for-each-ref: do not segv with %(HEAD) on an unborn branch

The code to flip between "*" and " " prefixes depending on what
branch is checked out used in --format='%(HEAD)' did not consider
that HEAD may resolve to an unborn branch and dereferenced a NULL.

This will become a lot easier to trigger as the codepath will be
used to reimplement "git branch [--list]" in the future.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/ref-filter.c b/ref-filter.c
index bc551a7..d7e91a7 100644 (file)
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -1017,7 +1017,7 @@ static void populate_value(struct ref_array_item *ref)
 
                        head = resolve_ref_unsafe("HEAD", RESOLVE_REF_READING,
                                                  sha1, NULL);
-                       if (!strcmp(ref->refname, head))
+                       if (head && !strcmp(ref->refname, head))
                                v->s = "*";
                        else
                                v->s = " ";

diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index 19a2823..039509a 100755 (executable)
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -553,4 +553,14 @@ test_expect_success 'Verify sort with multiple keys' '
                refs/tags/bogo refs/tags/master > actual &&
        test_cmp expected actual
 '
+
+test_expect_success 'do not dereference NULL upon %(HEAD) on unborn branch' '
+       test_when_finished "git checkout master" &&
+       git for-each-ref --format="%(HEAD) %(refname:short)" refs/heads/ >actual &&
+       sed -e "s/^\* /  /" actual >expect &&
+       git checkout --orphan HEAD &&
+       git for-each-ref --format="%(HEAD) %(refname:short)" refs/heads/ >actual &&
+       test_cmp expect actual
+'
+
 test_done