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/primitives/messages/src/lib.rs

@@ -176,12 +176,15 @@ impl<RelayerId> InboundLaneData<RelayerId> {
 	}
 }
 
-/// Message details, returned by runtime APIs.
+/// Outbound message details, returned by runtime APIs.
 #[derive(Clone, Encode, Decode, RuntimeDebug, PartialEq, Eq)]
-pub struct MessageDetails<OutboundMessageFee> {
+pub struct OutboundMessageDetails<OutboundMessageFee> {
 	/// Nonce assigned to the message.
 	pub nonce: MessageNonce,
-	/// Message dispatch weight, declared by the submitter.
+	/// Message dispatch weight.
+	///
+	/// Depending on messages pallet configuration, it may be declared by the message submitter,
+	/// computed automatically or just be zero if dispatch fee is paid at the target chain.
 	pub dispatch_weight: Weight,
 	/// Size of the encoded message.
 	pub size: u32,
@@ -191,6 +194,18 @@ pub struct MessageDetails<OutboundMessageFee> {
 	pub dispatch_fee_payment: DispatchFeePayment,
 }
 
+/// Inbound message details, returned by runtime APIs.
+#[derive(Clone, Encode, Decode, RuntimeDebug, PartialEq, Eq)]
+pub struct InboundMessageDetails {
+	/// Computed message dispatch weight.
+	///
+	/// Runtime API guarantees that it will match the value, returned by
+	/// `target_chain::MessageDispatch::dispatch_weight`. This means that if the runtime
+	/// has failed to decode the message, it will be zero - that's because `undecodable`
+	/// message cannot be dispatched.
+	pub dispatch_weight: Weight,
+}
+
 /// Bit vector of message dispatch results.
 pub type DispatchResultsBitVec = BitVec<u8, Msb0>;
 

bridges/primitives/messages/src/target_chain.rs

@@ -93,8 +93,9 @@ pub trait MessageDispatch<AccountId, Fee> {
 
 	/// Estimate dispatch weight.
 	///
-	/// This function must: (1) be instant and (2) return correct upper bound
-	/// of dispatch weight.
+	/// This function must return correct upper bound of dispatch weight. The return value
+	/// of this function is expected to match return value of the corresponding
+	/// `From<Chain>InboundLaneApi::message_details().dispatch_weight` call.
 	fn dispatch_weight(message: &mut DispatchMessage<Self::DispatchPayload, Fee>) -> Weight;
 
 	/// Called when inbound message is received.