Staking: Add dest to Rewarded to aid in reward calculations (#1602)

Addresses https://github.com/paritytech/polkadot-sdk/issues/129.

Returns `Self:payee()` from `make_payout` in a tuple alongside an
imbalance & adds it to `Rewarded` event.

substrate/frame/staking/src/pallet/impls.rs

@@ -236,11 +236,12 @@ impl<T: Config> Pallet<T> {
 
 		let mut total_imbalance = PositiveImbalanceOf::<T>::zero();
 		// We can now make total validator payout:
-		if let Some(imbalance) =
+		if let Some((imbalance, dest)) =
 			Self::make_payout(&ledger.stash, validator_staking_payout + validator_commission_payout)
 		{
 			Self::deposit_event(Event::<T>::Rewarded {
 				stash: ledger.stash,
+				dest,
 				amount: imbalance.peek(),
 			});
 			total_imbalance.subsume(imbalance);
@@ -259,11 +260,14 @@ impl<T: Config> Pallet<T> {
 			let nominator_reward: BalanceOf<T> =
 				nominator_exposure_part * validator_leftover_payout;
 			// We can now make nominator payout:
-			if let Some(imbalance) = Self::make_payout(&nominator.who, nominator_reward) {
+			if let Some((imbalance, dest)) = Self::make_payout(&nominator.who, nominator_reward) {
 				// Note: this logic does not count payouts for `RewardDestination::None`.
 				nominator_payout_count += 1;
-				let e =
-					Event::<T>::Rewarded { stash: nominator.who.clone(), amount: imbalance.peek() };
+				let e = Event::<T>::Rewarded {
+					stash: nominator.who.clone(),
+					dest,
+					amount: imbalance.peek(),
+				};
 				Self::deposit_event(e);
 				total_imbalance.subsume(imbalance);
 			}
@@ -293,9 +297,11 @@ impl<T: Config> Pallet<T> {
 
 	/// Actually make a payment to a staker. This uses the currency's reward function
 	/// to pay the right payee for the given staker account.
-	fn make_payout(stash: &T::AccountId, amount: BalanceOf<T>) -> Option<PositiveImbalanceOf<T>> {
-		let dest = Self::payee(stash);
-		match dest {
+	fn make_payout(
+		stash: &T::AccountId,
+		amount: BalanceOf<T>,
+	) -> Option<(PositiveImbalanceOf<T>, RewardDestination<T::AccountId>)> {
+		let maybe_imbalance = match Self::payee(stash) {
 			RewardDestination::Controller => Self::bonded(stash)
 				.map(|controller| T::Currency::deposit_creating(&controller, amount)),
 			RewardDestination::Stash => T::Currency::deposit_into_existing(stash, amount).ok(),
@@ -311,7 +317,8 @@ impl<T: Config> Pallet<T> {
 			RewardDestination::Account(dest_account) =>
 				Some(T::Currency::deposit_creating(&dest_account, amount)),
 			RewardDestination::None => None,
-		}
+		};
+		maybe_imbalance.map(|imbalance| (imbalance, Self::payee(stash)))
 	}
 
 	/// Plan a new session potentially trigger a new era.

substrate/frame/staking/src/pallet/mod.rs

@@ -664,8 +664,12 @@ pub mod pallet {
 		/// The era payout has been set; the first balance is the validator-payout; the second is
 		/// the remainder from the maximum amount of reward.
 		EraPaid { era_index: EraIndex, validator_payout: BalanceOf<T>, remainder: BalanceOf<T> },
-		/// The nominator has been rewarded by this amount.
-		Rewarded { stash: T::AccountId, amount: BalanceOf<T> },
+		/// The nominator has been rewarded by this amount to this destination.
+		Rewarded {
+			stash: T::AccountId,
+			dest: RewardDestination<T::AccountId>,
+			amount: BalanceOf<T>,
+		},
 		/// A staker (validator or nominator) has been slashed by the given amount.
 		Slashed { staker: T::AccountId, amount: BalanceOf<T> },
 		/// A slash for the given validator, for the given percentage of their stake, at the given

substrate/frame/staking/src/tests.rs

@@ -3759,6 +3759,16 @@ fn test_payout_stakers() {
 		);
 		assert!(RewardOnUnbalanceWasCalled::get());
 
+		// `Rewarded` events are being executed.
+		assert!(matches!(
+			staking_events_since_last_call().as_slice(),
+			&[
+				..,
+				Event::Rewarded { stash: 1037, dest: RewardDestination::Controller, amount: 108 },
+				Event::Rewarded { stash: 1036, dest: RewardDestination::Controller, amount: 108 }
+			]
+		));
+
 		// Top 64 nominators of validator 11 automatically paid out, including the validator
 		// Validator payout goes to controller.
 		assert!(Balances::free_balance(&11) > balance);