XCM: Tools for uniquely referencing messages (#7234)

* Tools for unique topic references

* Formatting

* Naming

* Repot into routing.rs.

* More things done

* Universal Exporter supports topic-as-reference

* Some tests for the topic routing

* More tests

* Paid bridge tests

* Add message ID to sending events

* Formatting

* fix and integrate into test nets

* Move DenyThenTry and friend from Cumulus

* Append SetTopic rather than prepend

* Docs

* Docs

* Work with new ProcessMessage ID API

* Formatting

* Fix build

* Fixes

* Formatting

* Update xcm/xcm-builder/src/barriers.rs

Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>

* Update xcm/xcm-builder/src/routing.rs

Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>

* Docs

* Rename message_hash

* Formatting

* ".git/.scripts/commands/fmt/fmt.sh"

* Rename

* Another Rename

* ".git/.scripts/commands/fmt/fmt.sh"

* ".git/.scripts/commands/fmt/fmt.sh"

* Update xcm/xcm-builder/src/routing.rs

Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

---------

Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>
Co-authored-by: command-bot <>
Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

polkadot/runtime/kusama/src/xcm_config.rs

@@ -41,8 +41,8 @@ use xcm_builder::{
 	ChildParachainConvertsVia, ChildSystemParachainAsSuperuser,
 	CurrencyAdapter as XcmCurrencyAdapter, FixedWeightBounds, IsChildSystemParachain, IsConcrete,
 	MintLocation, OriginToPluralityVoice, SignedAccountId32AsNative, SignedToAccountId32,
-	SovereignSignedViaLocation, TakeWeightCredit, UsingComponents, WeightInfoBounds,
-	WithComputedOrigin,
+	SovereignSignedViaLocation, TakeWeightCredit, TrailingSetTopicAsId, UsingComponents,
+	WeightInfoBounds, WithComputedOrigin, WithUniqueTopic,
 };
 use xcm_executor::traits::WithOriginFilter;
 
@@ -115,14 +115,14 @@ parameter_types! {
 
 /// The XCM router. When we want to send an XCM message, we use this type. It amalgamates all of our
 /// individual routers.
-pub type XcmRouter = (
+pub type XcmRouter = WithUniqueTopic<(
 	// Only one router so far - use DMP to communicate with child parachains.
 	ChildParachainRouter<
 		Runtime,
 		XcmPallet,
 		ExponentialPrice<FeeAssetId, BaseDeliveryFee, TransactionByteFee, Dmp>,
 	>,
-);
+)>;
 
 parameter_types! {
 	pub const Ksm: MultiAssetFilter = Wild(AllOf { fun: WildFungible, id: Concrete(TokenLocation::get()) });
@@ -142,7 +142,7 @@ match_types! {
 }
 
 /// The barriers one of which must be passed for an XCM message to be executed.
-pub type Barrier = (
+pub type Barrier = TrailingSetTopicAsId<(
 	// Weight that is paid for may be consumed.
 	TakeWeightCredit,
 	// Expected responses are OK.
@@ -159,7 +159,7 @@ pub type Barrier = (
 		UniversalLocation,
 		ConstU32<8>,
 	>,
-);
+)>;
 
 /// A call filter for the XCM Transact instruction. This is a temporary measure until we properly
 /// account for proof size weights.

polkadot/runtime/rococo/src/xcm_config.rs

@@ -40,7 +40,8 @@ use xcm_builder::{
 	ChildParachainAsNative, ChildParachainConvertsVia, ChildSystemParachainAsSuperuser,
 	CurrencyAdapter as XcmCurrencyAdapter, FixedWeightBounds, IsChildSystemParachain, IsConcrete,
 	MintLocation, SignedAccountId32AsNative, SignedToAccountId32, SovereignSignedViaLocation,
-	TakeWeightCredit, UsingComponents, WeightInfoBounds, WithComputedOrigin,
+	TakeWeightCredit, TrailingSetTopicAsId, UsingComponents, WeightInfoBounds, WithComputedOrigin,
+	WithUniqueTopic,
 };
 use xcm_executor::{traits::WithOriginFilter, XcmExecutor};
 
@@ -95,14 +96,14 @@ parameter_types! {
 
 /// The XCM router. When we want to send an XCM message, we use this type. It amalgamates all of our
 /// individual routers.
-pub type XcmRouter = (
+pub type XcmRouter = WithUniqueTopic<(
 	// Only one router so far - use DMP to communicate with child parachains.
 	ChildParachainRouter<
 		Runtime,
 		XcmPallet,
 		ExponentialPrice<FeeAssetId, BaseDeliveryFee, TransactionByteFee, Dmp>,
 	>,
-);
+)>;
 
 parameter_types! {
 	pub const Roc: MultiAssetFilter = Wild(AllOf { fun: WildFungible, id: Concrete(TokenLocation::get()) });
@@ -137,7 +138,7 @@ match_types! {
 }
 
 /// The barriers one of which must be passed for an XCM message to be executed.
-pub type Barrier = (
+pub type Barrier = TrailingSetTopicAsId<(
 	// Weight that is paid for may be consumed.
 	TakeWeightCredit,
 	// Expected responses are OK.
@@ -154,7 +155,7 @@ pub type Barrier = (
 		UniversalLocation,
 		ConstU32<8>,
 	>,
-);
+)>;
 
 /// A call filter for the XCM Transact instruction. This is a temporary measure until we
 /// properly account for proof size weights.

polkadot/runtime/westend/src/xcm_config.rs

@@ -39,7 +39,7 @@ use xcm_builder::{
 	ChildParachainConvertsVia, ChildSystemParachainAsSuperuser,
 	CurrencyAdapter as XcmCurrencyAdapter, IsChildSystemParachain, IsConcrete, MintLocation,
 	SignedAccountId32AsNative, SignedToAccountId32, SovereignSignedViaLocation, TakeWeightCredit,
-	UsingComponents, WeightInfoBounds, WithComputedOrigin,
+	TrailingSetTopicAsId, UsingComponents, WeightInfoBounds, WithComputedOrigin, WithUniqueTopic,
 };
 use xcm_executor::{traits::WithOriginFilter, XcmExecutor};
 
@@ -80,14 +80,14 @@ type LocalOriginConverter = (
 
 /// The XCM router. When we want to send an XCM message, we use this type. It amalgamates all of our
 /// individual routers.
-pub type XcmRouter = (
+pub type XcmRouter = WithUniqueTopic<(
 	// Only one router so far - use DMP to communicate with child parachains.
 	ChildParachainRouter<
 		Runtime,
 		XcmPallet,
 		ExponentialPrice<FeeAssetId, BaseDeliveryFee, TransactionByteFee, Dmp>,
 	>,
-);
+)>;
 
 parameter_types! {
 	pub const Westmint: MultiLocation = Parachain(1000).into_location();
@@ -108,7 +108,7 @@ pub type TrustedTeleporters =
 	(xcm_builder::Case<WndForWestmint>, xcm_builder::Case<WndForCollectives>);
 
 /// The barriers one of which must be passed for an XCM message to be executed.
-pub type Barrier = (
+pub type Barrier = TrailingSetTopicAsId<(
 	// Weight that is paid for may be consumed.
 	TakeWeightCredit,
 	// Expected responses are OK.
@@ -125,7 +125,7 @@ pub type Barrier = (
 		UniversalLocation,
 		ConstU32<8>,
 	>,
-);
+)>;
 
 /// A call filter for the XCM Transact instruction. This is a temporary measure until we
 /// properly account for proof size weights.

polkadot/xcm/pallet-xcm-benchmarks/src/fungible/benchmarking.rs

@@ -49,7 +49,7 @@ benchmarks_instance_pallet! {
 			&sender_location,
 			&XcmContext {
 				origin: Some(sender_location.clone()),
-				message_hash: [0; 32],
+				message_id: [0; 32],
 				topic: None,
 			},
 		).unwrap();
@@ -82,7 +82,7 @@ benchmarks_instance_pallet! {
 			&sender_location,
 			&XcmContext {
 				origin: Some(sender_location.clone()),
-				message_hash: [0; 32],
+				message_id: [0; 32],
 				topic: None,
 			},
 		).unwrap();
@@ -109,7 +109,7 @@ benchmarks_instance_pallet! {
 			&sender_location,
 			&XcmContext {
 				origin: Some(sender_location.clone()),
-				message_hash: [0; 32],
+				message_id: [0; 32],
 				topic: None,
 			},
 		).unwrap();

polkadot/xcm/pallet-xcm-benchmarks/src/generic/benchmarking.rs

@@ -209,7 +209,7 @@ benchmarks! {
 			assets.clone().into(),
 			&XcmContext {
 				origin: Some(origin.clone()),
-				message_hash: [0; 32],
+				message_id: [0; 32],
 				topic: None,
 			},
 		);
@@ -266,7 +266,7 @@ benchmarks! {
 			max_response_weight,
 			&XcmContext {
 				origin: Some(origin.clone()),
-				message_hash: [0; 32],
+				message_id: [0; 32],
 				topic: None,
 			},
 		).map_err(|_| "Could not start subscription")?;

polkadot/xcm/pallet-xcm/src/lib.rs

@@ -40,7 +40,7 @@ use sp_runtime::{
 };
 use sp_std::{boxed::Box, marker::PhantomData, prelude::*, result::Result, vec};
 use xcm::{latest::QueryResponseInfo, prelude::*};
-use xcm_executor::traits::{Convert, ConvertOrigin};
+use xcm_executor::traits::{Convert, ConvertOrigin, Properties};
 
 use frame_support::{
 	dispatch::{Dispatchable, GetDispatchInfo},
@@ -272,52 +272,49 @@ pub mod pallet {
 	#[pallet::generate_deposit(pub(super) fn deposit_event)]
 	pub enum Event<T: Config> {
 		/// Execution of an XCM message was attempted.
-		///
-		/// \[ outcome \]
-		Attempted(xcm::latest::Outcome),
+		Attempted { outcome: xcm::latest::Outcome },
 		/// A XCM message was sent.
-		///
-		/// \[ origin, destination, message \]
-		Sent(MultiLocation, MultiLocation, Xcm<()>),
+		Sent {
+			origin: MultiLocation,
+			destination: MultiLocation,
+			message: Xcm<()>,
+			message_id: XcmHash,
+		},
 		/// Query response received which does not match a registered query. This may be because a
 		/// matching query was never registered, it may be because it is a duplicate response, or
 		/// because the query timed out.
-		///
-		/// \[ origin location, id \]
-		UnexpectedResponse(MultiLocation, QueryId),
+		UnexpectedResponse { origin: MultiLocation, query_id: QueryId },
 		/// Query response has been received and is ready for taking with `take_response`. There is
 		/// no registered notification call.
-		///
-		/// \[ id, response \]
-		ResponseReady(QueryId, Response),
+		ResponseReady { query_id: QueryId, response: Response },
 		/// Query response has been received and query is removed. The registered notification has
 		/// been dispatched and executed successfully.
-		///
-		/// \[ id, pallet index, call index \]
-		Notified(QueryId, u8, u8),
+		Notified { query_id: QueryId, pallet_index: u8, call_index: u8 },
 		/// Query response has been received and query is removed. The registered notification could
 		/// not be dispatched because the dispatch weight is greater than the maximum weight
 		/// originally budgeted by this runtime for the query result.
-		///
-		/// \[ id, pallet index, call index, actual weight, max budgeted weight \]
-		NotifyOverweight(QueryId, u8, u8, Weight, Weight),
+		NotifyOverweight {
+			query_id: QueryId,
+			pallet_index: u8,
+			call_index: u8,
+			actual_weight: Weight,
+			max_budgeted_weight: Weight,
+		},
 		/// Query response has been received and query is removed. There was a general error with
 		/// dispatching the notification call.
-		///
-		/// \[ id, pallet index, call index \]
-		NotifyDispatchError(QueryId, u8, u8),
+		NotifyDispatchError { query_id: QueryId, pallet_index: u8, call_index: u8 },
 		/// Query response has been received and query is removed. The dispatch was unable to be
 		/// decoded into a `Call`; this might be due to dispatch function having a signature which
 		/// is not `(origin, QueryId, Response)`.
-		///
-		/// \[ id, pallet index, call index \]
-		NotifyDecodeFailed(QueryId, u8, u8),
+		NotifyDecodeFailed { query_id: QueryId, pallet_index: u8, call_index: u8 },
 		/// Expected query response has been received but the origin location of the response does
 		/// not match that expected. The query remains registered for a later, valid, response to
 		/// be received and acted upon.
-		///
-		/// \[ origin location, id, expected location \]
-		InvalidResponder(MultiLocation, QueryId, Option<MultiLocation>),
+		InvalidResponder {
+			origin: MultiLocation,
+			query_id: QueryId,
+			expected_location: Option<MultiLocation>,
+		},
 		/// Expected query response has been received but the expected origin location placed in
 		/// storage by this runtime previously cannot be decoded. The query remains registered.
 		///
@@ -325,38 +322,29 @@ pub mod pallet {
 		/// runtime should be readable prior to query timeout) and dangerous since the possibly
 		/// valid response will be dropped. Manual governance intervention is probably going to be
 		/// needed.
-		///
-		/// \[ origin location, id \]
-		InvalidResponderVersion(MultiLocation, QueryId),
+		InvalidResponderVersion { origin: MultiLocation, query_id: QueryId },
 		/// Received query response has been read and removed.
-		///
-		/// \[ id \]
-		ResponseTaken(QueryId),
+		ResponseTaken { query_id: QueryId },
 		/// Some assets have been placed in an asset trap.
-		///
-		/// \[ hash, origin, assets \]
-		AssetsTrapped(H256, MultiLocation, VersionedMultiAssets),
+		AssetsTrapped { hash: H256, origin: MultiLocation, assets: VersionedMultiAssets },
 		/// An XCM version change notification message has been attempted to be sent.
 		///
 		/// The cost of sending it (borne by the chain) is included.
-		///
-		/// \[ destination, result, cost \]
-		VersionChangeNotified(MultiLocation, XcmVersion, MultiAssets),
+		VersionChangeNotified {
+			destination: MultiLocation,
+			result: XcmVersion,
+			cost: MultiAssets,
+			message_id: XcmHash,
+		},
 		/// The supported version of a location has been changed. This might be through an
 		/// automatic notification or a manual intervention.
-		///
-		/// \[ location, XCM version \]
-		SupportedVersionChanged(MultiLocation, XcmVersion),
+		SupportedVersionChanged { location: MultiLocation, version: XcmVersion },
 		/// A given location which had a version change subscription was dropped owing to an error
 		/// sending the notification to it.
-		///
-		/// \[ location, query ID, error \]
-		NotifyTargetSendFail(MultiLocation, QueryId, XcmError),
+		NotifyTargetSendFail { location: MultiLocation, query_id: QueryId, error: XcmError },
 		/// A given location which had a version change subscription was dropped owing to an error
 		/// migrating the location to our new XCM format.
-		///
-		/// \[ location, query ID \]
-		NotifyTargetMigrationFail(VersionedMultiLocation, QueryId),
+		NotifyTargetMigrationFail { location: VersionedMultiLocation, query_id: QueryId },
 		/// Expected query response has been received but the expected querier location placed in
 		/// storage by this runtime previously cannot be decoded. The query remains registered.
 		///
@@ -364,36 +352,35 @@ pub mod pallet {
 		/// runtime should be readable prior to query timeout) and dangerous since the possibly
 		/// valid response will be dropped. Manual governance intervention is probably going to be
 		/// needed.
-		///
-		/// \[ origin location, id \]
-		InvalidQuerierVersion(MultiLocation, QueryId),
+		InvalidQuerierVersion { origin: MultiLocation, query_id: QueryId },
 		/// Expected query response has been received but the querier location of the response does
 		/// not match the expected. The query remains registered for a later, valid, response to
 		/// be received and acted upon.
-		///
-		/// \[ origin location, id, expected querier, maybe actual querier \]
-		InvalidQuerier(MultiLocation, QueryId, MultiLocation, Option<MultiLocation>),
+		InvalidQuerier {
+			origin: MultiLocation,
+			query_id: QueryId,
+			expected_querier: MultiLocation,
+			maybe_actual_querier: Option<MultiLocation>,
+		},
 		/// A remote has requested XCM version change notification from us and we have honored it.
 		/// A version information message is sent to them and its cost is included.
-		///
-		/// \[ destination location, cost \]
-		VersionNotifyStarted(MultiLocation, MultiAssets),
-		/// We have requested that a remote chain sends us XCM version change notifications.
-		///
-		/// \[ destination location, cost \]
-		VersionNotifyRequested(MultiLocation, MultiAssets),
+		VersionNotifyStarted { destination: MultiLocation, cost: MultiAssets, message_id: XcmHash },
+		/// We have requested that a remote chain send us XCM version change notifications.
+		VersionNotifyRequested {
+			destination: MultiLocation,
+			cost: MultiAssets,
+			message_id: XcmHash,
+		},
 		/// We have requested that a remote chain stops sending us XCM version change notifications.
-		///
-		/// \[ destination location, cost \]
-		VersionNotifyUnrequested(MultiLocation, MultiAssets),
+		VersionNotifyUnrequested {
+			destination: MultiLocation,
+			cost: MultiAssets,
+			message_id: XcmHash,
+		},
 		/// Fees were paid from a location for an operation (often for using `SendXcm`).
-		///
-		/// \[ paying location, fees \]
-		FeesPaid(MultiLocation, MultiAssets),
+		FeesPaid { paying: MultiLocation, fees: MultiAssets },
 		/// Some assets have been claimed from an asset trap
-		///
-		/// \[ hash, origin, assets \]
-		AssetsClaimed(H256, MultiLocation, VersionedMultiAssets),
+		AssetsClaimed { hash: H256, origin: MultiLocation, assets: VersionedMultiAssets },
 	}
 
 	#[pallet::origin]
@@ -793,8 +780,10 @@ pub mod pallet {
 			let dest = MultiLocation::try_from(*dest).map_err(|()| Error::<T>::BadVersion)?;
 			let message: Xcm<()> = (*message).try_into().map_err(|()| Error::<T>::BadVersion)?;
 
+			let message_id =
 				Self::send_xcm(interior, dest, message.clone()).map_err(Error::<T>::from)?;
-			Self::deposit_event(Event::Sent(origin_location, dest, message));
+			let e = Event::Sent { origin: origin_location, destination: dest, message, message_id };
+			Self::deposit_event(e);
 			Ok(())
 		}
 
@@ -927,7 +916,7 @@ pub mod pallet {
 			);
 			let result =
 				Ok(Some(outcome.weight_used().saturating_add(T::WeightInfo::execute())).into());
-			Self::deposit_event(Event::Attempted(outcome));
+			Self::deposit_event(Event::Attempted { outcome });
 			result
 		}
 
@@ -942,16 +931,16 @@ pub mod pallet {
 		pub fn force_xcm_version(
 			origin: OriginFor<T>,
 			location: Box<MultiLocation>,
-			xcm_version: XcmVersion,
+			version: XcmVersion,
 		) -> DispatchResult {
 			T::AdminOrigin::ensure_origin(origin)?;
 			let location = *location;
 			SupportedVersion::<T>::insert(
 				XCM_VERSION,
 				LatestVersionedMultiLocation(&location),
-				xcm_version,
+				version,
 			);
-			Self::deposit_event(Event::SupportedVersionChanged(location, xcm_version));
+			Self::deposit_event(Event::SupportedVersionChanged { location, version });
 			Ok(())
 		}
 
@@ -1195,7 +1184,7 @@ impl<T: Config> Pallet<T> {
 		let hash = message.using_encoded(sp_io::hashing::blake2_256);
 		let outcome =
 			T::XcmExecutor::execute_xcm_in_credit(origin_location, message, hash, weight, weight);
-		Self::deposit_event(Event::Attempted(outcome));
+		Self::deposit_event(Event::Attempted { outcome });
 		Ok(())
 	}
 
@@ -1256,7 +1245,7 @@ impl<T: Config> Pallet<T> {
 		let hash = message.using_encoded(sp_io::hashing::blake2_256);
 		let outcome =
 			T::XcmExecutor::execute_xcm_in_credit(origin_location, message, hash, weight, weight);
-		Self::deposit_event(Event::Attempted(outcome));
+		Self::deposit_event(Event::Attempted { outcome });
 		Ok(())
 	}
 
@@ -1331,14 +1320,19 @@ impl<T: Config> Pallet<T> {
 				let message =
 					Xcm(vec![QueryResponse { query_id, response, max_weight, querier: None }]);
 				let event = match send_xcm::<T::XcmRouter>(new_key, message) {
-					Ok((_hash, cost)) => {
+					Ok((message_id, cost)) => {
 						let value = (query_id, max_weight, xcm_version);
 						VersionNotifyTargets::<T>::insert(XCM_VERSION, key, value);
-						Event::VersionChangeNotified(new_key, xcm_version, cost)
+						Event::VersionChangeNotified {
+							destination: new_key,
+							result: xcm_version,
+							cost,
+							message_id,
+						}
 					},
 					Err(e) => {
 						VersionNotifyTargets::<T>::remove(XCM_VERSION, key);
-						Event::NotifyTargetSendFail(new_key, query_id, e.into())
+						Event::NotifyTargetSendFail { location: new_key, query_id, error: e.into() }
 					},
 				};
 				Self::deposit_event(event);
@@ -1357,7 +1351,10 @@ impl<T: Config> Pallet<T> {
 					let new_key = match MultiLocation::try_from(old_key.clone()) {
 						Ok(k) => k,
 						Err(()) => {
-							Self::deposit_event(Event::NotifyTargetMigrationFail(old_key, value.0));
+							Self::deposit_event(Event::NotifyTargetMigrationFail {
+								location: old_key,
+								query_id: value.0,
+							});
 							weight_used.saturating_accrue(vnt_migrate_fail_weight);
 							if weight_used.any_gte(weight_cutoff) {
 								return (weight_used, Some(stage))
@@ -1380,15 +1377,24 @@ impl<T: Config> Pallet<T> {
 							querier: None,
 						}]);
 						let event = match send_xcm::<T::XcmRouter>(new_key, message) {
-							Ok((_hash, cost)) => {
+							Ok((message_id, cost)) => {
 								VersionNotifyTargets::<T>::insert(
 									XCM_VERSION,
 									versioned_key,
 									(query_id, max_weight, xcm_version),
 								);
-								Event::VersionChangeNotified(new_key, xcm_version, cost)
+								Event::VersionChangeNotified {
+									destination: new_key,
+									result: xcm_version,
+									cost,
+									message_id,
+								}
+							},
+							Err(e) => Event::NotifyTargetSendFail {
+								location: new_key,
+								query_id,
+								error: e.into(),
 							},
-							Err(e) => Event::NotifyTargetSendFail(new_key, query_id, e.into()),
 						};
 						Self::deposit_event(event);
 						weight_used.saturating_accrue(vnt_notify_migrate_weight);
@@ -1415,8 +1421,8 @@ impl<T: Config> Pallet<T> {
 		});
 		// TODO #3735: Correct weight.
 		let instruction = SubscribeVersion { query_id, max_response_weight: Weight::zero() };
-		let (_hash, cost) = send_xcm::<T::XcmRouter>(dest, Xcm(vec![instruction]))?;
-		Self::deposit_event(Event::VersionNotifyRequested(dest, cost));
+		let (message_id, cost) = send_xcm::<T::XcmRouter>(dest, Xcm(vec![instruction]))?;
+		Self::deposit_event(Event::VersionNotifyRequested { destination: dest, cost, message_id });
 		VersionNotifiers::<T>::insert(XCM_VERSION, &versioned_dest, query_id);
 		let query_status =
 			QueryStatus::VersionNotifier { origin: versioned_dest, is_active: false };
@@ -1430,8 +1436,12 @@ impl<T: Config> Pallet<T> {
 		let versioned_dest = LatestVersionedMultiLocation(&dest);
 		let query_id = VersionNotifiers::<T>::take(XCM_VERSION, versioned_dest)
 			.ok_or(XcmError::InvalidLocation)?;
-		let (_hash, cost) = send_xcm::<T::XcmRouter>(dest, Xcm(vec![UnsubscribeVersion]))?;
-		Self::deposit_event(Event::VersionNotifyUnrequested(dest, cost));
+		let (message_id, cost) = send_xcm::<T::XcmRouter>(dest, Xcm(vec![UnsubscribeVersion]))?;
+		Self::deposit_event(Event::VersionNotifyUnrequested {
+			destination: dest,
+			cost,
+			message_id,
+		});
 		Queries::<T>::remove(query_id);
 		Ok(())
 	}
@@ -1589,7 +1599,7 @@ impl<T: Config> Pallet<T> {
 		if let Some(QueryStatus::Ready { response, at }) = Queries::<T>::get(query_id) {
 			let response = response.try_into().ok()?;
 			Queries::<T>::remove(query_id);
-			Self::deposit_event(Event::ResponseTaken(query_id));
+			Self::deposit_event(Event::ResponseTaken { query_id });
 			Some((response, at))
 		} else {
 			None
@@ -1623,7 +1633,7 @@ impl<T: Config> Pallet<T> {
 	fn charge_fees(location: MultiLocation, assets: MultiAssets) -> DispatchResult {
 		T::XcmExecutor::charge_fees(location, assets.clone())
 			.map_err(|_| Error::<T>::FeesNotMet)?;
-		Self::deposit_event(Event::FeesPaid(location, assets));
+		Self::deposit_event(Event::FeesPaid { paying: location, fees: assets });
 		Ok(())
 	}
 }
@@ -1861,8 +1871,12 @@ impl<T: Config> VersionChangeNotifier for Pallet<T> {
 		let xcm_version = T::AdvertisedXcmVersion::get();
 		let response = Response::Version(xcm_version);
 		let instruction = QueryResponse { query_id, response, max_weight, querier: None };
-		let (_hash, cost) = send_xcm::<T::XcmRouter>(*dest, Xcm(vec![instruction]))?;
-		Self::deposit_event(Event::<T>::VersionNotifyStarted(*dest, cost));
+		let (message_id, cost) = send_xcm::<T::XcmRouter>(*dest, Xcm(vec![instruction]))?;
+		Self::deposit_event(Event::<T>::VersionNotifyStarted {
+			destination: *dest,
+			cost,
+			message_id,
+		});
 
 		let value = (query_id, max_weight, xcm_version);
 		VersionNotifyTargets::<T>::insert(XCM_VERSION, versioned_dest, value);
@@ -1891,7 +1905,7 @@ impl<T: Config> DropAssets for Pallet<T> {
 		let versioned = VersionedMultiAssets::from(MultiAssets::from(assets));
 		let hash = BlakeTwo256::hash_of(&(&origin, &versioned));
 		AssetTraps::<T>::mutate(hash, |n| *n += 1);
-		Self::deposit_event(Event::AssetsTrapped(hash, *origin, versioned));
+		Self::deposit_event(Event::AssetsTrapped { hash, origin: *origin, assets: versioned });
 		// TODO #3735: Put the real weight in there.
 		Weight::zero()
 	}
@@ -1920,7 +1934,7 @@ impl<T: Config> ClaimAssets for Pallet<T> {
 			1 => AssetTraps::<T>::remove(hash),
 			n => AssetTraps::<T>::insert(hash, n - 1),
 		}
-		Self::deposit_event(Event::AssetsClaimed(hash, *origin, versioned));
+		Self::deposit_event(Event::AssetsClaimed { hash, origin: *origin, assets: versioned });
 		return true
 	}
 }
@@ -1953,19 +1967,28 @@ impl<T: Config> OnResponse for Pallet<T> {
 		max_weight: Weight,
 		_context: &XcmContext,
 	) -> Weight {
+		let origin = *origin;
 		match (response, Queries::<T>::get(query_id)) {
 			(
 				Response::Version(v),
 				Some(QueryStatus::VersionNotifier { origin: expected_origin, is_active }),
 			) => {
 				let origin: MultiLocation = match expected_origin.try_into() {
-					Ok(o) if &o == origin => o,
+					Ok(o) if o == origin => o,
 					Ok(o) => {
-						Self::deposit_event(Event::InvalidResponder(*origin, query_id, Some(o)));
+						Self::deposit_event(Event::InvalidResponder {
+							origin,
+							query_id,
+							expected_location: Some(o),
+						});
 						return Weight::zero()
 					},
 					_ => {
-						Self::deposit_event(Event::InvalidResponder(*origin, query_id, None));
+						Self::deposit_event(Event::InvalidResponder {
+							origin,
+							query_id,
+							expected_location: None,
+						});
 						// TODO #3735: Correct weight for this.
 						return Weight::zero()
 					},
@@ -1983,7 +2006,10 @@ impl<T: Config> OnResponse for Pallet<T> {
 					LatestVersionedMultiLocation(&origin),
 					v,
 				);
-				Self::deposit_event(Event::SupportedVersionChanged(origin, v));
+				Self::deposit_event(Event::SupportedVersionChanged {
+					location: origin,
+					version: v,
+				});
 				Weight::zero()
 			},
 			(
@@ -1994,33 +2020,33 @@ impl<T: Config> OnResponse for Pallet<T> {
 					let match_querier = match MultiLocation::try_from(match_querier) {
 						Ok(mq) => mq,
 						Err(_) => {
-							Self::deposit_event(Event::InvalidQuerierVersion(*origin, query_id));
+							Self::deposit_event(Event::InvalidQuerierVersion { origin, query_id });
 							return Weight::zero()
 						},
 					};
 					if querier.map_or(true, |q| q != &match_querier) {
-						Self::deposit_event(Event::InvalidQuerier(
-							*origin,
+						Self::deposit_event(Event::InvalidQuerier {
+							origin,
 							query_id,
-							match_querier,
-							querier.cloned(),
-						));
+							expected_querier: match_querier,
+							maybe_actual_querier: querier.cloned(),
+						});
 						return Weight::zero()
 					}
 				}
 				let responder = match MultiLocation::try_from(responder) {
 					Ok(r) => r,
 					Err(_) => {
-						Self::deposit_event(Event::InvalidResponderVersion(*origin, query_id));
+						Self::deposit_event(Event::InvalidResponderVersion { origin, query_id });
 						return Weight::zero()
 					},
 				};
-				if origin != &responder {
-					Self::deposit_event(Event::InvalidResponder(
-						*origin,
+				if origin != responder {
+					Self::deposit_event(Event::InvalidResponder {
+						origin,
 						query_id,
-						Some(responder),
-					));
+						expected_location: Some(responder),
+					});
 					return Weight::zero()
 				}
 				return match maybe_notify {
@@ -2035,29 +2061,29 @@ impl<T: Config> OnResponse for Pallet<T> {
 							Queries::<T>::remove(query_id);
 							let weight = call.get_dispatch_info().weight;
 							if weight.any_gt(max_weight) {
-								let e = Event::NotifyOverweight(
+								let e = Event::NotifyOverweight {
 									query_id,
 									pallet_index,
 									call_index,
-									weight,
-									max_weight,
-								);
+									actual_weight: weight,
+									max_budgeted_weight: max_weight,
+								};
 								Self::deposit_event(e);
 								return Weight::zero()
 							}
-							let dispatch_origin = Origin::Response(*origin).into();
+							let dispatch_origin = Origin::Response(origin).into();
 							match call.dispatch(dispatch_origin) {
 								Ok(post_info) => {
-									let e = Event::Notified(query_id, pallet_index, call_index);
+									let e = Event::Notified { query_id, pallet_index, call_index };
 									Self::deposit_event(e);
 									post_info.actual_weight
 								},
 								Err(error_and_info) => {
-									let e = Event::NotifyDispatchError(
+									let e = Event::NotifyDispatchError {
 										query_id,
 										pallet_index,
 										call_index,
-									);
+									};
 									Self::deposit_event(e);
 									// Not much to do with the result as it is. It's up to the parachain to ensure that the
 									// message makes sense.
@@ -2066,13 +2092,14 @@ impl<T: Config> OnResponse for Pallet<T> {
 							}
 							.unwrap_or(weight)
 						} else {
-							let e = Event::NotifyDecodeFailed(query_id, pallet_index, call_index);
+							let e =
+								Event::NotifyDecodeFailed { query_id, pallet_index, call_index };
 							Self::deposit_event(e);
 							Weight::zero()
 						}
 					},
 					None => {
-						let e = Event::ResponseReady(query_id, response.clone());
+						let e = Event::ResponseReady { query_id, response: response.clone() };
 						Self::deposit_event(e);
 						let at = frame_system::Pallet::<T>::current_block_number();
 						let response = response.into();
@@ -2082,7 +2109,8 @@ impl<T: Config> OnResponse for Pallet<T> {
 				}
 			},
 			_ => {
-				Self::deposit_event(Event::UnexpectedResponse(*origin, query_id));
+				let e = Event::UnexpectedResponse { origin, query_id };
+				Self::deposit_event(e);
 				Weight::zero()
 			},
 		}
@@ -2094,7 +2122,7 @@ impl<T: Config> CheckSuspension for Pallet<T> {
 		_origin: &MultiLocation,
 		_instructions: &mut [Instruction<Call>],
 		_max_weight: Weight,
-		_weight_credit: &mut Weight,
+		_properties: &mut Properties,
 	) -> bool {
 		XcmExecutionSuspended::<T>::get()
 	}

polkadot/xcm/pallet-xcm/src/tests.rs

@@ -27,7 +27,10 @@ use polkadot_parachain::primitives::Id as ParaId;
 use sp_runtime::traits::{AccountIdConversion, BlakeTwo256, Hash};
 use xcm::{latest::QueryResponseInfo, prelude::*};
 use xcm_builder::AllowKnownQueryResponses;
-use xcm_executor::{traits::ShouldExecute, XcmExecutor};
+use xcm_executor::{
+	traits::{Properties, ShouldExecute},
+	XcmExecutor,
+};
 
 const ALICE: AccountId = AccountId::new([0u8; 32]);
 const BOB: AccountId = AccountId::new([1u8; 32]);
@@ -101,7 +104,11 @@ fn report_outcome_notify_works() {
 					0,
 					Response::ExecutionResult(None),
 				)),
-				RuntimeEvent::XcmPallet(crate::Event::Notified(0, 4, 2)),
+				RuntimeEvent::XcmPallet(crate::Event::Notified {
+					query_id: 0,
+					pallet_index: 4,
+					call_index: 2
+				}),
 			]
 		);
 		assert_eq!(crate::Queries::<Test>::iter().collect::<Vec<_>>(), vec![]);
@@ -157,10 +164,10 @@ fn report_outcome_works() {
 		assert_eq!(r, Outcome::Complete(Weight::from_parts(1_000, 1_000)));
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::ResponseReady(
-				0,
-				Response::ExecutionResult(None),
-			))
+			RuntimeEvent::XcmPallet(crate::Event::ResponseReady {
+				query_id: 0,
+				response: Response::ExecutionResult(None),
+			})
 		);
 
 		let response = Some((Response::ExecutionResult(None), 1));
@@ -206,12 +213,12 @@ fn custom_querier_works() {
 		assert_eq!(r, Outcome::Complete(Weight::from_parts(1_000, 1_000)));
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::InvalidQuerier(
-				AccountId32 { network: None, id: ALICE.into() }.into(),
-				0,
-				querier.clone(),
-				None,
-			)),
+			RuntimeEvent::XcmPallet(crate::Event::InvalidQuerier {
+				origin: AccountId32 { network: None, id: ALICE.into() }.into(),
+				query_id: 0,
+				expected_querier: querier.clone(),
+				maybe_actual_querier: None,
+			}),
 		);
 
 		// Supplying the wrong querier will also fail
@@ -232,12 +239,12 @@ fn custom_querier_works() {
 		assert_eq!(r, Outcome::Complete(Weight::from_parts(1_000, 1_000)));
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::InvalidQuerier(
-				AccountId32 { network: None, id: ALICE.into() }.into(),
-				0,
-				querier.clone(),
-				Some(MultiLocation::here()),
-			)),
+			RuntimeEvent::XcmPallet(crate::Event::InvalidQuerier {
+				origin: AccountId32 { network: None, id: ALICE.into() }.into(),
+				query_id: 0,
+				expected_querier: querier.clone(),
+				maybe_actual_querier: Some(MultiLocation::here()),
+			}),
 		);
 
 		// Multiple failures should not have changed the query state
@@ -257,10 +264,10 @@ fn custom_querier_works() {
 		assert_eq!(r, Outcome::Complete(Weight::from_parts(1_000, 1_000)));
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::ResponseReady(
-				0,
-				Response::ExecutionResult(None),
-			))
+			RuntimeEvent::XcmPallet(crate::Event::ResponseReady {
+				query_id: 0,
+				response: Response::ExecutionResult(None),
+			})
 		);
 
 		let response = Some((Response::ExecutionResult(None), 1));
@@ -285,6 +292,7 @@ fn send_works() {
 			buy_execution((Parent, SEND_AMOUNT)),
 			DepositAsset { assets: AllCounted(1).into(), beneficiary: sender.clone() },
 		]);
+
 		let versioned_dest = Box::new(RelayLocation::get().into());
 		let versioned_message = Box::new(VersionedXcm::from(message.clone()));
 		assert_ok!(XcmPallet::send(
@@ -292,19 +300,20 @@ fn send_works() {
 			versioned_dest,
 			versioned_message
 		));
-		assert_eq!(
-			sent_xcm(),
-			vec![(
-				Here.into(),
-				Xcm(Some(DescendOrigin(sender.clone().try_into().unwrap()))
+		let sent_message = Xcm(Some(DescendOrigin(sender.clone().try_into().unwrap()))
 			.into_iter()
 			.chain(message.0.clone().into_iter())
-					.collect())
-			)],
-		);
+			.collect());
+		let id = fake_message_hash(&sent_message);
+		assert_eq!(sent_xcm(), vec![(Here.into(), sent_message)]);
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Sent(sender, RelayLocation::get(), message))
+			RuntimeEvent::XcmPallet(crate::Event::Sent {
+				origin: sender,
+				destination: RelayLocation::get(),
+				message,
+				message_id: id,
+			})
 		);
 	});
 }
@@ -376,7 +385,7 @@ fn teleport_assets_works() {
 		let _check_v2_ok: xcm::v2::Xcm<()> = versioned_sent.try_into().unwrap();
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Complete(weight)))
+			RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome: Outcome::Complete(weight) })
 		);
 	});
 }
@@ -420,7 +429,7 @@ fn limited_teleport_assets_works() {
 		let _check_v2_ok: xcm::v2::Xcm<()> = versioned_sent.try_into().unwrap();
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Complete(weight)))
+			RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome: Outcome::Complete(weight) })
 		);
 	});
 }
@@ -462,7 +471,7 @@ fn unlimited_teleport_assets_works() {
 		);
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Complete(weight)))
+			RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome: Outcome::Complete(weight) })
 		);
 	});
 }
@@ -509,7 +518,7 @@ fn reserve_transfer_assets_works() {
 		let _check_v2_ok: xcm::v2::Xcm<()> = versioned_sent.try_into().unwrap();
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Complete(weight)))
+			RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome: Outcome::Complete(weight) })
 		);
 	});
 }
@@ -557,7 +566,7 @@ fn limited_reserve_transfer_assets_works() {
 		let _check_v2_ok: xcm::v2::Xcm<()> = versioned_sent.try_into().unwrap();
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Complete(weight)))
+			RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome: Outcome::Complete(weight) })
 		);
 	});
 }
@@ -603,7 +612,7 @@ fn unlimited_reserve_transfer_assets_works() {
 		);
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Complete(weight)))
+			RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome: Outcome::Complete(weight) })
 		);
 	});
 }
@@ -635,7 +644,7 @@ fn execute_withdraw_to_deposit_works() {
 		assert_eq!(Balances::total_balance(&BOB), SEND_AMOUNT);
 		assert_eq!(
 			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Complete(weight)))
+			RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome: Outcome::Complete(weight) })
 		);
 	});
 }
@@ -670,10 +679,14 @@ fn trapped_assets_can_be_claimed() {
 		assert_eq!(
 			last_events(2),
 			vec![
-				RuntimeEvent::XcmPallet(crate::Event::AssetsTrapped(hash.clone(), source, vma)),
-				RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Complete(
-					BaseXcmWeight::get() * 5
-				)))
+				RuntimeEvent::XcmPallet(crate::Event::AssetsTrapped {
+					hash: hash.clone(),
+					origin: source,
+					assets: vma
+				}),
+				RuntimeEvent::XcmPallet(crate::Event::Attempted {
+					outcome: Outcome::Complete(BaseXcmWeight::get() * 5)
+				}),
 			]
 		);
 		assert_eq!(Balances::total_balance(&ALICE), INITIAL_BALANCE - SEND_AMOUNT);
@@ -707,13 +720,8 @@ fn trapped_assets_can_be_claimed() {
 			]))),
 			weight
 		));
-		assert_eq!(
-			last_event(),
-			RuntimeEvent::XcmPallet(crate::Event::Attempted(Outcome::Incomplete(
-				BaseXcmWeight::get(),
-				XcmError::UnknownClaim
-			)))
-		);
+		let outcome = Outcome::Incomplete(BaseXcmWeight::get(), XcmError::UnknownClaim);
+		assert_eq!(last_event(), RuntimeEvent::XcmPallet(crate::Event::Attempted { outcome }));
 	});
 }
 
@@ -768,7 +776,7 @@ fn basic_subscription_works() {
 			&remote,
 			message.inner_mut(),
 			weight,
-			&mut Weight::zero(),
+			&mut Properties { weight_credit: Weight::zero(), message_id: None },
 		));
 	});
 }

polkadot/xcm/src/v3/mod.rs

@@ -184,7 +184,7 @@ pub mod prelude {
 			NetworkId::{self, *},
 			OriginKind, Outcome, PalletInfo, Parent, ParentThen, PreparedMessage, QueryId,
 			QueryResponseInfo, Response, Result as XcmResult, SendError, SendResult, SendXcm,
-			Unwrappable,
+			Unwrappable, Weight,
 			WeightLimit::{self, *},
 			WildFungibility::{self, Fungible as WildFungible, NonFungible as WildNonFungible},
 			WildMultiAsset::{self, *},
@@ -337,19 +337,27 @@ impl TryFrom<OldWeightLimit> for WeightLimit {
 /// Contextual data pertaining to a specific list of XCM instructions.
 #[derive(Clone, Eq, PartialEq, Encode, Decode, Debug)]
 pub struct XcmContext {
-	/// The `MultiLocation` origin of the corresponding XCM.
+	/// The current value of the Origin register of the XCVM.
 	pub origin: Option<MultiLocation>,
-	/// The hash of the XCM.
-	pub message_hash: XcmHash,
-	/// The topic of the XCM.
+	/// The identity of the XCM; this may be a hash of its versioned encoding but could also be
+	/// a high-level identity set by an appropriate barrier.
+	pub message_id: XcmHash,
+	/// The current value of the Topic register of the XCVM.
 	pub topic: Option<[u8; 32]>,
 }
 
 impl XcmContext {
-	/// Constructor which sets the message hash to the supplied parameter and leaves the origin and
+	/// Constructor which sets the message ID to the supplied parameter and leaves the origin and
 	/// topic unset.
-	pub fn with_message_hash(message_hash: XcmHash) -> XcmContext {
-		XcmContext { origin: None, message_hash, topic: None }
+	#[deprecated = "Use `with_message_id` instead."]
+	pub fn with_message_hash(message_id: XcmHash) -> XcmContext {
+		XcmContext { origin: None, message_id, topic: None }
+	}
+
+	/// Constructor which sets the message ID to the supplied parameter and leaves the origin and
+	/// topic unset.
+	pub fn with_message_id(message_id: XcmHash) -> XcmContext {
+		XcmContext { origin: None, message_id, topic: None }
 	}
 }
 

polkadot/xcm/src/v3/traits.rs

@@ -212,6 +212,52 @@ impl From<SendError> for Error {
 
 pub type Result = result::Result<(), Error>;
 
+/*
+TODO: XCMv4
+/// Outcome of an XCM execution.
+#[derive(Clone, Encode, Decode, Eq, PartialEq, Debug, TypeInfo)]
+pub enum Outcome {
+	/// Execution completed successfully; given weight was used.
+	Complete { used: Weight },
+	/// Execution started, but did not complete successfully due to the given error; given weight
+	/// was used.
+	Incomplete { used: Weight, error: Error },
+	/// Execution did not start due to the given error.
+	Error { error: Error },
+}
+
+impl Outcome {
+	pub fn ensure_complete(self) -> Result {
+		match self {
+			Outcome::Complete { .. } => Ok(()),
+			Outcome::Incomplete { error, .. } => Err(error),
+			Outcome::Error { error, .. } => Err(error),
+		}
+	}
+	pub fn ensure_execution(self) -> result::Result<Weight, Error> {
+		match self {
+			Outcome::Complete { used, .. } => Ok(used),
+			Outcome::Incomplete { used, .. } => Ok(used),
+			Outcome::Error { error, .. } => Err(error),
+		}
+	}
+	/// How much weight was used by the XCM execution attempt.
+	pub fn weight_used(&self) -> Weight {
+		match self {
+			Outcome::Complete { used, .. } => *used,
+			Outcome::Incomplete { used, .. } => *used,
+			Outcome::Error { .. } => Weight::zero(),
+		}
+	}
+}
+
+impl From<Error> for Outcome {
+	fn from(error: Error) -> Self {
+		Self::Error { error, maybe_id: None }
+	}
+}
+*/
+
 /// Outcome of an XCM execution.
 #[derive(Clone, Encode, Decode, Eq, PartialEq, Debug, TypeInfo)]
 pub enum Outcome {
@@ -259,13 +305,34 @@ pub trait ExecuteXcm<Call> {
 	fn execute(
 		origin: impl Into<MultiLocation>,
 		pre: Self::Prepared,
-		hash: XcmHash,
+		id: &mut XcmHash,
 		weight_credit: Weight,
 	) -> Outcome;
+	fn prepare_and_execute(
+		origin: impl Into<MultiLocation>,
+		message: Xcm<Call>,
+		id: &mut XcmHash,
+		weight_limit: Weight,
+		weight_credit: Weight,
+	) -> Outcome {
+		let pre = match Self::prepare(message) {
+			Ok(x) => x,
+			Err(_) => return Outcome::Error(Error::WeightNotComputable),
+		};
+		let xcm_weight = pre.weight_of();
+		if xcm_weight.any_gt(weight_limit) {
+			return Outcome::Error(Error::WeightLimitReached(xcm_weight))
+		}
+		Self::execute(origin, pre, id, weight_credit)
+	}
 
-	/// Execute some XCM `message` with the message `hash` from `origin` using no more than `weight_limit` weight.
-	/// The weight limit is a basic hard-limit and the implementation may place further restrictions or requirements
-	/// on weight and other aspects.
+	/// Execute some XCM `message` with the message `hash` from `origin` using no more than
+	/// `weight_limit` weight.
+	///
+	/// The weight limit is a basic hard-limit and the implementation may place further
+	/// restrictions or requirements on weight and other aspects.
+	//	TODO: XCMv4
+	//	#[deprecated = "Use `prepare_and_execute` instead"]
 	fn execute_xcm(
 		origin: impl Into<MultiLocation>,
 		message: Xcm<Call>,
@@ -283,14 +350,17 @@ pub trait ExecuteXcm<Call> {
 		Self::execute_xcm_in_credit(origin, message, hash, weight_limit, Weight::zero())
 	}
 
-	/// Execute some XCM `message` with the message `hash` from `origin` using no more than `weight_limit` weight.
+	/// Execute some XCM `message` with the message `hash` from `origin` using no more than
+	/// `weight_limit` weight.
 	///
-	/// Some amount of `weight_credit` may be provided which, depending on the implementation, may allow
-	/// execution without associated payment.
+	/// Some amount of `weight_credit` may be provided which, depending on the implementation, may
+	/// allow execution without associated payment.
+	//	TODO: XCMv4
+	//	#[deprecated = "Use `prepare_and_execute` instead"]
 	fn execute_xcm_in_credit(
 		origin: impl Into<MultiLocation>,
 		message: Xcm<Call>,
-		hash: XcmHash,
+		mut hash: XcmHash,
 		weight_limit: Weight,
 		weight_credit: Weight,
 	) -> Outcome {
@@ -302,7 +372,7 @@ pub trait ExecuteXcm<Call> {
 		if xcm_weight.any_gt(weight_limit) {
 			return Outcome::Error(Error::WeightLimitReached(xcm_weight))
 		}
-		Self::execute(origin, pre, hash, weight_credit)
+		Self::execute(origin, pre, &mut hash, weight_credit)
 	}
 
 	/// Deduct some `fees` to the sovereign account of the given `location` and place them as per
@@ -322,7 +392,12 @@ impl<C> ExecuteXcm<C> for () {
 	fn prepare(message: Xcm<C>) -> result::Result<Self::Prepared, Xcm<C>> {
 		Err(message)
 	}
-	fn execute(_: impl Into<MultiLocation>, _: Self::Prepared, _: XcmHash, _: Weight) -> Outcome {
+	fn execute(
+		_: impl Into<MultiLocation>,
+		_: Self::Prepared,
+		_: &mut XcmHash,
+		_: Weight,
+	) -> Outcome {
 		unreachable!()
 	}
 	fn charge_fees(_location: impl Into<MultiLocation>, _fees: MultiAssets) -> Result {

polkadot/xcm/xcm-builder/src/barriers.rs

@@ -23,16 +23,10 @@ use frame_support::{
 };
 use polkadot_parachain::primitives::IsSystem;
 use sp_std::{cell::Cell, marker::PhantomData, ops::ControlFlow, result::Result};
-use xcm::latest::{
-	Instruction::{self, *},
-	InteriorMultiLocation, Junction, Junctions,
-	Junctions::X1,
-	MultiLocation, Weight,
-	WeightLimit::*,
-};
-use xcm_executor::traits::{CheckSuspension, OnResponse, ShouldExecute};
+use xcm::prelude::*;
+use xcm_executor::traits::{CheckSuspension, OnResponse, Properties, ShouldExecute};
 
-/// Execution barrier that just takes `max_weight` from `weight_credit`.
+/// Execution barrier that just takes `max_weight` from `properties.weight_credit`.
 ///
 /// Useful to allow XCM execution by local chain users via extrinsics.
 /// E.g. `pallet_xcm::reserve_asset_transfer` to transfer a reserve asset
@@ -43,14 +37,15 @@ impl ShouldExecute for TakeWeightCredit {
 		_origin: &MultiLocation,
 		_instructions: &mut [Instruction<RuntimeCall>],
 		max_weight: Weight,
-		weight_credit: &mut Weight,
+		properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
 		log::trace!(
 			target: "xcm::barriers",
-			"TakeWeightCredit origin: {:?}, instructions: {:?}, max_weight: {:?}, weight_credit: {:?}",
-			_origin, _instructions, max_weight, weight_credit,
+			"TakeWeightCredit origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
+			_origin, _instructions, max_weight, properties,
 		);
-		*weight_credit = weight_credit
+		properties.weight_credit = properties
+			.weight_credit
 			.checked_sub(&max_weight)
 			.ok_or(ProcessMessageError::Overweight(max_weight))?;
 		Ok(())
@@ -68,12 +63,12 @@ impl<T: Contains<MultiLocation>> ShouldExecute for AllowTopLevelPaidExecutionFro
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<RuntimeCall>],
 		max_weight: Weight,
-		_weight_credit: &mut Weight,
+		_properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
 		log::trace!(
 			target: "xcm::barriers",
-			"AllowTopLevelPaidExecutionFrom origin: {:?}, instructions: {:?}, max_weight: {:?}, weight_credit: {:?}",
-			origin, instructions, max_weight, _weight_credit,
+			"AllowTopLevelPaidExecutionFrom origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
+			origin, instructions, max_weight, _properties,
 		);
 
 		ensure!(T::contains(origin), ProcessMessageError::Unsupported);
@@ -166,12 +161,12 @@ impl<
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<Call>],
 		max_weight: Weight,
-		weight_credit: &mut Weight,
+		properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
 		log::trace!(
 			target: "xcm::barriers",
-			"WithComputedOrigin origin: {:?}, instructions: {:?}, max_weight: {:?}, weight_credit: {:?}",
-			origin, instructions, max_weight, weight_credit,
+			"WithComputedOrigin origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
+			origin, instructions, max_weight, properties,
 		);
 		let mut actual_origin = *origin;
 		let skipped = Cell::new(0usize);
@@ -205,11 +200,37 @@ impl<
 			&actual_origin,
 			&mut instructions[skipped.get()..],
 			max_weight,
-			weight_credit,
+			properties,
 		)
 	}
 }
 
+/// Sets the message ID to `t` using a `SetTopic(t)` in the last position if present.
+///
+/// Requires some inner barrier to pass on the rest of the message.
+pub struct TrailingSetTopicAsId<InnerBarrier>(PhantomData<InnerBarrier>);
+impl<InnerBarrier: ShouldExecute> ShouldExecute for TrailingSetTopicAsId<InnerBarrier> {
+	fn should_execute<Call>(
+		origin: &MultiLocation,
+		instructions: &mut [Instruction<Call>],
+		max_weight: Weight,
+		properties: &mut Properties,
+	) -> Result<(), ProcessMessageError> {
+		log::trace!(
+			target: "xcm::barriers",
+			"TrailingSetTopicAsId origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
+			origin, instructions, max_weight, properties,
+		);
+		let until = if let Some(SetTopic(t)) = instructions.last() {
+			properties.message_id = Some(*t);
+			instructions.len() - 1
+		} else {
+			instructions.len()
+		};
+		InnerBarrier::should_execute(&origin, &mut instructions[..until], max_weight, properties)
+	}
+}
+
 /// Barrier condition that allows for a `SuspensionChecker` that controls whether or not the XCM
 /// executor will be suspended from executing the given XCM.
 pub struct RespectSuspension<Inner, SuspensionChecker>(PhantomData<(Inner, SuspensionChecker)>);
@@ -222,12 +243,12 @@ where
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<Call>],
 		max_weight: Weight,
-		weight_credit: &mut Weight,
+		properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
-		if SuspensionChecker::is_suspended(origin, instructions, max_weight, weight_credit) {
+		if SuspensionChecker::is_suspended(origin, instructions, max_weight, properties) {
 			Err(ProcessMessageError::Yield)
 		} else {
-			Inner::should_execute(origin, instructions, max_weight, weight_credit)
+			Inner::should_execute(origin, instructions, max_weight, properties)
 		}
 	}
 }
@@ -242,12 +263,12 @@ impl<T: Contains<MultiLocation>> ShouldExecute for AllowUnpaidExecutionFrom<T> {
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<RuntimeCall>],
 		_max_weight: Weight,
-		_weight_credit: &mut Weight,
+		_properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
 		log::trace!(
 			target: "xcm::barriers",
-			"AllowUnpaidExecutionFrom origin: {:?}, instructions: {:?}, max_weight: {:?}, weight_credit: {:?}",
-			origin, instructions, _max_weight, _weight_credit,
+			"AllowUnpaidExecutionFrom origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
+			origin, instructions, _max_weight, _properties,
 		);
 		ensure!(T::contains(origin), ProcessMessageError::Unsupported);
 		Ok(())
@@ -264,12 +285,12 @@ impl<T: Contains<MultiLocation>> ShouldExecute for AllowExplicitUnpaidExecutionF
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<Call>],
 		max_weight: Weight,
-		_weight_credit: &mut Weight,
+		_properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
 		log::trace!(
 			target: "xcm::barriers",
-			"AllowExplicitUnpaidExecutionFrom origin: {:?}, instructions: {:?}, max_weight: {:?}, weight_credit: {:?}",
-			origin, instructions, max_weight, _weight_credit,
+			"AllowExplicitUnpaidExecutionFrom origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
+			origin, instructions, max_weight, _properties,
 		);
 		ensure!(T::contains(origin), ProcessMessageError::Unsupported);
 		instructions.matcher().match_next_inst(|inst| match inst {
@@ -300,12 +321,12 @@ impl<ResponseHandler: OnResponse> ShouldExecute for AllowKnownQueryResponses<Res
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<RuntimeCall>],
 		_max_weight: Weight,
-		_weight_credit: &mut Weight,
+		_properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
 		log::trace!(
 			target: "xcm::barriers",
-			"AllowKnownQueryResponses origin: {:?}, instructions: {:?}, max_weight: {:?}, weight_credit: {:?}",
-			origin, instructions, _max_weight, _weight_credit,
+			"AllowKnownQueryResponses origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
+			origin, instructions, _max_weight, _properties,
 		);
 		instructions
 			.matcher()
@@ -328,12 +349,12 @@ impl<T: Contains<MultiLocation>> ShouldExecute for AllowSubscriptionsFrom<T> {
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<RuntimeCall>],
 		_max_weight: Weight,
-		_weight_credit: &mut Weight,
+		_properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
 		log::trace!(
 			target: "xcm::barriers",
-			"AllowSubscriptionsFrom origin: {:?}, instructions: {:?}, max_weight: {:?}, weight_credit: {:?}",
-			origin, instructions, _max_weight, _weight_credit,
+			"AllowSubscriptionsFrom origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
+			origin, instructions, _max_weight, _properties,
 		);
 		ensure!(T::contains(origin), ProcessMessageError::Unsupported);
 		instructions
@@ -346,3 +367,72 @@ impl<T: Contains<MultiLocation>> ShouldExecute for AllowSubscriptionsFrom<T> {
 		Ok(())
 	}
 }
+
+/// Deny executing the XCM if it matches any of the Deny filter regardless of anything else.
+/// If it passes the Deny, and matches one of the Allow cases then it is let through.
+pub struct DenyThenTry<Deny, Allow>(PhantomData<Deny>, PhantomData<Allow>)
+where
+	Deny: ShouldExecute,
+	Allow: ShouldExecute;
+
+impl<Deny, Allow> ShouldExecute for DenyThenTry<Deny, Allow>
+where
+	Deny: ShouldExecute,
+	Allow: ShouldExecute,
+{
+	fn should_execute<RuntimeCall>(
+		origin: &MultiLocation,
+		message: &mut [Instruction<RuntimeCall>],
+		max_weight: Weight,
+		properties: &mut Properties,
+	) -> Result<(), ProcessMessageError> {
+		Deny::should_execute(origin, message, max_weight, properties)?;
+		Allow::should_execute(origin, message, max_weight, properties)
+	}
+}
+
+// See issue <https://github.com/paritytech/polkadot/issues/5233>
+pub struct DenyReserveTransferToRelayChain;
+impl ShouldExecute for DenyReserveTransferToRelayChain {
+	fn should_execute<RuntimeCall>(
+		origin: &MultiLocation,
+		message: &mut [Instruction<RuntimeCall>],
+		_max_weight: Weight,
+		_properties: &mut Properties,
+	) -> Result<(), ProcessMessageError> {
+		message.matcher().match_next_inst_while(
+			|_| true,
+			|inst| match inst {
+				InitiateReserveWithdraw {
+					reserve: MultiLocation { parents: 1, interior: Here },
+					..
+				} |
+				DepositReserveAsset {
+					dest: MultiLocation { parents: 1, interior: Here }, ..
+				} |
+				TransferReserveAsset {
+					dest: MultiLocation { parents: 1, interior: Here }, ..
+				} => {
+					Err(ProcessMessageError::Unsupported) // Deny
+				},
+
+				// An unexpected reserve transfer has arrived from the Relay Chain. Generally,
+				// `IsReserve` should not allow this, but we just log it here.
+				ReserveAssetDeposited { .. }
+					if matches!(origin, MultiLocation { parents: 1, interior: Here }) =>
+				{
+					log::warn!(
+						target: "xcm::barrier",
+						"Unexpected ReserveAssetDeposited from the Relay Chain",
+					);
+					Ok(ControlFlow::Continue(()))
+				},
+
+				_ => Ok(ControlFlow::Continue(())),
+			},
+		)?;
+
+		// Permit everything else
+		Ok(())
+	}
+}

polkadot/xcm/xcm-builder/src/lib.rs

@@ -50,8 +50,9 @@ pub use asset_conversion::{ConvertedAbstractAssetId, ConvertedConcreteAssetId};
 mod barriers;
 pub use barriers::{
 	AllowExplicitUnpaidExecutionFrom, AllowKnownQueryResponses, AllowSubscriptionsFrom,
-	AllowTopLevelPaidExecutionFrom, AllowUnpaidExecutionFrom, IsChildSystemParachain,
-	RespectSuspension, TakeWeightCredit, WithComputedOrigin,
+	AllowTopLevelPaidExecutionFrom, AllowUnpaidExecutionFrom, DenyReserveTransferToRelayChain,
+	DenyThenTry, IsChildSystemParachain, RespectSuspension, TakeWeightCredit, TrailingSetTopicAsId,
+	WithComputedOrigin,
 };
 
 mod process_xcm_message;
@@ -85,6 +86,9 @@ pub use matcher::{CreateMatcher, MatchXcm, Matcher};
 mod filter_asset_location;
 pub use filter_asset_location::{Case, NativeAsset};
 
+mod routing;
+pub use routing::{WithTopicSource, WithUniqueTopic};
+
 mod universal_exports;
 pub use universal_exports::{
 	ensure_is_remote, BridgeBlobDispatcher, BridgeMessage, DispatchBlob, DispatchBlobError,

polkadot/xcm/xcm-builder/src/process_xcm_message.rs

@@ -53,7 +53,7 @@ impl<
 		let required = pre.weight_of();
 		ensure!(meter.can_accrue(required), ProcessMessageError::Overweight(required));
 
-		let (consumed, result) = match XcmExecutor::execute(origin.into(), pre, *id, Weight::zero())
+		let (consumed, result) = match XcmExecutor::execute(origin.into(), pre, id, Weight::zero())
 		{
 			Outcome::Complete(w) => (w, Ok(true)),
 			Outcome::Incomplete(w, _) => (w, Ok(false)),

polkadot/xcm/xcm-builder/src/routing.rs

@@ -0,0 +1,102 @@
+// Copyright (C) Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Various implementations for `SendXcm`.
+
+use frame_system::unique;
+use parity_scale_codec::Encode;
+use sp_std::{marker::PhantomData, result::Result};
+use xcm::prelude::*;
+
+/// Wrapper router which, if the message does not already end with a `SetTopic` instruction,
+/// appends one to the message filled with a universally unique ID. This ID is returned from a
+/// successful `deliver`.
+///
+/// This is designed to be at the top-level of any routers, since it will always mutate the
+/// passed `message` reference into a `None`. Don't try to combine it within a tuple except as the
+/// last element.
+pub struct WithUniqueTopic<Inner>(PhantomData<Inner>);
+impl<Inner: SendXcm> SendXcm for WithUniqueTopic<Inner> {
+	type Ticket = (Inner::Ticket, [u8; 32]);
+
+	fn validate(
+		destination: &mut Option<MultiLocation>,
+		message: &mut Option<Xcm<()>>,
+	) -> SendResult<Self::Ticket> {
+		let mut message = message.take().ok_or(SendError::MissingArgument)?;
+		let unique_id = if let Some(SetTopic(id)) = message.last() {
+			*id
+		} else {
+			let unique_id = unique(&message);
+			message.0.push(SetTopic(unique_id.clone()));
+			unique_id
+		};
+		let (ticket, assets) = Inner::validate(destination, &mut Some(message))
+			.map_err(|_| SendError::NotApplicable)?;
+		Ok(((ticket, unique_id), assets))
+	}
+
+	fn deliver(ticket: Self::Ticket) -> Result<XcmHash, SendError> {
+		let (ticket, unique_id) = ticket;
+		Inner::deliver(ticket)?;
+		Ok(unique_id)
+	}
+}
+
+pub trait SourceTopic {
+	fn source_topic(entropy: impl Encode) -> XcmHash;
+}
+
+impl SourceTopic for () {
+	fn source_topic(_: impl Encode) -> XcmHash {
+		[0u8; 32]
+	}
+}
+
+/// Wrapper router which, if the message does not already end with a `SetTopic` instruction,
+/// prepends one to the message filled with an ID from `TopicSource`. This ID is returned from a
+/// successful `deliver`.
+///
+/// This is designed to be at the top-level of any routers, since it will always mutate the
+/// passed `message` reference into a `None`. Don't try to combine it within a tuple except as the
+/// last element.
+pub struct WithTopicSource<Inner, TopicSource>(PhantomData<(Inner, TopicSource)>);
+impl<Inner: SendXcm, TopicSource: SourceTopic> SendXcm for WithTopicSource<Inner, TopicSource> {
+	type Ticket = (Inner::Ticket, [u8; 32]);
+
+	fn validate(
+		destination: &mut Option<MultiLocation>,
+		message: &mut Option<Xcm<()>>,
+	) -> SendResult<Self::Ticket> {
+		let mut message = message.take().ok_or(SendError::MissingArgument)?;
+		let unique_id = if let Some(SetTopic(id)) = message.last() {
+			*id
+		} else {
+			let unique_id = TopicSource::source_topic(&message);
+			message.0.push(SetTopic(unique_id.clone()));
+			unique_id
+		};
+		let (ticket, assets) = Inner::validate(destination, &mut Some(message))
+			.map_err(|_| SendError::NotApplicable)?;
+		Ok(((ticket, unique_id), assets))
+	}
+
+	fn deliver(ticket: Self::Ticket) -> Result<XcmHash, SendError> {
+		let (ticket, unique_id) = ticket;
+		Inner::deliver(ticket)?;
+		Ok(unique_id)
+	}
+}

polkadot/xcm/xcm-builder/src/tests/barriers.rs

@@ -14,30 +14,36 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
+use xcm_executor::traits::Properties;
+
 use super::*;
 
+fn props(weight_credit: Weight) -> Properties {
+	Properties { weight_credit, message_id: None }
+}
+
 #[test]
 fn take_weight_credit_barrier_should_work() {
 	let mut message =
 		Xcm::<()>(vec![TransferAsset { assets: (Parent, 100).into(), beneficiary: Here.into() }]);
-	let mut weight_credit = Weight::from_parts(10, 10);
+	let mut properties = props(Weight::from_parts(10, 10));
 	let r = TakeWeightCredit::should_execute(
 		&Parent.into(),
 		message.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut weight_credit,
+		&mut properties,
 	);
 	assert_eq!(r, Ok(()));
-	assert_eq!(weight_credit, Weight::zero());
+	assert_eq!(properties.weight_credit, Weight::zero());
 
 	let r = TakeWeightCredit::should_execute(
 		&Parent.into(),
 		message.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut weight_credit,
+		&mut properties,
 	);
 	assert_eq!(r, Err(ProcessMessageError::Overweight(Weight::from_parts(10, 10))));
-	assert_eq!(weight_credit, Weight::zero());
+	assert_eq!(properties.weight_credit, Weight::zero());
 }
 
 #[test]
@@ -67,7 +73,7 @@ fn computed_origin_should_work() {
 		&Parent.into(),
 		message.inner_mut(),
 		Weight::from_parts(100, 100),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Unsupported));
 
@@ -79,7 +85,7 @@ fn computed_origin_should_work() {
 		&Parent.into(),
 		message.inner_mut(),
 		Weight::from_parts(100, 100),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Unsupported));
 
@@ -91,7 +97,7 @@ fn computed_origin_should_work() {
 		&Parent.into(),
 		message.inner_mut(),
 		Weight::from_parts(100, 100),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Ok(()));
 }
@@ -107,7 +113,7 @@ fn allow_unpaid_should_work() {
 		&Parachain(1).into(),
 		message.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Unsupported));
 
@@ -115,7 +121,7 @@ fn allow_unpaid_should_work() {
 		&Parent.into(),
 		message.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Ok(()));
 }
@@ -147,7 +153,7 @@ fn allow_explicit_unpaid_should_work() {
 		&Parachain(1).into(),
 		good_message.inner_mut(),
 		Weight::from_parts(20, 20),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Unsupported));
 
@@ -155,7 +161,7 @@ fn allow_explicit_unpaid_should_work() {
 		&Parent.into(),
 		bad_message1.inner_mut(),
 		Weight::from_parts(20, 20),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Overweight(Weight::from_parts(20, 20))));
 
@@ -163,7 +169,7 @@ fn allow_explicit_unpaid_should_work() {
 		&Parent.into(),
 		bad_message2.inner_mut(),
 		Weight::from_parts(20, 20),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Overweight(Weight::from_parts(20, 20))));
 
@@ -171,7 +177,7 @@ fn allow_explicit_unpaid_should_work() {
 		&Parent.into(),
 		good_message.inner_mut(),
 		Weight::from_parts(20, 20),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Ok(()));
 
@@ -187,7 +193,7 @@ fn allow_explicit_unpaid_should_work() {
 		&Parent.into(),
 		message_with_different_weight_parts.inner_mut(),
 		Weight::from_parts(20, 20),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Overweight(Weight::from_parts(20, 20))));
 
@@ -195,7 +201,7 @@ fn allow_explicit_unpaid_should_work() {
 		&Parent.into(),
 		message_with_different_weight_parts.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Ok(()));
 }
@@ -211,7 +217,7 @@ fn allow_paid_should_work() {
 		&Parachain(1).into(),
 		message.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Unsupported));
 
@@ -226,7 +232,7 @@ fn allow_paid_should_work() {
 		&Parent.into(),
 		underpaying_message.inner_mut(),
 		Weight::from_parts(30, 30),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Overweight(Weight::from_parts(30, 30))));
 
@@ -241,7 +247,7 @@ fn allow_paid_should_work() {
 		&Parachain(1).into(),
 		paying_message.inner_mut(),
 		Weight::from_parts(30, 30),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Unsupported));
 
@@ -249,7 +255,7 @@ fn allow_paid_should_work() {
 		&Parent.into(),
 		paying_message.inner_mut(),
 		Weight::from_parts(30, 30),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Ok(()));
 
@@ -264,7 +270,7 @@ fn allow_paid_should_work() {
 		&Parent.into(),
 		paying_message_with_different_weight_parts.inner_mut(),
 		Weight::from_parts(20, 20),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Overweight(Weight::from_parts(20, 20))));
 
@@ -272,7 +278,7 @@ fn allow_paid_should_work() {
 		&Parent.into(),
 		paying_message_with_different_weight_parts.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Ok(()))
 }
@@ -288,7 +294,7 @@ fn suspension_should_work() {
 		&Parent.into(),
 		message.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Err(ProcessMessageError::Yield));
 
@@ -299,7 +305,7 @@ fn suspension_should_work() {
 		&Parent.into(),
 		message.inner_mut(),
 		Weight::from_parts(10, 10),
-		&mut Weight::zero(),
+		&mut props(Weight::zero()),
 	);
 	assert_eq!(r, Ok(()));
 }

polkadot/xcm/xcm-builder/src/tests/bridging/local_para_para.rs

@@ -26,7 +26,8 @@ parameter_types! {
 }
 type TheBridge =
 	TestBridge<BridgeBlobDispatcher<TestRemoteIncomingRouter, RemoteUniversalLocation>>;
-type Router = UnpaidLocalExporter<HaulBlobExporter<TheBridge, Remote, Price>, UniversalLocation>;
+type Router =
+	TestTopic<UnpaidLocalExporter<HaulBlobExporter<TheBridge, Remote, Price>, UniversalLocation>>;
 
 /// ```nocompile
 ///  local                                  |                                      remote
@@ -40,6 +41,7 @@ type Router = UnpaidLocalExporter<HaulBlobExporter<TheBridge, Remote, Price>, Un
 /// ```
 #[test]
 fn sending_to_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Parent, Remote::get(), Parachain(1)).into();
 		assert_eq!(send_xcm::<Router>(dest, msg).unwrap().1, (Here, 100).into());
@@ -48,13 +50,17 @@ fn sending_to_bridged_chain_works() {
 			take_received_remote_messages(),
 			vec![(
 				Here.into(),
-			Xcm(vec![
+				xcm_with_topic(
+					[0; 32],
+					vec![
 						UniversalOrigin(Local::get().into()),
 						DescendOrigin(Parachain(1).into()),
 						Trap(1),
-			])
+					]
+				)
 			)]
 		);
+	});
 }
 
 /// ```nocompile
@@ -69,19 +75,24 @@ fn sending_to_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_parachain_of_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Parent, Remote::get(), Parachain(1000)).into();
 		assert_eq!(send_xcm::<Router>(dest, msg).unwrap().1, (Here, 100).into());
 		assert_eq!(TheBridge::service(), 1);
 		let expected = vec![(
 			(Parent, Parachain(1000)).into(),
-		Xcm(vec![
+			xcm_with_topic(
+				[0; 32],
+				vec![
 					UniversalOrigin(Local::get().into()),
 					DescendOrigin(Parachain(1).into()),
 					Trap(1),
-		]),
+				],
+			),
 		)];
 		assert_eq!(take_received_remote_messages(), expected);
+	});
 }
 
 /// ```nocompile
@@ -96,17 +107,22 @@ fn sending_to_parachain_of_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_relay_chain_of_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Parent, Remote::get()).into();
 		assert_eq!(send_xcm::<Router>(dest, msg).unwrap().1, (Here, 100).into());
 		assert_eq!(TheBridge::service(), 1);
 		let expected = vec![(
 			Parent.into(),
-		Xcm(vec![
+			xcm_with_topic(
+				[0; 32],
+				vec![
 					UniversalOrigin(Local::get().into()),
 					DescendOrigin(Parachain(1).into()),
 					Trap(1),
-		]),
+				],
+			),
 		)];
 		assert_eq!(take_received_remote_messages(), expected);
+	});
 }

polkadot/xcm/xcm-builder/src/tests/bridging/local_relay_relay.rs

@@ -26,7 +26,8 @@ parameter_types! {
 }
 type TheBridge =
 	TestBridge<BridgeBlobDispatcher<TestRemoteIncomingRouter, RemoteUniversalLocation>>;
-type Router = UnpaidLocalExporter<HaulBlobExporter<TheBridge, Remote, Price>, UniversalLocation>;
+type Router =
+	TestTopic<UnpaidLocalExporter<HaulBlobExporter<TheBridge, Remote, Price>, UniversalLocation>>;
 
 /// ```nocompile
 ///  local                                  |                                      remote
@@ -36,16 +37,20 @@ type Router = UnpaidLocalExporter<HaulBlobExporter<TheBridge, Remote, Price>, Un
 /// ```
 #[test]
 fn sending_to_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		assert_eq!(
 			send_xcm::<Router>((Parent, Remote::get()).into(), msg).unwrap().1,
 			(Here, 100).into()
 		);
 		assert_eq!(TheBridge::service(), 1);
-	assert_eq!(
-		take_received_remote_messages(),
-		vec![(Here.into(), Xcm(vec![UniversalOrigin(Local::get().into()), Trap(1)]))]
-	);
+		let expected = vec![(
+			Here.into(),
+			xcm_with_topic([0; 32], vec![UniversalOrigin(Local::get().into()), Trap(1)]),
+		)];
+		assert_eq!(take_received_remote_messages(), expected);
+		assert_eq!(RoutingLog::take(), vec![]);
+	});
 }
 
 /// ```nocompile
@@ -60,11 +65,16 @@ fn sending_to_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_parachain_of_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Remote::get(), Parachain(1000)).into();
 		assert_eq!(send_xcm::<Router>(dest, msg).unwrap().1, (Here, 100).into());
 		assert_eq!(TheBridge::service(), 1);
-	let expected =
-		vec![(Parachain(1000).into(), Xcm(vec![UniversalOrigin(Local::get().into()), Trap(1)]))];
+		let expected = vec![(
+			Parachain(1000).into(),
+			xcm_with_topic([0; 32], vec![UniversalOrigin(Local::get().into()), Trap(1)]),
+		)];
 		assert_eq!(take_received_remote_messages(), expected);
+		assert_eq!(RoutingLog::take(), vec![]);
+	});
 }

polkadot/xcm/xcm-builder/src/tests/bridging/mod.rs

@@ -17,7 +17,7 @@
 //! Tests specific to the bridging primitives
 
 use super::mock::*;
-use crate::universal_exports::*;
+use crate::{universal_exports::*, WithTopicSource};
 use frame_support::{parameter_types, traits::Get};
 use std::{cell::RefCell, marker::PhantomData};
 use xcm_executor::{
@@ -37,12 +37,73 @@ parameter_types! {
 	pub Local: NetworkId = ByGenesis([0; 32]);
 	pub Remote: NetworkId = ByGenesis([1; 32]);
 	pub Price: MultiAssets = MultiAssets::from((Here, 100u128));
+	pub static UsingTopic: bool = false;
 }
 
 std::thread_local! {
 	static BRIDGE_TRAFFIC: RefCell<Vec<Vec<u8>>> = RefCell::new(Vec::new());
 }
 
+fn maybe_with_topic(f: impl Fn()) {
+	UsingTopic::set(false);
+	f();
+	UsingTopic::set(true);
+	f();
+}
+
+fn xcm_with_topic<T>(topic: XcmHash, mut xcm: Vec<Instruction<T>>) -> Xcm<T> {
+	if UsingTopic::get() {
+		xcm.push(SetTopic(topic));
+	}
+	Xcm(xcm)
+}
+
+fn fake_id() -> XcmHash {
+	[255; 32]
+}
+
+fn test_weight(mut count: u64) -> Weight {
+	if UsingTopic::get() {
+		count += 1;
+	}
+	Weight::from_parts(count * 10, count * 10)
+}
+
+fn maybe_forward_id_for(topic: &XcmHash) -> XcmHash {
+	match UsingTopic::get() {
+		true => forward_id_for(topic),
+		false => fake_id(),
+	}
+}
+
+enum TestTicket<T: SendXcm> {
+	Basic(T::Ticket),
+	Topic(<WithTopicSource<T, ()> as SendXcm>::Ticket),
+}
+
+struct TestTopic<R>(PhantomData<R>);
+impl<R: SendXcm> SendXcm for TestTopic<R> {
+	type Ticket = TestTicket<R>;
+	fn deliver(ticket: Self::Ticket) -> core::result::Result<XcmHash, SendError> {
+		match ticket {
+			TestTicket::Basic(t) => R::deliver(t),
+			TestTicket::Topic(t) => WithTopicSource::<R, ()>::deliver(t),
+		}
+	}
+	fn validate(
+		destination: &mut Option<MultiLocation>,
+		message: &mut Option<Xcm<()>>,
+	) -> SendResult<Self::Ticket> {
+		Ok(if UsingTopic::get() {
+			let (t, a) = WithTopicSource::<R, ()>::validate(destination, message)?;
+			(TestTicket::Topic(t), a)
+		} else {
+			let (t, a) = R::validate(destination, message)?;
+			(TestTicket::Basic(t), a)
+		})
+	}
+}
+
 struct TestBridge<D>(PhantomData<D>);
 impl<D: DispatchBlob> TestBridge<D> {
 	fn service() -> u64 {
@@ -71,7 +132,7 @@ impl SendXcm for TestRemoteIncomingRouter {
 		Ok((pair, MultiAssets::new()))
 	}
 	fn deliver(pair: (MultiLocation, Xcm<()>)) -> Result<XcmHash, SendError> {
-		let hash = fake_message_hash(&pair.1);
+		let hash = fake_id();
 		REMOTE_INCOMING_XCM.with(|q| q.borrow_mut().push(pair));
 		Ok(hash)
 	}
@@ -107,6 +168,20 @@ fn deliver<RemoteExporter: ExportXcm>(
 	export_xcm::<RemoteExporter>(n, c, s, d, m).map(|(hash, _)| hash)
 }
 
+#[derive(Eq, PartialEq, Clone, Debug)]
+pub struct LogEntry {
+	local: Junctions,
+	remote: Junctions,
+	id: XcmHash,
+	message: Xcm<()>,
+	outcome: Outcome,
+	paid: bool,
+}
+
+parameter_types! {
+	pub static RoutingLog: Vec<LogEntry> = vec![];
+}
+
 impl<Local: Get<Junctions>, Remote: Get<Junctions>, RemoteExporter: ExportXcm> SendXcm
 	for UnpaidExecutingRouter<Local, Remote, RemoteExporter>
 {
@@ -133,15 +208,20 @@ impl<Local: Get<Junctions>, Remote: Get<Junctions>, RemoteExporter: ExportXcm> S
 		AllowUnpaidFrom::set(vec![origin.clone()]);
 		set_exporter_override(price::<RemoteExporter>, deliver::<RemoteExporter>);
 		// The we execute it:
-		let hash = fake_message_hash(&message);
-		let outcome = XcmExecutor::<TestConfig>::execute_xcm(
+		let mut id = fake_id();
+		let outcome = XcmExecutor::<TestConfig>::prepare_and_execute(
 			origin,
-			message.into(),
-			hash,
+			message.clone().into(),
+			&mut id,
 			Weight::from_parts(2_000_000_000_000, 2_000_000_000_000),
+			Weight::zero(),
 		);
+		let local = Local::get();
+		let remote = Remote::get();
+		let entry = LogEntry { local, remote, id, message, outcome: outcome.clone(), paid: false };
+		RoutingLog::mutate(|l| l.push(entry));
 		match outcome {
-			Outcome::Complete(..) => Ok(hash),
+			Outcome::Complete(..) => Ok(id),
 			Outcome::Incomplete(..) => Err(Transport("Error executing")),
 			Outcome::Error(..) => Err(Transport("Unable to execute")),
 		}
@@ -178,15 +258,20 @@ impl<Local: Get<Junctions>, Remote: Get<Junctions>, RemoteExporter: ExportXcm> S
 		AllowPaidFrom::set(vec![origin.clone()]);
 		set_exporter_override(price::<RemoteExporter>, deliver::<RemoteExporter>);
 		// Then we execute it:
-		let hash = fake_message_hash(&message);
-		let outcome = XcmExecutor::<TestConfig>::execute_xcm(
+		let mut id = fake_id();
+		let outcome = XcmExecutor::<TestConfig>::prepare_and_execute(
 			origin,
-			message.into(),
-			hash,
+			message.clone().into(),
+			&mut id,
 			Weight::from_parts(2_000_000_000_000, 2_000_000_000_000),
+			Weight::zero(),
 		);
+		let local = Local::get();
+		let remote = Remote::get();
+		let entry = LogEntry { local, remote, id, message, outcome: outcome.clone(), paid: true };
+		RoutingLog::mutate(|l| l.push(entry));
 		match outcome {
-			Outcome::Complete(..) => Ok(hash),
+			Outcome::Complete(..) => Ok(id),
 			Outcome::Incomplete(..) => Err(Transport("Error executing")),
 			Outcome::Error(..) => Err(Transport("Unable to execute")),
 		}

polkadot/xcm/xcm-builder/src/tests/bridging/paid_remote_relay_relay.rs

@@ -27,8 +27,8 @@ parameter_types! {
 	pub UniversalLocation: Junctions = X2(GlobalConsensus(Local::get()), Parachain(100));
 	pub RelayUniversalLocation: Junctions = X1(GlobalConsensus(Local::get()));
 	pub RemoteUniversalLocation: Junctions = X1(GlobalConsensus(Remote::get()));
-	pub static BridgeTable: Vec<(NetworkId, MultiLocation, Option<MultiAsset>)>
-		= vec![(Remote::get(), MultiLocation::parent(), Some((Parent, 200u128).into()))];
+	pub BridgeTable: Vec<(NetworkId, MultiLocation, Option<MultiAsset>)>
+		= vec![(Remote::get(), MultiLocation::parent(), Some((Parent, 200u128 + if UsingTopic::get() { 20 } else { 0 }).into()))];
 	// ^^^ 100 to use the bridge (export) and 100 for the remote execution weight (5 instructions
 	//     x (10 + 10) weight each).
 }
@@ -41,7 +41,7 @@ type LocalBridgeRouter = SovereignPaidRemoteExporter<
 	LocalInnerRouter,
 	UniversalLocation,
 >;
-type LocalRouter = (LocalInnerRouter, LocalBridgeRouter);
+type LocalRouter = TestTopic<(LocalInnerRouter, LocalBridgeRouter)>;
 
 /// ```nocompile
 ///  local                                  |                                      remote
@@ -55,33 +55,66 @@ type LocalRouter = (LocalInnerRouter, LocalBridgeRouter);
 /// ```
 #[test]
 fn sending_to_bridged_chain_works() {
+	maybe_with_topic(|| {
+		let dest: MultiLocation = (Parent, Parent, Remote::get()).into();
+
+		// Initialize the local relay so that our parachain has funds to pay for export.
+		clear_assets(Parachain(100));
+		add_asset(Parachain(100), (Here, 1000u128));
+
+		let price = 200u128 + if UsingTopic::get() { 20 } else { 0 };
+
+		let msg = Xcm(vec![Trap(1)]);
+		assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, (Parent, price).into());
+		assert_eq!(TheBridge::service(), 1);
+		let expected = vec![(
+			Here.into(),
+			xcm_with_topic(
+				[0; 32],
+				vec![
+					UniversalOrigin(Local::get().into()),
+					DescendOrigin(Parachain(100).into()),
+					Trap(1),
+				],
+			),
+		)];
+		assert_eq!(take_received_remote_messages(), expected);
+
+		// The export cost 50 ref time and 50 proof size weight units (and thus 100 units of balance).
+		assert_eq!(asset_list(Parachain(100)), vec![(Here, 1000u128 - price).into()]);
+
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: RelayUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					WithdrawAsset(MultiAsset::from((Here, price)).into()),
+					BuyExecution { fees: (Here, price).into(), weight_limit: Unlimited },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Here,
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+					RefundSurplus,
+					DepositAsset { assets: Wild(All), beneficiary: Parachain(100).into() },
+				],
+			),
+			outcome: Outcome::Complete(test_weight(5)),
+			paid: true,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
+}
+#[test]
+fn sending_to_bridged_chain_without_funds_fails() {
 	let dest: MultiLocation = (Parent, Parent, Remote::get()).into();
 	// Routing won't work if we don't have enough funds.
 	assert_eq!(
 		send_xcm::<LocalRouter>(dest.clone(), Xcm(vec![Trap(1)])),
 		Err(SendError::Transport("Error executing")),
 	);
-
-	// Initialize the local relay so that our parachain has funds to pay for export.
-	add_asset(Parachain(100), (Here, 1000u128));
-
-	let msg = Xcm(vec![Trap(1)]);
-	assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, (Parent, 200u128).into());
-	assert_eq!(TheBridge::service(), 1);
-	assert_eq!(
-		take_received_remote_messages(),
-		vec![(
-			Here.into(),
-			Xcm(vec![
-				UniversalOrigin(Local::get().into()),
-				DescendOrigin(Parachain(100).into()),
-				Trap(1),
-			])
-		)]
-	);
-
-	// The export cost 50 ref time and 50 proof size weight units (and thus 100 units of balance).
-	assert_eq!(asset_list(Parachain(100)), vec![(Here, 800u128).into()]);
 }
 
 /// ```nocompile
@@ -96,29 +129,64 @@ fn sending_to_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_parachain_of_bridged_chain_works() {
+	maybe_with_topic(|| {
+		let dest: MultiLocation = (Parent, Parent, Remote::get(), Parachain(100)).into();
+
+		// Initialize the local relay so that our parachain has funds to pay for export.
+		clear_assets(Parachain(100));
+		add_asset(Parachain(100), (Here, 1000u128));
+
+		let price = 200u128 + if UsingTopic::get() { 20 } else { 0 };
+
+		let msg = Xcm(vec![Trap(1)]);
+		assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, (Parent, price).into());
+		assert_eq!(TheBridge::service(), 1);
+		let expected = vec![(
+			Parachain(100).into(),
+			xcm_with_topic(
+				[0; 32],
+				vec![
+					UniversalOrigin(Local::get().into()),
+					DescendOrigin(Parachain(100).into()),
+					Trap(1),
+				],
+			),
+		)];
+		assert_eq!(take_received_remote_messages(), expected);
+
+		// The export cost 50 ref time and 50 proof size weight units (and thus 100 units of balance).
+		assert_eq!(asset_list(Parachain(100)), vec![(Here, 1000u128 - price).into()]);
+
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: RelayUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					WithdrawAsset(MultiAsset::from((Here, price)).into()),
+					BuyExecution { fees: (Here, price).into(), weight_limit: Unlimited },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Parachain(100).into(),
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+					RefundSurplus,
+					DepositAsset { assets: Wild(All), beneficiary: Parachain(100).into() },
+				],
+			),
+			outcome: Outcome::Complete(test_weight(5)),
+			paid: true,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
+}
+#[test]
+fn sending_to_parachain_of_bridged_chain_without_funds_fails() {
 	let dest: MultiLocation = (Parent, Parent, Remote::get(), Parachain(100)).into();
 	// Routing won't work if we don't have enough funds.
 	assert_eq!(
 		send_xcm::<LocalRouter>(dest.clone(), Xcm(vec![Trap(1)])),
 		Err(SendError::Transport("Error executing")),
 	);
-
-	// Initialize the local relay so that our parachain has funds to pay for export.
-	add_asset(Parachain(100), (Here, 1000u128));
-
-	let msg = Xcm(vec![Trap(1)]);
-	assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, (Parent, 200u128).into());
-	assert_eq!(TheBridge::service(), 1);
-	let expected = vec![(
-		Parachain(100).into(),
-		Xcm(vec![
-			UniversalOrigin(Local::get().into()),
-			DescendOrigin(Parachain(100).into()),
-			Trap(1),
-		]),
-	)];
-	assert_eq!(take_received_remote_messages(), expected);
-
-	// The export cost 50 ref time and 50 proof size weight units (and thus 100 units of balance).
-	assert_eq!(asset_list(Parachain(100)), vec![(Here, 800u128).into()]);
 }

polkadot/xcm/xcm-builder/src/tests/bridging/remote_para_para.rs

@@ -34,7 +34,7 @@ type LocalInnerRouter =
 	UnpaidExecutingRouter<UniversalLocation, ParaBridgeUniversalLocation, RelayExporter>;
 type LocalBridgingRouter =
 	UnpaidRemoteExporter<NetworkExportTable<BridgeTable>, LocalInnerRouter, UniversalLocation>;
-type LocalRouter = (LocalInnerRouter, LocalBridgingRouter);
+type LocalRouter = TestTopic<(LocalInnerRouter, LocalBridgingRouter)>;
 
 /// ```nocompile
 ///  local                                    |                                      remote
@@ -48,6 +48,7 @@ type LocalRouter = (LocalInnerRouter, LocalBridgingRouter);
 /// ```
 #[test]
 fn sending_to_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		assert_eq!(
 			send_xcm::<LocalRouter>((Parent, Parent, Remote::get(), Parachain(1)).into(), msg)
@@ -60,13 +61,36 @@ fn sending_to_bridged_chain_works() {
 			take_received_remote_messages(),
 			vec![(
 				Here.into(),
-			Xcm(vec![
+				xcm_with_topic(
+					[0; 32],
+					vec![
 						UniversalOrigin(Local::get().into()),
 						DescendOrigin(Parachain(1000).into()),
 						Trap(1)
-			])
+					]
+				)
 			)]
 		);
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: ParaBridgeUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					UnpaidExecution { weight_limit: Unlimited, check_origin: None },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Parachain(1).into(),
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+				],
+			),
+			outcome: Outcome::Complete(test_weight(2)),
+			paid: false,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
 }
 
 /// ```nocompile
@@ -81,19 +105,43 @@ fn sending_to_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_sibling_of_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Parent, Remote::get(), Parachain(1000)).into();
 		assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, MultiAssets::new());
 		assert_eq!(TheBridge::service(), 1);
 		let expected = vec![(
 			(Parent, Parachain(1000)).into(),
-		Xcm(vec![
+			xcm_with_topic(
+				[0; 32],
+				vec![
 					UniversalOrigin(Local::get().into()),
 					DescendOrigin(Parachain(1000).into()),
 					Trap(1),
-		]),
+				],
+			),
 		)];
 		assert_eq!(take_received_remote_messages(), expected);
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: ParaBridgeUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					UnpaidExecution { weight_limit: Unlimited, check_origin: None },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Parachain(1000).into(),
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+				],
+			),
+			outcome: Outcome::Complete(test_weight(2)),
+			paid: false,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
 }
 
 /// ```nocompile
@@ -108,17 +156,41 @@ fn sending_to_sibling_of_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_relay_of_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Parent, Remote::get()).into();
 		assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, MultiAssets::new());
 		assert_eq!(TheBridge::service(), 1);
 		let expected = vec![(
 			Parent.into(),
-		Xcm(vec![
+			xcm_with_topic(
+				[0; 32],
+				vec![
 					UniversalOrigin(Local::get().into()),
 					DescendOrigin(Parachain(1000).into()),
 					Trap(1),
-		]),
+				],
+			),
 		)];
 		assert_eq!(take_received_remote_messages(), expected);
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: ParaBridgeUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					UnpaidExecution { weight_limit: Unlimited, check_origin: None },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Here,
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+				],
+			),
+			outcome: Outcome::Complete(test_weight(2)),
+			paid: false,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
 }

polkadot/xcm/xcm-builder/src/tests/bridging/remote_para_para_via_relay.rs

@@ -34,7 +34,7 @@ type LocalInnerRouter =
 	UnpaidExecutingRouter<UniversalLocation, ParaBridgeUniversalLocation, RelayExporter>;
 type LocalBridgingRouter =
 	UnpaidRemoteExporter<NetworkExportTable<BridgeTable>, LocalInnerRouter, UniversalLocation>;
-type LocalRouter = (LocalInnerRouter, LocalBridgingRouter);
+type LocalRouter = TestTopic<(LocalInnerRouter, LocalBridgingRouter)>;
 
 /// ```nocompile
 ///  local                                    |                                      remote
@@ -48,6 +48,7 @@ type LocalRouter = (LocalInnerRouter, LocalBridgingRouter);
 /// ```
 #[test]
 fn sending_to_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		assert_eq!(
 			send_xcm::<LocalRouter>((Parent, Remote::get(), Parachain(1)).into(), msg)
@@ -56,10 +57,31 @@ fn sending_to_bridged_chain_works() {
 			MultiAssets::new()
 		);
 		assert_eq!(TheBridge::service(), 1);
-	assert_eq!(
-		take_received_remote_messages(),
-		vec![(Here.into(), Xcm(vec![UniversalOrigin(Local::get().into()), Trap(1)]))]
-	);
+		let expected = vec![(
+			Here.into(),
+			xcm_with_topic([0; 32], vec![UniversalOrigin(Local::get().into()), Trap(1)]),
+		)];
+		assert_eq!(take_received_remote_messages(), expected);
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: ParaBridgeUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					UnpaidExecution { weight_limit: Unlimited, check_origin: None },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Parachain(1).into(),
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+				],
+			),
+			outcome: Outcome::Complete(test_weight(2)),
+			paid: false,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
 }
 
 /// ```nocompile
@@ -74,15 +96,36 @@ fn sending_to_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_sibling_of_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Remote::get(), Parachain(1000)).into();
 		assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, MultiAssets::new());
 		assert_eq!(TheBridge::service(), 1);
 		let expected = vec![(
 			(Parent, Parachain(1000)).into(),
-		Xcm(vec![UniversalOrigin(Local::get().into()), Trap(1)]),
+			xcm_with_topic([0; 32], vec![UniversalOrigin(Local::get().into()), Trap(1)]),
 		)];
 		assert_eq!(take_received_remote_messages(), expected);
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: ParaBridgeUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					UnpaidExecution { weight_limit: Unlimited, check_origin: None },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Parachain(1000).into(),
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+				],
+			),
+			outcome: Outcome::Complete(test_weight(2)),
+			paid: false,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
 }
 
 /// ```nocompile
@@ -97,10 +140,34 @@ fn sending_to_sibling_of_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_relay_of_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Remote::get()).into();
 		assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, MultiAssets::new());
 		assert_eq!(TheBridge::service(), 1);
-	let expected = vec![(Parent.into(), Xcm(vec![UniversalOrigin(Local::get().into()), Trap(1)]))];
+		let expected = vec![(
+			Parent.into(),
+			xcm_with_topic([0; 32], vec![UniversalOrigin(Local::get().into()), Trap(1)]),
+		)];
 		assert_eq!(take_received_remote_messages(), expected);
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: ParaBridgeUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					UnpaidExecution { weight_limit: Unlimited, check_origin: None },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Here,
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+				],
+			),
+			outcome: Outcome::Complete(test_weight(2)),
+			paid: false,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
 }

polkadot/xcm/xcm-builder/src/tests/bridging/remote_relay_relay.rs

@@ -34,7 +34,7 @@ type LocalInnerRouter =
 	UnpaidExecutingRouter<UniversalLocation, RelayUniversalLocation, RelayExporter>;
 type LocalBridgeRouter =
 	UnpaidRemoteExporter<NetworkExportTable<BridgeTable>, LocalInnerRouter, UniversalLocation>;
-type LocalRouter = (LocalInnerRouter, LocalBridgeRouter);
+type LocalRouter = TestTopic<(LocalInnerRouter, LocalBridgeRouter)>;
 
 /// ```nocompile
 ///  local                                  |                                      remote
@@ -48,6 +48,7 @@ type LocalRouter = (LocalInnerRouter, LocalBridgeRouter);
 /// ```
 #[test]
 fn sending_to_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		assert_eq!(
 			send_xcm::<LocalRouter>((Parent, Parent, Remote::get()).into(), msg).unwrap().1,
@@ -58,13 +59,36 @@ fn sending_to_bridged_chain_works() {
 			take_received_remote_messages(),
 			vec![(
 				Here.into(),
-			Xcm(vec![
+				xcm_with_topic(
+					[0; 32],
+					vec![
 						UniversalOrigin(Local::get().into()),
 						DescendOrigin(Parachain(1000).into()),
 						Trap(1)
-			])
+					]
+				)
 			)]
 		);
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: RelayUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					UnpaidExecution { weight_limit: Unlimited, check_origin: None },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Here,
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+				],
+			),
+			outcome: Outcome::Complete(test_weight(2)),
+			paid: false,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	});
 }
 
 /// ```nocompile
@@ -79,17 +103,41 @@ fn sending_to_bridged_chain_works() {
 /// ```
 #[test]
 fn sending_to_parachain_of_bridged_chain_works() {
+	maybe_with_topic(|| {
 		let msg = Xcm(vec![Trap(1)]);
 		let dest = (Parent, Parent, Remote::get(), Parachain(1000)).into();
 		assert_eq!(send_xcm::<LocalRouter>(dest, msg).unwrap().1, MultiAssets::new());
 		assert_eq!(TheBridge::service(), 1);
 		let expected = vec![(
 			Parachain(1000).into(),
-		Xcm(vec![
+			xcm_with_topic(
+				[0; 32],
+				vec![
 					UniversalOrigin(Local::get().into()),
 					DescendOrigin(Parachain(1000).into()),
 					Trap(1),
-		]),
+				],
+			),
 		)];
 		assert_eq!(take_received_remote_messages(), expected);
+		let entry = LogEntry {
+			local: UniversalLocation::get(),
+			remote: RelayUniversalLocation::get(),
+			id: maybe_forward_id_for(&[0; 32]),
+			message: xcm_with_topic(
+				maybe_forward_id_for(&[0; 32]),
+				vec![
+					UnpaidExecution { weight_limit: Unlimited, check_origin: None },
+					ExportMessage {
+						network: ByGenesis([1; 32]),
+						destination: Parachain(1000).into(),
+						xcm: xcm_with_topic([0; 32], vec![Trap(1)]),
+					},
+				],
+			),
+			outcome: Outcome::Complete(test_weight(2)),
+			paid: false,
+		};
+		assert_eq!(RoutingLog::take(), vec![entry]);
+	})
 }

polkadot/xcm/xcm-builder/src/tests/mock.rs

@@ -15,7 +15,7 @@
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
 use crate::{
-	barriers::{AllowSubscriptionsFrom, RespectSuspension},
+	barriers::{AllowSubscriptionsFrom, RespectSuspension, TrailingSetTopicAsId},
 	test_utils::*,
 };
 pub use crate::{
@@ -41,6 +41,7 @@ pub use sp_std::{
 	marker::PhantomData,
 };
 pub use xcm::latest::{prelude::*, Weight};
+use xcm_executor::traits::Properties;
 pub use xcm_executor::{
 	traits::{
 		AssetExchange, AssetLock, CheckSuspension, ConvertOrigin, Enact, ExportXcm, FeeManager,
@@ -241,6 +242,9 @@ pub fn asset_list(who: impl Into<MultiLocation>) -> Vec<MultiAsset> {
 pub fn add_asset(who: impl Into<MultiLocation>, what: impl Into<MultiAsset>) {
 	ASSETS.with(|a| a.borrow_mut().entry(who.into()).or_insert(Assets::new()).subsume(what.into()));
 }
+pub fn clear_assets(who: impl Into<MultiLocation>) {
+	ASSETS.with(|a| a.borrow_mut().remove(&who.into()));
+}
 
 pub struct TestAssetTransactor;
 impl TransactAsset for TestAssetTransactor {
@@ -429,7 +433,7 @@ impl CheckSuspension for TestSuspender {
 		_origin: &MultiLocation,
 		_instructions: &mut [Instruction<Call>],
 		_max_weight: Weight,
-		_weight_credit: &mut Weight,
+		_properties: &mut Properties,
 	) -> bool {
 		SUSPENDED.with(|s| s.get())
 	}
@@ -651,7 +655,7 @@ impl Config for TestConfig {
 	type IsReserve = TestIsReserve;
 	type IsTeleporter = TestIsTeleporter;
 	type UniversalLocation = ExecutorUniversalLocation;
-	type Barrier = RespectSuspension<TestBarrier, TestSuspender>;
+	type Barrier = TrailingSetTopicAsId<RespectSuspension<TestBarrier, TestSuspender>>;
 	type Weigher = FixedWeightBounds<UnitWeightCost, TestCall, MaxInstructions>;
 	type Trader = FixedRateOfFungible<WeightPrice, ()>;
 	type ResponseHandler = TestResponseHandler;

polkadot/xcm/xcm-builder/src/universal_exports.rs

@@ -130,6 +130,10 @@ impl<T: Get<Vec<(NetworkId, MultiLocation, Option<MultiAsset>)>>> ExporterFor
 	}
 }
 
+pub fn forward_id_for(original_id: &XcmHash) -> XcmHash {
+	(b"forward_id_for", original_id).using_encoded(sp_io::hashing::blake2_256)
+}
+
 /// Implementation of `SendXcm` which wraps the message inside an `ExportMessage` instruction
 /// and sends it to a destination known to be able to handle it.
 ///
@@ -139,6 +143,16 @@ impl<T: Get<Vec<(NetworkId, MultiLocation, Option<MultiAsset>)>>> ExporterFor
 ///
 /// This is only useful if we have special dispensation by the remote bridges to have the
 /// `ExportMessage` instruction executed without payment.
+///
+/// The `XcmHash` value returned by `deliver` will always be the same as that returned by the
+/// message exporter (`Bridges`). Generally this should take notice of the message should it
+/// end with the `SetTopic` instruction.
+///
+/// In the case that the message ends with a `SetTopic(T)` (as should be the case if the top-level
+/// router is `EnsureUniqueTopic`), then the forwarding message (i.e. the one carrying the
+/// export instruction *to* the bridge in local consensus) will also end with a `SetTopic` whose
+/// inner is `forward_id_for(T)`. If this is not the case then the onward message will not be given
+/// the `SetTopic` afterword.
 pub struct UnpaidRemoteExporter<Bridges, Router, UniversalLocation>(
 	PhantomData<(Bridges, Router, UniversalLocation)>,
 );
@@ -155,21 +169,32 @@ impl<Bridges: ExporterFor, Router: SendXcm, UniversalLocation: Get<InteriorMulti
 		let devolved = ensure_is_remote(UniversalLocation::get(), d).map_err(|_| NotApplicable)?;
 		let (remote_network, remote_location) = devolved;
 		let xcm = xcm.take().ok_or(MissingArgument)?;
+
 		let (bridge, maybe_payment) =
 			Bridges::exporter_for(&remote_network, &remote_location, &xcm).ok_or(NotApplicable)?;
 		ensure!(maybe_payment.is_none(), Unroutable);
 
+		// `xcm` should already end with `SetTopic` - if it does, then extract and derive into
+		// an onward topic ID.
+		let maybe_forward_id = match xcm.last() {
+			Some(SetTopic(t)) => Some(forward_id_for(t)),
+			_ => None,
+		};
+
 		// We then send a normal message to the bridge asking it to export the prepended
 		// message to the remote chain. This will only work if the bridge will do the message
 		// export for free. Common-good chains will typically be afforded this.
-		let message = Xcm(vec![
+		let mut message = Xcm(vec![
 			UnpaidExecution { weight_limit: Unlimited, check_origin: None },
 			ExportMessage { network: remote_network, destination: remote_location, xcm },
 		]);
+		if let Some(forward_id) = maybe_forward_id {
+			message.0.push(SetTopic(forward_id));
+		}
 		validate_send::<Router>(bridge, message)
 	}
 
-	fn deliver(validation: Router::Ticket) -> Result<XcmHash, SendError> {
+	fn deliver(validation: Self::Ticket) -> Result<XcmHash, SendError> {
 		Router::deliver(validation)
 	}
 }
@@ -179,6 +204,16 @@ impl<Bridges: ExporterFor, Router: SendXcm, UniversalLocation: Get<InteriorMulti
 ///
 /// The `ExportMessage` instruction on the bridge is paid for from the local chain's sovereign
 /// account on the bridge. The amount paid is determined through the `ExporterFor` trait.
+///
+/// The `XcmHash` value returned by `deliver` will always be the same as that returned by the
+/// message exporter (`Bridges`). Generally this should take notice of the message should it
+/// end with the `SetTopic` instruction.
+///
+/// In the case that the message ends with a `SetTopic(T)` (as should be the case if the top-level
+/// router is `EnsureUniqueTopic`), then the forwarding message (i.e. the one carrying the
+/// export instruction *to* the bridge in local consensus) will also end with a `SetTopic` whose
+/// inner is `forward_id_for(T)`. If this is not the case then the onward message will not be given
+/// the `SetTopic` afterword.
 pub struct SovereignPaidRemoteExporter<Bridges, Router, UniversalLocation>(
 	PhantomData<(Bridges, Router, UniversalLocation)>,
 );
@@ -196,6 +231,14 @@ impl<Bridges: ExporterFor, Router: SendXcm, UniversalLocation: Get<InteriorMulti
 		let (remote_network, remote_location) = devolved;
 
 		let xcm = xcm.take().ok_or(MissingArgument)?;
+
+		// `xcm` should already end with `SetTopic` - if it does, then extract and derive into
+		// an onward topic ID.
+		let maybe_forward_id = match xcm.last() {
+			Some(SetTopic(t)) => Some(forward_id_for(t)),
+			_ => None,
+		};
+
 		let (bridge, maybe_payment) =
 			Bridges::exporter_for(&remote_network, &remote_location, &xcm).ok_or(NotApplicable)?;
 
@@ -204,7 +247,7 @@ impl<Bridges: ExporterFor, Router: SendXcm, UniversalLocation: Get<InteriorMulti
 		let export_instruction =
 			ExportMessage { network: remote_network, destination: remote_location, xcm };
 
-		let message = Xcm(if let Some(ref payment) = maybe_payment {
+		let mut message = Xcm(if let Some(ref payment) = maybe_payment {
 			let fees = payment
 				.clone()
 				.reanchored(&bridge, UniversalLocation::get())
@@ -219,6 +262,9 @@ impl<Bridges: ExporterFor, Router: SendXcm, UniversalLocation: Get<InteriorMulti
 		} else {
 			vec![export_instruction]
 		});
+		if let Some(forward_id) = maybe_forward_id {
+			message.0.push(SetTopic(forward_id));
+		}
 
 		// We then send a normal message to the bridge asking it to export the prepended
 		// message to the remote chain.
@@ -344,22 +390,24 @@ impl<Bridge: HaulBlob, BridgedNetwork: Get<NetworkId>, Price: Get<MultiAssets>>
 			.ok_or(SendError::MissingArgument)?
 			.split_global()
 			.map_err(|()| SendError::Unroutable)?;
-		let mut inner: Xcm<()> = vec![UniversalOrigin(GlobalConsensus(local_net))].into();
+		let mut message = message.take().ok_or(SendError::MissingArgument)?;
+		let maybe_id = match message.last() {
+			Some(SetTopic(t)) => Some(*t),
+			_ => None,
+		};
+		message.0.insert(0, UniversalOrigin(GlobalConsensus(local_net)));
 		if local_sub != Here {
-			inner.inner_mut().push(DescendOrigin(local_sub));
+			message.0.insert(1, DescendOrigin(local_sub));
 		}
-		inner
-			.inner_mut()
-			.extend(message.take().ok_or(SendError::MissingArgument)?.into_iter());
-		let message = VersionedXcm::from(inner);
-		let hash = message.using_encoded(sp_io::hashing::blake2_256);
+		let message = VersionedXcm::from(message);
+		let id = maybe_id.unwrap_or_else(|| message.using_encoded(sp_io::hashing::blake2_256));
 		let blob = BridgeMessage { universal_dest, message }.encode();
-		Ok(((blob, hash), Price::get()))
+		Ok(((blob, id), Price::get()))
 	}
 
-	fn deliver((blob, hash): (Vec<u8>, XcmHash)) -> Result<XcmHash, SendError> {
+	fn deliver((blob, id): (Vec<u8>, XcmHash)) -> Result<XcmHash, SendError> {
 		Bridge::haul_blob(blob)?;
-		Ok(hash)
+		Ok(id)
 	}
 }
 

polkadot/xcm/xcm-builder/tests/scenarios.rs

@@ -16,7 +16,6 @@
 
 mod mock;
 
-use frame_support::weights::Weight;
 use mock::{
 	fake_message_hash, kusama_like_with_balances, AccountId, Balance, Balances, BaseXcmWeight,
 	System, XcmConfig, CENTS,

polkadot/xcm/xcm-executor/integration-tests/src/lib.rs

@@ -65,9 +65,9 @@ fn basic_buy_fees_message_executes() {
 	client.state_at(block_hash).expect("state should exist").inspect_state(|| {
 		assert!(polkadot_test_runtime::System::events().iter().any(|r| matches!(
 			r.event,
-			polkadot_test_runtime::RuntimeEvent::Xcm(pallet_xcm::Event::Attempted(
-				Outcome::Complete(_)
-			)),
+			polkadot_test_runtime::RuntimeEvent::Xcm(pallet_xcm::Event::Attempted {
+				outcome: Outcome::Complete(_)
+			}),
 		)));
 	});
 }
@@ -118,9 +118,9 @@ fn transact_recursion_limit_works() {
 	client.state_at(block_hash).expect("state should exist").inspect_state(|| {
 		assert!(polkadot_test_runtime::System::events().iter().any(|r| matches!(
 			r.event,
-			polkadot_test_runtime::RuntimeEvent::Xcm(pallet_xcm::Event::Attempted(
-				Outcome::Incomplete(_, XcmError::ExceedsStackLimit)
-			)),
+			polkadot_test_runtime::RuntimeEvent::Xcm(pallet_xcm::Event::Attempted {
+				outcome: Outcome::Incomplete(_, XcmError::ExceedsStackLimit)
+			}),
 		)));
 	});
 }
@@ -195,10 +195,10 @@ fn query_response_fires() {
 	client.state_at(block_hash).expect("state should exist").inspect_state(|| {
 		assert!(polkadot_test_runtime::System::events().iter().any(|r| matches!(
 			r.event,
-			polkadot_test_runtime::RuntimeEvent::Xcm(pallet_xcm::Event::ResponseReady(
-				q,
-				Response::ExecutionResult(None),
-			)) if q == query_id,
+			polkadot_test_runtime::RuntimeEvent::Xcm(pallet_xcm::Event::ResponseReady {
+				query_id: q,
+				response: Response::ExecutionResult(None),
+			}) if q == query_id,
 		)));
 		assert_eq!(
 			polkadot_test_runtime::Xcm::query(query_id),

polkadot/xcm/xcm-executor/src/lib.rs

@@ -31,8 +31,8 @@ use xcm::latest::prelude::*;
 pub mod traits;
 use traits::{
 	validate_export, AssetExchange, AssetLock, CallDispatcher, ClaimAssets, ConvertOrigin,
-	DropAssets, Enact, ExportXcm, FeeManager, FeeReason, OnResponse, ShouldExecute, TransactAsset,
-	VersionChangeNotifier, WeightBounds, WeightTrader,
+	DropAssets, Enact, ExportXcm, FeeManager, FeeReason, OnResponse, Properties, ShouldExecute,
+	TransactAsset, VersionChangeNotifier, WeightBounds, WeightTrader,
 };
 
 mod assets;
@@ -193,8 +193,8 @@ impl<Config: config::Config> ExecuteXcm<Config::RuntimeCall> for XcmExecutor<Con
 	fn execute(
 		origin: impl Into<MultiLocation>,
 		WeighedMessage(xcm_weight, mut message): WeighedMessage<Config::RuntimeCall>,
-		message_hash: XcmHash,
-		mut weight_credit: Weight,
+		id: &mut XcmHash,
+		weight_credit: Weight,
 	) -> Outcome {
 		let origin = origin.into();
 		log::trace!(
@@ -204,24 +204,27 @@ impl<Config: config::Config> ExecuteXcm<Config::RuntimeCall> for XcmExecutor<Con
 			message,
 			weight_credit,
 		);
+		let mut properties = Properties { weight_credit, message_id: None };
 		if let Err(e) = Config::Barrier::should_execute(
 			&origin,
 			message.inner_mut(),
 			xcm_weight,
-			&mut weight_credit,
+			&mut properties,
 		) {
 			log::trace!(
 				target: "xcm::execute_xcm_in_credit",
-				"Barrier blocked execution! Error: {:?}. (origin: {:?}, message: {:?}, weight_credit: {:?})",
+				"Barrier blocked execution! Error: {:?}. (origin: {:?}, message: {:?}, properties: {:?})",
 				e,
 				origin,
 				message,
-				weight_credit,
+				properties,
 			);
 			return Outcome::Error(XcmError::Barrier)
 		}
 
-		let mut vm = Self::new(origin, message_hash);
+		*id = properties.message_id.unwrap_or(*id);
+
+		let mut vm = Self::new(origin, *id);
 
 		while !message.0.is_empty() {
 			let result = vm.process(message);
@@ -272,12 +275,12 @@ impl From<ExecutorError> for frame_benchmarking::BenchmarkError {
 }
 
 impl<Config: config::Config> XcmExecutor<Config> {
-	pub fn new(origin: impl Into<MultiLocation>, message_hash: XcmHash) -> Self {
+	pub fn new(origin: impl Into<MultiLocation>, message_id: XcmHash) -> Self {
 		let origin = origin.into();
 		Self {
 			holding: Assets::new(),
 			holding_limit: Config::MaxAssetsIntoHolding::get() as usize,
-			context: XcmContext { origin: Some(origin), message_hash, topic: None },
+			context: XcmContext { origin: Some(origin), message_id, topic: None },
 			original_origin: origin,
 			trader: Config::Trader::new(),
 			error: None,

polkadot/xcm/xcm-executor/src/traits/mod.rs

@@ -40,7 +40,7 @@ pub use token_matching::{
 mod on_response;
 pub use on_response::{OnResponse, VersionChangeNotifier};
 mod should_execute;
-pub use should_execute::{CheckSuspension, ShouldExecute};
+pub use should_execute::{CheckSuspension, Properties, ShouldExecute};
 mod transact_asset;
 pub use transact_asset::TransactAsset;
 mod weight;

polkadot/xcm/xcm-executor/src/traits/should_execute.rs

@@ -16,7 +16,19 @@
 
 use frame_support::traits::ProcessMessageError;
 use sp_std::result::Result;
-use xcm::latest::{Instruction, MultiLocation, Weight};
+use xcm::latest::{Instruction, MultiLocation, Weight, XcmHash};
+
+/// Properyies of an XCM message and its imminent execution.
+#[derive(Clone, Eq, PartialEq, Debug)]
+pub struct Properties {
+	/// The amount of weight that the system has determined this
+	/// message may utilize in its execution. Typically non-zero only because of prior fee
+	/// payment, but could in principle be due to other factors.
+	pub weight_credit: Weight,
+	/// The identity of the message, if one is known. If left as `None`, then it will generally
+	/// default to the hash of the message which may be non-unique.
+	pub message_id: Option<XcmHash>,
+}
 
 /// Trait to determine whether the execution engine should actually execute a given XCM.
 ///
@@ -28,14 +40,13 @@ pub trait ShouldExecute {
 	/// - `origin`: The origin (sender) of the message.
 	/// - `instructions`: The message itself.
 	/// - `max_weight`: The (possibly over-) estimation of the weight of execution of the message.
-	/// - `weight_credit`: The pre-established amount of weight that the system has determined this
-	///   message may utilize in its execution. Typically non-zero only because of prior fee
-	///   payment, but could in principle be due to other factors.
+	/// - `properties`: Various pre-established properties of the message which may be mutated by
+	///   this API.
 	fn should_execute<RuntimeCall>(
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<RuntimeCall>],
 		max_weight: Weight,
-		weight_credit: &mut Weight,
+		properties: &mut Properties,
 	) -> Result<(), ProcessMessageError>;
 }
 
@@ -45,21 +56,21 @@ impl ShouldExecute for Tuple {
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<RuntimeCall>],
 		max_weight: Weight,
-		weight_credit: &mut Weight,
+		properties: &mut Properties,
 	) -> Result<(), ProcessMessageError> {
 		for_tuples!( #(
-			match Tuple::should_execute(origin, instructions, max_weight, weight_credit) {
+			match Tuple::should_execute(origin, instructions, max_weight, properties) {
 				Ok(()) => return Ok(()),
 				_ => (),
 			}
 		)* );
 		log::trace!(
 			target: "xcm::should_execute",
-			"did not pass barrier: origin: {:?}, instructions: {:?}, max_weight: {:?}, weight_credit: {:?}",
+			"did not pass barrier: origin: {:?}, instructions: {:?}, max_weight: {:?}, properties: {:?}",
 			origin,
 			instructions,
 			max_weight,
-			weight_credit,
+			properties,
 		);
 		Err(ProcessMessageError::Unsupported)
 	}
@@ -79,7 +90,7 @@ pub trait CheckSuspension {
 		origin: &MultiLocation,
 		instructions: &mut [Instruction<Call>],
 		max_weight: Weight,
-		weight_credit: &mut Weight,
+		properties: &mut Properties,
 	) -> bool;
 }
 
@@ -89,10 +100,10 @@ impl CheckSuspension for Tuple {
 		origin: &MultiLocation,
 		instruction: &mut [Instruction<Call>],
 		max_weight: Weight,
-		weight_credit: &mut Weight,
+		properties: &mut Properties,
 	) -> bool {
 		for_tuples!( #(
-			if Tuple::is_suspended(origin, instruction, max_weight, weight_credit) {
+			if Tuple::is_suspended(origin, instruction, max_weight, properties) {
 				return true
 			}
 		)* );

polkadot/xcm/xcm-executor/src/traits/transact_asset.rs

@@ -397,7 +397,7 @@ mod tests {
 			MultiTransactor::deposit_asset(
 				&(Here, 1u128).into(),
 				&Here.into(),
-				&XcmContext::with_message_hash([0; 32]),
+				&XcmContext::with_message_id([0; 32]),
 			),
 			Err(XcmError::AssetNotFound)
 		);
@@ -411,7 +411,7 @@ mod tests {
 			MultiTransactor::deposit_asset(
 				&(Here, 1u128).into(),
 				&Here.into(),
-				&XcmContext::with_message_hash([0; 32]),
+				&XcmContext::with_message_id([0; 32]),
 			),
 			Ok(())
 		);
@@ -425,7 +425,7 @@ mod tests {
 			MultiTransactor::deposit_asset(
 				&(Here, 1u128).into(),
 				&Here.into(),
-				&XcmContext::with_message_hash([0; 32]),
+				&XcmContext::with_message_id([0; 32]),
 			),
 			Err(XcmError::Overflow)
 		);
@@ -439,7 +439,7 @@ mod tests {
 			MultiTransactor::deposit_asset(
 				&(Here, 1u128).into(),
 				&Here.into(),
-				&XcmContext::with_message_hash([0; 32]),
+				&XcmContext::with_message_id([0; 32]),
 			),
 			Ok(()),
 		);