Generic slashing side-effects

cumulus/parachains/runtimes/assets/asset-hub-rococo/src/lib.rs

@@ -214,6 +214,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/assets/asset-hub-westend/src/lib.rs

@@ -212,6 +212,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-rococo/src/lib.rs

@@ -338,6 +338,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-westend/src/lib.rs

@@ -313,6 +313,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
+
 }
 
 parameter_types! {

cumulus/parachains/runtimes/collectives/collectives-westend/src/lib.rs

@@ -222,6 +222,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/contracts/contracts-rococo/src/lib.rs

@@ -234,6 +234,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/coretime/coretime-rococo/src/lib.rs

@@ -246,6 +246,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/coretime/coretime-westend/src/lib.rs

@@ -246,6 +246,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/people/people-rococo/src/lib.rs

@@ -222,6 +222,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/people/people-westend/src/lib.rs

@@ -222,6 +222,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/testing/penpal/src/lib.rs

@@ -420,6 +420,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

cumulus/parachains/runtimes/testing/rococo-parachain/src/lib.rs

@@ -257,6 +257,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 impl pallet_transaction_payment::Config for Runtime {

polkadot/runtime/rococo/src/lib.rs

@@ -402,6 +402,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type MaxFreezes = ConstU32<1>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {
@@ -1236,6 +1237,7 @@ impl pallet_balances::Config<NisCounterpartInstance> for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<1>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

polkadot/runtime/test-runtime/src/lib.rs

@@ -236,6 +236,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
 	type MaxFreezes = ConstU32<0>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

polkadot/runtime/westend/src/lib.rs

@@ -402,6 +402,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = RuntimeFreezeReason;
 	type MaxFreezes = VariantCountOf<RuntimeFreezeReason>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

prdoc/pr_5623.prdoc

@@ -0,0 +1,32 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Generic slashing side-effects
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      What?
+      Make it possible for other pallets to implement their own logic when a slash on a balance occurs.
+
+      Why?
+      In the introduction of holds @gavofyork said:
+
+      Since Holds are designed to be infallibly slashed, this means that any logic using a Freeze must handle the possibility of the frozen amount being reduced, potentially to zero. A permissionless function should be provided in order to allow bookkeeping to be updated in this instance.
+
+      At Polimec we needed to find a way to reduce the vesting schedules of our users after a slash was made, and after talking to @kianenigma at the Web3Summit, we realized there was no easy way to implement this with the current traits, so we came up with this solution.
+
+      I also have a working implementation of done_slash for pallet_vesting which I can add to this PR or another one.
+
+      How?
+      First we abstract the done_slash function of holds::Balanced to it's own trait that any pallet can implement.
+      Then we add a config type in pallet-balances that accepts a callback tuple of all the pallets that implement this trait.
+      Finally implement done_slash for pallet-balances such that it calls the config type.
+      Integration
+      The default implementation of done_slash is still an empty function, and the new config type of pallet-balances can be set to an empty tuple, so nothing changes by default.
+
+crates:
+  - name: frame-support
+    bump: major
+  - name: pallet-balances
+    bump: major

substrate/bin/node/runtime/src/lib.rs

@@ -546,6 +546,7 @@ impl pallet_balances::Config for Runtime {
 	type WeightInfo = pallet_balances::weights::SubstrateWeight<Runtime>;
 	type FreezeIdentifier = RuntimeFreezeReason;
 	type MaxFreezes = VariantCountOf<RuntimeFreezeReason>;
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

substrate/frame/assets-freezer/src/mock.rs

@@ -87,6 +87,7 @@ impl pallet_balances::Config for Test {
 	type MaxFreezes = ();
 	type RuntimeHoldReason = ();
 	type RuntimeFreezeReason = ();
+	type DoneSlashHandler = ();
 }
 
 impl pallet_assets::Config for Test {

substrate/frame/balances/src/impl_fungible.rs

@@ -363,6 +363,12 @@ impl<T: Config<I>, I: 'static> fungible::Balanced<T::AccountId> for Pallet<T, I>
 
 impl<T: Config<I>, I: 'static> fungible::BalancedHold<T::AccountId> for Pallet<T, I> {}
 
+impl<T: Config<I>, I: 'static> fungible::hold::DoneSlash<T::RuntimeHoldReason, T::AccountId, T::Balance> for Pallet<T, I> {
+	fn done_slash(reason: &T::RuntimeHoldReason, who: &T::AccountId, amount: T::Balance) {
+		T::DoneSlashHandler::done_slash(reason, who, amount);
+	}
+}
+
 impl<T: Config<I>, I: 'static> AccountTouch<(), T::AccountId> for Pallet<T, I> {
 	type Balance = T::Balance;
 	fn deposit_required(_: ()) -> Self::Balance {

substrate/frame/balances/src/lib.rs

@@ -234,6 +234,7 @@ pub mod pallet {
 			type MaxFreezes = VariantCountOf<Self::RuntimeFreezeReason>;
 
 			type WeightInfo = ();
+			type DoneSlashHandler = ();
 		}
 	}
 
@@ -312,6 +313,8 @@ pub mod pallet {
 		/// The maximum number of individual freeze locks that can exist on an account at any time.
 		#[pallet::constant]
 		type MaxFreezes: Get<u32>;
+
+		type DoneSlashHandler: fungible::hold::DoneSlash<Self::RuntimeHoldReason, Self::AccountId, Self::Balance>;
 	}
 
 	/// The in-code storage version.

substrate/frame/contracts/mock-network/src/parachain.rs

@@ -94,6 +94,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type WeightInfo = ();
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

substrate/frame/contracts/mock-network/src/relay_chain.rs

@@ -89,6 +89,7 @@ impl pallet_balances::Config for Runtime {
 	type MaxFreezes = ConstU32<0>;
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
+	type DoneSlashHandler = ();
 }
 
 impl shared::Config for Runtime {

substrate/frame/nis/src/mock.rs

@@ -64,6 +64,7 @@ impl pallet_balances::Config<Instance1> for Test {
 	type MaxFreezes = ();
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
+	type DoneSlashHandler = ();
 }
 
 impl pallet_balances::Config<Instance2> for Test {
@@ -84,6 +85,7 @@ impl pallet_balances::Config<Instance2> for Test {
 	type MaxFreezes = ();
 	type RuntimeHoldReason = ();
 	type RuntimeFreezeReason = ();
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

substrate/frame/revive/mock-network/src/parachain.rs

@@ -94,6 +94,7 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type WeightInfo = ();
+	type DoneSlashHandler = ();
 }
 
 parameter_types! {

substrate/frame/revive/mock-network/src/relay_chain.rs

@@ -89,6 +89,7 @@ impl pallet_balances::Config for Runtime {
 	type MaxFreezes = ConstU32<0>;
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
+	type DoneSlashHandler = ();
 }
 
 impl shared::Config for Runtime {

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

@@ -430,7 +430,7 @@ pub trait Mutate<AccountId>:
 }
 
 /// Trait for slashing a fungible asset which can be place on hold.
-pub trait Balanced<AccountId>: super::Balanced<AccountId> + Unbalanced<AccountId> {
+pub trait Balanced<AccountId>: super::Balanced<AccountId> + Unbalanced<AccountId> + DoneSlash<Self::Reason, AccountId, Self::Balance> {
 	/// Reduce the balance of some funds on hold in an account.
 	///
 	/// The resulting imbalance is the first item of the tuple returned.
@@ -449,6 +449,16 @@ pub trait Balanced<AccountId>: super::Balanced<AccountId> + Unbalanced<AccountId
 		Self::done_slash(reason, who, decrease);
 		(credit, amount.saturating_sub(decrease))
 	}
+}
 
-	fn done_slash(_reason: &Self::Reason, _who: &AccountId, _amount: Self::Balance) {}
+pub trait DoneSlash<Reason, AccountId, Balance> {
+	fn done_slash(_reason: &Reason, _who: &AccountId, _amount: Balance) {}
 }
+
+#[impl_trait_for_tuples::impl_for_tuples(30)]
+impl<Reason, AccountId, Balance: Copy> DoneSlash<Reason, AccountId, Balance> for Tuple {
+	fn done_slash(reason: &Reason, who: &AccountId, amount: Balance) {
+		for_tuples!( #( Tuple::done_slash(reason, who, amount); )* );
+	}
+}
+

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

@@ -22,6 +22,7 @@
 //!
 //! See the [`crate::traits::fungible`] doc for more information about fungible traits.
 
+use frame_support::traits::fungible::hold::DoneSlash;
 use super::*;
 use crate::traits::{
 	fungible::imbalance,
@@ -467,5 +468,16 @@ impl<
 	}
 }
 
+impl<
+	F: fungibles::BalancedHold<AccountId>,
+	A: Get<<F as fungibles::Inspect<AccountId>>::AssetId>,
+	AccountId,
+> DoneSlash<F::Reason, AccountId, F::Balance> for ItemOf<F, A, AccountId>
+{
+	fn done_slash(reason: &F::Reason, who: &AccountId, amount: F::Balance) {
+		<F as fungibles::hold::DoneSlash<F::AssetId, F::Reason, AccountId, F::Balance>>::done_slash(A::get(), reason, who, amount)
+	}
+}
+
 #[test]
 fn test() {}

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

@@ -844,8 +844,8 @@ impl<
 }
 
 impl<
-		Left: fungible::BalancedHold<AccountId>,
-		Right: fungibles::BalancedHold<AccountId, Balance = Left::Balance, Reason = Left::Reason>,
+		Left: fungible::BalancedHold<AccountId> + fungible::hold::DoneSlash<Self::Reason, AccountId, Self::Balance>,
+		Right: fungibles::BalancedHold<AccountId, Balance = Left::Balance, Reason = Left::Reason> + fungibles::hold::DoneSlash<AssetKind, Left::Reason, AccountId, Left::Balance>,
 		Criterion: Convert<AssetKind, Either<(), Right::AssetId>>,
 		AssetKind: AssetId,
 		AccountId,
@@ -871,6 +871,26 @@ impl<
 		}
 	}
 }
+impl<
+	Reason,
+	Balance,
+	Left: fungible::hold::DoneSlash<Reason, AccountId, Balance>,
+	Right: fungibles::hold::DoneSlash<Right::AssetId, Reason, AccountId, Balance> + fungibles::Inspect<AccountId>,
+	Criterion: Convert<AssetKind, Either<(), Right::AssetId>>,
+	AssetKind: AssetId,
+	AccountId,
+> fungibles::hold::DoneSlash<AssetKind, Reason, AccountId, Balance> for UnionOf<Left, Right, Criterion, AssetKind, AccountId> {
+	fn done_slash(asset: AssetKind, reason: &Reason, who: &AccountId, amount: Balance) {
+		match Criterion::convert(asset.clone()) {
+			Left(()) => {
+					Left::done_slash(reason, who, amount);
+			},
+			Right(a) => {
+					Right::done_slash(a, reason, who, amount);
+			},
+		}
+	}
+}
 
 impl<
 		Left: fungible::Inspect<AccountId>,

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

@@ -214,7 +214,7 @@ pub trait Unbalanced<AccountId>: Inspect<AccountId> {
 }
 
 /// Trait for slashing a fungible asset which can be place on hold.
-pub trait Balanced<AccountId>: super::Balanced<AccountId> + Unbalanced<AccountId> {
+pub trait Balanced<AccountId>: super::Balanced<AccountId> + Unbalanced<AccountId> + DoneSlash<Self::AssetId, Self::Reason, AccountId, Self::Balance> {
 	/// Reduce the balance of some funds on hold in an account.
 	///
 	/// The resulting imbalance is the first item of the tuple returned.
@@ -238,13 +238,16 @@ pub trait Balanced<AccountId>: super::Balanced<AccountId> + Unbalanced<AccountId
 		Self::done_slash(asset, reason, who, decrease);
 		(credit, amount.saturating_sub(decrease))
 	}
+}
 
-	fn done_slash(
-		_asset: Self::AssetId,
-		_reason: &Self::Reason,
-		_who: &AccountId,
-		_amount: Self::Balance,
-	) {
+pub trait DoneSlash<AssetId, Reason, AccountId, Balance> {
+	fn done_slash(_asset: AssetId, _reason: &Reason, _who: &AccountId, _amount: Balance) {}
+}
+
+#[impl_trait_for_tuples::impl_for_tuples(30)]
+impl<AssetId: Copy, Reason, AccountId, Balance: Copy> DoneSlash<AssetId, Reason, AccountId, Balance> for Tuple {
+	fn done_slash(asset_id: AssetId, reason: &Reason, who: &AccountId, amount: Balance) {
+		for_tuples!( #( Tuple::done_slash(asset_id, reason, who, amount); )* );
 	}
 }