[PATCH v3 1/2] revision: ensure MERGE_HEAD is a ref in prepare_show_merge

[Michael Lohmann <mi.al.lohmann@gmail.com>]

This is done to
(1) ensure MERGE_HEAD is a ref,
(2) obtain the oid without any prefixing by refs.c:repo_dwim_ref()
(3) error out when MERGE_HEAD is a symref.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Michael Lohmann <mi.al.lohmann@gmail.com>
---

Changes with respect to v2:
- use read_ref_full instead of refs_resolve_ref_unsafe
- don't use "other_head" variable to store MERGE_HEAD
- check for symbolic ref

 revision.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/revision.c b/revision.c
index 2424c9bd67..aa4c4dc778 100644
--- a/revision.c
+++ b/revision.c
@@ -1973,8 +1973,12 @@ static void prepare_show_merge(struct rev_info *revs)
 	if (repo_get_oid(the_repository, "HEAD", &oid))
 		die("--merge without HEAD?");
 	head = lookup_commit_or_die(&oid, "HEAD");
-	if (repo_get_oid(the_repository, "MERGE_HEAD", &oid))
+	if (read_ref_full("MERGE_HEAD",
+			RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+			&oid, NULL))
 		die("--merge without MERGE_HEAD?");
+	if (is_null_oid(&oid))
+		die("MERGE_HEAD is a symbolic ref???");
 	other = lookup_commit_or_die(&oid, "MERGE_HEAD");
 	add_pending_object(revs, &head->object, "HEAD");
 	add_pending_object(revs, &other->object, "MERGE_HEAD");
-- 
2.39.3 (Apple Git-145)