Pallet Lottery migrate to Fungibles traits

prdoc/pr_1810.prdoc

@@ -0,0 +1,19 @@
+# Schema: Parity PR Documentation Schema (prdoc)
+# See doc at https://github.com/paritytech/prdoc
+
+title: Pallet Lottery migrate to Fungibles traits
+
+doc:
+  - audience: Core Dev
+    description: |
+      Part of <https://github.com/paritytech/polkadot-sdk/issues/226>.
+
+      This pallet used `type Currency: ReservableCurrency<Self::AccountId>;` but in the logic, no reservation/hold logic existed, or exists in now. Thus we now only use a simple `type Currency: fungible::Balanced<Self::AccountId> + fungible::Mutate<Self::AccountId>;` to manage the lottery's pot.
+
+      We know of no downstream runtimes that are somehow able to place reservations/holds/locks/... on the `T::PalletId::get().into_account_truncating()` account for the pot, so no migrations are needed at all in this PR. There are no braking changes whatsoever here.
+
+migrations:
+  db: []
+  runtime: []
+crates: []
+host_functions: []

substrate/frame/lottery/src/benchmarking.rs

@@ -60,7 +60,7 @@ mod benchmarks {
 	#[benchmark]
 	fn buy_ticket() -> Result<(), BenchmarkError> {
 		let caller = whitelisted_caller();
-		T::Currency::make_free_balance_be(&caller, BalanceOf::<T>::max_value());
+		T::Currency::set_balance(&caller, BalanceOf::<T>::max_value());
 		setup_lottery::<T>(false)?;
 		// force user to have a long vec of calls participating
 		let set_code_index: CallIndex = Lottery::<T>::call_to_index(
@@ -140,18 +140,15 @@ mod benchmarks {
 		setup_lottery::<T>(false)?;
 		let winner = account("winner", 0, 0);
 		// User needs more than min balance to get ticket
-		T::Currency::make_free_balance_be(&winner, T::Currency::minimum_balance() * 10u32.into());
+		T::Currency::set_balance(&winner, T::Currency::minimum_balance() * 10u32.into());
 		// Make sure lottery account has at least min balance too
 		let lottery_account = Lottery::<T>::account_id();
-		T::Currency::make_free_balance_be(
-			&lottery_account,
-			T::Currency::minimum_balance() * 10u32.into(),
-		);
+		T::Currency::set_balance(&lottery_account, T::Currency::minimum_balance() * 10u32.into());
 		// Buy a ticket
 		let call = frame_system::Call::<T>::remark { remark: vec![] };
 		Lottery::<T>::buy_ticket(RawOrigin::Signed(winner.clone()).into(), Box::new(call.into()))?;
 		// Kill user account for worst case
-		T::Currency::make_free_balance_be(&winner, 0u32.into());
+		T::Currency::set_balance(&winner, 0u32.into());
 		// Assert that lotto is set up for winner
 		assert_eq!(TicketsCount::<T>::get(), 1);
 		assert!(!Lottery::<T>::pot().1.is_zero());
@@ -169,7 +166,7 @@ mod benchmarks {
 		assert!(crate::Lottery::<T>::get().is_none());
 		assert_eq!(TicketsCount::<T>::get(), 0);
 		assert_eq!(Lottery::<T>::pot().1, 0u32.into());
-		assert!(!T::Currency::free_balance(&winner).is_zero());
+		assert!(!T::Currency::total_balance(&winner).is_zero());
 
 		Ok(())
 	}
@@ -179,18 +176,15 @@ mod benchmarks {
 		setup_lottery::<T>(true)?;
 		let winner = account("winner", 0, 0);
 		// User needs more than min balance to get ticket
-		T::Currency::make_free_balance_be(&winner, T::Currency::minimum_balance() * 10u32.into());
+		T::Currency::set_balance(&winner, T::Currency::minimum_balance() * 10u32.into());
 		// Make sure lottery account has at least min balance too
 		let lottery_account = Lottery::<T>::account_id();
-		T::Currency::make_free_balance_be(
-			&lottery_account,
-			T::Currency::minimum_balance() * 10u32.into(),
-		);
+		T::Currency::set_balance(&lottery_account, T::Currency::minimum_balance() * 10u32.into());
 		// Buy a ticket
 		let call = frame_system::Call::<T>::remark { remark: vec![] };
 		Lottery::<T>::buy_ticket(RawOrigin::Signed(winner.clone()).into(), Box::new(call.into()))?;
 		// Kill user account for worst case
-		T::Currency::make_free_balance_be(&winner, 0u32.into());
+		T::Currency::set_balance(&winner, 0u32.into());
 		// Assert that lotto is set up for winner
 		assert_eq!(TicketsCount::<T>::get(), 1);
 		assert!(!Lottery::<T>::pot().1.is_zero());
@@ -209,7 +203,7 @@ mod benchmarks {
 		assert_eq!(LotteryIndex::<T>::get(), 2);
 		assert_eq!(TicketsCount::<T>::get(), 0);
 		assert_eq!(Lottery::<T>::pot().1, 0u32.into());
-		assert!(!T::Currency::free_balance(&winner).is_zero());
+		assert!(!T::Currency::total_balance(&winner).is_zero());
 
 		Ok(())
 	}

substrate/frame/lottery/src/lib.rs

@@ -60,7 +60,11 @@ use frame_support::{
 	ensure,
 	pallet_prelude::MaxEncodedLen,
 	storage::bounded_vec::BoundedVec,
-	traits::{Currency, ExistenceRequirement::KeepAlive, Get, Randomness, ReservableCurrency},
+	traits::{
+		fungible::{self, Inspect as _, Mutate as _},
+		tokens::{Fortitude, Preservation},
+		Get, Randomness,
+	},
 	PalletId,
 };
 pub use pallet::*;
@@ -71,8 +75,8 @@ use sp_runtime::{
 use sp_std::prelude::*;
 pub use weights::WeightInfo;
 
-type BalanceOf<T> =
-	<<T as Config>::Currency as Currency<<T as frame_system::Config>::AccountId>>::Balance;
+type AccountIdOf<T> = <T as frame_system::Config>::AccountId;
+type BalanceOf<T> = <<T as Config>::Currency as fungible::Inspect<AccountIdOf<T>>>::Balance;
 
 // Any runtime call can be encoded into two bytes which represent the pallet and call index.
 // We use this to uniquely match someone's incoming call with the calls configured for the lottery.
@@ -138,8 +142,8 @@ pub mod pallet {
 			+ GetDispatchInfo
 			+ From<frame_system::Call<Self>>;
 
-		/// The currency trait.
-		type Currency: ReservableCurrency<Self::AccountId>;
+		/// The fungible currency used for the lottery pot.
+		type Currency: fungible::Balanced<Self::AccountId> + fungible::Mutate<Self::AccountId>;
 
 		/// Something that provides randomness in the runtime.
 		type Randomness: Randomness<Self::Hash, BlockNumberFor<Self>>;
@@ -253,7 +257,7 @@ pub mod pallet {
 							&Self::account_id(),
 							&winner,
 							lottery_balance,
-							KeepAlive,
+							Preservation::Preserve,
 						);
 						debug_assert!(res.is_ok());
 
@@ -368,7 +372,7 @@ pub mod pallet {
 			// Make sure pot exists.
 			let lottery_account = Self::account_id();
 			if T::Currency::total_balance(&lottery_account).is_zero() {
-				T::Currency::deposit_creating(&lottery_account, T::Currency::minimum_balance());
+				let _ = T::Currency::mint_into(&lottery_account, T::Currency::minimum_balance());
 			}
 			Self::deposit_event(Event::<T>::LotteryStarted);
 			Ok(())
@@ -406,7 +410,7 @@ impl<T: Config> Pallet<T> {
 	fn pot() -> (T::AccountId, BalanceOf<T>) {
 		let account_id = Self::account_id();
 		let balance =
-			T::Currency::free_balance(&account_id).saturating_sub(T::Currency::minimum_balance());
+			T::Currency::reducible_balance(&account_id, Preservation::Preserve, Fortitude::Polite);
 
 		(account_id, balance)
 	}
@@ -463,7 +467,12 @@ impl<T: Config> Pallet<T> {
 				}
 				participating_calls.try_push(call_index).map_err(|_| Error::<T>::TooManyCalls)?;
 				// Check user has enough funds and send it to the Lottery account.
-				T::Currency::transfer(caller, &Self::account_id(), config.price, KeepAlive)?;
+				T::Currency::transfer(
+					caller,
+					&Self::account_id(),
+					config.price,
+					Preservation::Preserve,
+				)?;
 				// Create a new ticket.
 				TicketsCount::<T>::put(new_ticket_count);
 				Tickets::<T>::insert(ticket_count, caller.clone());