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 <>

substrate/frame/support/src/traits/tokens.rs

@@ -31,6 +31,7 @@ pub mod pay;
 pub use misc::{
 	AssetId, Balance, BalanceStatus, ConversionFromAssetBalance, ConversionToAssetBalance,
 	ConvertRank, DepositConsequence, ExistenceRequirement, Fortitude, GetSalary, Locker, Precision,
-	Preservation, Provenance, Restriction, WithdrawConsequence, WithdrawReasons,
+	Preservation, Provenance, Restriction, UnityAssetBalanceConversion, WithdrawConsequence,
+	WithdrawReasons,
 };
 pub use pay::{Pay, PayFromAccount, PaymentStatus};

substrate/frame/support/src/traits/tokens/misc.rs

@@ -277,6 +277,26 @@ pub trait ConversionFromAssetBalance<AssetBalance, AssetId, OutBalance> {
 		balance: AssetBalance,
 		asset_id: AssetId,
 	) -> Result<OutBalance, Self::Error>;
+	/// Ensures that a conversion for the `asset_id` will be successful if done immediately after
+	/// this call.
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_successful(asset_id: AssetId);
+}
+
+/// Implements [`ConversionFromAssetBalance`], enabling a 1:1 conversion of the asset balance
+/// value to the balance.
+pub struct UnityAssetBalanceConversion;
+impl<AssetBalance, AssetId, OutBalance>
+	ConversionFromAssetBalance<AssetBalance, AssetId, OutBalance> for UnityAssetBalanceConversion
+where
+	AssetBalance: Into<OutBalance>,
+{
+	type Error = ();
+	fn from_asset_balance(balance: AssetBalance, _: AssetId) -> Result<OutBalance, Self::Error> {
+		Ok(balance.into())
+	}
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_successful(_: AssetId) {}
 }
 
 /// Trait to handle NFT locking mechanism to ensure interactions with the asset can be implemented

substrate/frame/support/src/traits/tokens/pay.rs

@@ -23,7 +23,7 @@ use sp_core::{RuntimeDebug, TypedGet};
 use sp_runtime::DispatchError;
 use sp_std::fmt::Debug;
 
-use super::{fungible, Balance, Preservation::Expendable};
+use super::{fungible, fungibles, Balance, Preservation::Expendable};
 
 /// Can be implemented by `PayFromAccount` using a `fungible` impl, but can also be implemented with
 /// XCM/MultiAsset and made generic over assets.
@@ -107,3 +107,36 @@ impl<A: TypedGet, F: fungible::Mutate<A::Type>> Pay for PayFromAccount<F, A> {
 	#[cfg(feature = "runtime-benchmarks")]
 	fn ensure_concluded(_: Self::Id) {}
 }
+
+/// Simple implementation of `Pay` for assets which makes a payment from a "pot" - i.e. a single
+/// account.
+pub struct PayAssetFromAccount<F, A>(sp_std::marker::PhantomData<(F, A)>);
+impl<A, F> frame_support::traits::tokens::Pay for PayAssetFromAccount<F, A>
+where
+	A: TypedGet,
+	F: fungibles::Mutate<A::Type> + fungibles::Create<A::Type>,
+{
+	type Balance = F::Balance;
+	type Beneficiary = A::Type;
+	type AssetKind = F::AssetId;
+	type Id = ();
+	type Error = DispatchError;
+	fn pay(
+		who: &Self::Beneficiary,
+		asset: Self::AssetKind,
+		amount: Self::Balance,
+	) -> Result<Self::Id, Self::Error> {
+		<F as fungibles::Mutate<_>>::transfer(asset, &A::get(), who, amount, Expendable)?;
+		Ok(())
+	}
+	fn check_payment(_: ()) -> PaymentStatus {
+		PaymentStatus::Success
+	}
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_successful(_: &Self::Beneficiary, asset: Self::AssetKind, amount: Self::Balance) {
+		<F as fungibles::Create<_>>::create(asset.clone(), A::get(), true, amount).unwrap();
+		<F as fungibles::Mutate<_>>::mint_into(asset, &A::get(), amount).unwrap();
+	}
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_concluded(_: Self::Id) {}
+}