Tx Payment: drop ED requirements for tx payments with exchangeable asset

cumulus/parachains/runtimes/assets/asset-hub-rococo/src/lib.rs

@@ -69,7 +69,7 @@ use frame_system::{
 	limits::{BlockLength, BlockWeights},
 	EnsureRoot, EnsureSigned, EnsureSignedBy,
 };
-use pallet_asset_conversion_tx_payment::AssetConversionAdapter;
+use pallet_asset_conversion_tx_payment::SwapAssetAdapter;
 use pallet_nfts::PalletFeatures;
 use parachains_common::{
 	impls::DealWithFees,
@@ -766,11 +766,20 @@ impl pallet_collator_selection::Config for Runtime {
 	type WeightInfo = weights::pallet_collator_selection::WeightInfo<Runtime>;
 }
 
+parameter_types! {
+	pub StakingPot: AccountId = CollatorSelection::account_id();
+}
+
 impl pallet_asset_conversion_tx_payment::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
-	type Fungibles = LocalAndForeignAssets;
-	type OnChargeAssetTransaction =
-		AssetConversionAdapter<Balances, AssetConversion, TokenLocationV3>;
+	type AssetId = xcm::v3::Location;
+	type OnChargeAssetTransaction = SwapAssetAdapter<
+		TokenLocationV3,
+		NativeAndAssets,
+		AssetConversion,
+		ResolveAssetTo<StakingPot, NativeAndAssets>,
+		ResolveAssetTo<StakingPot, NativeAndAssets>,
+	>;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/assets/asset-hub-westend/src/lib.rs

@@ -52,7 +52,7 @@ use frame_system::{
 	limits::{BlockLength, BlockWeights},
 	EnsureRoot, EnsureSigned, EnsureSignedBy,
 };
-use pallet_asset_conversion_tx_payment::AssetConversionAdapter;
+use pallet_asset_conversion_tx_payment::SwapAssetAdapter;
 use pallet_nfts::{DestroyWitness, PalletFeatures};
 use pallet_xcm::EnsureXcm;
 use parachains_common::{
@@ -758,11 +758,20 @@ impl pallet_collator_selection::Config for Runtime {
 	type WeightInfo = weights::pallet_collator_selection::WeightInfo<Runtime>;
 }
 
+parameter_types! {
+	pub StakingPot: AccountId = CollatorSelection::account_id();
+}
+
 impl pallet_asset_conversion_tx_payment::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
-	type Fungibles = LocalAndForeignAssets;
-	type OnChargeAssetTransaction =
-		AssetConversionAdapter<Balances, AssetConversion, WestendLocationV3>;
+	type AssetId = xcm::v3::Location;
+	type OnChargeAssetTransaction = SwapAssetAdapter<
+		WestendLocationV3,
+		NativeAndAssets,
+		AssetConversion,
+		ResolveAssetTo<StakingPot, NativeAndAssets>,
+		ResolveAssetTo<StakingPot, NativeAndAssets>,
+	>;
 }
 
 parameter_types! {

prdoc/pr_4488.prdoc

@@ -0,0 +1,14 @@
+title: "Tx Payment: drop ED requirements for tx payments with exchangeable asset"
+
+doc:
+  - audience: Runtime Dev
+    description: |
+        Drop the Existential Deposit requirement for the asset amount exchangeable for the fee asset
+        (eg. DOT/KSM) during transaction payments.
+
+        This achieved by using `SwapCredit` implementation of asset conversion, which works with
+        imbalances and does not require a temporary balance account within the transaction payment.
+
+crates:
+  - name: pallet-asset-conversion-tx-payment
+    bump: major

substrate/bin/node/runtime/src/lib.rs

@@ -64,6 +64,7 @@ use frame_system::{
 pub use node_primitives::{AccountId, Signature};
 use node_primitives::{AccountIndex, Balance, BlockNumber, Hash, Moment, Nonce};
 use pallet_asset_conversion::{AccountIdConverter, Ascending, Chain, WithFirstAsset};
+use pallet_asset_conversion_tx_payment::SwapAssetAdapter;
 use pallet_broker::{CoreAssignment, CoreIndex, CoretimeInterface, PartsOf57600};
 use pallet_election_provider_multi_phase::{GeometricDepositBase, SolutionAccuracyOf};
 use pallet_identity::legacy::IdentityInfo;
@@ -119,7 +120,7 @@ pub use sp_runtime::BuildStorage;
 pub mod impls;
 #[cfg(not(feature = "runtime-benchmarks"))]
 use impls::AllianceIdentityVerifier;
-use impls::{AllianceProposalProvider, Author, CreditToBlockAuthor};
+use impls::{AllianceProposalProvider, Author};
 
 /// Constant values used within the runtime.
 pub mod constants;
@@ -570,22 +571,15 @@ impl pallet_transaction_payment::Config for Runtime {
 	>;
 }
 
-impl pallet_asset_tx_payment::Config for Runtime {
-	type RuntimeEvent = RuntimeEvent;
-	type Fungibles = Assets;
-	type OnChargeAssetTransaction = pallet_asset_tx_payment::FungiblesAdapter<
-		pallet_assets::BalanceToAssetBalance<Balances, Runtime, ConvertInto, Instance1>,
-		CreditToBlockAuthor,
-	>;
-}
-
 impl pallet_asset_conversion_tx_payment::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
-	type Fungibles = Assets;
-	type OnChargeAssetTransaction = pallet_asset_conversion_tx_payment::AssetConversionAdapter<
-		Balances,
-		AssetConversion,
+	type AssetId = NativeOrWithId<u32>;
+	type OnChargeAssetTransaction = SwapAssetAdapter<
 		Native,
+		NativeAndAssets,
+		AssetConversion,
+		ResolveAssetTo<TreasuryAccount, NativeAndAssets>,
+		ResolveAssetTo<TreasuryAccount, NativeAndAssets>,
 	>;
 }
 
@@ -1701,12 +1695,15 @@ parameter_types! {
 	pub const Native: NativeOrWithId<u32> = NativeOrWithId::Native;
 }
 
+pub type NativeAndAssets =
+	UnionOf<Balances, Assets, NativeFromLeft, NativeOrWithId<u32>, AccountId>;
+
 impl pallet_asset_conversion::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type Balance = u128;
 	type HigherPrecisionBalance = sp_core::U256;
 	type AssetKind = NativeOrWithId<u32>;
-	type Assets = UnionOf<Balances, Assets, NativeFromLeft, NativeOrWithId<u32>, AccountId>;
+	type Assets = NativeAndAssets;
 	type PoolId = (Self::AssetKind, Self::AssetKind);
 	type PoolLocator = Chain<
 		WithFirstAsset<
@@ -2281,9 +2278,6 @@ mod runtime {
 	#[runtime::pallet_index(7)]
 	pub type TransactionPayment = pallet_transaction_payment;
 
-	#[runtime::pallet_index(8)]
-	pub type AssetTxPayment = pallet_asset_tx_payment;
-
 	#[runtime::pallet_index(9)]
 	pub type AssetConversionTxPayment = pallet_asset_conversion_tx_payment;
 

substrate/frame/asset-conversion/src/swap.rs

@@ -112,6 +112,37 @@ pub trait SwapCredit<AccountId> {
 	) -> Result<(Self::Credit, Self::Credit), (Self::Credit, DispatchError)>;
 }
 
+/// Trait providing methods to quote swap prices between asset classes.
+///
+/// The quoted price is only guaranteed if no other swaps are made after the price is quoted and
+/// before the target swap (e.g., the swap is made immediately within the same transaction).
+pub trait QuotePrice {
+	/// Measurement units of the asset classes for pricing.
+	type Balance: Balance;
+	/// Type representing the kind of assets for which the price is being quoted.
+	type AssetKind;
+	/// Quotes the amount of `asset1` required to obtain the exact `amount` of `asset2`.
+	///
+	/// If `include_fee` is set to `true`, the price will include the pool's fee.
+	/// If the pool does not exist or the swap cannot be made, `None` is returned.
+	fn quote_price_tokens_for_exact_tokens(
+		asset1: Self::AssetKind,
+		asset2: Self::AssetKind,
+		amount: Self::Balance,
+		include_fee: bool,
+	) -> Option<Self::Balance>;
+	/// Quotes the amount of `asset2` resulting from swapping the exact `amount` of `asset1`.
+	///
+	/// If `include_fee` is set to `true`, the price will include the pool's fee.
+	/// If the pool does not exist or the swap cannot be made, `None` is returned.
+	fn quote_price_exact_tokens_for_tokens(
+		asset1: Self::AssetKind,
+		asset2: Self::AssetKind,
+		amount: Self::Balance,
+		include_fee: bool,
+	) -> Option<Self::Balance>;
+}
+
 impl<T: Config> Swap<T::AccountId> for Pallet<T> {
 	type Balance = T::Balance;
 	type AssetKind = T::AssetKind;
@@ -210,3 +241,24 @@ impl<T: Config> SwapCredit<T::AccountId> for Pallet<T> {
 		.map_err(|_| (Self::Credit::zero(credit_asset), DispatchError::Corruption))?
 	}
 }
+
+impl<T: Config> QuotePrice for Pallet<T> {
+	type Balance = T::Balance;
+	type AssetKind = T::AssetKind;
+	fn quote_price_exact_tokens_for_tokens(
+		asset1: Self::AssetKind,
+		asset2: Self::AssetKind,
+		amount: Self::Balance,
+		include_fee: bool,
+	) -> Option<Self::Balance> {
+		Self::quote_price_exact_tokens_for_tokens(asset1, asset2, amount, include_fee)
+	}
+	fn quote_price_tokens_for_exact_tokens(
+		asset1: Self::AssetKind,
+		asset2: Self::AssetKind,
+		amount: Self::Balance,
+		include_fee: bool,
+	) -> Option<Self::Balance> {
+		Self::quote_price_tokens_for_exact_tokens(asset1, asset2, amount, include_fee)
+	}
+}