fix update validation

pallets/rolldown/src/lib.rs

@@ -1449,7 +1449,7 @@ impl<T: Config> Pallet<T> {
 			Error::<T>::WrongRequestId
 		);
 
-		let last_id = lowest_id +
+		let last_id = lowest_id.saturating_sub(1u128) +
 			(update.pendingDeposits.len() as u128) +
 			(update.pendingCancelResolutions.len() as u128);
 

pallets/rolldown/src/tests.rs

@@ -979,6 +979,31 @@ fn reject_update_with_invalid_too_high_request_id() {
 	});
 }
 
+#[test]
+#[serial]
+fn reject_update_without_new_updates() {
+	ExtBuilder::new().execute_with_default_mocks(|| {
+		forward_to_block::<Test>(10);
+
+		let deposit_update = L1UpdateBuilder::default()
+			.with_requests(vec![L1UpdateRequest::Deposit(Default::default())])
+			.with_offset(1u128)
+			.build();
+
+		Rolldown::update_l2_from_l1_unsafe(RuntimeOrigin::signed(ALICE), deposit_update.clone())
+			.unwrap();
+		assert_eq!(LastProcessedRequestOnL2::<Test>::get(consts::CHAIN), 0u128.into());
+
+		forward_to_block::<Test>(16);
+		assert_eq!(LastProcessedRequestOnL2::<Test>::get(consts::CHAIN), 1u128.into());
+
+		assert_err!(
+			Rolldown::update_l2_from_l1_unsafe(RuntimeOrigin::signed(ALICE), deposit_update),
+			Error::<Test>::WrongRequestId
+		);
+	});
+}
+
 #[test]
 #[serial]
 fn reject_second_update_in_the_same_block() {