Introduce XcmFeesToAccount fee manager

runtime/kusama/src/xcm_config.rs

@@ -18,7 +18,7 @@
 
 use super::{
 	parachains_origin, AccountId, AllPalletsWithSystem, Balances, Fellows, ParaId, Runtime,
-	RuntimeCall, RuntimeEvent, RuntimeOrigin, StakingAdmin, WeightToFee, XcmPallet,
+	RuntimeCall, RuntimeEvent, RuntimeOrigin, StakingAdmin, Treasury, WeightToFee, XcmPallet,
 };
 use frame_support::{
 	match_types, parameter_types,
@@ -36,7 +36,7 @@ use xcm_builder::{
 	CurrencyAdapter as XcmCurrencyAdapter, FixedWeightBounds, IsChildSystemParachain, IsConcrete,
 	MintLocation, OriginToPluralityVoice, SignedAccountId32AsNative, SignedToAccountId32,
 	SovereignSignedViaLocation, TakeWeightCredit, UsingComponents, WeightInfoBounds,
-	WithComputedOrigin,
+	WithComputedOrigin, XcmFeesToAccount,
 };
 use xcm_executor::traits::WithOriginFilter;
 
@@ -55,6 +55,8 @@ parameter_types! {
 	pub CheckAccount: AccountId = XcmPallet::check_account();
 	/// The check account that is allowed to mint assets locally.
 	pub LocalCheckAccount: (AccountId, MintLocation) = (CheckAccount::get(), MintLocation::Local);
+	/// The treasury account where XCM fees would be sent to.
+	pub TreasuryAccount: Option<AccountId> = Some(Treasury::account_id());
 }
 
 /// The canonical means of converting a `MultiLocation` into an `AccountId`, used when we want to determine
@@ -125,6 +127,9 @@ match_types! {
 	pub type OnlyParachains: impl Contains<MultiLocation> = {
 		MultiLocation { parents: 0, interior: X1(Parachain(_)) }
 	};
+	pub type SystemParachains: impl Contains<MultiLocation> = {
+		MultiLocation { parents: 0, interior: X1(Parachain(1000)) }
+	}
 }
 
 /// The barriers one of which must be passed for an XCM message to be executed.
@@ -335,7 +340,7 @@ impl xcm_executor::Config for XcmConfig {
 	type SubscriptionService = XcmPallet;
 	type PalletInstancesInfo = AllPalletsWithSystem;
 	type MaxAssetsIntoHolding = MaxAssetsIntoHolding;
-	type FeeManager = ();
+	type FeeManager = XcmFeesToAccount<Self, SystemParachains, AccountId, TreasuryAccount>;
 	// No bridges yet...
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;

runtime/polkadot/src/xcm_config.rs

@@ -19,7 +19,7 @@
 use super::{
 	parachains_origin, AccountId, AllPalletsWithSystem, Balances, CouncilCollective,
 	FellowshipAdmin, ParaId, Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin, StakingAdmin,
-	WeightToFee, XcmPallet,
+	Treasury, WeightToFee, XcmPallet,
 };
 use frame_support::{
 	match_types, parameter_types,
@@ -38,7 +38,7 @@ use xcm_builder::{
 	ChildParachainAsNative, ChildParachainConvertsVia, CurrencyAdapter as XcmCurrencyAdapter,
 	FixedWeightBounds, IsConcrete, MintLocation, OriginToPluralityVoice, SignedAccountId32AsNative,
 	SignedToAccountId32, SovereignSignedViaLocation, TakeWeightCredit, UsingComponents,
-	WithComputedOrigin,
+	WithComputedOrigin, XcmFeesToAccount,
 };
 use xcm_executor::traits::WithOriginFilter;
 
@@ -55,6 +55,8 @@ parameter_types! {
 	pub CheckAccount: AccountId = XcmPallet::check_account();
 	/// The Checking Account along with the indication that the local chain is able to mint tokens.
 	pub LocalCheckAccount: (AccountId, MintLocation) = (CheckAccount::get(), MintLocation::Local);
+	/// The treasury account where XCM fees would be sent to.
+	pub TreasuryAccount: Option<AccountId> = Some(Treasury::account_id());
 }
 
 /// The canonical means of converting a `MultiLocation` into an `AccountId`, used when we want to determine
@@ -135,6 +137,9 @@ match_types! {
 		MultiLocation { parents: 0, interior: X1(Parachain(COLLECTIVES_ID)) } |
 		MultiLocation { parents: 0, interior: X2(Parachain(COLLECTIVES_ID), Plurality { id: BodyId::Technical, .. }) }
 	};
+	pub type SystemParachains: impl Contains<MultiLocation> = {
+		MultiLocation { parents: 0, interior: X1(Parachain(STATEMINT_ID | COLLECTIVES_ID)) }
+	}
 }
 
 /// The barriers one of which must be passed for an XCM message to be executed.
@@ -354,7 +359,7 @@ impl xcm_executor::Config for XcmConfig {
 	type SubscriptionService = XcmPallet;
 	type PalletInstancesInfo = AllPalletsWithSystem;
 	type MaxAssetsIntoHolding = MaxAssetsIntoHolding;
-	type FeeManager = ();
+	type FeeManager = XcmFeesToAccount<Self, SystemParachains, AccountId, TreasuryAccount>;
 	// No bridges yet...
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;

runtime/rococo/src/xcm_config.rs

@@ -18,7 +18,7 @@
 
 use super::{
 	parachains_origin, AccountId, AllPalletsWithSystem, Balances, CouncilCollective, ParaId,
-	Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin, WeightToFee, XcmPallet,
+	Runtime, RuntimeCall, RuntimeEvent, RuntimeOrigin, Treasury, WeightToFee, XcmPallet,
 };
 use frame_support::{
 	match_types, parameter_types,
@@ -35,7 +35,7 @@ use xcm_builder::{
 	ChildParachainAsNative, ChildParachainConvertsVia, ChildSystemParachainAsSuperuser,
 	CurrencyAdapter as XcmCurrencyAdapter, FixedWeightBounds, IsChildSystemParachain, IsConcrete,
 	MintLocation, SignedAccountId32AsNative, SignedToAccountId32, SovereignSignedViaLocation,
-	TakeWeightCredit, UsingComponents, WeightInfoBounds, WithComputedOrigin,
+	TakeWeightCredit, UsingComponents, WeightInfoBounds, WithComputedOrigin, XcmFeesToAccount,
 };
 use xcm_executor::{traits::WithOriginFilter, XcmExecutor};
 
@@ -45,6 +45,7 @@ parameter_types! {
 	pub UniversalLocation: InteriorMultiLocation = ThisNetwork::get().into();
 	pub CheckAccount: AccountId = XcmPallet::check_account();
 	pub LocalCheckAccount: (AccountId, MintLocation) = (CheckAccount::get(), MintLocation::Local);
+	pub TreasuryAccount: Option<AccountId> = Some(Treasury::account_id());
 }
 
 pub type LocationConverter =
@@ -120,6 +121,9 @@ match_types! {
 	pub type OnlyParachains: impl Contains<MultiLocation> = {
 		MultiLocation { parents: 0, interior: X1(Parachain(_)) }
 	};
+	pub type SystemParachains: impl Contains<MultiLocation> = {
+		MultiLocation { parents: 0, interior: X1(Parachain(1000 | 1002)) }
+	};
 }
 
 /// The barriers one of which must be passed for an XCM message to be executed.
@@ -313,7 +317,7 @@ impl xcm_executor::Config for XcmConfig {
 	type SubscriptionService = XcmPallet;
 	type PalletInstancesInfo = AllPalletsWithSystem;
 	type MaxAssetsIntoHolding = MaxAssetsIntoHolding;
-	type FeeManager = ();
+	type FeeManager = XcmFeesToAccount<Self, SystemParachains, AccountId, TreasuryAccount>;
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;
 	type CallDispatcher = WithOriginFilter<SafeCallFilter>;

runtime/westend/src/xcm_config.rs

@@ -18,10 +18,10 @@
 
 use super::{
 	parachains_origin, weights, AccountId, AllPalletsWithSystem, Balances, ParaId, Runtime,
-	RuntimeCall, RuntimeEvent, RuntimeOrigin, WeightToFee, XcmPallet,
+	RuntimeCall, RuntimeEvent, RuntimeOrigin, Treasury, WeightToFee, XcmPallet,
 };
 use frame_support::{
-	parameter_types,
+	match_types, parameter_types,
 	traits::{Contains, Everything, Nothing},
 };
 use frame_system::EnsureRoot;
@@ -34,7 +34,7 @@ use xcm_builder::{
 	ChildParachainConvertsVia, ChildSystemParachainAsSuperuser,
 	CurrencyAdapter as XcmCurrencyAdapter, IsChildSystemParachain, IsConcrete, MintLocation,
 	SignedAccountId32AsNative, SignedToAccountId32, SovereignSignedViaLocation, TakeWeightCredit,
-	UsingComponents, WeightInfoBounds, WithComputedOrigin,
+	UsingComponents, WeightInfoBounds, WithComputedOrigin, XcmFeesToAccount,
 };
 use xcm_executor::{traits::WithOriginFilter, XcmExecutor};
 
@@ -44,6 +44,7 @@ parameter_types! {
 	pub UniversalLocation: InteriorMultiLocation = ThisNetwork::get().into();
 	pub CheckAccount: AccountId = XcmPallet::check_account();
 	pub LocalCheckAccount: (AccountId, MintLocation) = (CheckAccount::get(), MintLocation::Local);
+	pub TreasuryAccount: Option<AccountId> = Some(Treasury::account_id());
 }
 
 pub type LocationConverter =
@@ -228,6 +229,12 @@ impl Contains<RuntimeCall> for SafeCallFilter {
 	}
 }
 
+match_types! {
+	pub type SystemParachains: impl Contains<MultiLocation> = {
+		MultiLocation { parents: 0, interior: X1(Parachain(1000 | 1001)) }
+	};
+}
+
 pub struct XcmConfig;
 impl xcm_executor::Config for XcmConfig {
 	type RuntimeCall = RuntimeCall;
@@ -250,7 +257,7 @@ impl xcm_executor::Config for XcmConfig {
 	type SubscriptionService = XcmPallet;
 	type PalletInstancesInfo = AllPalletsWithSystem;
 	type MaxAssetsIntoHolding = MaxAssetsIntoHolding;
-	type FeeManager = ();
+	type FeeManager = XcmFeesToAccount<Self, SystemParachains, AccountId, TreasuryAccount>;
 	type MessageExporter = ();
 	type UniversalAliases = Nothing;
 	type CallDispatcher = WithOriginFilter<SafeCallFilter>;

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

@@ -44,15 +44,7 @@ benchmarks_instance_pallet! {
 		let worst_case_holding = T::worst_case_holding(0);
 		let asset = T::get_multi_asset();
 
-		<AssetTransactorOf<T>>::deposit_asset(
-			&asset,
-			&sender_location,
-			&XcmContext {
-				origin: Some(sender_location.clone()),
-				message_hash: [0; 32],
-				topic: None,
-			},
-		).unwrap();
+		<AssetTransactorOf<T>>::deposit_asset(&asset, &sender_location, &None).unwrap();
 		// check the assets of origin.
 		assert!(!T::TransactAsset::balance(&sender_account).is_zero());
 
@@ -77,15 +69,7 @@ benchmarks_instance_pallet! {
 		let dest_location = T::valid_destination()?;
 		let dest_account = T::AccountIdConverter::convert(dest_location.clone()).unwrap();
 
-		<AssetTransactorOf<T>>::deposit_asset(
-			&asset,
-			&sender_location,
-			&XcmContext {
-				origin: Some(sender_location.clone()),
-				message_hash: [0; 32],
-				topic: None,
-			},
-		).unwrap();
+		<AssetTransactorOf<T>>::deposit_asset(&asset, &sender_location, &None).unwrap();
 		assert!(T::TransactAsset::balance(&dest_account).is_zero());
 
 		let mut executor = new_executor::<T>(sender_location);
@@ -104,15 +88,7 @@ benchmarks_instance_pallet! {
 		let dest_account = T::AccountIdConverter::convert(dest_location.clone()).unwrap();
 
 		let asset = T::get_multi_asset();
-		<AssetTransactorOf<T>>::deposit_asset(
-			&asset,
-			&sender_location,
-			&XcmContext {
-				origin: Some(sender_location.clone()),
-				message_hash: [0; 32],
-				topic: None,
-			},
-		).unwrap();
+		<AssetTransactorOf<T>>::deposit_asset(&asset, &sender_location, &None).unwrap();
 		let assets: MultiAssets = vec![ asset ].into();
 		assert!(T::TransactAsset::balance(&dest_account).is_zero());
 

xcm/pallet-xcm-benchmarks/src/generic/mock.rs

@@ -88,7 +88,11 @@ impl frame_system::Config for Test {
 /// The benchmarks in this pallet should never need an asset transactor to begin with.
 pub struct NoAssetTransactor;
 impl xcm_executor::traits::TransactAsset for NoAssetTransactor {
-	fn deposit_asset(_: &MultiAsset, _: &MultiLocation, _: &XcmContext) -> Result<(), XcmError> {
+	fn deposit_asset(
+		_: &MultiAsset,
+		_: &MultiLocation,
+		_: Option<&XcmContext>,
+	) -> Result<(), XcmError> {
 		unreachable!();
 	}
 

xcm/xcm-builder/src/currency_adapter.rs

@@ -191,7 +191,11 @@ impl<
 		}
 	}
 
-	fn deposit_asset(what: &MultiAsset, who: &MultiLocation, _context: &XcmContext) -> Result {
+	fn deposit_asset(
+		what: &MultiAsset,
+		who: &MultiLocation,
+		_context: Option<&XcmContext>,
+	) -> Result {
 		log::trace!(target: "xcm::currency_adapter", "deposit_asset what: {:?}, who: {:?}", what, who);
 		// Check we handle this asset.
 		let amount = Matcher::matches_fungible(&what).ok_or(Error::AssetNotHandled)?;

xcm/xcm-builder/src/fee_handling.rs

@@ -0,0 +1,51 @@
+// Copyright 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/>.
+
+use core::marker::PhantomData;
+use frame_support::traits::{Contains, Get};
+use xcm::prelude::*;
+use xcm_executor::traits::{FeeManager, FeeReason, TransactAsset};
+
+/// A `FeeManager` implementation that simply deposits the fees handled into a specific on-chain
+/// `ReceiverAccount`.
+///
+/// It reuses the `AssetTransactor` configured on the XCM executor to deposit fee assets, and also
+/// permits specifying `WaivedLocations` for locations that are privileged to not pay for fees.
+pub struct XcmFeesToAccount<XcmConfig, WaivedLocations, AccountId, ReceiverAccount>(
+	PhantomData<(XcmConfig, WaivedLocations, AccountId, ReceiverAccount)>,
+);
+impl<
+		XcmConfig: xcm_executor::Config,
+		WaivedLocations: Contains<MultiLocation>,
+		AccountId: Clone + Into<[u8; 32]>,
+		ReceiverAccount: Get<Option<AccountId>>,
+	> FeeManager for XcmFeesToAccount<XcmConfig, WaivedLocations, AccountId, ReceiverAccount>
+{
+	fn is_waived(origin: Option<&MultiLocation>, _: FeeReason) -> bool {
+		let Some(loc) = origin else { return false };
+		WaivedLocations::contains(loc)
+	}
+
+	fn handle_fee(fees: MultiAssets, context: Option<&XcmContext>) {
+		if let Some(receiver) = ReceiverAccount::get() {
+			let dest = AccountId32 { network: None, id: receiver.into() }.into();
+			for asset in fees.into_inner() {
+				let ok = XcmConfig::AssetTransactor::deposit_asset(&asset, &dest, context).is_ok();
+				debug_assert!(ok, "`deposit_asset` cannot generally fail");
+			}
+		}
+	}
+}

xcm/xcm-builder/src/fungibles_adapter.rs

@@ -274,7 +274,11 @@ impl<
 		}
 	}
 
-	fn deposit_asset(what: &MultiAsset, who: &MultiLocation, _context: &XcmContext) -> XcmResult {
+	fn deposit_asset(
+		what: &MultiAsset,
+		who: &MultiLocation,
+		_context: Option<&XcmContext>,
+	) -> XcmResult {
 		log::trace!(
 			target: "xcm::fungibles_adapter",
 			"deposit_asset what: {:?}, who: {:?}",
@@ -371,7 +375,11 @@ impl<
 		>::check_out(dest, what, context)
 	}
 
-	fn deposit_asset(what: &MultiAsset, who: &MultiLocation, context: &XcmContext) -> XcmResult {
+	fn deposit_asset(
+		what: &MultiAsset,
+		who: &MultiLocation,
+		context: Option<&XcmContext>,
+	) -> XcmResult {
 		FungiblesMutateAdapter::<
 			Assets,
 			Matcher,

xcm/xcm-builder/src/lib.rs

@@ -57,6 +57,9 @@ pub use barriers::{
 mod currency_adapter;
 pub use currency_adapter::CurrencyAdapter;
 
+mod fee_handling;
+pub use fee_handling::XcmFeesToAccount;
+
 mod fungibles_adapter;
 pub use fungibles_adapter::{
 	AssetChecking, DualMint, FungiblesAdapter, FungiblesMutateAdapter, FungiblesTransferAdapter,

xcm/xcm-builder/src/nonfungibles_adapter.rs

@@ -192,7 +192,11 @@ impl<
 		}
 	}
 
-	fn deposit_asset(what: &MultiAsset, who: &MultiLocation, context: &XcmContext) -> XcmResult {
+	fn deposit_asset(
+		what: &MultiAsset,
+		who: &MultiLocation,
+		context: Option<&XcmContext>,
+	) -> XcmResult {
 		log::trace!(
 			target: "xcm::fungibles_adapter",
 			"deposit_asset what: {:?}, who: {:?}, context: {:?}",
@@ -288,7 +292,11 @@ impl<
 		>::check_out(dest, what, context)
 	}
 
-	fn deposit_asset(what: &MultiAsset, who: &MultiLocation, context: &XcmContext) -> XcmResult {
+	fn deposit_asset(
+		what: &MultiAsset,
+		who: &MultiLocation,
+		context: Option<&XcmContext>,
+	) -> XcmResult {
 		NonFungiblesMutateAdapter::<
 			Assets,
 			Matcher,

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

@@ -243,7 +243,7 @@ impl TransactAsset for TestAssetTransactor {
 	fn deposit_asset(
 		what: &MultiAsset,
 		who: &MultiLocation,
-		_context: &XcmContext,
+		_context: Option<&XcmContext>,
 	) -> Result<(), XcmError> {
 		add_asset(who.clone(), what.clone());
 		Ok(())
@@ -441,7 +441,7 @@ impl FeeManager for TestFeeManager {
 	fn is_waived(_: Option<&MultiLocation>, r: FeeReason) -> bool {
 		IS_WAIVED.with(|l| l.borrow().contains(&r))
 	}
-	fn handle_fee(_: MultiAssets) {}
+	fn handle_fee(_: MultiAssets, _: Option<&XcmContext>) {}
 }
 
 #[derive(Clone, Eq, PartialEq, Debug)]