Refactor CurrencyToVote (#6896)

* Refactor CurrencyToVote to avoid calls to total_issuance.

* Update frame/support/src/traits.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Some grumbles

* Fix last grumbles.

* Fix comment

* Final fix

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

bin/node/runtime/src/impls.rs

@@ -17,8 +17,6 @@
 
 //! Some configurable implementations as associated type for the substrate runtime.
 
-use node_primitives::Balance;
-use sp_runtime::traits::Convert;
 use frame_support::traits::{OnUnbalanced, Currency};
 use crate::{Balances, Authorship, NegativeImbalance};
 
@@ -29,26 +27,9 @@ impl OnUnbalanced<NegativeImbalance> for Author {
 	}
 }
 
-/// Struct that handles the conversion of Balance -> `u64`. This is used for staking's election
-/// calculation.
-pub struct CurrencyToVoteHandler;
-
-impl CurrencyToVoteHandler {
-	fn factor() -> Balance { (Balances::total_issuance() / u64::max_value() as Balance).max(1) }
-}
-
-impl Convert<Balance, u64> for CurrencyToVoteHandler {
-	fn convert(x: Balance) -> u64 { (x / Self::factor()) as u64 }
-}
-
-impl Convert<u128, Balance> for CurrencyToVoteHandler {
-	fn convert(x: u128) -> Balance { x * Self::factor() }
-}
-
 #[cfg(test)]
 mod multiplier_tests {
-	use super::*;
-	use sp_runtime::{assert_eq_error_rate, FixedPointNumber};
+	use sp_runtime::{assert_eq_error_rate, FixedPointNumber, traits::Convert};
 	use pallet_transaction_payment::{Multiplier, TargetedFeeAdjustment};
 
 	use crate::{

bin/node/runtime/src/lib.rs

@@ -30,7 +30,10 @@ use frame_support::{
 		Weight, IdentityFee,
 		constants::{BlockExecutionWeight, ExtrinsicBaseWeight, RocksDbWeight, WEIGHT_PER_SECOND},
 	},
-	traits::{Currency, Imbalance, KeyOwnerProofSystem, OnUnbalanced, Randomness, LockIdentifier},
+	traits::{
+		Currency, Imbalance, KeyOwnerProofSystem, OnUnbalanced, Randomness, LockIdentifier,
+		U128CurrencyToVote,
+	},
 };
 use frame_system::{EnsureRoot, EnsureOneOf};
 use frame_support::traits::InstanceFilter;
@@ -78,7 +81,7 @@ pub use pallet_staking::StakerStatus;
 
 /// Implementations of some helper traits passed into runtime modules as associated types.
 pub mod impls;
-use impls::{CurrencyToVoteHandler, Author};
+use impls::Author;
 
 /// Constant values used within the runtime.
 pub mod constants;
@@ -448,7 +451,7 @@ parameter_types! {
 impl pallet_staking::Trait for Runtime {
 	type Currency = Balances;
 	type UnixTime = Timestamp;
-	type CurrencyToVote = CurrencyToVoteHandler;
+	type CurrencyToVote = U128CurrencyToVote;
 	type RewardRemainder = Treasury;
 	type Event = Event;
 	type Slash = Treasury; // send the slashed funds to the treasury.
@@ -574,7 +577,7 @@ impl pallet_elections_phragmen::Trait for Runtime {
 	// NOTE: this implies that council's genesis members cannot be set directly and must come from
 	// this module.
 	type InitializeMembers = Council;
-	type CurrencyToVote = CurrencyToVoteHandler;
+	type CurrencyToVote = U128CurrencyToVote;
 	type CandidacyBond = CandidacyBond;
 	type VotingBond = VotingBond;
 	type LoserCandidate = ();

frame/babe/src/mock.rs

@@ -23,7 +23,7 @@ use sp_runtime::{
 	Perbill, impl_opaque_keys,
 	curve::PiecewiseLinear,
 	testing::{Digest, DigestItem, Header, TestXt,},
-	traits::{Convert, Header as _, IdentityLookup, OpaqueKeys, SaturatedConversion},
+	traits::{Header as _, IdentityLookup, OpaqueKeys},
 };
 use frame_system::InitKind;
 use frame_support::{
@@ -183,23 +183,9 @@ parameter_types! {
 	pub const StakingUnsignedPriority: u64 = u64::max_value() / 2;
 }
 
-pub struct CurrencyToVoteHandler;
-
-impl Convert<u128, u128> for CurrencyToVoteHandler {
-	fn convert(x: u128) -> u128 {
-		x
-	}
-}
-
-impl Convert<u128, u64> for CurrencyToVoteHandler {
-	fn convert(x: u128) -> u64 {
-		x.saturated_into()
-	}
-}
-
 impl pallet_staking::Trait for Test {
 	type RewardRemainder = ();
-	type CurrencyToVote = CurrencyToVoteHandler;
+	type CurrencyToVote = frame_support::traits::SaturatingCurrencyToVote;
 	type Event = ();
 	type Currency = Balances;
 	type Slash = ();

frame/elections-phragmen/src/lib.rs

@@ -83,25 +83,26 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
-use codec::{Encode, Decode};
-use sp_std::prelude::*;
-use sp_runtime::{
-	DispatchError, RuntimeDebug, Perbill,
-	traits::{Zero, StaticLookup, Convert, Saturating},
-};
+use codec::{Decode, Encode};
 use frame_support::{
-	decl_storage, decl_event, ensure, decl_module, decl_error,
-	weights::Weight,
-	storage::{StorageMap, IterableStorageMap},
+	decl_error, decl_event, decl_module, decl_storage,
 	dispatch::{DispatchResultWithPostInfo, WithPostDispatchInfo},
+	ensure,
+	storage::{IterableStorageMap, StorageMap},
 	traits::{
-		Currency, Get, LockableCurrency, LockIdentifier, ReservableCurrency, WithdrawReasons,
-		ChangeMembers, OnUnbalanced, WithdrawReason, Contains, InitializeMembers, BalanceStatus,
-		ContainsLengthBound,
-	}
+		BalanceStatus, ChangeMembers, Contains, ContainsLengthBound, Currency, CurrencyToVote, Get,
+		InitializeMembers, LockIdentifier, LockableCurrency, OnUnbalanced, ReservableCurrency,
+		WithdrawReason, WithdrawReasons,
+	},
+	weights::Weight,
 };
-use sp_npos_elections::{ExtendedBalance, VoteWeight, ElectionResult};
-use frame_system::{ensure_signed, ensure_root};
+use frame_system::{ensure_root, ensure_signed};
+use sp_npos_elections::{ElectionResult, ExtendedBalance};
+use sp_runtime::{
+	traits::{Saturating, StaticLookup, Zero},
+	DispatchError, Perbill, RuntimeDebug,
+};
+use sp_std::prelude::*;
 
 mod benchmarking;
 mod default_weights;
@@ -172,7 +173,7 @@ pub trait Trait: frame_system::Trait {
 
 	/// Convert a balance into a number used for election calculation.
 	/// This must fit into a `u64` but is allowed to be sensibly lossy.
-	type CurrencyToVote: Convert<BalanceOf<Self>, VoteWeight> + Convert<ExtendedBalance, BalanceOf<Self>>;
+	type CurrencyToVote: CurrencyToVote<BalanceOf<Self>>;
 
 	/// How much should be locked up in order to submit one's candidacy.
 	type CandidacyBond: Get<BalanceOf<Self>>;
@@ -871,16 +872,13 @@ impl<T: Trait> Module<T> {
 		}
 
 		// helper closures to deal with balance/stake.
-		let to_votes = |b: BalanceOf<T>| -> VoteWeight {
-			<T::CurrencyToVote as Convert<BalanceOf<T>, VoteWeight>>::convert(b)
-		};
-		let to_balance = |e: ExtendedBalance| -> BalanceOf<T> {
-			<T::CurrencyToVote as Convert<ExtendedBalance, BalanceOf<T>>>::convert(e)
-		};
+		let total_issuance = T::Currency::total_issuance();
+		let to_votes = |b: BalanceOf<T>| T::CurrencyToVote::to_vote(b, total_issuance);
+		let to_balance = |e: ExtendedBalance| T::CurrencyToVote::to_currency(e, total_issuance);
 
 		// used for prime election.
 		let voters_and_stakes = Voting::<T>::iter()
-			.map(|(voter, (stake, votes))| { (voter, stake, votes) })
+			.map(|(voter, (stake, votes))| (voter, stake, votes))
 			.collect::<Vec<_>>();
 		// used for phragmen.
 		let voters_and_votes = voters_and_stakes.iter()
@@ -1186,17 +1184,6 @@ mod tests {
 		}
 	}
 
-	/// Simple structure that exposes how u64 currency can be represented as... u64.
-	pub struct CurrencyToVoteHandler;
-	impl Convert<u64, u64> for CurrencyToVoteHandler {
-		fn convert(x: u64) -> u64 { x }
-	}
-	impl Convert<u128, u64> for CurrencyToVoteHandler {
-		fn convert(x: u128) -> u64 {
-			x as u64
-		}
-	}
-
 	parameter_types!{
 		pub const ElectionsPhragmenModuleId: LockIdentifier = *b"phrelect";
 	}
@@ -1205,7 +1192,7 @@ mod tests {
 		type ModuleId = ElectionsPhragmenModuleId;
 		type Event = Event;
 		type Currency = Balances;
-		type CurrencyToVote = CurrencyToVoteHandler;
+		type CurrencyToVote = frame_support::traits::SaturatingCurrencyToVote;
 		type ChangeMembers = TestChangeMembers;
 		type InitializeMembers = ();
 		type CandidacyBond = CandidacyBond;

frame/grandpa/src/mock.rs

@@ -36,7 +36,7 @@ use sp_runtime::{
 	curve::PiecewiseLinear,
 	impl_opaque_keys,
 	testing::{Header, TestXt, UintAuthorityId},
-	traits::{Convert, IdentityLookup, OpaqueKeys, SaturatedConversion},
+	traits::{IdentityLookup, OpaqueKeys},
 	DigestItem, Perbill,
 };
 use sp_staking::SessionIndex;
@@ -198,23 +198,9 @@ parameter_types! {
 	pub const StakingUnsignedPriority: u64 = u64::max_value() / 2;
 }
 
-pub struct CurrencyToVoteHandler;
-
-impl Convert<u128, u128> for CurrencyToVoteHandler {
-	fn convert(x: u128) -> u128 {
-		x
-	}
-}
-
-impl Convert<u128, u64> for CurrencyToVoteHandler {
-	fn convert(x: u128) -> u64 {
-		x.saturated_into()
-	}
-}
-
 impl pallet_staking::Trait for Test {
 	type RewardRemainder = ();
-	type CurrencyToVote = CurrencyToVoteHandler;
+	type CurrencyToVote = frame_support::traits::SaturatingCurrencyToVote;
 	type Event = TestEvent;
 	type Currency = Balances;
 	type Slash = ();

frame/offences/benchmarking/src/mock.rs

@@ -26,7 +26,6 @@ use frame_support::{
 };
 use frame_system as system;
 use sp_runtime::{
-	SaturatedConversion,
 	traits::{IdentityLookup, Block as BlockT},
 	testing::{Header, UintAuthorityId},
 };
@@ -150,22 +149,10 @@ parameter_types! {
 
 pub type Extrinsic = sp_runtime::testing::TestXt<Call, ()>;
 
-pub struct CurrencyToVoteHandler;
-impl Convert<u64, u64> for CurrencyToVoteHandler {
-	fn convert(x: u64) -> u64 {
-		x
-	}
-}
-impl Convert<u128, u64> for CurrencyToVoteHandler {
-	fn convert(x: u128) -> u64 {
-		x.saturated_into()
-	}
-}
-
 impl pallet_staking::Trait for Test {
 	type Currency = Balances;
 	type UnixTime = pallet_timestamp::Module<Self>;
-	type CurrencyToVote = CurrencyToVoteHandler;
+	type CurrencyToVote = frame_support::traits::SaturatingCurrencyToVote;
 	type RewardRemainder = ();
 	type Event = Event;
 	type Slash = ();

frame/session/benchmarking/src/mock.rs

@@ -19,7 +19,7 @@
 
 #![cfg(test)]
 
-use sp_runtime::traits::{Convert, SaturatedConversion, IdentityLookup};
+use sp_runtime::traits::IdentityLookup;
 use frame_support::{impl_outer_origin, impl_outer_dispatch, parameter_types};
 
 type AccountId = u64;
@@ -42,18 +42,6 @@ impl_outer_dispatch! {
 	}
 }
 
-pub struct CurrencyToVoteHandler;
-impl Convert<u64, u64> for CurrencyToVoteHandler {
-	fn convert(x: u64) -> u64 {
-		x
-	}
-}
-impl Convert<u128, u64> for CurrencyToVoteHandler {
-	fn convert(x: u128) -> u64 {
-		x.saturated_into()
-	}
-}
-
 #[derive(Clone, Eq, PartialEq, Debug)]
 pub struct Test;
 
@@ -172,7 +160,7 @@ impl<C> frame_system::offchain::SendTransactionTypes<C> for Test where
 impl pallet_staking::Trait for Test {
 	type Currency = Balances;
 	type UnixTime = pallet_timestamp::Module<Self>;
-	type CurrencyToVote = CurrencyToVoteHandler;
+	type CurrencyToVote = frame_support::traits::SaturatingCurrencyToVote;
 	type RewardRemainder = ();
 	type Event = ();
 	type Slash = ();

frame/staking/fuzzer/src/mock.rs

@@ -17,7 +17,6 @@
 
 //! Mock file for staking fuzzing.
 
-use sp_runtime::traits::{Convert, SaturatedConversion};
 use frame_support::{impl_outer_origin, impl_outer_dispatch, parameter_types};
 
 type AccountId = u64;
@@ -41,18 +40,6 @@ impl_outer_dispatch! {
 	}
 }
 
-pub struct CurrencyToVoteHandler;
-impl Convert<u64, u64> for CurrencyToVoteHandler {
-	fn convert(x: u64) -> u64 {
-		x
-	}
-}
-impl Convert<u128, u64> for CurrencyToVoteHandler {
-	fn convert(x: u128) -> u64 {
-		x.saturated_into()
-	}
-}
-
 #[derive(Clone, Eq, PartialEq, Debug)]
 pub struct Test;
 
@@ -177,7 +164,7 @@ impl<C> frame_system::offchain::SendTransactionTypes<C> for Test where
 impl pallet_staking::Trait for Test {
 	type Currency = Balances;
 	type UnixTime = pallet_timestamp::Module<Self>;
-	type CurrencyToVote = CurrencyToVoteHandler;
+	type CurrencyToVote = frame_support::traits::SaturatingCurrencyToVote;
 	type RewardRemainder = ();
 	type Event = ();
 	type Slash = ();