Statemint runtimes to accept sufficient assets as xcm fee payment

parachains/common/Cargo.toml

@@ -31,9 +31,11 @@ polkadot-primitives = { git = "https://github.com/paritytech/polkadot", default-
 polkadot-runtime-common = { git = "https://github.com/paritytech/polkadot", default-features = false, branch = "master" }
 xcm = { git = "https://github.com/paritytech/polkadot", default-features = false, branch = "master" }
 xcm-executor = { git = "https://github.com/paritytech/polkadot", default-features = false, branch = "master" }
+xcm-builder = { git = "https://github.com/paritytech/polkadot", default-features = false, branch = "master" }
 
 # Cumulus
 pallet-collator-selection = { path = "../../pallets/collator-selection", default-features = false }
+cumulus-primitives-utility = { path = "../../primitives/utility", default-features = false }
 
 [dev-dependencies]
 pallet-authorship = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
@@ -60,4 +62,6 @@ std = [
 	"sp-io/std",
 	"sp-std/std",
 	"pallet-collator-selection/std",
+	"cumulus-primitives-utility/std",
+	"xcm-builder/std"
 ]

parachains/common/src/xcm_config.rs

@@ -1,7 +1,13 @@
+use crate::impls::AccountIdOf;
 use core::marker::PhantomData;
-use frame_support::{log, weights::Weight};
+use frame_support::{
+	log,
+	traits::{fungibles::Inspect, tokens::BalanceConversion},
+	weights::{Weight, WeightToFee, WeightToFeePolynomial},
+};
 use xcm::latest::prelude::*;
-use xcm_executor::traits::ShouldExecute;
+use xcm_builder::{AsPrefixedGeneralIndex, ConvertedConcreteAssetId};
+use xcm_executor::traits::{JustTry, ShouldExecute};
 
 //TODO: move DenyThenTry to polkadot's xcm module.
 /// Deny executing the XCM if it matches any of the Deny filter regardless of anything else.
@@ -66,3 +72,58 @@ impl ShouldExecute for DenyReserveTransferToRelayChain {
 		Ok(())
 	}
 }
+
+/// A `ChargeFeeInFungibles` implementation that converts the output of
+/// a given WeightToFee implementation an amount charged in
+/// a particular assetId from pallet-assets
+pub struct AssetFeeAsExistentialDepositMultiplier<R, WeightToFee, CON>(
+	PhantomData<(R, WeightToFee, CON)>,
+);
+impl<CurrencyBalance, R, WeightToFee, CON>
+	cumulus_primitives_utility::ChargeWeightInFungibles<AccountIdOf<R>, pallet_assets::Pallet<R>>
+	for AssetFeeAsExistentialDepositMultiplier<R, WeightToFee, CON>
+where
+	R: pallet_assets::Config,
+	WeightToFee: WeightToFeePolynomial<Balance = CurrencyBalance>,
+	CON: BalanceConversion<
+		CurrencyBalance,
+		<R as pallet_assets::Config>::AssetId,
+		<R as pallet_assets::Config>::Balance,
+	>,
+	AccountIdOf<R>:
+		From<polkadot_primitives::v2::AccountId> + Into<polkadot_primitives::v2::AccountId>,
+{
+	fn charge_weight_in_fungibles(
+		asset_id: <pallet_assets::Pallet<R> as Inspect<AccountIdOf<R>>>::AssetId,
+		weight: Weight,
+	) -> Result<<pallet_assets::Pallet<R> as Inspect<AccountIdOf<R>>>::Balance, XcmError> {
+		let amount = WeightToFee::weight_to_fee(&weight);
+		let minimum_balance = pallet_assets::Pallet::<R>::minimum_balance(asset_id);
+		// If the amount gotten is not at least the ED, then make it be the ED of the asset
+		// This is to avoid burning assets and decreasing the supply
+		let asset_amount = CON::to_asset_balance(amount, asset_id)
+			.map_err(|_| XcmError::TooExpensive)
+			.map(|amount| if amount < minimum_balance { minimum_balance } else { amount })?;
+		Ok(asset_amount)
+	}
+}
+
+/// This is the type that will handle the fees
+/// It receives the pallet-asset location for multilocation
+/// and the fees receiver
+pub type XcmAssetFeesHandler<R, AssetsPalletLocation, XcmAssetFeesReceiver> =
+	cumulus_primitives_utility::XcmFeesToAccount<
+		pallet_assets::Pallet<R>,
+		ConvertedConcreteAssetId<
+			<R as pallet_assets::Config>::AssetId,
+			<R as pallet_balances::Config>::Balance,
+			AsPrefixedGeneralIndex<
+				AssetsPalletLocation,
+				<R as pallet_assets::Config>::AssetId,
+				JustTry,
+			>,
+			JustTry,
+		>,
+		<R as frame_system::Config>::AccountId,
+		XcmAssetFeesReceiver,
+	>;

parachains/runtimes/assets/statemine/src/xcm_config.rs

@@ -14,7 +14,7 @@
 // limitations under the License.
 
 use super::{
-	AccountId, AssetId, Assets, Balance, Balances, Call, Event, Origin, ParachainInfo,
+	AccountId, AssetId, Assets, Authorship, Balance, Balances, Call, Event, Origin, ParachainInfo,
 	ParachainSystem, PolkadotXcm, Runtime, WeightToFee, XcmpQueue,
 };
 use frame_support::{
@@ -25,9 +25,12 @@ use frame_support::{
 use pallet_xcm::XcmPassthrough;
 use parachains_common::{
 	impls::ToStakingPot,
-	xcm_config::{DenyReserveTransferToRelayChain, DenyThenTry},
+	xcm_config::{
+		AssetFeeAsExistentialDepositMultiplier, DenyReserveTransferToRelayChain, DenyThenTry,
+	},
 };
 use polkadot_parachain::primitives::Sibling;
+use sp_runtime::traits::ConvertInto;
 use xcm::latest::prelude::*;
 use xcm_builder::{
 	AccountId32Aliases, AllowKnownQueryResponses, AllowSubscriptionsFrom,
@@ -129,6 +132,7 @@ parameter_types! {
 	// One XCM operation is 1_000_000_000 weight - almost certainly a conservative estimate.
 	pub UnitWeightCost: Weight = 1_000_000_000;
 	pub const MaxInstructions: u32 = 100;
+	pub XcmAssetFeesReceiver: Option<AccountId> = Authorship::author();
 }
 
 match_types! {
@@ -170,8 +174,29 @@ impl xcm_executor::Config for XcmConfig {
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;
 	type Weigher = FixedWeightBounds<UnitWeightCost, Call, MaxInstructions>;
-	type Trader =
-		UsingComponents<WeightToFee, KsmLocation, AccountId, Balances, ToStakingPot<Runtime>>;
+	type Trader = (
+		UsingComponents<WeightToFee, KsmLocation, AccountId, Balances, ToStakingPot<Runtime>>,
+		cumulus_primitives_utility::TakeFirstAssetTrader<
+			AccountId,
+			AssetFeeAsExistentialDepositMultiplier<
+				Runtime,
+				WeightToFee,
+				pallet_assets::BalanceToAssetBalance<Balances, Runtime, ConvertInto>,
+			>,
+			ConvertedConcreteAssetId<
+				AssetId,
+				Balance,
+				AsPrefixedGeneralIndex<AssetsPalletLocation, AssetId, JustTry>,
+				JustTry,
+			>,
+			Assets,
+			parachains_common::xcm_config::XcmAssetFeesHandler<
+				Runtime,
+				AssetsPalletLocation,
+				XcmAssetFeesReceiver,
+			>,
+		>,
+	);
 	type ResponseHandler = PolkadotXcm;
 	type AssetTrap = PolkadotXcm;
 	type AssetClaims = PolkadotXcm;