Get dispatch weight from the target chain (when DispatchFeePayment::AtTargetChain is used) (#1430)

* reintroduce From<SourceChain>InboundLaneApi

* impl From<Chain>InboundLaneApi for testnet runtimes

* use inboundlaneapi in relay

* remove unused OutboundXcmWeigher

* spelling

* added the only test to messages pallet

* fmt

bridges/modules/messages/src/lib.rs

@@ -56,9 +56,10 @@ use bp_messages::{
 	target_chain::{
 		DispatchMessage, MessageDispatch, ProvedLaneMessages, ProvedMessages, SourceHeaderChain,
 	},
-	total_unrewarded_messages, DeliveredMessages, InboundLaneData, LaneId, MessageData, MessageKey,
-	MessageNonce, OperatingMode, OutboundLaneData, Parameter as MessagesParameter,
-	UnrewardedRelayer, UnrewardedRelayersState,
+	total_unrewarded_messages, DeliveredMessages, InboundLaneData, InboundMessageDetails, LaneId,
+	MessageData, MessageKey, MessageNonce, MessagePayload, OperatingMode, OutboundLaneData,
+	OutboundMessageDetails, Parameter as MessagesParameter, UnrewardedRelayer,
+	UnrewardedRelayersState,
 };
 use bp_runtime::{ChainId, Size};
 use codec::{Decode, Encode};
@@ -156,7 +157,7 @@ pub mod pallet {
 		/// Payload type of inbound messages. This payload is dispatched on this chain.
 		type InboundPayload: Decode;
 		/// Message fee type of inbound messages. This fee is paid on the bridged chain.
-		type InboundMessageFee: Decode;
+		type InboundMessageFee: Decode + Zero;
 		/// Identifier of relayer that deliver messages to this chain. Relayer reward is paid on the
 		/// bridged chain.
 		type InboundRelayer: Parameter;
@@ -762,6 +763,22 @@ pub mod pallet {
 		) -> Option<MessageData<T::OutboundMessageFee>> {
 			OutboundMessages::<T, I>::get(MessageKey { lane_id: lane, nonce })
 		}
+
+		/// Prepare data, related to given inbound message.
+		pub fn inbound_message_data(
+			lane: LaneId,
+			payload: MessagePayload,
+			outbound_details: OutboundMessageDetails<T::InboundMessageFee>,
+		) -> InboundMessageDetails {
+			let mut dispatch_message = DispatchMessage {
+				key: MessageKey { lane_id: lane, nonce: outbound_details.nonce },
+				data: MessageData { payload, fee: outbound_details.delivery_and_dispatch_fee }
+					.into(),
+			};
+			InboundMessageDetails {
+				dispatch_weight: T::MessageDispatch::dispatch_weight(&mut dispatch_message),
+			}
+		}
 	}
 }
 
@@ -2332,4 +2349,25 @@ mod tests {
 			bp_messages::storage_keys::inbound_lane_data_key("Messages", &TEST_LANE_ID).0,
 		);
 	}
+
+	#[test]
+	fn inbound_message_details_works() {
+		run_test(|| {
+			assert_eq!(
+				Pallet::<TestRuntime>::inbound_message_data(
+					TEST_LANE_ID,
+					REGULAR_PAYLOAD.encode(),
+					OutboundMessageDetails {
+						nonce: 0,
+						dispatch_weight: 0,
+						size: 0,
+						delivery_and_dispatch_fee: 0,
+						dispatch_fee_payment:
+							bp_runtime::messages::DispatchFeePayment::AtTargetChain,
+					},
+				),
+				InboundMessageDetails { dispatch_weight: REGULAR_PAYLOAD.declared_weight },
+			);
+		});
+	}
 }