[PATCH v5 2/4] merge: use return value of resolve_ref() to determine if HEAD is invalid

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

resolve_ref() only updates "head" when it returns non NULL value (it
may update "head" even when returning NULL, but not in all cases).

Because "head" is not initialized before the call, is_null_sha1() is
not enough. Check also resolve_ref() return value.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 > Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:
 >> -     if (is_null_sha1(head))
 >> -             head_invalid = 1;
 >> +     if (!is_null_sha1(head)) {
 >> +             head_commit = lookup_commit(head);
 >> +             if (!head_commit)
 >> +                     die(_("could not parse HEAD"));
 >> +     }
 >
 > Is this is_null_sha1() valid without first clearing head[]?

 No it's not.

 builtin/merge.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/builtin/merge.c b/builtin/merge.c
index a068660..c371484 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1030,7 +1030,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	branch = resolve_ref("HEAD", head, 0, &flag);
 	if (branch && !prefixcmp(branch, "refs/heads/"))
 		branch += 11;
-	if (is_null_sha1(head))
+	if (!branch || is_null_sha1(head))
 		head_invalid = 1;
 
 	git_config(git_merge_config, NULL);
-- 
1.7.3.1.256.g2539c.dirty