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>

polkadot-parachains/parachains-common/Cargo.toml

@@ -28,6 +28,8 @@ node-primitives = { git = 'https://github.com/paritytech/substrate', branch = "m
 # Polkadot dependencies
 polkadot-runtime-common = { git = 'https://github.com/paritytech/polkadot', branch = "master", default-features = false }
 polkadot-primitives = { git = 'https://github.com/paritytech/polkadot', branch = "master", default-features = false }
+xcm = { git = 'https://github.com/paritytech/polkadot', branch = "master", default-features = false }
+xcm-executor = { git = 'https://github.com/paritytech/polkadot', branch = "master", default-features = false }
 
 # Local dependencies
 pallet-collator-selection = { path = '../../pallets/collator-selection', default-features = false }

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"
+		);
+	}
 }

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.

polkadot-parachains/rococo/Cargo.toml

@@ -39,6 +39,8 @@ pallet-transaction-payment = { git = "https://github.com/paritytech/substrate",
 pallet-aura = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 pallet-transaction-payment-rpc-runtime-api = { git = "https://github.com/paritytech/substrate", default-features = false, branch = "master" }
 
+parachains-common = { path = "../parachains-common", default-features = false }
+
 # Cumulus dependencies
 cumulus-pallet-aura-ext = { path = "../../pallets/aura-ext", default-features = false }
 cumulus-pallet-parachain-system = { path = "../../pallets/parachain-system", default-features = false }

polkadot-parachains/rococo/src/lib.rs

@@ -45,14 +45,24 @@ pub use frame_support::{
 	},
 	StorageValue,
 };
-use frame_system::limits::{BlockLength, BlockWeights};
+use frame_system::{
+	limits::{BlockLength, BlockWeights},
+	EnsureOneOf, EnsureRoot,
+};
 pub use pallet_balances::Call as BalancesCall;
 pub use pallet_timestamp::Call as TimestampCall;
 pub use sp_consensus_aura::sr25519::AuthorityId as AuraId;
 #[cfg(any(feature = "std", test))]
 pub use sp_runtime::BuildStorage;
 pub use sp_runtime::{Perbill, Permill};
 
+use parachains_common::{
+	impls::{AssetsFrom, NonZeroIssuance},
+	AssetId,
+};
+use xcm_builder::{AsPrefixedGeneralIndex, ConvertedConcreteAssetId, FungiblesAdapter};
+use xcm_executor::traits::JustTry;
+
 // XCM imports
 use pallet_xcm::{EnsureXcm, IsMajorityOfBody, XcmPassthrough};
 use polkadot_parachain::primitives::Sibling;
@@ -258,6 +268,7 @@ parameter_types! {
 	pub const RococoNetwork: NetworkId = NetworkId::Polkadot;
 	pub RelayChainOrigin: Origin = cumulus_pallet_xcm::Origin::Relay.into();
 	pub Ancestry: MultiLocation = Parachain(ParachainInfo::parachain_id().into()).into();
+	pub CheckingAccount: AccountId = PolkadotXcm::check_account();
 }
 
 /// Type for specifying how a `MultiLocation` can be converted into an `AccountId`. This is used
@@ -273,7 +284,7 @@ pub type LocationToAccountId = (
 );
 
 /// Means for transacting assets on this chain.
-pub type LocalAssetTransactor = CurrencyAdapter<
+pub type CurrencyTransactor = CurrencyAdapter<
 	// Use this currency:
 	Balances,
 	// Use this currency when it is a fungible asset matching the given location or name:
@@ -286,6 +297,30 @@ pub type LocalAssetTransactor = CurrencyAdapter<
 	(),
 >;
 
+/// Means for transacting assets besides the native currency on this chain.
+pub type FungiblesTransactor = FungiblesAdapter<
+	// Use this fungibles implementation:
+	Assets,
+	// Use this currency when it is a fungible asset matching the given location or name:
+	ConvertedConcreteAssetId<
+		AssetId,
+		u64,
+		AsPrefixedGeneralIndex<StatemintLocation, AssetId, JustTry>,
+		JustTry,
+	>,
+	// Convert an XCM MultiLocation into a local account id:
+	LocationToAccountId,
+	// Our chain's account ID type (we can't get away without mentioning it explicitly):
+	AccountId,
+	// We only want to allow teleports of known assets. We use non-zero issuance as an indication
+	// that this asset is known.
+	NonZeroIssuance<AccountId, Assets>,
+	// The account to use for tracking teleports.
+	CheckingAccount,
+>;
+/// Means for transacting assets on this chain.
+pub type AssetTransactors = (CurrencyTransactor, FungiblesTransactor);
+
 /// This is the type we use to convert an (incoming) XCM origin into a local `Origin` instance,
 /// ready for dispatching a transaction with Xcm's `Transact`. There is an `OriginKind` which can
 /// biases the kind of local `Origin` it will become.
@@ -324,22 +359,34 @@ match_type! {
 		MultiLocation { parents: 1, interior: X1(Plurality { id: BodyId::Unit, .. }) }
 	};
 }
+match_type! {
+	pub type Statemint: impl Contains<MultiLocation> = {
+		MultiLocation { parents: 1, interior: X1(Parachain(1000)) }
+	};
+}
 
 pub type Barrier = (
 	TakeWeightCredit,
 	AllowTopLevelPaidExecutionFrom<Everything>,
 	AllowUnpaidExecutionFrom<ParentOrParentsUnitPlurality>,
 	// ^^^ Parent & its unit plurality gets free execution
+	AllowUnpaidExecutionFrom<Statemint>,
 );
 
+parameter_types! {
+	pub StatemintLocation: MultiLocation = MultiLocation::new(1, X1(Parachain(1000)));
+}
+
+pub type Reserves = (NativeAsset, AssetsFrom<StatemintLocation>);
+
 pub struct XcmConfig;
 impl Config for XcmConfig {
 	type Call = Call;
 	type XcmSender = XcmRouter;
 	// How to withdraw and deposit an asset.
-	type AssetTransactor = LocalAssetTransactor;
+	type AssetTransactor = AssetTransactors;
 	type OriginConverter = XcmOriginToTransactDispatchOrigin;
-	type IsReserve = NativeAsset;
+	type IsReserve = Reserves;
 	type IsTeleporter = NativeAsset; // <- should be enough to allow teleportation of ROC
 	type LocationInverter = LocationInverter<Ancestry>;
 	type Barrier = Barrier;
@@ -416,12 +463,16 @@ parameter_types! {
 }
 
 /// A majority of the Unit body from Rococo over XCM is our required administration origin.
-pub type AdminOrigin = EnsureXcm<IsMajorityOfBody<RocLocation, UnitBody>>;
+pub type AdminOrigin = EnsureOneOf<
+	AccountId,
+	EnsureRoot<AccountId>,
+	EnsureXcm<IsMajorityOfBody<RocLocation, UnitBody>>,
+>;
 
 impl pallet_assets::Config for Runtime {
 	type Event = Event;
 	type Balance = u64;
-	type AssetId = u32;
+	type AssetId = AssetId;
 	type Currency = Balances;
 	type ForceOrigin = AdminOrigin;
 	type AssetDeposit = AssetDeposit;

polkadot-parachains/statemine/src/lib.rs

@@ -31,7 +31,7 @@ use sp_runtime::{
 	create_runtime_str, generic, impl_opaque_keys,
 	traits::{AccountIdLookup, BlakeTwo256, Block as BlockT},
 	transaction_validity::{TransactionSource, TransactionValidity},
-	ApplyExtrinsicResult,
+	ApplyExtrinsicResult, Perbill,
 };
 
 use sp_std::prelude::*;
@@ -56,11 +56,10 @@ use frame_system::{
 };
 pub use parachains_common as common;
 use parachains_common::{
-	impls::DealWithFees, opaque, AccountId, AuraId, Balance, BlockNumber, Hash, Header, Index,
-	Signature, AVERAGE_ON_INITIALIZE_RATIO, HOURS, MAXIMUM_BLOCK_WEIGHT, NORMAL_DISPATCH_RATIO,
-	SLOT_DURATION,
+	impls::{DealWithFees, NonZeroIssuance},
+	opaque, AccountId, AssetId, AuraId, Balance, BlockNumber, Hash, Header, Index, Signature,
+	AVERAGE_ON_INITIALIZE_RATIO, HOURS, MAXIMUM_BLOCK_WEIGHT, NORMAL_DISPATCH_RATIO, SLOT_DURATION,
 };
-use sp_runtime::Perbill;
 
 #[cfg(any(feature = "std", test))]
 pub use sp_runtime::BuildStorage;
@@ -71,13 +70,14 @@ use polkadot_parachain::primitives::Sibling;
 use polkadot_runtime_common::{BlockHashCount, RocksDbWeight, SlowAdjustingFeeUpdate};
 use xcm::latest::prelude::*;
 use xcm_builder::{
-	AccountId32Aliases, AllowTopLevelPaidExecutionFrom, AllowUnpaidExecutionFrom, CurrencyAdapter,
-	EnsureXcmOrigin, FixedWeightBounds, IsConcrete, LocationInverter, NativeAsset,
+	AccountId32Aliases, AllowTopLevelPaidExecutionFrom, AllowUnpaidExecutionFrom,
+	AsPrefixedGeneralIndex, ConvertedConcreteAssetId, CurrencyAdapter, EnsureXcmOrigin,
+	FixedWeightBounds, FungiblesAdapter, IsConcrete, LocationInverter, NativeAsset,
 	ParentAsSuperuser, ParentIsDefault, RelayChainAsNative, SiblingParachainAsNative,
 	SiblingParachainConvertsVia, SignedAccountId32AsNative, SignedToAccountId32,
 	SovereignSignedViaLocation, TakeWeightCredit, UsingComponents,
 };
-use xcm_executor::{Config, XcmExecutor};
+use xcm_executor::{traits::JustTry, Config, XcmExecutor};
 
 impl_opaque_keys! {
 	pub struct SessionKeys {
@@ -238,7 +238,7 @@ pub type AssetsForceOrigin = EnsureOneOf<
 impl pallet_assets::Config for Runtime {
 	type Event = Event;
 	type Balance = Balance;
-	type AssetId = u32;
+	type AssetId = AssetId;
 	type Currency = Balances;
 	type ForceOrigin = AssetsForceOrigin;
 	type AssetDeposit = AssetDeposit;
@@ -465,6 +465,8 @@ parameter_types! {
 	pub const RelayNetwork: NetworkId = NetworkId::Kusama;
 	pub RelayChainOrigin: Origin = cumulus_pallet_xcm::Origin::Relay.into();
 	pub Ancestry: MultiLocation = Parachain(ParachainInfo::parachain_id().into()).into();
+	pub const Local: MultiLocation = Here.into();
+	pub CheckingAccount: AccountId = PolkadotXcm::check_account();
 }
 
 /// Type for specifying how a `MultiLocation` can be converted into an `AccountId`. This is used
@@ -479,20 +481,44 @@ pub type LocationToAccountId = (
 	AccountId32Aliases<RelayNetwork, AccountId>,
 );
 
-/// Means for transacting assets on this chain.
-pub type LocalAssetTransactor = CurrencyAdapter<
+/// Means for transacting the native currency on this chain.
+pub type CurrencyTransactor = CurrencyAdapter<
 	// Use this currency:
 	Balances,
 	// Use this currency when it is a fungible asset matching the given location or name:
 	IsConcrete<KsmLocation>,
-	// Do a simple punn to convert an AccountId32 MultiLocation into a native chain account ID:
+	// Convert an XCM MultiLocation into a local account id:
 	LocationToAccountId,
 	// Our chain's account ID type (we can't get away without mentioning it explicitly):
 	AccountId,
-	// We don't track any teleports.
+	// We don't track any teleports of `Balances`.
 	(),
 >;
 
+/// Means for transacting assets besides the native currency on this chain.
+pub type FungiblesTransactor = FungiblesAdapter<
+	// Use this fungibles implementation:
+	Assets,
+	// Use this currency when it is a fungible asset matching the given location or name:
+	ConvertedConcreteAssetId<
+		AssetId,
+		Balance,
+		AsPrefixedGeneralIndex<Local, AssetId, JustTry>,
+		JustTry,
+	>,
+	// Convert an XCM MultiLocation into a local account id:
+	LocationToAccountId,
+	// Our chain's account ID type (we can't get away without mentioning it explicitly):
+	AccountId,
+	// We only want to allow teleports of known assets. We use non-zero issuance as an indication
+	// that this asset is known.
+	NonZeroIssuance<AccountId, Assets>,
+	// The account to use for tracking teleports.
+	CheckingAccount,
+>;
+/// Means for transacting assets on this chain.
+pub type AssetTransactors = (CurrencyTransactor, FungiblesTransactor);
+
 /// This is the type we use to convert an (incoming) XCM origin into a local `Origin` instance,
 /// ready for dispatching a transaction with Xcm's `Transact`. There is an `OriginKind` which can
 /// biases the kind of local `Origin` it will become.
@@ -542,7 +568,7 @@ impl Config for XcmConfig {
 	type Call = Call;
 	type XcmSender = XcmRouter;
 	// How to withdraw and deposit an asset.
-	type AssetTransactor = LocalAssetTransactor;
+	type AssetTransactor = AssetTransactors;
 	type OriginConverter = XcmOriginToTransactDispatchOrigin;
 	type IsReserve = NativeAsset;
 	type IsTeleporter = NativeAsset; // <- should be enough to allow teleportation of KSM