Treasury spends various asset kinds (#1333)

### Summary 

This PR introduces new dispatchables to the treasury pallet, allowing
spends of various asset types. The enhanced features of the treasury
pallet, in conjunction with the asset-rate pallet, are set up and
enabled for Westend and Rococo.

### Westend and Rococo runtimes.

Polkadot/Kusams/Rococo Treasury can accept proposals for `spends` of
various asset kinds by specifying the asset's location and ID.

#### Treasury Instance New Dispatchables:
- `spend(AssetKind, AssetBalance, Beneficiary, Option<ValidFrom>)` -
propose and approve a spend;
- `payout(SpendIndex)` - payout an approved spend or retry a failed
payout
- `check_payment(SpendIndex)` - check the status of a payout;
- `void_spend(SpendIndex)` - void previously approved spend;
> existing spend dispatchable renamed to spend_local

in this context, the `AssetKind` parameter contains the asset's location
and it's corresponding `asset_id`, for example:
`USDT` on `AssetHub`,
``` rust
location = MultiLocation(0, X1(Parachain(1000)))
asset_id = MultiLocation(0, X2(PalletInstance(50), GeneralIndex(1984)))
```

the `Beneficiary` parameter is a `MultiLocation` in the context of the
asset's location, for example
``` rust
// the Fellowship salary pallet's location / account
FellowshipSalaryPallet = MultiLocation(1, X2(Parachain(1001), PalletInstance(64)))
// or custom `AccountId`
Alice = MultiLocation(0, AccountId32(network: None, id: [1,...]))
```

the `AssetBalance` represents the amount of the `AssetKind` to be
transferred to the `Beneficiary`. For permission checks, the asset
amount is converted to the native amount and compared against the
maximum spendable amount determined by the commanding spend origin.

the `spend` dispatchable allows for batching spends with different
`ValidFrom` arguments, enabling milestone-based spending. If the
expectations tied to an approved spend are not met, it is possible to
void the spend later using the `void_spend` dispatchable.

Asset Rate Pallet provides the conversion rate from the `AssetKind` to
the native balance.

#### Asset Rate Instance Dispatchables:
- `create(AssetKind, Rate)` - initialize a conversion rate to the native
balance for the given asset
- `update(AssetKind, Rate)` - update the conversion rate to the native
balance for the given asset
- `remove(AssetKind)` - remove an existing conversion rate to the native
balance for the given asset

the pallet's dispatchables can be executed by the Root or Treasurer
origins.

### Treasury Pallet

Treasury Pallet can accept proposals for `spends` of various asset kinds
and pay them out through the implementation of the `Pay` trait.

New Dispatchables:
- `spend(Config::AssetKind, AssetBalance, Config::Beneficiary,
Option<ValidFrom>)` - propose and approve a spend;
- `payout(SpendIndex)` - payout an approved spend or retry a failed
payout;
- `check_payment(SpendIndex)` - check the status of a payout;
- `void_spend(SpendIndex)` - void previously approved spend;
> existing spend dispatchable renamed to spend_local

The parameters' types of the `spend` dispatchable exposed via the
pallet's `Config` and allows to propose and accept a spend of a certain
amount.

An approved spend can be claimed via the `payout` within the
`Config::SpendPeriod`. Clients provide an implementation of the `Pay`
trait which can pay an asset of the `AssetKind` to the `Beneficiary` in
`AssetBalance` units.

The implementation of the Pay trait might not have an immediate final
payment status, for example if implemented over `XCM` and the actual
transfer happens on a remote chain.

The `check_status` dispatchable can be executed to update the spend's
payment state and retry the `payout` if the payment has failed.

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: command-bot <>

polkadot/runtime/common/src/impls.rs

@@ -18,8 +18,10 @@
 
 use crate::NegativeImbalance;
 use frame_support::traits::{Currency, Imbalance, OnUnbalanced};
+use parity_scale_codec::{Decode, Encode, MaxEncodedLen};
 use primitives::Balance;
-use sp_runtime::Perquintill;
+use sp_runtime::{traits::TryConvert, Perquintill, RuntimeDebug};
+use xcm::VersionedMultiLocation;
 
 /// Logic for the author to get a portion of fees.
 pub struct ToAuthor<R>(sp_std::marker::PhantomData<R>);
@@ -98,13 +100,104 @@ pub fn era_payout(
 	(staking_payout, rest)
 }
 
+/// Versioned locatable asset type which contains both an XCM `location` and `asset_id` to identify
+/// an asset which exists on some chain.
+#[derive(
+	Encode, Decode, Eq, PartialEq, Clone, RuntimeDebug, scale_info::TypeInfo, MaxEncodedLen,
+)]
+pub enum VersionedLocatableAsset {
+	#[codec(index = 3)]
+	V3 {
+		/// The (relative) location in which the asset ID is meaningful.
+		location: xcm::v3::MultiLocation,
+		/// The asset's ID.
+		asset_id: xcm::v3::AssetId,
+	},
+}
+
+/// Converts the [`VersionedLocatableAsset`] to the [`xcm_builder::LocatableAssetId`].
+pub struct LocatableAssetConverter;
+impl TryConvert<VersionedLocatableAsset, xcm_builder::LocatableAssetId>
+	for LocatableAssetConverter
+{
+	fn try_convert(
+		asset: VersionedLocatableAsset,
+	) -> Result<xcm_builder::LocatableAssetId, VersionedLocatableAsset> {
+		match asset {
+			VersionedLocatableAsset::V3 { location, asset_id } =>
+				Ok(xcm_builder::LocatableAssetId { asset_id, location }),
+		}
+	}
+}
+
+/// Converts the [`VersionedMultiLocation`] to the [`xcm::latest::MultiLocation`].
+pub struct VersionedMultiLocationConverter;
+impl TryConvert<&VersionedMultiLocation, xcm::latest::MultiLocation>
+	for VersionedMultiLocationConverter
+{
+	fn try_convert(
+		location: &VersionedMultiLocation,
+	) -> Result<xcm::latest::MultiLocation, &VersionedMultiLocation> {
+		let latest = match location.clone() {
+			VersionedMultiLocation::V2(l) => l.try_into().map_err(|_| location)?,
+			VersionedMultiLocation::V3(l) => l,
+		};
+		Ok(latest)
+	}
+}
+
+#[cfg(feature = "runtime-benchmarks")]
+pub mod benchmarks {
+	use super::VersionedLocatableAsset;
+	use pallet_asset_rate::AssetKindFactory;
+	use pallet_treasury::ArgumentsFactory as TreasuryArgumentsFactory;
+	use xcm::prelude::*;
+
+	/// Provides a factory method for the [`VersionedLocatableAsset`].
+	/// The location of the asset is determined as a Parachain with an ID equal to the passed seed.
+	pub struct AssetRateArguments;
+	impl AssetKindFactory<VersionedLocatableAsset> for AssetRateArguments {
+		fn create_asset_kind(seed: u32) -> VersionedLocatableAsset {
+			VersionedLocatableAsset::V3 {
+				location: xcm::v3::MultiLocation::new(0, X1(Parachain(seed))),
+				asset_id: xcm::v3::MultiLocation::new(
+					0,
+					X2(PalletInstance(seed.try_into().unwrap()), GeneralIndex(seed.into())),
+				)
+				.into(),
+			}
+		}
+	}
+
+	/// Provide factory methods for the [`VersionedLocatableAsset`] and the `Beneficiary` of the
+	/// [`VersionedMultiLocation`]. The location of the asset is determined as a Parachain with an
+	/// ID equal to the passed seed.
+	pub struct TreasuryArguments;
+	impl TreasuryArgumentsFactory<VersionedLocatableAsset, VersionedMultiLocation>
+		for TreasuryArguments
+	{
+		fn create_asset_kind(seed: u32) -> VersionedLocatableAsset {
+			AssetRateArguments::create_asset_kind(seed)
+		}
+		fn create_beneficiary(seed: [u8; 32]) -> VersionedMultiLocation {
+			VersionedMultiLocation::V3(xcm::v3::MultiLocation::new(
+				0,
+				X1(AccountId32 { network: None, id: seed }),
+			))
+		}
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;
 	use frame_support::{
 		dispatch::DispatchClass,
 		parameter_types,
-		traits::{ConstU32, FindAuthor},
+		traits::{
+			tokens::{PayFromAccount, UnityAssetBalanceConversion},
+			ConstU32, FindAuthor,
+		},
 		weights::Weight,
 		PalletId,
 	};
@@ -189,6 +282,7 @@ mod tests {
 	parameter_types! {
 		pub const TreasuryPalletId: PalletId = PalletId(*b"py/trsry");
 		pub const MaxApprovals: u32 = 100;
+		pub TreasuryAccount: AccountId = Treasury::account_id();
 	}
 
 	impl pallet_treasury::Config for Test {
@@ -208,6 +302,14 @@ mod tests {
 		type MaxApprovals = MaxApprovals;
 		type WeightInfo = ();
 		type SpendOrigin = frame_support::traits::NeverEnsureOrigin<u64>;
+		type AssetKind = ();
+		type Beneficiary = Self::AccountId;
+		type BeneficiaryLookup = IdentityLookup<Self::AccountId>;
+		type Paymaster = PayFromAccount<Balances, TreasuryAccount>;
+		type BalanceConverter = UnityAssetBalanceConversion;
+		type PayoutPeriod = ConstU64<0>;
+		#[cfg(feature = "runtime-benchmarks")]
+		type BenchmarkHelper = ();
 	}
 
 	pub struct OneAuthor;