strbuf_check_ref_format(): expand only local branches

This function asks strbuf_branchname() to expand any @-marks
in the branchname, and then we blindly stick refs/heads/ in
front of the result. This is obviously nonsense if the
expansion is "HEAD" or a ref in refs/remotes/.

The most obvious end-user effect is that creating or
renaming a branch with an expansion may have confusing
results (e.g., creating refs/heads/origin/master from
"@{upstream}" when the operation should be disallowed).

We can fix this by telling strbuf_branchname() that we are
only interested in local expansions. Any unexpanded bits are
then fed to check_ref_format(), which either disallows them
(in the case of "@{upstream}") or lets them through
("refs/heads/@" is technically valid, if a bit silly).
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

sha1_name.c

@@ -1319,7 +1319,7 @@ 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, 0);
+	strbuf_branchname(sb, name, INTERPRET_BRANCH_LOCAL);
 	if (name[0] == '-')
 		return -1;
 	strbuf_splice(sb, 0, 0, "refs/heads/", 11);

t/t3204-branch-name-interpretation.sh

@@ -42,7 +42,7 @@ test_expect_success 'update branch via local @{upstream}' '
 	expect_branch local two
 '
 
-test_expect_failure 'disallow updating branch via remote @{upstream}' '
+test_expect_success 'disallow updating branch via remote @{upstream}' '
 	git update-ref refs/remotes/origin/remote one &&
 	git branch --set-upstream-to=origin/remote &&
 
@@ -109,7 +109,7 @@ test_expect_success 'disallow deleting remote branch via @{-1}' '
 # and not refs/heads/HEAD. These tests should not imply that refs/heads/@ is a
 # sane thing, but it _is_ technically allowed for now. If we disallow it, these
 # can be switched to test_must_fail.
-test_expect_failure 'create branch named "@"' '
+test_expect_success 'create branch named "@"' '
 	git branch -f @ one &&
 	expect_branch refs/heads/@ one
 '