Avoid bad pattern of wildcard fees (#3578)

* Avoid bad pattern of wildcard fees

* spelling

* fmt

* Fix runtimes

* spelling

polkadot/runtime/kusama/src/lib.rs

@@ -1380,6 +1380,7 @@ impl pallet_xcm::Config for Runtime {
 	type XcmTeleportFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type XcmReserveTransferFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type Weigher = FixedWeightBounds<BaseXcmWeight, Call>;
+	type LocationInverter = LocationInverter<Ancestry>;
 }
 
 parameter_types! {

polkadot/runtime/rococo/src/lib.rs

@@ -755,6 +755,7 @@ impl pallet_xcm::Config for Runtime {
 	type XcmTeleportFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type XcmReserveTransferFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type Weigher = FixedWeightBounds<BaseXcmWeight, Call>;
+	type LocationInverter = LocationInverter<Ancestry>;
 }
 
 impl parachains_session_info::Config for Runtime {}

polkadot/runtime/westend/src/lib.rs

@@ -1012,6 +1012,7 @@ impl pallet_xcm::Config for Runtime {
 	type XcmTeleportFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type XcmReserveTransferFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type Weigher = FixedWeightBounds<BaseXcmWeight, Call>;
+	type LocationInverter = LocationInverter<Ancestry>;
 }
 
 construct_runtime! {

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

@@ -38,7 +38,7 @@ pub mod pallet {
 	use frame_support::pallet_prelude::*;
 	use frame_system::pallet_prelude::*;
 	use sp_runtime::traits::AccountIdConversion;
-	use xcm_executor::traits::WeightBounds;
+	use xcm_executor::traits::{InvertLocation, WeightBounds};
 
 	#[pallet::pallet]
 	#[pallet::generate_store(pub(super) trait Store)]
@@ -76,6 +76,9 @@ pub mod pallet {
 
 		/// Means of measuring the weight consumed by an XCM message locally.
 		type Weigher: WeightBounds<Self::Call>;
+
+		/// Means of inverting a location.
+		type LocationInverter: InvertLocation;
 	}
 
 	#[pallet::event]
@@ -93,6 +96,10 @@ pub mod pallet {
 		Filtered,
 		/// The message's weight could not be determined.
 		UnweighableMessage,
+		/// The assets to be sent are empty.
+		Empty,
+		/// Could not reanchor the assets to declare the fees for the destination chain.
+		CannotReanchor,
 	}
 
 	#[pallet::hooks]
@@ -115,6 +122,8 @@ pub mod pallet {
 
 		/// Teleport some assets from the local chain to some destination chain.
 		///
+		/// Fee payment on the destination side is made from the first asset listed in the `assets` vector.
+		///
 		/// - `origin`: Must be capable of withdrawing the `assets` and executing XCM.
 		/// - `dest`: Destination context for the assets. Will typically be `X2(Parent, Parachain(..))` to send
 		///   from parachain to parachain, or `X1(Parachain(..))` to send from relay to parachain.
@@ -146,6 +155,9 @@ pub mod pallet {
 			let value = (origin_location, assets);
 			ensure!(T::XcmTeleportFilter::contains(&value), Error::<T>::Filtered);
 			let (origin_location, assets) = value;
+			let inv_dest = T::LocationInverter::invert_location(&dest);
+			let mut fees = assets.first().ok_or(Error::<T>::Empty)?.clone();
+			fees.reanchor(&inv_dest).map_err(|_| Error::<T>::CannotReanchor)?;
 			let mut message = Xcm::WithdrawAsset {
 				assets,
 				effects: vec![InitiateTeleport {
@@ -153,7 +165,7 @@ pub mod pallet {
 					dest,
 					effects: vec![
 						BuyExecution {
-							fees: All,
+							fees,
 							// Zero weight for additional XCM (since there are none to execute)
 							weight: 0,
 							debt: dest_weight,
@@ -175,6 +187,8 @@ pub mod pallet {
 		/// Transfer some assets from the local chain to the sovereign account of a destination chain and forward
 		/// a notification XCM.
 		///
+		/// Fee payment on the destination side is made from the first asset listed in the `assets` vector.
+		///
 		/// - `origin`: Must be capable of withdrawing the `assets` and executing XCM.
 		/// - `dest`: Destination context for the assets. Will typically be `X2(Parent, Parachain(..))` to send
 		///   from parachain to parachain, or `X1(Parachain(..))` to send from relay to parachain.
@@ -203,12 +217,15 @@ pub mod pallet {
 			let value = (origin_location, assets);
 			ensure!(T::XcmReserveTransferFilter::contains(&value), Error::<T>::Filtered);
 			let (origin_location, assets) = value;
+			let inv_dest = T::LocationInverter::invert_location(&dest);
+			let mut fees = assets.first().ok_or(Error::<T>::Empty)?.clone();
+			fees.reanchor(&inv_dest).map_err(|_| Error::<T>::CannotReanchor)?;
 			let mut message = Xcm::TransferReserveAsset {
 				assets,
 				dest,
 				effects: vec![
 					BuyExecution {
-						fees: All,
+						fees,
 						// Zero weight for additional XCM (since there are none to execute)
 						weight: 0,
 						debt: dest_weight,

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

@@ -186,6 +186,7 @@ impl pallet_xcm::Config for Test {
 	type XcmTeleportFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type XcmReserveTransferFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type Weigher = FixedWeightBounds<BaseXcmWeight, Call>;
+	type LocationInverter = LocationInverter<Ancestry>;
 }
 
 impl origin::Config for Test {}
@@ -194,9 +195,9 @@ pub(crate) fn last_event() -> Event {
 	System::events().pop().expect("Event expected").event
 }
 
-pub(crate) fn buy_execution<C>(debt: Weight) -> Order<C> {
+pub(crate) fn buy_execution<C>(debt: Weight, fees: MultiAsset) -> Order<C> {
 	use xcm::opaque::v0::prelude::*;
-	Order::BuyExecution { fees: All, weight: 0, debt, halt_on_error: false, xcm: vec![] }
+	Order::BuyExecution { fees, weight: 0, debt, halt_on_error: false, xcm: vec![] }
 }
 
 pub(crate) fn new_test_ext_with_balances(

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

@@ -42,7 +42,10 @@ fn send_works() {
 		let message = Xcm::ReserveAssetDeposit {
 			assets: vec![ConcreteFungible { id: Parent.into(), amount: SEND_AMOUNT }],
 			effects: vec![
-				buy_execution(weight),
+				buy_execution(
+					weight,
+					ConcreteFungible { id: MultiLocation::Null, amount: SEND_AMOUNT },
+				),
 				DepositAsset { assets: vec![All], dest: sender.clone() },
 			],
 		};
@@ -76,7 +79,10 @@ fn send_fails_when_xcm_router_blocks() {
 		let message = Xcm::ReserveAssetDeposit {
 			assets: vec![ConcreteFungible { id: Parent.into(), amount: SEND_AMOUNT }],
 			effects: vec![
-				buy_execution(weight),
+				buy_execution(
+					weight,
+					ConcreteFungible { id: MultiLocation::Null, amount: SEND_AMOUNT },
+				),
 				DepositAsset { assets: vec![All], dest: sender.clone() },
 			],
 		};
@@ -157,7 +163,13 @@ fn reserve_transfer_assets_works() {
 				Parachain(PARA_ID).into(),
 				Xcm::ReserveAssetDeposit {
 					assets: vec![ConcreteFungible { id: Parent.into(), amount: SEND_AMOUNT }],
-					effects: vec![buy_execution(weight), DepositAsset { assets: vec![All], dest },]
+					effects: vec![
+						buy_execution(
+							weight,
+							ConcreteFungible { id: Parent.into(), amount: SEND_AMOUNT }
+						),
+						DepositAsset { assets: vec![All], dest },
+					]
 				}
 			)]
 		);
@@ -185,7 +197,13 @@ fn execute_withdraw_to_deposit_works() {
 			Origin::signed(ALICE),
 			Box::new(Xcm::WithdrawAsset {
 				assets: vec![ConcreteFungible { id: MultiLocation::Null, amount: SEND_AMOUNT }],
-				effects: vec![buy_execution(weight), DepositAsset { assets: vec![All], dest }],
+				effects: vec![
+					buy_execution(
+						weight,
+						ConcreteFungible { id: MultiLocation::Null, amount: SEND_AMOUNT }
+					),
+					DepositAsset { assets: vec![All], dest },
+				],
 			}),
 			weight
 		));

polkadot/xcm/xcm-simulator/example/src/parachain.rs

@@ -187,7 +187,7 @@ pub mod mock_msg_queue {
 	#[pallet::generate_deposit(pub(super) fn deposit_event)]
 	pub enum Event<T: Config> {
 		// XCMP
-		/// Some XCM was executed ok.
+		/// Some XCM was executed OK.
 		Success(Option<T::Hash>),
 		/// Some XCM failed.
 		Fail(Option<T::Hash>, XcmError),
@@ -302,6 +302,7 @@ impl pallet_xcm::Config for Runtime {
 	type XcmTeleportFilter = ();
 	type XcmReserveTransferFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type Weigher = FixedWeightBounds<UnitWeightCost, Call>;
+	type LocationInverter = LocationInverter<Ancestry>;
 }
 
 type UncheckedExtrinsic = frame_system::mocking::MockUncheckedExtrinsic<Runtime>;

polkadot/xcm/xcm-simulator/example/src/relay_chain.rs

@@ -148,6 +148,7 @@ impl pallet_xcm::Config for Runtime {
 	type XcmTeleportFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type XcmReserveTransferFilter = All<(MultiLocation, Vec<MultiAsset>)>;
 	type Weigher = FixedWeightBounds<BaseXcmWeight, Call>;
+	type LocationInverter = LocationInverter<Ancestry>;
 }
 
 parameter_types! {