[PATCH 3/3] branch: forbid refs/heads/HEAD

[Junio C Hamano <gitster@pobox.com>]

strbuf_check_branch_ref() is the central place where many codepaths
see if a proposed name is suitable for the name of a branch.  It was
designed to allow us to get stricter than the check_refname_format()
check used for refnames in general, and we already use it to reject
a branch whose name begins with a '-'.

Use it to also reject "HEAD" as a branch name.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 sha1_name.c             | 2 +-
 t/t1430-bad-ref-name.sh | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/sha1_name.c b/sha1_name.c
index c7c5ab376c..1b8c503095 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -1332,7 +1332,7 @@ 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 (name[0] == '-')
+	if (*name == '-' || !strcmp(name, "HEAD"))
 		return -1;
 	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
 	return check_refname_format(sb->buf, 0);
diff --git a/t/t1430-bad-ref-name.sh b/t/t1430-bad-ref-name.sh
index e88349c8a0..3ecb2eab0c 100755
--- a/t/t1430-bad-ref-name.sh
+++ b/t/t1430-bad-ref-name.sh
@@ -331,4 +331,12 @@ test_expect_success 'update-ref --stdin -z fails delete with bad ref name' '
 	grep "fatal: invalid ref format: ~a" err
 '
 
+test_expect_success 'branch rejects HEAD as a branch name' '
+	test_must_fail git branch HEAD HEAD^
+'
+
+test_expect_success 'checkout -b rejects HEAD as a branch name' '
+	test_must_fail git checkout -B HEAD HEAD^
+'
+
 test_done
-- 
2.15.0-rc1-158-gbd035ae683