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

From: Junio C Hamano <[email-masked]>
Date: Sat, 14 Oct 2017 11:20:11 +0900

Junio C Hamano <[email-masked]> writes:

>> Should we test that:
>>
>>   git update-ref refs/heads/HEAD HEAD^
>>
>> continues to work?
>
> Perhaps.  Also we may want to make sure that "git branch -D HEAD"
> still works as a way to recover from historical mistakes.

The only difference is improved tests where we use show-ref to make
sure refs/heads/HEAD does not exist when it shouldn't, exercise
update-ref to create and delete refs/heads/HEAD, and also make sure
it can be deleted with "git branch -d".

-- >8 --
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.

Helped-by: Jeff King <[email-masked]>
Signed-off-by: Junio C Hamano <[email-masked]>
---
 sha1_name.c             |  2 +-
 t/t1430-bad-ref-name.sh | 23 +++++++++++++++++++++++
 2 files changed, 24 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..4556aa66b8 100755
--- a/t/t1430-bad-ref-name.sh
+++ b/t/t1430-bad-ref-name.sh
@@ -331,4 +331,27 @@ 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_must_fail git show-ref refs/heads/HEAD
+'
+
+test_expect_success 'checkout -b rejects HEAD as a branch name' '
+	test_must_fail git checkout -B HEAD HEAD^ &&
+	test_must_fail git show-ref refs/heads/HEAD
+'
+
+test_expect_success 'update-ref can operate on refs/heads/HEAD' '
+	git update-ref refs/heads/HEAD HEAD^ &&
+	git show-ref refs/heads/HEAD &&
+	git update-ref -d refs/heads/HEAD &&
+	test_must_fail git show-ref refs/heads/HEAD
+'
+
+test_expect_success 'branch -d can remove refs/heads/HEAD' '
+	git update-ref refs/heads/HEAD HEAD^ &&
+	git branch -d HEAD &&
+	test_must_fail git show-ref refs/heads/HEAD
+'
+
 test_done
-- 
2.15.0-rc1-158-gbd035ae683