[Pools] Refactors and runtime apis for DelegateStake (#4537)

## Runtime Apis
Introduces the following runtime apis to facilitate dapps and wallets in
integrating with the `DelegateStake` functionalities of the pools
(related: #3905). These
apis are meant to support pool and member migration, as well as lazy
application of pending slashes of pool members.

```rust
fn pool_pending_slash(pool_id: PoolId) -> Balance;
fn member_pending_slash(member: AccountId) -> Balance;
fn pool_needs_delegate_migration(pool_id: PoolId) -> bool;
fn member_needs_delegate_migration(member: AccountId) -> bool;
```

## Refactors
- Introduces newtypes for `Agent`, `Delegator`, `Pool` and
`[Pool]Member`. And refactors `StakeAdapter` and `DelegationInterface`
to accept the above types. This will help make these apis typesafe
against using wrong account type.
- Fixing `DelegationInterface` apis to return optional (instead of
default value if key does not exist).
- Rename struct `Agent` that wraps `AgentLedger` to `AgentOuterLedger`
which is clearer (naming wise) and different from the newtype `Agent`.
- Cleaning up new Pool events (related to `Delegation` feature of pool).

---------

Signed-off-by: Matteo Muraca <mmuraca247@gmail.com>
Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>
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polkadot/runtime/westend/src/lib.rs

@@ -2287,6 +2287,22 @@ sp_api::impl_runtime_apis! {
 		fn balance_to_points(pool_id: pallet_nomination_pools::PoolId, new_funds: Balance) -> Balance {
 			NominationPools::api_balance_to_points(pool_id, new_funds)
 		}
+
+		fn pool_pending_slash(pool_id: pallet_nomination_pools::PoolId) -> Balance {
+			NominationPools::api_pool_pending_slash(pool_id)
+		}
+
+		fn member_pending_slash(member: AccountId) -> Balance {
+			NominationPools::api_member_pending_slash(member)
+		}
+
+		fn pool_needs_delegate_migration(pool_id: pallet_nomination_pools::PoolId) -> bool {
+			NominationPools::api_pool_needs_delegate_migration(pool_id)
+		}
+
+		fn member_needs_delegate_migration(member: AccountId) -> bool {
+			NominationPools::api_member_needs_delegate_migration(member)
+		}
 	}
 
 	impl pallet_staking_runtime_api::StakingApi<Block, Balance, AccountId> for Runtime {

prdoc/pr_4537.prdoc

@@ -0,0 +1,27 @@
+# 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: Runtime apis to help with delegate-stake based Nomination Pools.
+
+doc:
+  - audience: Runtime User
+    description: |
+      Introduces a new set of runtime apis to facilitate dapps and wallets to integrate with delegate-stake
+      functionalities of Nomination Pools. These apis support pool and member migration, as well as lazy application of
+      pending slashes of the pool members.
+
+crates:
+  - name: pallet-nomination-pools
+    bump: minor
+  - name: westend-runtime
+    bump: minor
+  - name: kitchensink-runtime
+    bump: minor
+  - name: pallet-delegated-staking
+    bump: minor
+  - name: sp-staking
+    bump: minor
+  - name: pallet-nomination-pools-benchmarking
+    bump: patch
+  - name: pallet-nomination-pools-runtime-api
+    bump: minor

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

@@ -2774,6 +2774,22 @@ impl_runtime_apis! {
 		fn balance_to_points(pool_id: pallet_nomination_pools::PoolId, new_funds: Balance) -> Balance {
 			NominationPools::api_balance_to_points(pool_id, new_funds)
 		}
+
+		fn pool_pending_slash(pool_id: pallet_nomination_pools::PoolId) -> Balance {
+			NominationPools::api_pool_pending_slash(pool_id)
+		}
+
+		fn member_pending_slash(member: AccountId) -> Balance {
+			NominationPools::api_member_pending_slash(member)
+		}
+
+		fn pool_needs_delegate_migration(pool_id: pallet_nomination_pools::PoolId) -> bool {
+			NominationPools::api_pool_needs_delegate_migration(pool_id)
+		}
+
+		fn member_needs_delegate_migration(member: AccountId) -> bool {
+			NominationPools::api_member_needs_delegate_migration(member)
+		}
 	}
 
 	impl pallet_staking_runtime_api::StakingApi<Block, Balance, AccountId> for Runtime {

substrate/frame/delegated-staking/src/impls.rs

@@ -19,80 +19,78 @@
 //! Implementations of public traits, namely [`DelegationInterface`] and [`OnStakingUpdate`].
 
 use super::*;
-use sp_staking::{DelegationInterface, DelegationMigrator, OnStakingUpdate};
+use sp_staking::{Agent, DelegationInterface, DelegationMigrator, Delegator, OnStakingUpdate};
 
 impl<T: Config> DelegationInterface for Pallet<T> {
 	type Balance = BalanceOf<T>;
 	type AccountId = T::AccountId;
 
 	/// Effective balance of the `Agent` account.
-	fn agent_balance(who: &Self::AccountId) -> Self::Balance {
-		Agent::<T>::get(who)
-			.map(|agent| agent.ledger.effective_balance())
-			.unwrap_or_default()
+	fn agent_balance(agent: Agent<Self::AccountId>) -> Option<Self::Balance> {
+		AgentLedgerOuter::<T>::get(&agent.get())
+			.map(|a| a.ledger.effective_balance())
+			.ok()
 	}
 
-	fn delegator_balance(delegator: &Self::AccountId) -> Self::Balance {
-		Delegation::<T>::get(delegator).map(|d| d.amount).unwrap_or_default()
+	fn delegator_balance(delegator: Delegator<Self::AccountId>) -> Option<Self::Balance> {
+		Delegation::<T>::get(&delegator.get()).map(|d| d.amount)
 	}
 
 	/// Delegate funds to an `Agent`.
 	fn delegate(
-		who: &Self::AccountId,
-		agent: &Self::AccountId,
+		who: Delegator<Self::AccountId>,
+		agent: Agent<Self::AccountId>,
 		reward_account: &Self::AccountId,
 		amount: Self::Balance,
 	) -> DispatchResult {
 		Pallet::<T>::register_agent(
-			RawOrigin::Signed(agent.clone()).into(),
+			RawOrigin::Signed(agent.clone().get()).into(),
 			reward_account.clone(),
 		)?;
 
 		// Delegate the funds from who to the `Agent` account.
-		Pallet::<T>::delegate_to_agent(RawOrigin::Signed(who.clone()).into(), agent.clone(), amount)
+		Pallet::<T>::delegate_to_agent(RawOrigin::Signed(who.get()).into(), agent.get(), amount)
 	}
 
 	/// Add more delegation to the `Agent` account.
 	fn delegate_extra(
-		who: &Self::AccountId,
-		agent: &Self::AccountId,
+		who: Delegator<Self::AccountId>,
+		agent: Agent<Self::AccountId>,
 		amount: Self::Balance,
 	) -> DispatchResult {
-		Pallet::<T>::delegate_to_agent(RawOrigin::Signed(who.clone()).into(), agent.clone(), amount)
+		Pallet::<T>::delegate_to_agent(RawOrigin::Signed(who.get()).into(), agent.get(), amount)
 	}
 
 	/// Withdraw delegation of `delegator` to `Agent`.
 	///
 	/// If there are funds in `Agent` account that can be withdrawn, then those funds would be
 	/// unlocked/released in the delegator's account.
 	fn withdraw_delegation(
-		delegator: &Self::AccountId,
-		agent: &Self::AccountId,
+		delegator: Delegator<Self::AccountId>,
+		agent: Agent<Self::AccountId>,
 		amount: Self::Balance,
 		num_slashing_spans: u32,
 	) -> DispatchResult {
 		Pallet::<T>::release_delegation(
-			RawOrigin::Signed(agent.clone()).into(),
-			delegator.clone(),
+			RawOrigin::Signed(agent.get()).into(),
+			delegator.get(),
 			amount,
 			num_slashing_spans,
 		)
 	}
 
-	/// Returns true if the `Agent` have any slash pending to be applied.
-	fn has_pending_slash(agent: &Self::AccountId) -> bool {
-		Agent::<T>::get(agent)
-			.map(|d| !d.ledger.pending_slash.is_zero())
-			.unwrap_or(false)
+	/// Returns pending slash of the `agent`.
+	fn pending_slash(agent: Agent<Self::AccountId>) -> Option<Self::Balance> {
+		AgentLedgerOuter::<T>::get(&agent.get()).map(|d| d.ledger.pending_slash).ok()
 	}
 
 	fn delegator_slash(
-		agent: &Self::AccountId,
-		delegator: &Self::AccountId,
+		agent: Agent<Self::AccountId>,
+		delegator: Delegator<Self::AccountId>,
 		value: Self::Balance,
 		maybe_reporter: Option<Self::AccountId>,
 	) -> sp_runtime::DispatchResult {
-		Pallet::<T>::do_slash(agent.clone(), delegator.clone(), value, maybe_reporter)
+		Pallet::<T>::do_slash(agent, delegator, value, maybe_reporter)
 	}
 }
 
@@ -101,32 +99,29 @@ impl<T: Config> DelegationMigrator for Pallet<T> {
 	type AccountId = T::AccountId;
 
 	fn migrate_nominator_to_agent(
-		agent: &Self::AccountId,
+		agent: Agent<Self::AccountId>,
 		reward_account: &Self::AccountId,
 	) -> DispatchResult {
-		Pallet::<T>::migrate_to_agent(
-			RawOrigin::Signed(agent.clone()).into(),
-			reward_account.clone(),
-		)
+		Pallet::<T>::migrate_to_agent(RawOrigin::Signed(agent.get()).into(), reward_account.clone())
 	}
 	fn migrate_delegation(
-		agent: &Self::AccountId,
-		delegator: &Self::AccountId,
+		agent: Agent<Self::AccountId>,
+		delegator: Delegator<Self::AccountId>,
 		value: Self::Balance,
 	) -> DispatchResult {
 		Pallet::<T>::migrate_delegation(
-			RawOrigin::Signed(agent.clone()).into(),
-			delegator.clone(),
+			RawOrigin::Signed(agent.get()).into(),
+			delegator.get(),
 			value,
 		)
 	}
 
 	/// Only used for testing.
 	#[cfg(feature = "runtime-benchmarks")]
-	fn drop_agent(agent: &T::AccountId) {
-		<Agents<T>>::remove(agent);
+	fn drop_agent(agent: Agent<Self::AccountId>) {
+		<Agents<T>>::remove(agent.clone().get());
 		<Delegators<T>>::iter()
-			.filter(|(_, delegation)| delegation.agent == *agent)
+			.filter(|(_, delegation)| delegation.agent == agent.clone().get())
 			.for_each(|(delegator, _)| {
 				let _ = T::Currency::release_all(
 					&HoldReason::StakingDelegation.into(),
@@ -136,7 +131,7 @@ impl<T: Config> DelegationMigrator for Pallet<T> {
 				<Delegators<T>>::remove(&delegator);
 			});
 
-		T::CoreStaking::migrate_to_direct_staker(agent);
+		T::CoreStaking::migrate_to_direct_staker(&agent.get());
 	}
 }
 
@@ -158,7 +153,7 @@ impl<T: Config> OnStakingUpdate<T::AccountId, BalanceOf<T>> for Pallet<T> {
 
 	fn on_withdraw(stash: &T::AccountId, amount: BalanceOf<T>) {
 		// if there is a withdraw to the agent, then add it to the unclaimed withdrawals.
-		let _ = Agent::<T>::get(stash)
+		let _ = AgentLedgerOuter::<T>::get(stash)
 			// can't do anything if there is an overflow error. Just raise a defensive error.
 			.and_then(|agent| agent.add_unclaimed_withdraw(amount).defensive())
 			.map(|agent| agent.save());