Merge branch 'jc/check-ref-format-oor' into maint

"git check-ref-format --branch @{-1}" bit a "BUG()" when run
outside a repository for obvious reasons; clarify the documentation
and make sure we do not even try to expand the at-mark magic in
such a case, but still call the validation logic for branch names.

* jc/check-ref-format-oor:
  check-ref-format doc: --branch validates and expands <branch>
  check-ref-format --branch: strip refs/heads/ using skip_prefix
  check-ref-format --branch: do not expand @{...} outside repository

Documentation/git-check-ref-format.txt

@@ -77,7 +77,14 @@ reference name expressions (see linkgit:gitrevisions[7]):
 
 . at-open-brace `@{` is used as a notation to access a reflog entry.
 
-With the `--branch` option, it expands the ``previous branch syntax''
+With the `--branch` option, the command takes a name and checks if
+it can be used as a valid branch name (e.g. when creating a new
+branch).  The rule `git check-ref-format --branch $name` implements
+may be stricter than what `git check-ref-format refs/heads/$name`
+says (e.g. a dash may appear at the beginning of a ref component,
+but it is explicitly forbidden at the beginning of a branch name).
+When run with `--branch` option in a repository, the input is first
+expanded for the ``previous branch syntax''
 `@{-n}`.  For example, `@{-1}` is a way to refer the last branch you
 were on.  This option should be used by porcelains to accept this
 syntax anywhere a branch name is expected, so they can act as if you

builtin/check-ref-format.c

@@ -39,12 +39,14 @@ static char *collapse_slashes(const char *refname)
 static int check_ref_format_branch(const char *arg)
 {
 	struct strbuf sb = STRBUF_INIT;
+	const char *name;
 	int nongit;
 
 	setup_git_directory_gently(&nongit);
-	if (strbuf_check_branch_ref(&sb, arg))
+	if (strbuf_check_branch_ref(&sb, arg) ||
+	    !skip_prefix(sb.buf, "refs/heads/", &name))
 		die("'%s' is not a valid branch name", arg);
-	printf("%s\n", sb.buf + 11);
+	printf("%s\n", name);
 	strbuf_release(&sb);
 	return 0;
 }

sha1_name.c

@@ -1331,7 +1331,10 @@ void strbuf_branchname(struct strbuf *sb, const char *name, unsigned allowed)
 
 int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
 {
-	strbuf_branchname(sb, name, INTERPRET_BRANCH_LOCAL);
+	if (startup_info->have_repository)
+		strbuf_branchname(sb, name, INTERPRET_BRANCH_LOCAL);
+	else
+		strbuf_addstr(sb, name);
 	if (name[0] == '-')
 		return -1;
 	strbuf_splice(sb, 0, 0, "refs/heads/", 11);

t/t1402-check-ref-format.sh

@@ -144,6 +144,11 @@ 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 -naster' '
+	test_must_fail git check-ref-format --branch -naster >actual &&
+	test_must_be_empty actual
+'
+
 test_expect_success 'check-ref-format --branch from subdir' '
 	mkdir subdir &&
 
@@ -161,6 +166,17 @@ test_expect_success 'check-ref-format --branch from subdir' '
 	test "$refname" = "$sha1"
 '
 
+test_expect_success 'check-ref-format --branch @{-1} from non-repo' '
+	nongit test_must_fail git check-ref-format --branch @{-1} >actual &&
+	test_must_be_empty actual
+'
+
+test_expect_success 'check-ref-format --branch master from non-repo' '
+	echo master >expect &&
+	nongit git check-ref-format --branch master >actual &&
+	test_cmp expect actual
+'
+
 valid_ref_normalized() {
 	prereq=
 	case $1 in