API for registering inactive funds

frame/balances/src/lib.rs

@@ -161,6 +161,7 @@ mod tests_local;
 #[cfg(test)]
 mod tests_reentrancy;
 pub mod weights;
+pub mod migration;
 
 pub use self::imbalances::{NegativeImbalance, PositiveImbalance};
 use codec::{Codec, Decode, Encode, MaxEncodedLen};
@@ -497,6 +498,12 @@ pub mod pallet {
 	#[pallet::whitelist_storage]
 	pub type TotalIssuance<T: Config<I>, I: 'static = ()> = StorageValue<_, T::Balance, ValueQuery>;
 
+	/// The total units of outstanding deactivated balance in the system.
+	#[pallet::storage]
+	#[pallet::getter(fn inactive_issuance)]
+	#[pallet::whitelist_storage]
+	pub type InactiveIssuance<T: Config<I>, I: 'static = ()> = StorageValue<_, T::Balance, ValueQuery>;
+
 	/// The Balances pallet example of storing the balance of an account.
 	///
 	/// # Example
@@ -1067,6 +1074,9 @@ impl<T: Config<I>, I: 'static> fungible::Inspect<T::AccountId> for Pallet<T, I>
 	fn total_issuance() -> Self::Balance {
 		TotalIssuance::<T, I>::get()
 	}
+	fn active_issuance() -> Self::Balance {
+		TotalIssuance::<T, I>::get().saturating_sub(InactiveIssuance::<T, I>::get())
+	}
 	fn minimum_balance() -> Self::Balance {
 		T::ExistentialDeposit::get()
 	}
@@ -1145,6 +1155,14 @@ impl<T: Config<I>, I: 'static> fungible::Transfer<T::AccountId> for Pallet<T, I>
 		let er = if keep_alive { KeepAlive } else { AllowDeath };
 		<Self as Currency<T::AccountId>>::transfer(source, dest, amount, er).map(|_| amount)
 	}
+
+	fn deactivate(amount: Self::Balance) {
+		InactiveIssuance::<T, I>::mutate(|b| b.saturating_accrue(amount));
+	}
+
+	fn reactivate(amount: Self::Balance) {
+		InactiveIssuance::<T, I>::mutate(|b| b.saturating_reduce(amount));
+	}
 }
 
 impl<T: Config<I>, I: 'static> fungible::Unbalanced<T::AccountId> for Pallet<T, I> {
@@ -1418,7 +1436,19 @@ where
 	}
 
 	fn total_issuance() -> Self::Balance {
-		<TotalIssuance<T, I>>::get()
+		TotalIssuance::<T, I>::get()
+	}
+
+	fn active_issuance() -> Self::Balance {
+		<Self as fungibles::Inspect>::active_issuance()
+	}
+
+	fn deactivate(amount: Self::Balance) {
+		<Self as fungibles::Transfer>::deactivate(amount);
+	}
+
+	fn reactivate(amount: Self::Balance) {
+		<Self as fungibles::Transfer>::reactivate(amount);
 	}
 
 	fn minimum_balance() -> Self::Balance {

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

@@ -59,6 +59,16 @@ pub trait Currency<AccountId> {
 	/// The total amount of issuance in the system.
 	fn total_issuance() -> Self::Balance;
 
+	/// The total amount of issuance in the system excluding those which are controlled by the
+	/// system.
+	fn active_issuance() -> Self::Balance { Self::total_issuance() }
+
+	/// Reduce the active issuance by some amount.
+	fn deactivate(_: Self::Balance) {}
+
+	/// Increase the active issuance by some amount, up to the outstanding amount reduced.
+	fn reactivate(_: Self::Balance) {}
+
 	/// The minimum balance any single account may have. This is equivalent to the `Balances`
 	/// module's `ExistentialDeposit`.
 	fn minimum_balance() -> Self::Balance;
@@ -212,6 +222,15 @@ impl<C: Currency<A>, A> Get<C::Balance> for TotalIssuanceOf<C, A> {
 	}
 }
 
+/// A non-const `Get` implementation parameterised by a `Currency` impl which provides the result
+/// of `active_issuance`.
+pub struct ActiveIssuanceOf<C: Currency<A>, A>(sp_std::marker::PhantomData<(C, A)>);
+impl<C: Currency<A>, A> Get<C::Balance> for ActiveIssuanceOf<C, A> {
+	fn get() -> C::Balance {
+		C::active_issuance()
+	}
+}
+
 #[cfg(feature = "std")]
 impl<AccountId> Currency<AccountId> for () {
 	type Balance = u32;

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

@@ -40,6 +40,10 @@ pub trait Inspect<AccountId> {
 	/// The total amount of issuance in the system.
 	fn total_issuance() -> Self::Balance;
 
+	/// The total amount of issuance in the system excluding those which are controlled by the
+	/// system.
+	fn active_issuance() -> Self::Balance { Self::total_issuance() }
+
 	/// The minimum balance any single account may have.
 	fn minimum_balance() -> Self::Balance;
 
@@ -120,6 +124,12 @@ pub trait Transfer<AccountId>: Inspect<AccountId> {
 		amount: Self::Balance,
 		keep_alive: bool,
 	) -> Result<Self::Balance, DispatchError>;
+
+	/// Reduce the active issuance by some amount.
+	fn deactivate(_: Self::Balance) {}
+
+	/// Increase the active issuance by some amount, up to the outstanding amount reduced.
+	fn reactivate(_: Self::Balance) {}
 }
 
 /// Trait for inspecting a fungible asset which can be reserved.
@@ -213,6 +223,9 @@ impl<
 	fn total_issuance() -> Self::Balance {
 		<F as fungibles::Inspect<AccountId>>::total_issuance(A::get())
 	}
+	fn active_issuance() -> Self::Balance {
+		<F as fungibles::Inspect<AccountId>>::active_issuance(A::get())
+	}
 	fn minimum_balance() -> Self::Balance {
 		<F as fungibles::Inspect<AccountId>>::minimum_balance(A::get())
 	}
@@ -258,6 +271,12 @@ impl<
 	) -> Result<Self::Balance, DispatchError> {
 		<F as fungibles::Transfer<AccountId>>::transfer(A::get(), source, dest, amount, keep_alive)
 	}
+	fn deactivate(amount: Self::Balance) {
+		<F as fungibles::Transfer<AccountId>>::deactivate(A::get(), amount)
+	}
+	fn reactivate(amount: Self::Balance) {
+		<F as fungibles::Transfer<AccountId>>::reactivate(A::get(), amount)
+	}
 }
 
 impl<

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

@@ -46,6 +46,10 @@ pub trait Inspect<AccountId> {
 	/// The total amount of issuance in the system.
 	fn total_issuance(asset: Self::AssetId) -> Self::Balance;
 
+	/// The total amount of issuance in the system excluding those which are controlled by the
+	/// system.
+	fn active_issuance(asset: Self::AssetId) -> Self::Balance { Self::total_issuance(asset) }
+
 	/// The minimum balance any single account may have.
 	fn minimum_balance(asset: Self::AssetId) -> Self::Balance;
 
@@ -177,6 +181,12 @@ pub trait Transfer<AccountId>: Inspect<AccountId> {
 		amount: Self::Balance,
 		keep_alive: bool,
 	) -> Result<Self::Balance, DispatchError>;
+
+	/// Reduce the active issuance by some amount.
+	fn deactivate(_: Self::AssetId, _: Self::Balance) {}
+
+	/// Increase the active issuance by some amount, up to the outstanding amount reduced.
+	fn reactivate(_: Self::AssetId, _: Self::Balance) {}
 }
 
 /// Trait for inspecting a set of named fungible assets which can be placed on hold.

frame/treasury/src/lib.rs

@@ -62,6 +62,7 @@ mod benchmarking;
 #[cfg(test)]
 mod tests;
 pub mod weights;
+pub mod migration;
 
 use codec::{Decode, Encode, MaxEncodedLen};
 use scale_info::TypeInfo;
@@ -138,6 +139,7 @@ pub mod pallet {
 	use super::*;
 	use frame_support::pallet_prelude::*;
 	use frame_system::pallet_prelude::*;
+use sp_runtime::traits::CheckedSub;
 
 	#[pallet::pallet]
 	#[pallet::generate_store(pub(super) trait Store)]
@@ -229,6 +231,11 @@ pub mod pallet {
 	pub type Approvals<T: Config<I>, I: 'static = ()> =
 		StorageValue<_, BoundedVec<ProposalIndex, T::MaxApprovals>, ValueQuery>;
 
+	/// The amount which has been reported as inactive to Currency.
+	#[pallet::storage]
+	pub type Deactivated<T: Config<I>, I: 'static = ()> =
+		StorageValue<_, BalanceOf<T>, ValueQuery>;
+
 	#[pallet::genesis_config]
 	pub struct GenesisConfig;
 
@@ -322,6 +329,14 @@ pub mod pallet {
 			} else {
 				Weight::zero()
 			}
+			let pot = Self::pot();
+			let deactivated = Deactivated::<T>::get();
+			if let Some(v) = pot.checked_sub(&deactivated) {
+				T::Currency::deactivate(v)
+			}
+			else if let Some(v) = deactivated.checked_sub(&pot) {
+				T::Currency::reactivate(v)
+			}
 		}
 	}