refs/reftable: refactor reflog expiry to use reftable backend

Refactor the callback function that expires reflog entries in the
reftable backend to use `reftable_backend_read_ref()` instead of
accessing the reftable stack directly. This ensures that the function
will benefit from the new caching layer that we're about to introduce.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

refs/reftable-backend.c

@@ -2444,14 +2444,15 @@ static int reftable_be_reflog_expire(struct ref_store *ref_store,
 		reftable_be_downcast(ref_store, REF_STORE_WRITE, "reflog_expire");
 	struct reftable_log_record *logs = NULL;
 	struct reftable_log_record *rewritten = NULL;
-	struct reftable_ref_record ref_record = {0};
 	struct reftable_iterator it = {0};
 	struct reftable_addition *add = NULL;
 	struct reflog_expiry_arg arg = {0};
 	struct reftable_backend *be;
 	struct object_id oid = {0};
+	struct strbuf referent = STRBUF_INIT;
 	uint8_t *last_hash = NULL;
 	size_t logs_nr = 0, logs_alloc = 0, i;
+	unsigned int type = 0;
 	int ret;
 
 	if (refs->err < 0)
@@ -2473,12 +2474,9 @@ static int reftable_be_reflog_expire(struct ref_store *ref_store,
 	if (ret < 0)
 		goto done;
 
-	ret = reftable_stack_read_ref(be->stack, refname, &ref_record);
+	ret = reftable_backend_read_ref(be, refname, &oid, &referent, &type);
 	if (ret < 0)
 		goto done;
-	if (reftable_ref_record_val1(&ref_record))
-		oidread(&oid, reftable_ref_record_val1(&ref_record),
-			ref_store->repo->hash_algo);
 	prepare_fn(refname, &oid, policy_cb_data);
 
 	while (1) {
@@ -2545,8 +2543,7 @@ static int reftable_be_reflog_expire(struct ref_store *ref_store,
 		}
 	}
 
-	if (flags & EXPIRE_REFLOGS_UPDATE_REF && last_hash &&
-	    reftable_ref_record_val1(&ref_record))
+	if (flags & EXPIRE_REFLOGS_UPDATE_REF && last_hash && !is_null_oid(&oid))
 		oidread(&arg.update_oid, last_hash, ref_store->repo->hash_algo);
 
 	arg.refs = refs;
@@ -2571,11 +2568,11 @@ static int reftable_be_reflog_expire(struct ref_store *ref_store,
 		cleanup_fn(policy_cb_data);
 	assert(ret != REFTABLE_API_ERROR);
 
-	reftable_ref_record_release(&ref_record);
 	reftable_iterator_destroy(&it);
 	reftable_addition_destroy(add);
 	for (i = 0; i < logs_nr; i++)
 		reftable_log_record_release(&logs[i]);
+	strbuf_release(&referent);
 	free(logs);
 	free(rewritten);
 	return ret;