clean the interface of supports map (#9674)

* clean the interface of supports map, make it a bit cleaner and more efficients

* Fix stiff

* fix one test

* Fix warnings

substrate/primitives/npos-elections/fuzzer/src/phragmen_balancing.rs

@@ -24,7 +24,7 @@ use honggfuzz::fuzz;
 use rand::{self, SeedableRng};
 use sp_npos_elections::{
 	assignment_ratio_to_staked_normalized, is_score_better, seq_phragmen, to_supports,
-	to_without_backing, EvaluateSupport, VoteWeight,
+	EvaluateSupport, VoteWeight,
 };
 use sp_runtime::Perbill;
 
@@ -58,8 +58,7 @@ fn main() {
 					&stake_of,
 				)
 				.unwrap();
-				let winners = to_without_backing(unbalanced.winners.clone());
-				let score = to_supports(winners.as_ref(), staked.as_ref()).unwrap().evaluate();
+				let score = to_supports(staked.as_ref()).evaluate();
 
 				if score[0] == 0 {
 					// such cases cannot be improved by balancing.
@@ -83,8 +82,7 @@ fn main() {
 						&stake_of,
 					)
 					.unwrap();
-					let winners = to_without_backing(balanced.winners);
-					to_supports(winners.as_ref(), staked.as_ref()).unwrap().evaluate()
+					to_supports(staked.as_ref()).evaluate()
 				};
 
 				let enhance = is_score_better(balanced_score, unbalanced_score, Perbill::zero());

substrate/primitives/npos-elections/fuzzer/src/phragmms_balancing.rs

@@ -23,8 +23,8 @@ use common::*;
 use honggfuzz::fuzz;
 use rand::{self, SeedableRng};
 use sp_npos_elections::{
-	assignment_ratio_to_staked_normalized, is_score_better, phragmms, to_supports,
-	to_without_backing, EvaluateSupport, VoteWeight,
+	assignment_ratio_to_staked_normalized, is_score_better, phragmms, to_supports, EvaluateSupport,
+	VoteWeight,
 };
 use sp_runtime::Perbill;
 
@@ -58,8 +58,7 @@ fn main() {
 					&stake_of,
 				)
 				.unwrap();
-				let winners = to_without_backing(unbalanced.winners.clone());
-				let score = to_supports(&winners, &staked).unwrap().evaluate();
+				let score = to_supports(&staked).evaluate();
 
 				if score[0] == 0 {
 					// such cases cannot be improved by balancing.
@@ -80,8 +79,7 @@ fn main() {
 				let staked =
 					assignment_ratio_to_staked_normalized(balanced.assignments.clone(), &stake_of)
 						.unwrap();
-				let winners = to_without_backing(balanced.winners);
-				to_supports(winners.as_ref(), staked.as_ref()).unwrap().evaluate()
+				to_supports(staked.as_ref()).evaluate()
 			};
 
 			let enhance = is_score_better(balanced_score, unbalanced_score, Perbill::zero());

substrate/primitives/npos-elections/fuzzer/src/reduce.rs

@@ -104,13 +104,11 @@ fn generate_random_phragmen_assignment(
 }
 
 fn assert_assignments_equal(
-	winners: &Vec<AccountId>,
 	ass1: &Vec<StakedAssignment<AccountId>>,
 	ass2: &Vec<StakedAssignment<AccountId>>,
 ) {
-	let support_1 = to_support_map::<AccountId>(winners, ass1).unwrap();
-	let support_2 = to_support_map::<AccountId>(winners, ass2).unwrap();
-
+	let support_1 = to_support_map::<AccountId>(ass1);
+	let support_2 = to_support_map::<AccountId>(ass2);
 	for (who, support) in support_1.iter() {
 		assert_eq!(support.total, support_2.get(who).unwrap().total);
 	}
@@ -134,7 +132,7 @@ fn reduce_and_compare(assignment: &Vec<StakedAssignment<AccountId>>, winners: &V
 		num_changed,
 	);
 
-	assert_assignments_equal(winners, &assignment, &altered_assignment);
+	assert_assignments_equal(&assignment, &altered_assignment);
 }
 
 fn assignment_len(assignments: &[StakedAssignment<AccountId>]) -> u32 {

substrate/primitives/npos-elections/src/helpers.rs

@@ -17,9 +17,7 @@
 
 //! Helper methods for npos-elections.
 
-use crate::{
-	Assignment, Error, IdentifierT, PerThing128, StakedAssignment, VoteWeight, WithApprovalOf,
-};
+use crate::{Assignment, Error, IdentifierT, PerThing128, StakedAssignment, VoteWeight};
 use sp_arithmetic::PerThing;
 use sp_std::prelude::*;
 
@@ -81,11 +79,6 @@ pub fn assignment_staked_to_ratio_normalized<A: IdentifierT, P: PerThing128>(
 	Ok(ratio)
 }
 
-/// consumes a vector of winners with backing stake to just winners.
-pub fn to_without_backing<A: IdentifierT>(winners: Vec<WithApprovalOf<A>>) -> Vec<A> {
-	winners.into_iter().map(|(who, _)| who).collect::<Vec<A>>()
-}
-
 #[cfg(test)]
 mod tests {
 	use super::*;

substrate/primitives/npos-elections/src/lib.rs

@@ -146,9 +146,6 @@ pub type ExtendedBalance = u128;
 /// [`EvaluateSupport::evaluate`].
 pub type ElectionScore = [ExtendedBalance; 3];
 
-/// A winner, with their respective approval stake.
-pub type WithApprovalOf<A> = (A, ExtendedBalance);
-
 /// A pointer to a candidate struct with interior mutability.
 pub type CandidatePtr<A> = Rc<RefCell<Candidate<A>>>;
 
@@ -327,7 +324,7 @@ impl<AccountId: IdentifierT> Voter<AccountId> {
 pub struct ElectionResult<AccountId, P: PerThing> {
 	/// Just winners zipped with their approval stake. Note that the approval stake is merely the
 	/// sub of their received stake and could be used for very basic sorting and approval voting.
-	pub winners: Vec<WithApprovalOf<AccountId>>,
+	pub winners: Vec<(AccountId, ExtendedBalance)>,
 	/// Individual assignments. for each tuple, the first elements is a voter and the second is the
 	/// list of candidates that it supports.
 	pub assignments: Vec<Assignment<AccountId, P>>,
@@ -361,107 +358,50 @@ pub type Supports<A> = Vec<(A, Support<A>)>;
 /// This is more helpful than a normal [`Supports`] as it allows faster error checking.
 pub type SupportMap<A> = BTreeMap<A, Support<A>>;
 
-/// Helper trait to convert from a support map to a flat support vector.
-pub trait FlattenSupportMap<A> {
-	/// Flatten the support.
-	fn flatten(self) -> Supports<A>;
-}
-
-impl<A> FlattenSupportMap<A> for SupportMap<A> {
-	fn flatten(self) -> Supports<A> {
-		self.into_iter().collect::<Vec<_>>()
-	}
-}
-
-/// Build the support map from the winners and assignments.
-///
-/// The list of winners is basically a redundancy for error checking only; It ensures that all the
-/// targets pointed to by the [`Assignment`] are present in the `winners`.
+/// Build the support map from the assignments.
 pub fn to_support_map<AccountId: IdentifierT>(
-	winners: &[AccountId],
 	assignments: &[StakedAssignment<AccountId>],
-) -> Result<SupportMap<AccountId>, Error> {
-	// Initialize the support of each candidate.
-	let mut supports = <SupportMap<AccountId>>::new();
-	winners.iter().for_each(|e| {
-		supports.insert(e.clone(), Default::default());
-	});
+) -> SupportMap<AccountId> {
+	let mut supports = <BTreeMap<AccountId, Support<AccountId>>>::new();
 
 	// build support struct.
-	for StakedAssignment { who, distribution } in assignments.iter() {
-		for (c, weight_extended) in distribution.iter() {
-			if let Some(support) = supports.get_mut(c) {
-				support.total = support.total.saturating_add(*weight_extended);
-				support.voters.push((who.clone(), *weight_extended));
-			} else {
-				return Err(Error::InvalidSupportEdge)
-			}
+	for StakedAssignment { who, distribution } in assignments.into_iter() {
+		for (c, weight_extended) in distribution.into_iter() {
+			let mut support = supports.entry(c.clone()).or_default();
+			support.total = support.total.saturating_add(*weight_extended);
+			support.voters.push((who.clone(), *weight_extended));
 		}
 	}
-	Ok(supports)
+
+	supports
 }
 
-/// Same as [`to_support_map`] except it calls `FlattenSupportMap` on top of the result to return a
+/// Same as [`to_support_map`] except it returns a
 /// flat vector.
-///
-/// Similar to [`to_support_map`], `winners` is used for error checking.
 pub fn to_supports<AccountId: IdentifierT>(
-	winners: &[AccountId],
 	assignments: &[StakedAssignment<AccountId>],
-) -> Result<Supports<AccountId>, Error> {
-	to_support_map(winners, assignments).map(FlattenSupportMap::flatten)
+) -> Supports<AccountId> {
+	to_support_map(assignments).into_iter().collect()
 }
 
 /// Extension trait for evaluating a support map or vector.
-pub trait EvaluateSupport<K> {
+pub trait EvaluateSupport {
 	/// Evaluate a support map. The returned tuple contains:
 	///
 	/// - Minimum support. This value must be **maximized**.
 	/// - Sum of all supports. This value must be **maximized**.
 	/// - Sum of all supports squared. This value must be **minimized**.
-	fn evaluate(self) -> ElectionScore;
+	fn evaluate(&self) -> ElectionScore;
 }
 
-/// A common wrapper trait for both (&A, &B) and &(A, B).
-///
-/// This allows us to implemented something for both `Vec<_>` and `BTreeMap<_>`, such as
-/// [`EvaluateSupport`].
-pub trait TupleRef<K, V> {
-	fn extract(&self) -> (&K, &V);
-}
-
-impl<K, V> TupleRef<K, V> for &(K, V) {
-	fn extract(&self) -> (&K, &V) {
-		(&self.0, &self.1)
-	}
-}
-
-impl<K, V> TupleRef<K, V> for (K, V) {
-	fn extract(&self) -> (&K, &V) {
-		(&self.0, &self.1)
-	}
-}
-
-impl<K, V> TupleRef<K, V> for (&K, &V) {
-	fn extract(&self) -> (&K, &V) {
-		(self.0, self.1)
-	}
-}
-
-impl<A, C, I> EvaluateSupport<A> for C
-where
-	C: IntoIterator<Item = I>,
-	I: TupleRef<A, Support<A>>,
-	A: IdentifierT,
-{
-	fn evaluate(self) -> ElectionScore {
+impl<AccountId: IdentifierT> EvaluateSupport for Supports<AccountId> {
+	fn evaluate(&self) -> ElectionScore {
 		let mut min_support = ExtendedBalance::max_value();
 		let mut sum: ExtendedBalance = Zero::zero();
 		// NOTE: The third element might saturate but fine for now since this will run on-chain and
 		// need to be fast.
 		let mut sum_squared: ExtendedBalance = Zero::zero();
-		for item in self {
-			let (_, support) = item.extract();
+		for (_, support) in self {
 			sum = sum.saturating_add(support.total);
 			let squared = support.total.saturating_mul(support.total);
 			sum_squared = sum_squared.saturating_add(squared);

substrate/primitives/npos-elections/src/tests.rs

@@ -19,8 +19,8 @@
 
 use crate::{
 	balancing, helpers::*, is_score_better, mock::*, seq_phragmen, seq_phragmen_core, setup_inputs,
-	to_support_map, to_supports, Assignment, ElectionResult, EvaluateSupport, ExtendedBalance,
-	IndexAssignment, NposSolution, StakedAssignment, Support, Voter,
+	to_support_map, Assignment, ElectionResult, ExtendedBalance, IndexAssignment, NposSolution,
+	StakedAssignment, Support, Voter,
 };
 use rand::{self, SeedableRng};
 use sp_arithmetic::{PerU16, Perbill, Percent, Permill};
@@ -259,8 +259,7 @@ fn phragmen_poc_works() {
 	);
 
 	let staked = assignment_ratio_to_staked(assignments, &stake_of);
-	let winners = to_without_backing(winners);
-	let support_map = to_support_map::<AccountId>(&winners, &staked).unwrap();
+	let support_map = to_support_map::<AccountId>(&staked);
 
 	assert_eq_uvec!(
 		staked,
@@ -315,8 +314,7 @@ fn phragmen_poc_works_with_balancing() {
 	);
 
 	let staked = assignment_ratio_to_staked(assignments, &stake_of);
-	let winners = to_without_backing(winners);
-	let support_map = to_support_map::<AccountId>(&winners, &staked).unwrap();
+	let support_map = to_support_map::<AccountId>(&staked);
 
 	assert_eq_uvec!(
 		staked,
@@ -515,7 +513,7 @@ fn phragmen_large_scale_test() {
 	)
 	.unwrap();
 
-	assert_eq_uvec!(to_without_backing(winners.clone()), vec![24, 22]);
+	assert_eq_uvec!(winners.iter().map(|(x, _)| *x).collect::<Vec<_>>(), vec![24, 22]);
 	check_assignments_sum(&assignments);
 }
 
@@ -649,8 +647,7 @@ fn phragmen_self_votes_should_be_kept() {
 	);
 
 	let staked_assignments = assignment_ratio_to_staked(result.assignments, &stake_of);
-	let winners = to_without_backing(result.winners);
-	let supports = to_support_map::<AccountId>(&winners, &staked_assignments).unwrap();
+	let supports = to_support_map::<AccountId>(&staked_assignments);
 
 	assert_eq!(supports.get(&5u64), None);
 	assert_eq!(
@@ -670,9 +667,8 @@ fn duplicate_target_is_ignored() {
 
 	let ElectionResult { winners, assignments } =
 		seq_phragmen::<_, Perbill>(2, candidates, voters, None).unwrap();
-	let winners = to_without_backing(winners);
 
-	assert_eq!(winners, vec![(2), (3)]);
+	assert_eq!(winners, vec![(2, 140), (3, 110)]);
 	assert_eq!(
 		assignments
 			.into_iter()
@@ -689,9 +685,8 @@ fn duplicate_target_is_ignored_when_winner() {
 
 	let ElectionResult { winners, assignments } =
 		seq_phragmen::<_, Perbill>(2, candidates, voters, None).unwrap();
-	let winners = to_without_backing(winners);
 
-	assert_eq!(winners, vec![1, 2]);
+	assert_eq!(winners, vec![(1, 100), (2, 100)]);
 	assert_eq!(
 		assignments
 			.into_iter()
@@ -701,31 +696,6 @@ fn duplicate_target_is_ignored_when_winner() {
 	);
 }
 
-#[test]
-fn support_map_and_vec_can_be_evaluated() {
-	let candidates = vec![1, 2, 3];
-	let voters = vec![(10, vec![1, 2]), (20, vec![1, 3]), (30, vec![2, 3])];
-
-	let stake_of = create_stake_of(&[(10, 10), (20, 20), (30, 30)]);
-	let ElectionResult { winners, assignments } = seq_phragmen::<_, Perbill>(
-		2,
-		candidates,
-		voters
-			.iter()
-			.map(|(ref v, ref vs)| (v.clone(), stake_of(v), vs.clone()))
-			.collect::<Vec<_>>(),
-		None,
-	)
-	.unwrap();
-
-	let staked = assignment_ratio_to_staked(assignments, &stake_of);
-	let winners = to_without_backing(winners);
-	let support_map = to_support_map::<AccountId>(&winners, &staked).unwrap();
-	let support_vec = to_supports(&winners, &staked).unwrap();
-
-	assert_eq!(support_map.evaluate(), support_vec.evaluate());
-}
-
 mod assignment_convert_normalize {
 	use super::*;
 	#[test]

substrate/primitives/npos-elections/src/traits.rs

@@ -112,7 +112,6 @@ where
 	/// Compute the score of this solution type.
 	fn score<A, FS>(
 		self,
-		winners: &[A],
 		stake_of: FS,
 		voter_at: impl Fn(Self::VoterIndex) -> Option<A>,
 		target_at: impl Fn(Self::TargetIndex) -> Option<A>,
@@ -123,7 +122,7 @@ where
 	{
 		let ratio = self.into_assignment(voter_at, target_at)?;
 		let staked = crate::helpers::assignment_ratio_to_staked_normalized(ratio, stake_of)?;
-		let supports = crate::to_supports(winners, &staked)?;
+		let supports = crate::to_supports(&staked);
 		Ok(supports.evaluate())
 	}