[PATCH 7/8] strbuf_check_ref_format(): expand only local branches

[Jeff King]

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: Jeff King <p...@peff.net>
---
 sha1_name.c                           | 2 +-
 t/t3204-branch-name-interpretation.sh | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/sha1_name.c b/sha1_name.c
index b21997c29..c0cfb69a4 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -1317,7 +1317,7 @@ 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);
diff --git a/t/t3204-branch-name-interpretation.sh 
b/t/t3204-branch-name-interpretation.sh
index c8fec5b8c..6115ad504 100755
--- a/t/t3204-branch-name-interpretation.sh
+++ b/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 &&
 
@@ -98,7 +98,7 @@ test_expect_success 'delete @{upstream} expansion matches -r 
option' '
 # 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
 '
-- 
2.12.0.359.gd4c8c42e9