Deprecate RewardDestination::Controller

substrate/frame/staking/src/benchmarking.rs

@@ -467,9 +467,9 @@ benchmarks! {
 		let (stash, controller) = create_stash_controller::<T>(USER_SEED, 100, Default::default())?;
 		assert_eq!(Payee::<T>::get(&stash), RewardDestination::Staked);
 		whitelist_account!(controller);
-	}: _(RawOrigin::Signed(controller), RewardDestination::Controller)
+	}: _(RawOrigin::Signed(controller), RewardDestination::DeprecatedController)
 	verify {
-		assert_eq!(Payee::<T>::get(&stash), RewardDestination::Controller);
+		assert_eq!(Payee::<T>::get(&stash), RewardDestination::DeprecatedController);
 	}
 
 	set_controller {
@@ -558,7 +558,7 @@ benchmarks! {
 			T::MaxExposurePageSize::get() as u32,
 			true,
 			true,
-			RewardDestination::Controller,
+			RewardDestination::DeprecatedController,
 		)?;
 
 		let current_era = CurrentEra::<T>::get().unwrap();

substrate/frame/staking/src/lib.rs

@@ -404,8 +404,8 @@ pub enum RewardDestination<AccountId> {
 	Staked,
 	/// Pay into the stash account, not increasing the amount at stake.
 	Stash,
-	/// Pay into the controller account.
-	Controller,
+	/// Deprecated: This variant now behaves the same as `Stash` variant.
+	DeprecatedController,
 	/// Pay into a specified account.
 	Account(AccountId),
 	/// Receive no reward.

substrate/frame/staking/src/mock.rs

@@ -594,7 +594,11 @@ pub(crate) fn current_era() -> EraIndex {
 
 pub(crate) fn bond(who: AccountId, val: Balance) {
 	let _ = Balances::make_free_balance_be(&who, val);
-	assert_ok!(Staking::bond(RuntimeOrigin::signed(who), val, RewardDestination::Controller));
+	assert_ok!(Staking::bond(
+		RuntimeOrigin::signed(who),
+		val,
+		RewardDestination::DeprecatedController
+	));
 }
 
 pub(crate) fn bond_validator(who: AccountId, val: Balance) {

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

@@ -338,9 +338,10 @@ impl<T: Config> Pallet<T> {
 
 		let dest = Self::payee(StakingAccount::Stash(stash.clone()));
 		let maybe_imbalance = match dest {
-			RewardDestination::Controller => Self::bonded(stash)
-				.map(|controller| T::Currency::deposit_creating(&controller, amount)),
-			RewardDestination::Stash => T::Currency::deposit_into_existing(stash, amount).ok(),
+			// Note: Controller accounts are being deprecated and will no longer point to a separate
+			// account. `Controller` variant now points to the `stash`.
+			RewardDestination::Stash | RewardDestination::DeprecatedController =>
+				T::Currency::deposit_into_existing(stash, amount).ok(),
 			RewardDestination::Staked => Self::ledger(Stash(stash.clone()))
 				.and_then(|mut ledger| {
 					ledger.active += amount;

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

@@ -1283,10 +1283,20 @@ pub mod pallet {
 			payee: RewardDestination<T::AccountId>,
 		) -> DispatchResult {
 			let controller = ensure_signed(origin)?;
-			let ledger = Self::ledger(Controller(controller))?;
+			let ledger = Self::ledger(Controller(controller.clone()))?;
+
+			// Ensure that the `DeprecatedController` variant is not assigned. Controller accounts
+			// are being deprecated and the `DeprecatedController` variant is being phased out via
+			// the `update_payee` call.
+			let payee_final = if payee == RewardDestination::DeprecatedController {
+				RewardDestination::Account(controller)
+			} else {
+				payee
+			};
+
 			let _ = ledger
-				.set_payee(payee)
-				.defensive_proof("ledger was retrieved from storage, thus its bonded; qed.");
+				.set_payee(payee_final)
+				.defensive_proof("ledger was retrieved from storage, thus its bonded; qed.")?;
 
 			Ok(())
 		}
@@ -1872,6 +1882,35 @@ pub mod pallet {
 			ensure_signed(origin)?;
 			Self::do_payout_stakers_by_page(validator_stash, era, page)
 		}
+
+		/// Migrates an account's `RewardDestination::Controller` to
+		/// `RewardDestination::Account(controller)`.
+		///
+		/// Effects will be felt instantly (as soon as this function is completed successfully).
+		///
+		/// This will waive the transaction fee if the `payee` is successfully migrated.
+		#[pallet::call_index(27)]
+		#[pallet::weight(T::WeightInfo::set_payee())]
+		pub fn update_payee(
+			origin: OriginFor<T>,
+			controller: T::AccountId,
+		) -> DispatchResultWithPostInfo {
+			let _ = ensure_signed(origin)?;
+			let ledger = Self::ledger(StakingAccount::Controller(controller.clone()))?;
+
+			if !Payee::<T>::contains_key(&ledger.stash) {
+				return Ok(Pays::Yes.into())
+			}
+			if Payee::<T>::get(&ledger.stash) != RewardDestination::DeprecatedController {
+				return Ok(Pays::Yes.into())
+			}
+
+			let _ = ledger
+				.set_payee(RewardDestination::Account(controller))
+				.defensive_proof("ledger was retrieved from storage, thus its bonded; qed.")?;
+
+			Ok(Pays::No.into())
+		}
 	}
 }