Statemint Reserve Asset Transfer (#552)

* add AssetId type alias in statemint-common

* add FungiblesAdapter to allow for asset transactions via XCM

* use custom Polkadot

* fix FungiblesAdapter usage and add CheckingAccount

* update deps

* remove polkadot overrides

* update deps

* pull NonZeroIssuance struct into common + add FungiblesTransactor to Statemine and Westmint

* remove unnecessary tuple wrapping + adjust asset transactor comments

* accept statemint as reserve in rococo test parachain

* adjust parachain config (add Statemint as reserve)

* add test and docs for AssetsFrom

* cargo fmt

Co-authored-by: Ricardo Rius <ricardo@parity.io>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

cumulus/polkadot-parachains/parachains-common/src/impls.rs

@@ -16,7 +16,11 @@
 //! Auxillary struct/enums for parachain runtimes.
 //! Taken from polkadot/runtime/common (at a21cd64) and adapted for parachains.
 
-use frame_support::traits::{Currency, Imbalance, OnUnbalanced};
+use frame_support::traits::{fungibles, Contains, Currency, Get, Imbalance, OnUnbalanced};
+use sp_runtime::traits::Zero;
+use sp_std::marker::PhantomData;
+use xcm::latest::{AssetId, Fungibility::Fungible, MultiAsset, MultiLocation};
+use xcm_executor::traits::FilterAssetLocation;
 
 pub type NegativeImbalance<T> = <pallet_balances::Pallet<T> as Currency<
 	<T as frame_system::Config>::AccountId,
@@ -42,6 +46,7 @@ where
 	}
 }
 
+/// Merge the fees into one item and pass them on to the staking pot.
 pub struct DealWithFees<R>(sp_std::marker::PhantomData<R>);
 impl<R> OnUnbalanced<NegativeImbalance<R>> for DealWithFees<R>
 where
@@ -60,6 +65,29 @@ where
 	}
 }
 
+/// Allow checking in assets that have issuance > 0.
+pub struct NonZeroIssuance<AccountId, Assets>(PhantomData<(AccountId, Assets)>);
+impl<AccountId, Assets> Contains<<Assets as fungibles::Inspect<AccountId>>::AssetId>
+	for NonZeroIssuance<AccountId, Assets>
+where
+	Assets: fungibles::Inspect<AccountId>,
+{
+	fn contains(id: &<Assets as fungibles::Inspect<AccountId>>::AssetId) -> bool {
+		!Assets::total_issuance(*id).is_zero()
+	}
+}
+
+/// Asset filter that allows all assets from a certain location.
+pub struct AssetsFrom<T>(PhantomData<T>);
+impl<T: Get<MultiLocation>> FilterAssetLocation for AssetsFrom<T> {
+	fn filter_asset_location(asset: &MultiAsset, origin: &MultiLocation) -> bool {
+		let loc = T::get();
+		&loc == origin &&
+			matches!(asset, MultiAsset { id: AssetId::Concrete(asset_loc), fun: Fungible(_a) }
+			if asset_loc.match_and_split(&loc).is_some())
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
@@ -77,6 +105,7 @@ mod tests {
 		traits::{BlakeTwo256, IdentityLookup},
 		Perbill,
 	};
+	use xcm::prelude::*;
 
 	type UncheckedExtrinsic = frame_system::mocking::MockUncheckedExtrinsic<Test>;
 	type Block = frame_system::mocking::MockBlock<Test>;
@@ -207,4 +236,24 @@ mod tests {
 			assert_eq!(Balances::free_balance(CollatorSelection::account_id()), 30);
 		});
 	}
+
+	#[test]
+	fn assets_from_filters_correctly() {
+		parameter_types! {
+			pub SomeSiblingParachain: MultiLocation = MultiLocation::new(1, X1(Parachain(1234)));
+		}
+
+		let asset_location = SomeSiblingParachain::get()
+			.clone()
+			.pushed_with_interior(GeneralIndex(42))
+			.expect("multilocation will only have 2 junctions; qed");
+		let asset = MultiAsset { id: Concrete(asset_location), fun: 1_000_000.into() };
+		assert!(
+			AssetsFrom::<SomeSiblingParachain>::filter_asset_location(
+				&asset,
+				&SomeSiblingParachain::get()
+			),
+			"AssetsFrom should allow assets from any of its interior locations"
+		);
+	}
 }

cumulus/polkadot-parachains/parachains-common/src/lib.rs

@@ -51,6 +51,9 @@ mod types {
 
 	// Aura consensus authority.
 	pub type AuraId = sp_consensus_aura::sr25519::AuthorityId;
+
+	// Id used for identifying assets.
+	pub type AssetId = u32;
 }
 
 /// Common constants of parachains.