backport #1278

parachains/common/src/xcm_config.rs

@@ -1,5 +1,10 @@
+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;
 
@@ -66,3 +71,39 @@ 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<Runtime, WeightToFee, BalanceConverter>(
+	PhantomData<(Runtime, WeightToFee, BalanceConverter)>,
+);
+impl<CurrencyBalance, Runtime, WeightToFee, BalanceConverter>
+	cumulus_primitives_utility::ChargeWeightInFungibles<
+		AccountIdOf<Runtime>,
+		pallet_assets::Pallet<Runtime>,
+	> for AssetFeeAsExistentialDepositMultiplier<Runtime, WeightToFee, BalanceConverter>
+where
+	Runtime: pallet_assets::Config,
+	WeightToFee: WeightToFeePolynomial<Balance = CurrencyBalance>,
+	BalanceConverter: BalanceConversion<
+		CurrencyBalance,
+		<Runtime as pallet_assets::Config>::AssetId,
+		<Runtime as pallet_assets::Config>::Balance,
+	>,
+	AccountIdOf<Runtime>:
+		From<polkadot_primitives::v2::AccountId> + Into<polkadot_primitives::v2::AccountId>,
+{
+	fn charge_weight_in_fungibles(
+		asset_id: <pallet_assets::Pallet<Runtime> as Inspect<AccountIdOf<Runtime>>>::AssetId,
+		weight: Weight,
+	) -> Result<<pallet_assets::Pallet<Runtime> as Inspect<AccountIdOf<Runtime>>>::Balance, XcmError>
+	{
+		let amount = WeightToFee::weight_to_fee(&weight);
+		// 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 = BalanceConverter::to_asset_balance(amount, asset_id)
+			.map_err(|_| XcmError::TooExpensive)?;
+		Ok(asset_amount)
+	}
+}