pallet-asset-conversion: Decoupling Native Currency Dependancy (#2031)

closes https://github.com/paritytech/polkadot-sdk/issues/1842

Decoupling Pallet from the Concept of Native Currency

Currently, the pallet is intrinsically linked with the concept of native
currency, requiring users to provide implementations of the
`fungible::*` and `fungibles::*` traits to interact with native and non
native assets. This incapsulates some non-related to the pallet
complexity and makes it less adaptable in contexts where the native
currency concept is absent.

With this PR, the dependence on `fungible::*` for liquidity-supplying
assets has been removed. Instead, the native and non-native currencies'
handling is now overseen by a single type that implements the
`fungibles::*` traits. To simplify this integration, types have been
introduced to facilitate the creation of a union between `fungible::*`
and `fungibles::*` implementations, producing a unified `fungibles::*`
type.

One of the reasons driving these changes is the ambition to create a
more user-friendly API for the `SwapCredit` implementation. Given that
it interacts with two distinct credit types from `fungible` and
`fungibles`, a unified type was introduced. Clients now manage potential
conversion failures for those credit types. In certain contexts, it's
vital to guarantee that operations are fail-safe, like in this impl -
[PR](https://github.com/paritytech/polkadot-sdk/pull/1845), place in
[code](https://github.com/paritytech/polkadot-sdk/blob/20b85a5fada8f55c98ba831964f5866ffeadf4da/cumulus/primitives/utility/src/lib.rs#L429).

Additional Updates:
- abstracted the pool ID and its account derivation logic via trait
bounds, along with common implementation offerings;
- removed `inc_providers` on a pool creation for the pool account;
- benchmarks:
-- swap complexity is N, not const;
-- removed `From<u128> + Into<u128>` bound from `T::Balance`;
-- removed swap/liquidity/.. amount constants, resolve them dynamically
based on pallet configuration;
-- migrated to v2 API;
- `OnUnbalanced` handler for the pool creation fee, replacing direct
transfers to a specified account ID;
- renamed `MultiAssetId` to `AssetKind` aligning with naming across
frame crates;

related PRs:
- (depends) https://github.com/paritytech/polkadot-sdk/pull/1677
- (caused) https://github.com/paritytech/polkadot-sdk/pull/2033
- (caused) https://github.com/paritytech/polkadot-sdk/pull/1876

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>

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

@@ -29,7 +29,7 @@ pub mod xcm_config;
 
 use assets_common::{
 	foreign_creators::ForeignCreators,
-	local_and_foreign_assets::{LocalAndForeignAssets, MultiLocationConverter},
+	local_and_foreign_assets::{LocalFromLeft, TargetFromLeft},
 	matching::FromSiblingParachain,
 	AssetIdForTrustBackedAssetsConvert, MultiLocationForAssetId,
 };
@@ -57,8 +57,9 @@ use frame_support::{
 	genesis_builder_helper::{build_config, create_default_config},
 	ord_parameter_types, parameter_types,
 	traits::{
-		AsEnsureOriginWithArg, ConstBool, ConstU128, ConstU32, ConstU64, ConstU8, EitherOfDiverse,
-		Equals, InstanceFilter, TransformOrigin,
+		fungible, fungibles, tokens::imbalance::ResolveAssetTo, AsEnsureOriginWithArg, ConstBool,
+		ConstU128, ConstU32, ConstU64, ConstU8, EitherOfDiverse, Equals, InstanceFilter,
+		TransformOrigin,
 	},
 	weights::{ConstantMultiplier, Weight},
 	BoundedVec, PalletId,
@@ -82,8 +83,9 @@ use parachains_common::{
 use sp_runtime::{Perbill, RuntimeDebug};
 use xcm::opaque::v3::MultiLocation;
 use xcm_config::{
-	ForeignAssetsConvertedConcreteId, GovernanceLocation, PoolAssetsConvertedConcreteId,
-	TokenLocation, TrustBackedAssetsConvertedConcreteId,
+	ForeignAssetsConvertedConcreteId, ForeignCreatorsSovereignAccountOf, GovernanceLocation,
+	PoolAssetsConvertedConcreteId, TokenLocation, TrustBackedAssetsConvertedConcreteId,
+	TrustBackedAssetsPalletLocation,
 };
 
 #[cfg(any(feature = "std", test))]
@@ -94,10 +96,6 @@ use pallet_xcm::{EnsureXcm, IsVoiceOfBody};
 use polkadot_runtime_common::{BlockHashCount, SlowAdjustingFeeUpdate};
 use xcm::latest::prelude::*;
 
-use crate::xcm_config::{
-	ForeignCreatorsSovereignAccountOf, LocalAndForeignAssetsMultiLocationMatcher,
-	TrustBackedAssetsPalletLocation,
-};
 use weights::{BlockExecutionWeight, ExtrinsicBaseWeight, RocksDbWeight};
 
 impl_opaque_keys! {
@@ -279,8 +277,6 @@ impl pallet_assets::Config<TrustBackedAssetsInstance> for Runtime {
 
 parameter_types! {
 	pub const AssetConversionPalletId: PalletId = PalletId(*b"py/ascon");
-	pub const AllowMultiAssetPools: bool = false;
-	// should be non-zero if AllowMultiAssetPools is true, otherwise can be zero
 	pub const LiquidityWithdrawalFee: Permill = Permill::from_percent(0);
 }
 
@@ -315,35 +311,50 @@ impl pallet_assets::Config<PoolAssetsInstance> for Runtime {
 	type BenchmarkHelper = ();
 }
 
+/// Union fungibles implementation for `Assets`` and `ForeignAssets`.
+pub type LocalAndForeignAssets = fungibles::UnionOf<
+	Assets,
+	ForeignAssets,
+	LocalFromLeft<
+		AssetIdForTrustBackedAssetsConvert<TrustBackedAssetsPalletLocation>,
+		AssetIdForTrustBackedAssets,
+	>,
+	MultiLocation,
+	AccountId,
+>;
+
 impl pallet_asset_conversion::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type Balance = Balance;
 	type HigherPrecisionBalance = sp_core::U256;
-	type Currency = Balances;
-	type AssetId = MultiLocation;
-	type Assets = LocalAndForeignAssets<
-		Assets,
-		AssetIdForTrustBackedAssetsConvert<TrustBackedAssetsPalletLocation>,
-		ForeignAssets,
+	type AssetKind = MultiLocation;
+	type Assets = fungible::UnionOf<
+		Balances,
+		LocalAndForeignAssets,
+		TargetFromLeft<TokenLocation>,
+		Self::AssetKind,
+		Self::AccountId,
 	>;
-	type PoolAssets = PoolAssets;
+	type PoolId = (Self::AssetKind, Self::AssetKind);
+	type PoolLocator =
+		pallet_asset_conversion::WithFirstAsset<TokenLocation, AccountId, Self::AssetKind>;
 	type PoolAssetId = u32;
+	type PoolAssets = PoolAssets;
 	type PoolSetupFee = ConstU128<0>; // Asset class deposit fees are sufficient to prevent spam
-	type PoolSetupFeeReceiver = AssetConversionOrigin;
-	// should be non-zero if `AllowMultiAssetPools` is true, otherwise can be zero.
+	type PoolSetupFeeAsset = TokenLocation;
+	type PoolSetupFeeTarget = ResolveAssetTo<AssetConversionOrigin, Self::Assets>;
 	type LiquidityWithdrawalFee = LiquidityWithdrawalFee;
 	type LPFee = ConstU32<3>;
 	type PalletId = AssetConversionPalletId;
-	type AllowMultiAssetPools = AllowMultiAssetPools;
-	type MaxSwapPathLength = ConstU32<4>;
-	type MultiAssetId = MultiLocation;
-	type MultiAssetIdConverter =
-		MultiLocationConverter<TokenLocation, LocalAndForeignAssetsMultiLocationMatcher>;
+	type MaxSwapPathLength = ConstU32<3>;
 	type MintMinLiquidity = ConstU128<100>;
 	type WeightInfo = weights::pallet_asset_conversion::WeightInfo<Runtime>;
 	#[cfg(feature = "runtime-benchmarks")]
-	type BenchmarkHelper =
-		crate::xcm_config::BenchmarkMultiLocationConverter<parachain_info::Pallet<Runtime>>;
+	type BenchmarkHelper = assets_common::benchmarks::AssetPairFactory<
+		TokenLocation,
+		parachain_info::Pallet<Runtime>,
+		xcm_config::AssetsPalletIndex,
+	>;
 }
 
 parameter_types! {
@@ -733,12 +744,9 @@ impl pallet_collator_selection::Config for Runtime {
 
 impl pallet_asset_conversion_tx_payment::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
-	type Fungibles = LocalAndForeignAssets<
-		Assets,
-		AssetIdForTrustBackedAssetsConvert<TrustBackedAssetsPalletLocation>,
-		ForeignAssets,
-	>;
-	type OnChargeAssetTransaction = AssetConversionAdapter<Balances, AssetConversion>;
+	type Fungibles = LocalAndForeignAssets;
+	type OnChargeAssetTransaction =
+		AssetConversionAdapter<Balances, AssetConversion, TokenLocation>;
 }
 
 parameter_types! {
@@ -1154,7 +1162,7 @@ impl_runtime_apis! {
 		}
 
 		fn get_reserves(asset1: MultiLocation, asset2: MultiLocation) -> Option<(Balance, Balance)> {
-			AssetConversion::get_reserves(&asset1, &asset2).ok()
+			AssetConversion::get_reserves(asset1, asset2).ok()
 		}
 	}