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

Jeff King [off-list ref] writes:

On Fri, Oct 13, 2017 at 02:11:32PM +0900, Junio C Hamano wrote:

quoted

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.

Heh, I just pointed somebody to this a day or two ago as #leftoverbit. I
guess it's taken now. :)

Didn't notice /remember it; sorry about that.  I can retract it if
you want, but perhaps they cannot unsee it ;-)

quoted

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^
+'

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.