Allow "check-ref-format --branch" from subdirectory

check-ref-format --branch requires access to the repository
to resolve refs like @{-1}.

Noticed by Nguyễn Thái Ngọc Duy.

Cc: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/check-ref-format.c

@@ -36,7 +36,9 @@ static void collapse_slashes(char *dst, const char *src)
 static int check_ref_format_branch(const char *arg)
 {
 	struct strbuf sb = STRBUF_INIT;
+	int nongit;
 
+	setup_git_directory_gently(&nongit);
 	if (strbuf_check_branch_ref(&sb, arg))
 		die("'%s' is not a valid branch name", arg);
 	printf("%s\n", sb.buf + 11);

t/t1402-check-ref-format.sh

@@ -41,6 +41,23 @@ test_expect_success "check-ref-format --branch @{-1}" '
 	refname2=$(git check-ref-format --branch @{-2}) &&
 	test "$refname2" = master'
 
+test_expect_success 'check-ref-format --branch from subdir' '
+	mkdir subdir &&
+
+	T=$(git write-tree) &&
+	sha1=$(echo A | git commit-tree $T) &&
+	git update-ref refs/heads/master $sha1 &&
+	git update-ref refs/remotes/origin/master $sha1
+	git checkout master &&
+	git checkout origin/master &&
+	git checkout master &&
+	refname=$(
+		cd subdir &&
+		git check-ref-format --branch @{-1}
+	) &&
+	test "$refname" = "$sha1"
+'
+
 valid_ref_normalized() {
 	test_expect_success "ref name '$1' simplifies to '$2'" "
 		refname=\$(git check-ref-format --print '$1') &&