Add an adapter for configuring AssetExchanger

cumulus/primitives/utility/src/lib.rs

@@ -407,10 +407,22 @@ impl<
 		let first_asset: Asset =
 			payment.fungible.pop_first().ok_or(XcmError::AssetNotFound)?.into();
 		let (fungibles_asset, balance) = FungiblesAssetMatcher::matches_fungibles(&first_asset)
-			.map_err(|_| XcmError::AssetNotFound)?;
+			.map_err(|error| {
+				log::trace!(
+					target: "xcm::weight",
+					"SwapFirstAssetTrader::buy_weight asset {:?} didn't match. Error: {:?}",
+					first_asset,
+					error,
+				);
+				XcmError::AssetNotFound
+			})?;
 
 		let swap_asset = fungibles_asset.clone().into();
 		if Target::get().eq(&swap_asset) {
+			log::trace!(
+				target: "xcm::weight",
+				"SwapFirstAssetTrader::buy_weight Asset was same as Target, swap not needed.",
+			);
 			// current trader is not applicable.
 			return Err(XcmError::FeesNotMet)
 		}
@@ -424,7 +436,12 @@ impl<
 			credit_in,
 			fee,
 		)
-		.map_err(|(credit_in, _)| {
+		.map_err(|(credit_in, error)| {
+			log::trace!(
+				target: "xcm::weight",
+				"SwapFirstAssetTrader::buy_weight swap couldn't be done. Error was: {:?}",
+				error,
+			);
 			drop(credit_in);
 			XcmError::FeesNotMet
 		})?;

polkadot/xcm/xcm-builder/Cargo.toml

@@ -22,13 +22,15 @@ sp-weights = { workspace = true }
 frame-support = { workspace = true }
 frame-system = { workspace = true }
 pallet-transaction-payment = { workspace = true }
+pallet-asset-conversion = { workspace = true }
 log = { workspace = true }
 
 # Polkadot dependencies
 polkadot-parachain-primitives = { workspace = true }
 
 [dev-dependencies]
-primitive-types = { workspace = true, default-features = true }
+sp-core = { workspace = true, default-features = true }
+primitive-types = { features = ["codec", "num-traits", "scale-info"], workspace = true }
 pallet-balances = { workspace = true, default-features = true }
 pallet-xcm = { workspace = true, default-features = true }
 pallet-salary = { workspace = true, default-features = true }
@@ -43,6 +45,7 @@ default = ["std"]
 runtime-benchmarks = [
 	"frame-support/runtime-benchmarks",
 	"frame-system/runtime-benchmarks",
+	"pallet-asset-conversion/runtime-benchmarks",
 	"pallet-assets/runtime-benchmarks",
 	"pallet-balances/runtime-benchmarks",
 	"pallet-salary/runtime-benchmarks",
@@ -59,8 +62,10 @@ std = [
 	"frame-support/std",
 	"frame-system/std",
 	"log/std",
+	"pallet-asset-conversion/std",
 	"pallet-transaction-payment/std",
 	"polkadot-parachain-primitives/std",
+	"primitive-types/std",
 	"scale-info/std",
 	"sp-arithmetic/std",
 	"sp-io/std",

polkadot/xcm/xcm-builder/src/asset_exchange/mod.rs

@@ -0,0 +1,22 @@
+// Copyright (C) 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/>.
+
+//! Adapters for the AssetExchanger config item.
+//!
+//! E.g. types that implement the [`xcm_executor::traits::AssetExchange`] trait.
+
+mod single_asset_adapter;
+pub use single_asset_adapter::SingleAssetExchangeAdapter;

polkadot/xcm/xcm-builder/src/asset_exchange/single_asset_adapter/adapter.rs

@@ -0,0 +1,205 @@
+// Copyright (C) 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/>.
+
+//! Single asset exchange adapter.
+
+extern crate alloc;
+use alloc::vec;
+use core::marker::PhantomData;
+use frame_support::{ensure, traits::tokens::fungibles};
+use pallet_asset_conversion::{QuotePrice, SwapCredit};
+use xcm::prelude::*;
+use xcm_executor::{
+	traits::{AssetExchange, MatchesFungibles},
+	AssetsInHolding,
+};
+
+/// An adapter from [`pallet_asset_conversion::SwapCredit`] and
+/// [`pallet_asset_conversion::QuotePrice`] to [`xcm_executor::traits::AssetExchange`].
+///
+/// This adapter takes just one fungible asset in `give` and allows only one fungible asset in
+/// `want`. If you need to handle more assets in either `give` or `want`, then you should use
+/// another type that implements [`xcm_executor::traits::AssetExchange`] or build your own.
+///
+/// This adapter also only works for fungible assets.
+///
+/// `exchange_asset` will return an error if there's more than one asset in `give` or `want`.
+pub struct SingleAssetExchangeAdapter<AssetConversion, Fungibles, Matcher, AccountId>(
+	PhantomData<(AssetConversion, Fungibles, Matcher, AccountId)>,
+);
+impl<AssetConversion, Fungibles, Matcher, AccountId> AssetExchange
+	for SingleAssetExchangeAdapter<AssetConversion, Fungibles, Matcher, AccountId>
+where
+	AssetConversion: SwapCredit<
+			AccountId,
+			Balance = u128,
+			AssetKind = Fungibles::AssetId,
+			Credit = fungibles::Credit<AccountId, Fungibles>,
+		> + QuotePrice<Balance = u128, AssetKind = Fungibles::AssetId>,
+	Fungibles: fungibles::Balanced<AccountId, Balance = u128>,
+	Matcher: MatchesFungibles<Fungibles::AssetId, Fungibles::Balance>,
+{
+	fn exchange_asset(
+		_: Option<&Location>,
+		give: AssetsInHolding,
+		want: &Assets,
+		maximal: bool,
+	) -> Result<AssetsInHolding, AssetsInHolding> {
+		let mut give_iter = give.fungible_assets_iter();
+		let give_asset = give_iter.next().ok_or_else(|| {
+			log::trace!(
+				target: "xcm::SingleAssetExchangeAdapter::exchange_asset",
+				"No fungible asset was in `give`.",
+			);
+			give.clone()
+		})?;
+		ensure!(give_iter.next().is_none(), give.clone()); // We only support 1 asset in `give`.
+		ensure!(give.non_fungible_assets_iter().next().is_none(), give.clone()); // We don't allow non-fungible assets.
+		ensure!(want.len() == 1, give.clone()); // We only support 1 asset in `want`.
+		let want_asset = want.get(0).ok_or_else(|| give.clone())?;
+		let (give_asset_id, give_amount) =
+			Matcher::matches_fungibles(&give_asset).map_err(|error| {
+				log::trace!(
+					target: "xcm::SingleAssetExchangeAdapter::exchange_asset",
+					"Could not map XCM asset give {:?} to FRAME asset. Error: {:?}",
+					give_asset,
+					error,
+				);
+				give.clone()
+			})?;
+		let (want_asset_id, want_amount) =
+			Matcher::matches_fungibles(&want_asset).map_err(|error| {
+				log::trace!(
+					target: "xcm::SingleAssetExchangeAdapter::exchange_asset",
+					"Could not map XCM asset want {:?} to FRAME asset. Error: {:?}",
+					want_asset,
+					error,
+				);
+				give.clone()
+			})?;
+
+		// We have to do this to convert the XCM assets into credit the pool can use.
+		let swap_asset = give_asset_id.clone().into();
+		let credit_in = Fungibles::issue(give_asset_id, give_amount);
+
+		// Do the swap.
+		let (credit_out, maybe_credit_change) = if maximal {
+			// If `maximal`, then we swap exactly `credit_in` to get as much of `want_asset_id` as
+			// we can, with a minimum of `want_amount`.
+			let credit_out = <AssetConversion as SwapCredit<_>>::swap_exact_tokens_for_tokens(
+				vec![swap_asset, want_asset_id],
+				credit_in,
+				Some(want_amount),
+			)
+			.map_err(|(credit_in, error)| {
+				log::error!(
+					target: "xcm::SingleAssetExchangeAdapter::exchange_asset",
+					"Could not perform the swap, error: {:?}.",
+					error
+				);
+				drop(credit_in);
+				give.clone()
+			})?;
+
+			// We don't have leftover assets if exchange was maximal.
+			(credit_out, None)
+		} else {
+			// If `minimal`, then we swap as little of `credit_in` as we can to get exactly
+			// `want_amount` of `want_asset_id`.
+			let (credit_out, credit_change) =
+				<AssetConversion as SwapCredit<_>>::swap_tokens_for_exact_tokens(
+					vec![swap_asset, want_asset_id],
+					credit_in,
+					want_amount,
+				)
+				.map_err(|(credit_in, error)| {
+					log::error!(
+						target: "xcm::SingleAssetExchangeAdapter::exchange_asset",
+						"Could not perform the swap, error: {:?}.",
+						error
+					);
+					drop(credit_in);
+					give.clone()
+				})?;
+
+			(credit_out, Some(credit_change))
+		};
+
+		// We create an `AssetsInHolding` instance by putting in the resulting asset
+		// of the exchange.
+		let resulting_asset: Asset = (want_asset.id.clone(), credit_out.peek()).into();
+		let mut result: AssetsInHolding = resulting_asset.into();
+
+		// If we have some leftover assets from the exchange, also put them in the result.
+		if let Some(credit_change) = maybe_credit_change {
+			let leftover_asset: Asset = (give_asset.id.clone(), credit_change.peek()).into();
+			result.subsume(leftover_asset);
+		}
+
+		Ok(result.into())
+	}
+
+	fn quote_exchange_price(asset1: &Asset, asset2: &Asset, maximal: bool) -> Option<u128> {
+		// We first match both XCM assets to the asset ID types `AssetConversion` can handle.
+		let (asset1_id, asset1_amount) = Matcher::matches_fungibles(asset1)
+			.map_err(|error| {
+				log::trace!(
+					target: "xcm::SingleAssetExchangeAdapter::quote_exchange_price",
+					"Could not map XCM asset {:?} to FRAME asset. Error: {:?}.",
+					asset1,
+					error,
+				);
+				()
+			})
+			.ok()?;
+		// For `asset2`, we also want the desired amount.
+		let (asset2_id, asset2_amount) = Matcher::matches_fungibles(asset2)
+			.map_err(|error| {
+				log::trace!(
+					target: "xcm::SingleAssetExchangeAdapter::quote_exchange_price",
+					"Could not map XCM asset {:?} to FRAME asset. Error: {:?}.",
+					asset2,
+					error,
+				);
+				()
+			})
+			.ok()?;
+		// We quote the price.
+		if maximal {
+			// The amount of `asset2` resulting from swapping the `asset1_amount` of `asset1`.
+			let resulting_asset2_amount =
+				<AssetConversion as QuotePrice>::quote_price_exact_tokens_for_tokens(
+					asset1_id,
+					asset2_id,
+					asset1_amount,
+					true,
+				)?;
+
+			Some(resulting_asset2_amount)
+		} else {
+			// The `asset1` amount required to obtain `asset2_amount` of `asset2`.
+			let necessary_asset1_amount =
+				<AssetConversion as QuotePrice>::quote_price_tokens_for_exact_tokens(
+					asset1_id,
+					asset2_id,
+					asset2_amount,
+					true,
+				)?;
+
+			Some(necessary_asset1_amount)
+		}
+	}
+}