Make Pay trait from salaries pallet more generic (#13609)

* Make Pay trait from salaries pallet more generic

* Rename and add missing

* Update frame/support/src/traits/tokens/pay.rs

* Update pay.rs

* Update pay.rs

* Update pay.rs

* Add better documentation for the AssetKind associated type

---------

Co-authored-by: Gavin Wood <gavin@parity.io>
Co-authored-by: parity-processbot <>

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

@@ -27,7 +27,9 @@ pub mod nonfungible_v2;
 pub mod nonfungibles;
 pub mod nonfungibles_v2;
 pub use imbalance::Imbalance;
+pub mod pay;
 pub use misc::{
 	AssetId, Balance, BalanceConversion, BalanceStatus, ConvertRank, DepositConsequence,
 	ExistenceRequirement, GetSalary, Locker, WithdrawConsequence, WithdrawReasons,
 };
+pub use pay::{Pay, PayFromAccount, PaymentStatus};

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

@@ -0,0 +1,103 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! The Pay trait and associated types.
+
+use codec::{Decode, Encode, FullCodec, MaxEncodedLen};
+use scale_info::TypeInfo;
+use sp_core::{RuntimeDebug, TypedGet};
+use sp_std::fmt::Debug;
+
+use super::{fungible, Balance};
+
+/// Can be implemented by `PayFromAccount` using a `fungible` impl, but can also be implemented with
+/// XCM/MultiAsset and made generic over assets.
+pub trait Pay {
+	/// The type by which we measure units of the currency in which we make payments.
+	type Balance: Balance;
+	/// The type by which we identify the beneficiaries to whom a payment may be made.
+	type Beneficiary;
+	/// The type for the kinds of asset that are going to be paid.
+	///
+	/// The unit type can be used here to indicate there's only one kind of asset to do payments
+	/// with. When implementing, it should be clear from the context what that asset is.
+	type AssetKind;
+	/// An identifier given to an individual payment.
+	type Id: FullCodec + MaxEncodedLen + TypeInfo + Clone + Eq + PartialEq + Debug + Copy;
+	/// Make a payment and return an identifier for later evaluation of success in some off-chain
+	/// mechanism (likely an event, but possibly not on this chain).
+	fn pay(
+		who: &Self::Beneficiary,
+		asset_kind: Self::AssetKind,
+		amount: Self::Balance,
+	) -> Result<Self::Id, ()>;
+	/// Check how a payment has proceeded. `id` must have been previously returned by `pay` for
+	/// the result of this call to be meaningful. Once this returns anything other than
+	/// `InProgress` for some `id` it must return `Unknown` rather than the actual result
+	/// value.
+	fn check_payment(id: Self::Id) -> PaymentStatus;
+	/// Ensure that a call to pay with the given parameters will be successful if done immediately
+	/// after this call. Used in benchmarking code.
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_successful(who: &Self::Beneficiary, amount: Self::Balance);
+	/// Ensure that a call to `check_payment` with the given parameters will return either `Success`
+	/// or `Failure`.
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_concluded(id: Self::Id);
+}
+
+/// Status for making a payment via the `Pay::pay` trait function.
+#[derive(Encode, Decode, Eq, PartialEq, Clone, TypeInfo, MaxEncodedLen, RuntimeDebug)]
+pub enum PaymentStatus {
+	/// Payment is in progress. Nothing to report yet.
+	InProgress,
+	/// Payment status is unknowable. It may already have reported the result, or if not then
+	/// it will never be reported successful or failed.
+	Unknown,
+	/// Payment happened successfully.
+	Success,
+	/// Payment failed. It may safely be retried.
+	Failure,
+}
+
+/// Simple implementation of `Pay` which makes a payment from a "pot" - i.e. a single account.
+pub struct PayFromAccount<F, A>(sp_std::marker::PhantomData<(F, A)>);
+impl<A: TypedGet, F: fungible::Transfer<A::Type> + fungible::Mutate<A::Type>> Pay
+	for PayFromAccount<F, A>
+{
+	type Balance = F::Balance;
+	type Beneficiary = A::Type;
+	type AssetKind = ();
+	type Id = ();
+	fn pay(
+		who: &Self::Beneficiary,
+		_: Self::AssetKind,
+		amount: Self::Balance,
+	) -> Result<Self::Id, ()> {
+		<F as fungible::Transfer<_>>::transfer(&A::get(), who, amount, false).map_err(|_| ())?;
+		Ok(())
+	}
+	fn check_payment(_: ()) -> PaymentStatus {
+		PaymentStatus::Success
+	}
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_successful(_: &Self::Beneficiary, amount: Self::Balance) {
+		<F as fungible::Mutate<_>>::mint_into(&A::get(), amount).unwrap();
+	}
+	#[cfg(feature = "runtime-benchmarks")]
+	fn ensure_concluded(_: Self::Id) {}
+}