next = NULL;
				newtail = &ref->next;
			}
		}
		if (return_refs != fastarray)
			free(return_refs);
	}
	*refs = newlist;
}

int notes_merge(struct notes_merge_options *o,
		struct notes_tree *local_tree,
		unsigned char *result_sha1)
{
	unsigned char local_sha1[20], remote_sha1[20];
	struct commit *local, *remote;
	struct commit_list *bases = NULL;
	const unsigned char *base_sha1, *base_tree_sha1;
	int result = 0;

	assert(o->local_ref && o->remote_ref);
	assert(!strcmp(o->local_ref, local_tree->ref));
	hashclr(result_sha1);

	trace_printf("notes_merge(o->local_ref = %s, o->remote_ref = %s)\n",
	       o->local_ref, o->remote_ref);

	/* Dereference o->local_ref into local_sha1 */
	if (read_ref_full(o->local_ref, local_sha1, 0, NULL))
		die("Failed to resolve local notes ref '%s'", o->local_ref);
	else if (!check_refname_format(o->local_ref, 0) &&
		is_null_sha1(local_sha1))
		local = NULL; /* local_sha1 == null_sha1 indicates unborn ref */
	else if (!(local = lookup_commit_reference(local_sha1)))
		die("Could not parse local commit %s (%s)",
		    sha1_to_hex(local_sha1), o->local_ref);
	trace_printf("\tlocal commit: %.7s\n", sha1_to_hex(local_sha1));

	/* Dereference o->remote_ref into remote_sha1 */
	if (get_sha1(o->remote_ref, remote_sha1)) {
		/*
		 * Failed to get remote_sha1. If o->remote_ref looks like an
		 * unborn ref, perform the merge using an empty notes tree.
		 */
		if (!check_refname_format(o->remote_ref, 0)) {
			hashclr(remote_sha1);
			remote = NULL;
		} else {
			die("Failed to resolve remote notes ref '%s'",
			    o->remote_ref);
		}
	} else if (!(remote = lookup_commit_reference(remote_sha1))) {
		die("Could not parse remote commit %s (%s)",
		    sha1_to_hex(remote_sha1), o->remote_ref);
	}
	trace_printf("\tremote commit: %.7s\n", sha1_to_hex(remote_sha1));

	if (!local && !remote)
		die("Cannot merge empty notes ref (%s) into empty notes ref "
		    "(%s)", o->remote_ref, o->local_ref);
	if (!local) {
		/* result == remote commit */
		hashcpy(result_sha1, remote_sha1);
		goto found_result;
	}
	if (!remote) {
		/* result == local commit */
		hashcpy(result_sha1, local_sha1);
		goto found_result;
	}
	assert(local && remote);

	/* Find merge bases */
	bases = get_merge_bases(local, remote, 1);
	if (!bases) {
		base_sha1 = null_sha1;
		base_tree_sha1 = EMPTY_TREE_SHA1_BIN;
		if (o->verbosity >= 4)
			printf("No merge base found; doing history-less merge\n");
	} else if (!bases->next) {
		base_sha1 = bases->item->object.sha1;
		base_tree_sha1 = bases->item->tree->object.sha1;
		if (o->verbosity >= 4)
			printf("One merge base found (%.7s)\n",
				sha1_to_hex(base_sha1));
	} else {
		/* TODO: How to handle multiple merge-bases? */
		base_sha1 = bases->item->object.sha1;
		base_tree_sha1 = bases->item->tree->object.sha1;
		if (o->verbosity >= 3)
			printf("Multiple merge bases found. Using the first "
				"(%.7s)\n", sha1_to_hex(base_sha1));
	}

	if (o->verbosity >= 4)
		printf("Merging remote commit %.7s into local commit %.7s with "
			"merge-base %.7s\n", sha1_to_hex(remote->object.sha1),
			sha1_to_hex(local->object.sha1),
			sha1_to_hex(base_sha1));

	if (!hashcmp(remote->object.sha1, base_sha1)) {
		/* Already merged; result == local commit */
		if (o->verbosity >= 2)
			printf("Already up-to-date!\n");
		hashcpy(result_sha1, local->object.sha1);
		goto found_result;
	}
	if (!hashcmp(local->object.sha1, base_sha1)) {
		/* Fast-forward; result == remote commit */
		if (o->verbosity >= 2)
//.........这里部分代码省略.........

/* This function needs to return a meaningful errno on failure */
static const char *resolve_ref_recursively(struct ref_store *refs,
					   const char *refname,
					   int resolve_flags,
					   unsigned char *sha1, int *flags)
{
	static struct strbuf sb_refname = STRBUF_INIT;
	int unused_flags;
	int symref_count;

	if (!flags)
		flags = &unused_flags;

	*flags = 0;

	if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
		if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
		    !refname_is_safe(refname)) {
			errno = EINVAL;
			return NULL;
		}

		/*
		 * dwim_ref() uses REF_ISBROKEN to distinguish between
		 * missing refs and refs that were present but invalid,
		 * to complain about the latter to stderr.
		 *
		 * We don't know whether the ref exists, so don't set
		 * REF_ISBROKEN yet.
		 */
		*flags |= REF_BAD_NAME;
	}

	for (symref_count = 0; symref_count < SYMREF_MAXDEPTH; symref_count++) {
		unsigned int read_flags = 0;

		if (refs->be->read_raw_ref(refs, refname,
					   sha1, &sb_refname, &read_flags)) {
			*flags |= read_flags;
			if (errno != ENOENT || (resolve_flags & RESOLVE_REF_READING))
				return NULL;
			hashclr(sha1);
			if (*flags & REF_BAD_NAME)
				*flags |= REF_ISBROKEN;
			return refname;
		}

		*flags |= read_flags;

		if (!(read_flags & REF_ISSYMREF)) {
			if (*flags & REF_BAD_NAME) {
				hashclr(sha1);
				*flags |= REF_ISBROKEN;
			}
			return refname;
		}

		refname = sb_refname.buf;
		if (resolve_flags & RESOLVE_REF_NO_RECURSE) {
			hashclr(sha1);
			return refname;
		}
		if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
			if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
			    !refname_is_safe(refname)) {
				errno = EINVAL;
				return NULL;
			}

			*flags |= REF_ISBROKEN | REF_BAD_NAME;
		}
	}

	errno = ELOOP;
	return NULL;
}