refs: expose peeled object ID via the iterator

Both the "files" and "reftable" backend are able to store peeled values
for tags in the respective formats. This allows for a more efficient
lookup of the target object of such a tag without having to manually
peel via the object database.

The infrastructure to access these peeled object IDs is somewhat funky
though. When iterating through objects, we store a pointer reference to
the current iterator in a global variable. The callbacks invoked by that
iterator are then expected to call `peel_iterated_oid()`, which checks
whether the globally-stored iterator's current reference refers to the
one handed into that function. If so, we ask the iterator to peel the
object, otherwise we manually peel the object via the object database.
Depending on global state like this is somewhat weird and also quite
fragile.

Introduce a new `struct reference::peeled_oid` field that can be
populated by the reference backends. This field can be accessed via a
new function `reference_get_peeled_oid()` that either uses that value,
if set, or alternatively peels via the ODB. With this change we don't
have to rely on global state anymore, but make the peeled object ID
available to the callback functions directly.

Adjust trivial callers that already have a `struct reference` available.
Remaining callers will be adjusted in subsequent commits.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 6 insertions, 0 deletions

diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index 711e07f832..1fefefd54e 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -963,6 +963,7 @@ static int next_record(struct packed_ref_iterator *iter)
 			iter->base.ref.flags &= ~REF_KNOWS_PEELED;
 		} else {
 			iter->base.ref.flags |= REF_KNOWS_PEELED;
+			iter->base.ref.peeled_oid = &iter->peeled;
 		}
 	} else {
 		oidclr(&iter->peeled, iter->repo->hash_algo);
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 728886eafd..e214e120d7 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -547,6 +547,7 @@ struct reftable_ref_iterator {
 	struct reftable_iterator iter;
 	struct reftable_ref_record ref;
 	struct object_id oid;
+	struct object_id peeled_oid;
 
 	char *prefix;
 	size_t prefix_len;
@@ -671,6 +672,8 @@ static int reftable_ref_iterator_advance(struct ref_iterator *ref_iterator)
 		case REFTABLE_REF_VAL2:
 			oidread(&iter->oid, iter->ref.value.val2.value,
 				refs->base.repo->hash_algo);
+			oidread(&iter->peeled_oid, iter->ref.value.val2.target_value,
+				refs->base.repo->hash_algo);
 			break;
 		case REFTABLE_REF_SYMREF:
 			referent = refs_resolve_ref_unsafe(&iter->refs->base,
@@ -708,6 +711,8 @@ static int reftable_ref_iterator_advance(struct ref_iterator *ref_iterator)
 		iter->base.ref.name = iter->ref.refname;
 		iter->base.ref.target = referent;
 		iter->base.ref.oid = &iter->oid;
+		if (iter->ref.value_type == REFTABLE_REF_VAL2)
+			iter->base.ref.peeled_oid = &iter->peeled_oid;
 		iter->base.ref.flags = flags;
 
 		break;