[PATCH v3 2/2] revision: Implement `git log --merge` also for rebase/cherry_pick/revert

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

Co-authored-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Michael Lohmann <mi.al.lohmann@gmail.com>
---

On 12. Jan 2024, at 21:18, Junio C Hamano <gitster@pobox.com> wrote:
> I like the way your other_merge_candidate() loops over an array of
> possible candidates, which makes it a lot easier to extend, though,
> admittedly the "die()" message needs auto-generating if we really
> wanted to make it maintenance free ;-)

I would certainly like that but I did not find an easy way of achieving
this in C. Help wanted.

Changes with respect to v2:
- use read_ref_full instead of refs_resolve_ref_unsafe
- check for symbolic ref
- extract "other_name" in this patch, instead of patch 1

 revision.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/revision.c b/revision.c
index aa4c4dc778..c778413c7d 100644
--- a/revision.c
+++ b/revision.c
@@ -1961,11 +1961,31 @@ static void add_pending_commit_list(struct rev_info *revs,
 	}
 }
 
+static const char *lookup_other_head(struct object_id *oid)
+{
+	int i;
+	static const char *const other_head[] = {
+		"MERGE_HEAD", "REBASE_HEAD", "CHERRY_PICK_HEAD", "REVERT_HEAD"
+	};
+
+	for (i = 0; i < ARRAY_SIZE(other_head); i++)
+		if (!read_ref_full(other_head[i],
+				RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+				oid, NULL)) {
+			if (is_null_oid(oid))
+				die("%s is a symbolic ref???", other_head[i]);
+			return other_head[i];
+		}
+
+	die("--merge without MERGE_HEAD, REBASE_HEAD, CHERRY_PICK_HEAD or REVERT_HEAD?");
+}
+
 static void prepare_show_merge(struct rev_info *revs)
 {
 	struct commit_list *bases;
 	struct commit *head, *other;
 	struct object_id oid;
+	const char *other_name;
 	const char **prune = NULL;
 	int i, prune_num = 1; /* counting terminating NULL */
 	struct index_state *istate = revs->repo->index;
@@ -1973,15 +1993,10 @@ 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 (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");
+	other_name = lookup_other_head(&oid);
+	other = lookup_commit_or_die(&oid, other_name);
 	add_pending_object(revs, &head->object, "HEAD");
-	add_pending_object(revs, &other->object, "MERGE_HEAD");
+	add_pending_object(revs, &other->object, other_name);
 	bases = repo_get_merge_bases(the_repository, head, other);
 	add_rev_cmdline_list(revs, bases, REV_CMD_MERGE_BASE, UNINTERESTING | BOTTOM);
 	add_pending_commit_list(revs, bases, UNINTERESTING | BOTTOM);
-- 
2.39.3 (Apple Git-145)