Clean Phragmén Equlise API (#5452)

* Clean phragmen API and equalise()

* Stabilize new api

* Fix phragmen fuzzers

* More fixes

* Make fuzzers reproducible

* improvements

* Make equalize update assignments as well.

* total function for staked_assignment.

* Fix fuzzer build

* remvoe TODO

* Fix a bunch more.

* clean stray debug stuff

* Update primitives/phragmen/src/lib.rs

Co-Authored-By: thiolliere <gui.thiolliere@gmail.com>

* fix range function

* fix number generator

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

substrate/frame/elections-phragmen/src/lib.rs

@@ -94,7 +94,7 @@ use frame_support::{
 		ChangeMembers, OnUnbalanced, WithdrawReason, Contains, BalanceStatus, InitializeMembers,
 	}
 };
-use sp_phragmen::{build_support_map, ExtendedBalance};
+use sp_phragmen::{build_support_map, ExtendedBalance, VoteWeight, PhragmenResult};
 use frame_system::{self as system, ensure_signed, ensure_root};
 
 const MODULE_ID: LockIdentifier = *b"phrelect";
@@ -123,7 +123,7 @@ 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>, u64> + Convert<u128, BalanceOf<Self>>;
+	type CurrencyToVote: Convert<BalanceOf<Self>, VoteWeight> + Convert<ExtendedBalance, BalanceOf<Self>>;
 
 	/// How much should be locked up in order to submit one's candidacy.
 	type CandidacyBond: Get<BalanceOf<Self>>;
@@ -703,17 +703,28 @@ impl<T: Trait> Module<T> {
 		// previous runners_up are also always candidates for the next round.
 		candidates.append(&mut Self::runners_up_ids());
 
+		// 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 stake_of = |who: &T::AccountId| -> VoteWeight {
+			to_votes(Self::locked_stake_of(who))
+		};
+
 		let voters_and_votes = Voting::<T>::iter()
-			.map(|(voter, (stake, targets))| { (voter, stake, targets) })
+			.map(|(voter, (stake, targets))| { (voter, to_votes(stake), targets) })
 			.collect::<Vec<_>>();
-		let maybe_phragmen_result = sp_phragmen::elect::<_, _, T::CurrencyToVote, Perbill>(
+		let maybe_phragmen_result = sp_phragmen::elect::<T::AccountId, Perbill>(
 			num_to_elect,
 			0,
 			candidates,
 			voters_and_votes.clone(),
 		);
 
-		if let Some(phragmen_result) = maybe_phragmen_result {
+		if let Some(PhragmenResult { winners, assignments }) = maybe_phragmen_result {
 			let old_members_ids = <Members<T>>::take().into_iter()
 				.map(|(m, _)| m)
 				.collect::<Vec<T::AccountId>>();
@@ -726,26 +737,19 @@ impl<T: Trait> Module<T> {
 			// vote are still considered by phragmen and when good candidates are scarce, then these
 			// cheap ones might get elected. We might actually want to remove the filter and allow
 			// zero-voted candidates to also make it to the membership set.
-			let new_set_with_approval = phragmen_result.winners;
+			let new_set_with_approval = winners;
 			let new_set = new_set_with_approval
 				.into_iter()
 				.filter_map(|(m, a)| if a.is_zero() { None } else { Some(m) } )
 				.collect::<Vec<T::AccountId>>();
 
-			let stake_of = |who: &T::AccountId| -> ExtendedBalance {
-				<T::CurrencyToVote as Convert<BalanceOf<T>, u64>>::convert(
-					Self::locked_stake_of(who)
-				) as ExtendedBalance
-			};
 			let staked_assignments = sp_phragmen::assignment_ratio_to_staked(
-				phragmen_result.assignments,
+				assignments,
 				stake_of,
 			);
 
 			let (support_map, _) = build_support_map::<T::AccountId>(&new_set, &staked_assignments);
 
-			let to_balance = |e: ExtendedBalance|
-				<T::CurrencyToVote as Convert<ExtendedBalance, BalanceOf<T>>>::convert(e);
 			let new_set_with_stake = new_set
 				.into_iter()
 				.map(|ref m| {
@@ -766,14 +770,14 @@ impl<T: Trait> Module<T> {
 			// save the members, sorted based on account id.
 			new_members.sort_by(|i, j| i.0.cmp(&j.0));
 
-			let mut prime_votes: Vec<_> = new_members.iter().map(|c| (&c.0, BalanceOf::<T>::zero())).collect();
+			let mut prime_votes: Vec<_> = new_members.iter().map(|c| (&c.0, VoteWeight::zero())).collect();
 			for (_, stake, targets) in voters_and_votes.into_iter() {
 				for (votes, who) in targets.iter()
 					.enumerate()
 					.map(|(votes, who)| ((MAXIMUM_VOTE - votes) as u32, who))
 				{
 					if let Ok(i) = prime_votes.binary_search_by_key(&who, |k| k.0) {
-						prime_votes[i].1 += stake * votes.into();
+						prime_votes[i].1 += stake * votes as VoteWeight;
 					}
 				}
 			}

substrate/frame/staking/src/lib.rs

@@ -308,7 +308,7 @@ use frame_system::{
 };
 use sp_phragmen::{
 	ExtendedBalance, Assignment, PhragmenScore, PhragmenResult, build_support_map, evaluate_support,
-	elect, generate_compact_solution_type, is_score_better, VotingLimit, SupportMap,
+	elect, generate_compact_solution_type, is_score_better, VotingLimit, SupportMap, VoteWeight,
 };
 
 const DEFAULT_MINIMUM_VALIDATOR_COUNT: u32 = 4;
@@ -737,12 +737,11 @@ pub trait Trait: frame_system::Trait {
 	/// is not used.
 	type UnixTime: UnixTime;
 
-	/// Convert a balance into a number used for election calculation.
-	/// This must fit into a `u64` but is allowed to be sensibly lossy.
-	/// TODO: #1377
-	/// The backward convert should be removed as the new Phragmen API returns ratio.
-	/// The post-processing needs it but will be moved to off-chain. TODO: #2908
-	type CurrencyToVote: Convert<BalanceOf<Self>, u64> + Convert<u128, BalanceOf<Self>>;
+	/// Convert a balance into a number used for election calculation. This must fit into a `u64`
+	/// but is allowed to be sensibly lossy. The `u64` is used to communicate with the
+	/// [`sp_phragmen`] crate which accepts u64 numbers and does operations in 128. Consequently,
+	/// the backward convert is used convert the u128s from phragmen back to a [`BalanceOf`].
+	type CurrencyToVote: Convert<BalanceOf<Self>, VoteWeight> + Convert<u128, BalanceOf<Self>>;
 
 	/// Tokens have been minted and are unused for validator-reward.
 	type RewardRemainder: OnUnbalanced<NegativeImbalanceOf<Self>>;
@@ -1853,7 +1852,7 @@ decl_module! {
 		/// - Memory: O(n + m) reads to map index to `AccountId` for un-compact.
 		///
 		/// - Storage: O(e) accountid reads from `Nomination` to read correct nominations.
-		/// - Storage: O(e) calls into `slashable_balance_of_extended` to convert ratio to staked.
+		/// - Storage: O(e) calls into `slashable_balance_of_vote_weight` to convert ratio to staked.
 		///
 		/// - Memory: build_support_map. O(e).
 		/// - Memory: evaluate_support: O(E).
@@ -1953,11 +1952,11 @@ impl<T: Trait> Module<T> {
 		Self::bonded(stash).and_then(Self::ledger).map(|l| l.active).unwrap_or_default()
 	}
 
-	/// internal impl of [`slashable_balance_of`] that returns [`ExtendedBalance`].
-	fn slashable_balance_of_extended(stash: &T::AccountId) -> ExtendedBalance {
-		<T::CurrencyToVote as Convert<BalanceOf<T>, u64>>::convert(
+	/// internal impl of [`slashable_balance_of`] that returns [`VoteWeight`].
+	fn slashable_balance_of_vote_weight(stash: &T::AccountId) -> VoteWeight {
+		<T::CurrencyToVote as Convert<BalanceOf<T>, VoteWeight>>::convert(
 			Self::slashable_balance_of(stash)
-		) as ExtendedBalance
+		)
 	}
 
 	/// Dump the list of validators and nominators into vectors and keep them on-chain.
@@ -2456,7 +2455,7 @@ impl<T: Trait> Module<T> {
 		// convert into staked assignments.
 		let staked_assignments = sp_phragmen::assignment_ratio_to_staked(
 			assignments,
-			Self::slashable_balance_of_extended,
+			Self::slashable_balance_of_vote_weight,
 		);
 
 		// build the support map thereof in order to evaluate.
@@ -2711,7 +2710,7 @@ impl<T: Trait> Module<T> {
 
 			let staked_assignments = sp_phragmen::assignment_ratio_to_staked(
 				assignments,
-				Self::slashable_balance_of_extended,
+				Self::slashable_balance_of_vote_weight,
 			);
 
 			let (supports, _) = build_support_map::<T::AccountId>(
@@ -2747,11 +2746,11 @@ impl<T: Trait> Module<T> {
 	///
 	/// No storage item is updated.
 	fn do_phragmen<Accuracy: PerThing>() -> Option<PhragmenResult<T::AccountId, Accuracy>> {
-		let mut all_nominators: Vec<(T::AccountId, BalanceOf<T>, Vec<T::AccountId>)> = Vec::new();
+		let mut all_nominators: Vec<(T::AccountId, VoteWeight, Vec<T::AccountId>)> = Vec::new();
 		let mut all_validators = Vec::new();
 		for (validator, _) in <Validators<T>>::iter() {
 			// append self vote
-			let self_vote = (validator.clone(), Self::slashable_balance_of(&validator), vec![validator.clone()]);
+			let self_vote = (validator.clone(), Self::slashable_balance_of_vote_weight(&validator), vec![validator.clone()]);
 			all_nominators.push(self_vote);
 			all_validators.push(validator);
 		}
@@ -2771,11 +2770,11 @@ impl<T: Trait> Module<T> {
 			(nominator, targets)
 		});
 		all_nominators.extend(nominator_votes.map(|(n, ns)| {
-			let s = Self::slashable_balance_of(&n);
+			let s = Self::slashable_balance_of_vote_weight(&n);
 			(n, s, ns)
 		}));
 
-		elect::<_, _, T::CurrencyToVote, Accuracy>(
+		elect::<_, Accuracy>(
 			Self::validator_count() as usize,
 			Self::minimum_validator_count().max(1) as usize,
 			all_validators,

substrate/frame/staking/src/mock.rs

@@ -33,6 +33,7 @@ use frame_system::offchain::TransactionSubmitter;
 use sp_io;
 use sp_phragmen::{
 	build_support_map, evaluate_support, reduce, ExtendedBalance, StakedAssignment, PhragmenScore,
+	VoteWeight,
 };
 use crate::*;
 
@@ -846,10 +847,10 @@ pub(crate) fn prepare_submission_with(
 	} = Staking::do_phragmen::<OffchainAccuracy>().unwrap();
 	let winners = winners.into_iter().map(|(w, _)| w).collect::<Vec<AccountId>>();
 
-	let stake_of = |who: &AccountId| -> ExtendedBalance {
-		<CurrencyToVoteHandler as Convert<Balance, u64>>::convert(
+	let stake_of = |who: &AccountId| -> VoteWeight {
+		<CurrencyToVoteHandler as Convert<Balance, VoteWeight>>::convert(
 			Staking::slashable_balance_of(&who)
-		) as ExtendedBalance
+		)
 	};
 	let mut staked = sp_phragmen::assignment_ratio_to_staked(assignments, stake_of);
 
@@ -888,7 +889,7 @@ pub(crate) fn prepare_submission_with(
 	let score = {
 		let staked = sp_phragmen::assignment_ratio_to_staked(
 			assignments_reduced.clone(),
-			Staking::slashable_balance_of_extended,
+			Staking::slashable_balance_of_vote_weight,
 		);
 
 		let (support_map, _) = build_support_map::<AccountId>(

substrate/frame/staking/src/offchain_election.rs

@@ -167,7 +167,7 @@ pub fn prepare_submission<T: Trait>(
 	// convert into absolute value and to obtain the reduced version.
 	let mut staked = sp_phragmen::assignment_ratio_to_staked(
 		assignments,
-		<Module<T>>::slashable_balance_of_extended,
+		<Module<T>>::slashable_balance_of_vote_weight,
 	);
 
 	if do_reduce {
@@ -188,7 +188,7 @@ pub fn prepare_submission<T: Trait>(
 	let score = {
 		let staked = sp_phragmen::assignment_ratio_to_staked(
 			low_accuracy_assignment.clone(),
-			<Module<T>>::slashable_balance_of_extended,
+			<Module<T>>::slashable_balance_of_vote_weight,
 		);
 
 		let (support_map, _) = build_support_map::<T::AccountId>(&winners, &staked);