Introduce XcmFeesToAccount fee manager

runtime/kusama/constants/src/lib.rs

@@ -97,6 +97,12 @@ pub mod fee {
 	}
 }
 
+/// System Parachains.
+pub mod system_parachain {
+	/// Statemine parachain ID.
+	pub const STATEMINE_ID: u32 = 1000;
+}
+
 #[cfg(test)]
 mod tests {
 	use super::{

runtime/kusama/src/xcm_config.rs

@@ -18,14 +18,15 @@
 
 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,
 	traits::{Contains, Everything, Nothing},
 	weights::Weight,
 };
 use frame_system::EnsureRoot;
+use kusama_runtime_constants::system_parachain::*;
 use runtime_common::{crowdloan, paras_registrar, xcm_sender, ToAuthor};
 use sp_core::ConstU32;
 use xcm::latest::prelude::*;
@@ -36,7 +37,7 @@ 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 +56,8 @@ 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
@@ -112,7 +115,7 @@ pub type XcmRouter = (
 
 parameter_types! {
 	pub const Ksm: MultiAssetFilter = Wild(AllOf { fun: WildFungible, id: Concrete(TokenLocation::get()) });
-	pub const Statemine: MultiLocation = Parachain(1000).into_location();
+	pub const Statemine: MultiLocation = Parachain(STATEMINE_ID).into_location();
 	pub const Encointer: MultiLocation = Parachain(1001).into_location();
 	pub const KsmForStatemine: (MultiAssetFilter, MultiLocation) = (Ksm::get(), Statemine::get());
 	pub const KsmForEncointer: (MultiAssetFilter, MultiLocation) = (Ksm::get(), Encointer::get());
@@ -125,6 +128,9 @@ 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(STATEMINE_ID)) }
+	};
 }
 
 /// The barriers one of which must be passed for an XCM message to be executed.
@@ -335,7 +341,7 @@ 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;
@@ -352,7 +358,7 @@ parameter_types! {
 
 #[cfg(feature = "runtime-benchmarks")]
 parameter_types! {
-	pub ReachableDest: Option<MultiLocation> = Some(Parachain(1000).into());
+	pub ReachableDest: Option<MultiLocation> = Some(Parachain(STATEMINE_ID).into());
 }
 
 /// Type to convert an `Origin` type value into a `MultiLocation` value which represents an interior location

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/constants/src/lib.rs

@@ -99,6 +99,14 @@ pub mod fee {
 	}
 }
 
+/// System Parachains.
+pub mod system_parachain {
+	/// Statemine parachain ID.
+	pub const STATEMINE_ID: u32 = 1000;
+	/// Contracts parachain ID.
+	pub const CONTRACTS_ID: u32 = 1002;
+}
+
 #[cfg(test)]
 mod tests {
 	use super::{

runtime/rococo/src/xcm_config.rs

@@ -18,14 +18,15 @@
 
 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,
 	traits::{Contains, Everything, Nothing},
 	weights::Weight,
 };
 use frame_system::EnsureRoot;
+use rococo_runtime_constants::system_parachain::*;
 use runtime_common::{crowdloan, paras_registrar, xcm_sender, ToAuthor};
 use sp_core::ConstU32;
 use xcm::latest::prelude::*;
@@ -35,7 +36,7 @@ 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 +46,7 @@ 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 =
@@ -92,8 +94,8 @@ pub type XcmRouter = (
 
 parameter_types! {
 	pub const Roc: MultiAssetFilter = Wild(AllOf { fun: WildFungible, id: Concrete(TokenLocation::get()) });
-	pub const Statemine: MultiLocation = Parachain(1000).into_location();
-	pub const Contracts: MultiLocation = Parachain(1002).into_location();
+	pub const Statemine: MultiLocation = Parachain(STATEMINE_ID).into_location();
+	pub const Contracts: MultiLocation = Parachain(CONTRACTS_ID).into_location();
 	pub const Encointer: MultiLocation = Parachain(1003).into_location();
 	pub const Tick: MultiLocation = Parachain(100).into_location();
 	pub const Trick: MultiLocation = Parachain(110).into_location();
@@ -120,6 +122,9 @@ 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(STATEMINE_ID | CONTRACTS_ID)) }
+	};
 }
 
 /// The barriers one of which must be passed for an XCM message to be executed.
@@ -313,7 +318,7 @@ 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>;
@@ -330,7 +335,7 @@ parameter_types! {
 
 #[cfg(feature = "runtime-benchmarks")]
 parameter_types! {
-	pub ReachableDest: Option<MultiLocation> = Some(Parachain(1000).into());
+	pub ReachableDest: Option<MultiLocation> = Some(Parachain(STATEMINE_ID).into());
 }
 
 /// Type to convert the council origin to a Plurality `MultiLocation` value.

runtime/westend/constants/src/lib.rs

@@ -96,6 +96,14 @@ pub mod fee {
 	}
 }
 
+/// System Parachains.
+pub mod system_parachain {
+	/// Westmint parachain ID.
+	pub const WESTMINT_ID: u32 = 1000;
+	/// Collectives parachain ID.
+	pub const COLLECTIVES_ID: u32 = 1001;
+}
+
 #[cfg(test)]
 mod tests {
 	use super::{

runtime/westend/src/xcm_config.rs

@@ -27,6 +27,7 @@ use frame_support::{
 use frame_system::EnsureRoot;
 use runtime_common::{crowdloan, paras_registrar, xcm_sender, ToAuthor};
 use sp_core::ConstU32;
+use westend_runtime_constants::system_parachain::*;
 use xcm::latest::prelude::*;
 use xcm_builder::{
 	AccountId32Aliases, AllowExplicitUnpaidExecutionFrom, AllowKnownQueryResponses,
@@ -77,8 +78,8 @@ pub type XcmRouter = (
 );
 
 parameter_types! {
-	pub const Westmint: MultiLocation = Parachain(1000).into_location();
-	pub const Collectives: MultiLocation = Parachain(1001).into_location();
+	pub const Westmint: MultiLocation = Parachain(WESTMINT_ID).into_location();
+	pub const Collectives: MultiLocation = Parachain(COLLECTIVES_ID).into_location();
 	pub const Wnd: MultiAssetFilter = Wild(AllOf { fun: WildFungible, id: Concrete(TokenLocation::get()) });
 	pub const WndForWestmint: (MultiAssetFilter, MultiLocation) = (Wnd::get(), Westmint::get());
 	pub const WndForCollectives: (MultiAssetFilter, MultiLocation) = (Wnd::get(), Collectives::get());
@@ -88,7 +89,7 @@ parameter_types! {
 
 #[cfg(feature = "runtime-benchmarks")]
 parameter_types! {
-	pub ReachableDest: Option<MultiLocation> = Some(Parachain(1000).into());
+	pub ReachableDest: Option<MultiLocation> = Some(Parachain(WESTMINT_ID).into());
 }
 
 pub type TrustedTeleporters =

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");
+			}
+		}
+	}
+}