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/westend/src/lib.rs

@@ -53,9 +53,14 @@ use primitives::{
 	ValidatorSignature, PARACHAIN_KEY_TYPE_ID,
 };
 use runtime_common::{
-	assigned_slots, auctions, crowdloan, elections::OnChainAccuracy, impl_runtime_weights,
-	impls::ToAuthor, paras_registrar, paras_sudo_wrapper, prod_or_fast, slots, BalanceToU256,
-	BlockHashCount, BlockLength, CurrencyToVote, SlowAdjustingFeeUpdate, U256ToBalance,
+	assigned_slots, auctions, crowdloan,
+	elections::OnChainAccuracy,
+	impl_runtime_weights,
+	impls::{
+		LocatableAssetConverter, ToAuthor, VersionedLocatableAsset, VersionedMultiLocationConverter,
+	},
+	paras_registrar, paras_sudo_wrapper, prod_or_fast, slots, BalanceToU256, BlockHashCount,
+	BlockLength, CurrencyToVote, SlowAdjustingFeeUpdate, U256ToBalance,
 };
 use runtime_parachains::{
 	assigner_parachains as parachains_assigner_parachains,
@@ -77,7 +82,7 @@ use sp_runtime::{
 	generic, impl_opaque_keys,
 	traits::{
 		AccountIdLookup, BlakeTwo256, Block as BlockT, ConvertInto, Extrinsic as ExtrinsicT,
-		Keccak256, OpaqueKeys, SaturatedConversion, Verify,
+		IdentityLookup, Keccak256, OpaqueKeys, SaturatedConversion, Verify,
 	},
 	transaction_validity::{TransactionPriority, TransactionSource, TransactionValidity},
 	ApplyExtrinsicResult, FixedU128, KeyTypeId, Perbill, Percent, Permill,
@@ -87,7 +92,11 @@ use sp_std::{collections::btree_map::BTreeMap, prelude::*};
 #[cfg(any(feature = "std", test))]
 use sp_version::NativeVersion;
 use sp_version::RuntimeVersion;
-use xcm::latest::Junction;
+use xcm::{
+	latest::{InteriorMultiLocation, Junction, Junction::PalletInstance},
+	VersionedMultiLocation,
+};
+use xcm_builder::PayOverXcm;
 
 pub use frame_system::Call as SystemCall;
 pub use pallet_balances::Call as BalancesCall;
@@ -698,6 +707,10 @@ parameter_types! {
 	pub const SpendPeriod: BlockNumber = 6 * DAYS;
 	pub const Burn: Permill = Permill::from_perthousand(2);
 	pub const TreasuryPalletId: PalletId = PalletId(*b"py/trsry");
+	pub const PayoutSpendPeriod: BlockNumber = 30 * DAYS;
+	// The asset's interior location for the paying account. This is the Treasury
+	// pallet instance (which sits at index 37).
+	pub TreasuryInteriorLocation: InteriorMultiLocation = PalletInstance(37).into();
 
 	pub const TipCountdown: BlockNumber = 1 * DAYS;
 	pub const TipFindersFee: Percent = Percent::from_percent(20);
@@ -707,6 +720,7 @@ parameter_types! {
 	pub const MaxAuthorities: u32 = 100_000;
 	pub const MaxKeys: u32 = 10_000;
 	pub const MaxPeerInHeartbeats: u32 = 10_000;
+	pub const MaxBalance: Balance = Balance::max_value();
 }
 
 impl pallet_treasury::Config for Runtime {
@@ -726,6 +740,23 @@ impl pallet_treasury::Config for Runtime {
 	type WeightInfo = weights::pallet_treasury::WeightInfo<Runtime>;
 	type SpendFunds = ();
 	type SpendOrigin = TreasurySpender;
+	type AssetKind = VersionedLocatableAsset;
+	type Beneficiary = VersionedMultiLocation;
+	type BeneficiaryLookup = IdentityLookup<Self::Beneficiary>;
+	type Paymaster = PayOverXcm<
+		TreasuryInteriorLocation,
+		crate::xcm_config::XcmRouter,
+		crate::XcmPallet,
+		ConstU32<{ 6 * HOURS }>,
+		Self::Beneficiary,
+		Self::AssetKind,
+		LocatableAssetConverter,
+		VersionedMultiLocationConverter,
+	>;
+	type BalanceConverter = AssetRate;
+	type PayoutPeriod = PayoutSpendPeriod;
+	#[cfg(feature = "runtime-benchmarks")]
+	type BenchmarkHelper = runtime_common::impls::benchmarks::TreasuryArguments;
 }
 
 impl pallet_offences::Config for Runtime {
@@ -1331,6 +1362,18 @@ parameter_types! {
 	pub const MigrationMaxKeyLen: u32 = 512;
 }
 
+impl pallet_asset_rate::Config for Runtime {
+	type WeightInfo = weights::pallet_asset_rate::WeightInfo<Runtime>;
+	type RuntimeEvent = RuntimeEvent;
+	type CreateOrigin = EnsureRoot<AccountId>;
+	type RemoveOrigin = EnsureRoot<AccountId>;
+	type UpdateOrigin = EnsureRoot<AccountId>;
+	type Currency = Balances;
+	type AssetKind = <Runtime as pallet_treasury::Config>::AssetKind;
+	#[cfg(feature = "runtime-benchmarks")]
+	type BenchmarkHelper = runtime_common::impls::benchmarks::AssetRateArguments;
+}
+
 construct_runtime! {
 	pub enum Runtime
 	{
@@ -1443,6 +1486,9 @@ construct_runtime! {
 
 		// Generalized message queue
 		MessageQueue: pallet_message_queue::{Pallet, Call, Storage, Event<T>} = 100,
+
+		// Asset rate.
+		AssetRate: pallet_asset_rate::{Pallet, Call, Storage, Event<T>} = 101,
 	}
 }
 
@@ -1574,6 +1620,7 @@ mod benches {
 		[pallet_utility, Utility]
 		[pallet_vesting, Vesting]
 		[pallet_whitelist, Whitelist]
+		[pallet_asset_rate, AssetRate]
 		// XCM
 		[pallet_xcm, XcmPallet]
 		// NOTE: Make sure you point to the individual modules below.