frame epm: expose feasibility_check in MinerConfig (paritytech#13555)

* frame epm: expose feasibity_check in miner

The goal with this commit is to expose the `feasibity_check` such
that anyone that implements the `MinerConfig trait` can utilize it

* cleanup

* fix tests

bin/node/runtime/src/lib.rs

@@ -702,6 +702,7 @@ impl pallet_election_provider_multi_phase::MinerConfig for Runtime {
 	type Solution = NposSolution16;
 	type MaxVotesPerVoter =
 	<<Self as pallet_election_provider_multi_phase::Config>::DataProvider as ElectionDataProvider>::MaxVotesPerVoter;
+	type MaxWinners = MaxActiveValidators;
 
 	// The unsigned submissions have to respect the weight of the submit_unsigned call, thus their
 	// weight estimate function is wired to this call's weight.

frame/election-provider-multi-phase/src/lib.rs

@@ -247,10 +247,7 @@ use sp_arithmetic::{
 	traits::{CheckedAdd, Zero},
 	UpperOf,
 };
-use sp_npos_elections::{
-	assignment_ratio_to_staked_normalized, BoundedSupports, ElectionScore, EvaluateSupport,
-	Supports, VoteWeight,
-};
+use sp_npos_elections::{BoundedSupports, ElectionScore, IdentifierT, Supports, VoteWeight};
 use sp_runtime::{
 	transaction_validity::{
 		InvalidTransaction, TransactionPriority, TransactionSource, TransactionValidity,
@@ -430,13 +427,17 @@ impl<C: Default> Default for RawSolution<C> {
 	DefaultNoBound,
 	scale_info::TypeInfo,
 )]
-#[scale_info(skip_type_params(T))]
-pub struct ReadySolution<T: Config> {
+#[scale_info(skip_type_params(AccountId, MaxWinners))]
+pub struct ReadySolution<AccountId, MaxWinners>
+where
+	AccountId: IdentifierT,
+	MaxWinners: Get<u32>,
+{
 	/// The final supports of the solution.
 	///
 	/// This is target-major vector, storing each winners, total backing, and each individual
 	/// backer.
-	pub supports: BoundedSupports<T::AccountId, T::MaxWinners>,
+	pub supports: BoundedSupports<AccountId, MaxWinners>,
 	/// The score of the solution.
 	///
 	/// This is needed to potentially challenge the solution.
@@ -451,11 +452,11 @@ pub struct ReadySolution<T: Config> {
 /// These are stored together because they are often accessed together.
 #[derive(PartialEq, Eq, Clone, Encode, Decode, RuntimeDebug, Default, TypeInfo)]
 #[scale_info(skip_type_params(T))]
-pub struct RoundSnapshot<T: Config> {
+pub struct RoundSnapshot<AccountId, DataProvider> {
 	/// All of the voters.
-	pub voters: Vec<VoterOf<T>>,
+	pub voters: Vec<DataProvider>,
 	/// All of the targets.
-	pub targets: Vec<T::AccountId>,
+	pub targets: Vec<AccountId>,
 }
 
 /// Encodes the length of a solution or a snapshot.
@@ -614,6 +615,7 @@ pub mod pallet {
 		type MinerConfig: crate::unsigned::MinerConfig<
 			AccountId = Self::AccountId,
 			MaxVotesPerVoter = <Self::DataProvider as ElectionDataProvider>::MaxVotesPerVoter,
+			MaxWinners = Self::MaxWinners,
 		>;
 
 		/// Maximum number of signed submissions that can be queued.
@@ -733,6 +735,11 @@ pub mod pallet {
 		fn max_votes_per_voter() -> u32 {
 			<T::MinerConfig as MinerConfig>::MaxVotesPerVoter::get()
 		}
+
+		#[pallet::constant_name(MinerMaxWinners)]
+		fn max_winners() -> u32 {
+			<T::MinerConfig as MinerConfig>::MaxWinners::get()
+		}
 	}
 
 	#[pallet::hooks]
@@ -1247,14 +1254,15 @@ pub mod pallet {
 	/// Current best solution, signed or unsigned, queued to be returned upon `elect`.
 	#[pallet::storage]
 	#[pallet::getter(fn queued_solution)]
-	pub type QueuedSolution<T: Config> = StorageValue<_, ReadySolution<T>>;
+	pub type QueuedSolution<T: Config> =
+		StorageValue<_, ReadySolution<T::AccountId, T::MaxWinners>>;
 
 	/// Snapshot data of the round.
 	///
 	/// This is created at the beginning of the signed phase and cleared upon calling `elect`.
 	#[pallet::storage]
 	#[pallet::getter(fn snapshot)]
-	pub type Snapshot<T: Config> = StorageValue<_, RoundSnapshot<T>>;
+	pub type Snapshot<T: Config> = StorageValue<_, RoundSnapshot<T::AccountId, VoterOf<T>>>;
 
 	/// Desired number of targets to elect for this round.
 	///
@@ -1385,7 +1393,7 @@ impl<T: Config> Pallet<T> {
 		// instead of using storage APIs, we do a manual encoding into a fixed-size buffer.
 		// `encoded_size` encodes it without storing it anywhere, this should not cause any
 		// allocation.
-		let snapshot = RoundSnapshot::<T> { voters, targets };
+		let snapshot = RoundSnapshot::<T::AccountId, VoterOf<T>> { voters, targets };
 		let size = snapshot.encoded_size();
 		log!(debug, "snapshot pre-calculated size {:?}", size);
 		let mut buffer = Vec::with_capacity(size);
@@ -1479,89 +1487,22 @@ impl<T: Config> Pallet<T> {
 	pub fn feasibility_check(
 		raw_solution: RawSolution<SolutionOf<T::MinerConfig>>,
 		compute: ElectionCompute,
-	) -> Result<ReadySolution<T>, FeasibilityError> {
-		let RawSolution { solution, score, round } = raw_solution;
-
-		// First, check round.
-		ensure!(Self::round() == round, FeasibilityError::InvalidRound);
-
-		// Winners are not directly encoded in the solution.
-		let winners = solution.unique_targets();
-
+	) -> Result<ReadySolution<T::AccountId, T::MaxWinners>, FeasibilityError> {
 		let desired_targets =
 			Self::desired_targets().ok_or(FeasibilityError::SnapshotUnavailable)?;
 
-		ensure!(winners.len() as u32 == desired_targets, FeasibilityError::WrongWinnerCount);
-		// Fail early if targets requested by data provider exceed maximum winners supported.
-		ensure!(
-			desired_targets <= <T as pallet::Config>::MaxWinners::get(),
-			FeasibilityError::TooManyDesiredTargets
-		);
-
-		// Ensure that the solution's score can pass absolute min-score.
-		let submitted_score = raw_solution.score;
-		ensure!(
-			Self::minimum_untrusted_score().map_or(true, |min_score| {
-				submitted_score.strict_threshold_better(min_score, Perbill::zero())
-			}),
-			FeasibilityError::UntrustedScoreTooLow
-		);
-
-		// Read the entire snapshot.
-		let RoundSnapshot { voters: snapshot_voters, targets: snapshot_targets } =
-			Self::snapshot().ok_or(FeasibilityError::SnapshotUnavailable)?;
-
-		// ----- Start building. First, we need some closures.
-		let cache = helpers::generate_voter_cache::<T::MinerConfig>(&snapshot_voters);
-		let voter_at = helpers::voter_at_fn::<T::MinerConfig>(&snapshot_voters);
-		let target_at = helpers::target_at_fn::<T::MinerConfig>(&snapshot_targets);
-		let voter_index = helpers::voter_index_fn_usize::<T::MinerConfig>(&cache);
-
-		// Then convert solution -> assignment. This will fail if any of the indices are gibberish,
-		// namely any of the voters or targets.
-		let assignments = solution
-			.into_assignment(voter_at, target_at)
-			.map_err::<FeasibilityError, _>(Into::into)?;
-
-		// Ensure that assignments is correct.
-		let _ = assignments.iter().try_for_each(|assignment| {
-			// Check that assignment.who is actually a voter (defensive-only).
-			// NOTE: while using the index map from `voter_index` is better than a blind linear
-			// search, this *still* has room for optimization. Note that we had the index when
-			// we did `solution -> assignment` and we lost it. Ideal is to keep the index
-			// around.
-
-			// Defensive-only: must exist in the snapshot.
-			let snapshot_index =
-				voter_index(&assignment.who).ok_or(FeasibilityError::InvalidVoter)?;
-			// Defensive-only: index comes from the snapshot, must exist.
-			let (_voter, _stake, targets) =
-				snapshot_voters.get(snapshot_index).ok_or(FeasibilityError::InvalidVoter)?;
-
-			// Check that all of the targets are valid based on the snapshot.
-			if assignment.distribution.iter().any(|(d, _)| !targets.contains(d)) {
-				return Err(FeasibilityError::InvalidVote)
-			}
-			Ok(())
-		})?;
-
-		// ----- Start building support. First, we need one more closure.
-		let stake_of = helpers::stake_of_fn::<T::MinerConfig>(&snapshot_voters, &cache);
-
-		// This might fail if the normalization fails. Very unlikely. See `integrity_test`.
-		let staked_assignments = assignment_ratio_to_staked_normalized(assignments, stake_of)
-			.map_err::<FeasibilityError, _>(Into::into)?;
-		let supports = sp_npos_elections::to_supports(&staked_assignments);
-
-		// Finally, check that the claimed score was indeed correct.
-		let known_score = supports.evaluate();
-		ensure!(known_score == score, FeasibilityError::InvalidScore);
-
-		// Size of winners in miner solution is equal to `desired_targets` <= `MaxWinners`.
-		let supports = supports
-			.try_into()
-			.defensive_map_err(|_| FeasibilityError::BoundedConversionFailed)?;
-		Ok(ReadySolution { supports, compute, score })
+		let snapshot = Self::snapshot().ok_or(FeasibilityError::SnapshotUnavailable)?;
+		let round = Self::round();
+		let minimum_untrusted_score = Self::minimum_untrusted_score();
+
+		Miner::<T::MinerConfig>::feasibility_check(
+			raw_solution,
+			compute,
+			desired_targets,
+			snapshot,
+			round,
+			minimum_untrusted_score,
+		)
 	}
 
 	/// Perform the tasks to be done after a new `elect` has been triggered:

frame/election-provider-multi-phase/src/mock.rs

@@ -297,6 +297,8 @@ parameter_types! {
 	pub static MockWeightInfo: MockedWeightInfo = MockedWeightInfo::Real;
 	pub static MaxElectingVoters: VoterIndex = u32::max_value();
 	pub static MaxElectableTargets: TargetIndex = TargetIndex::max_value();
+
+	#[derive(Debug)]
 	pub static MaxWinners: u32 = 200;
 
 	pub static EpochLength: u64 = 30;
@@ -359,6 +361,7 @@ impl MinerConfig for Runtime {
 	type MaxLength = MinerMaxLength;
 	type MaxWeight = MinerMaxWeight;
 	type MaxVotesPerVoter = <StakingMock as ElectionDataProvider>::MaxVotesPerVoter;
+	type MaxWinners = MaxWinners;
 	type Solution = TestNposSolution;
 
 	fn solution_weight(v: u32, t: u32, a: u32, d: u32) -> Weight {

frame/election-provider-multi-phase/src/signed.rs

@@ -462,7 +462,7 @@ impl<T: Config> Pallet<T> {
 	///
 	/// Infallible
 	pub fn finalize_signed_phase_accept_solution(
-		ready_solution: ReadySolution<T>,
+		ready_solution: ReadySolution<T::AccountId, T::MaxWinners>,
 		who: &T::AccountId,
 		deposit: BalanceOf<T>,
 		call_fee: BalanceOf<T>,

frame/election-provider-multi-phase/src/unsigned.rs

@@ -23,12 +23,17 @@ use crate::{
 };
 use codec::Encode;
 use frame_election_provider_support::{NposSolution, NposSolver, PerThing128, VoteWeight};
-use frame_support::{dispatch::DispatchResult, ensure, traits::Get, BoundedVec};
+use frame_support::{
+	dispatch::DispatchResult,
+	ensure,
+	traits::{DefensiveResult, Get},
+	BoundedVec,
+};
 use frame_system::offchain::SubmitTransaction;
 use scale_info::TypeInfo;
 use sp_npos_elections::{
 	assignment_ratio_to_staked_normalized, assignment_staked_to_ratio_normalized, ElectionResult,
-	ElectionScore,
+	ElectionScore, EvaluateSupport,
 };
 use sp_runtime::{
 	offchain::storage::{MutateStorageError, StorageValueRef},
@@ -351,7 +356,7 @@ impl<T: Config> Pallet<T> {
 
 		// ensure score is being improved. Panic henceforth.
 		ensure!(
-			Self::queued_solution().map_or(true, |q: ReadySolution<_>| raw_solution
+			Self::queued_solution().map_or(true, |q: ReadySolution<_, _>| raw_solution
 				.score
 				.strict_threshold_better(q.score, T::BetterUnsignedThreshold::get())),
 			Error::<T>::PreDispatchWeakSubmission,
@@ -387,6 +392,8 @@ pub trait MinerConfig {
 	///
 	/// The weight is computed using `solution_weight`.
 	type MaxWeight: Get<Weight>;
+	/// The maximum number of winners that can be elected.
+	type MaxWinners: Get<u32>;
 	/// Something that can compute the weight of a solution.
 	///
 	/// This weight estimate is then used to trim the solution, based on [`MinerConfig::MaxWeight`].
@@ -689,6 +696,91 @@ impl<T: MinerConfig> Miner<T> {
 		);
 		final_decision
 	}
+
+	/// Checks the feasibility of a solution.
+	pub fn feasibility_check(
+		raw_solution: RawSolution<SolutionOf<T>>,
+		compute: ElectionCompute,
+		desired_targets: u32,
+		snapshot: RoundSnapshot<T::AccountId, MinerVoterOf<T>>,
+		current_round: u32,
+		minimum_untrusted_score: Option<ElectionScore>,
+	) -> Result<ReadySolution<T::AccountId, T::MaxWinners>, FeasibilityError> {
+		let RawSolution { solution, score, round } = raw_solution;
+		let RoundSnapshot { voters: snapshot_voters, targets: snapshot_targets } = snapshot;
+
+		// First, check round.
+		ensure!(current_round == round, FeasibilityError::InvalidRound);
+
+		// Winners are not directly encoded in the solution.
+		let winners = solution.unique_targets();
+
+		ensure!(winners.len() as u32 == desired_targets, FeasibilityError::WrongWinnerCount);
+		// Fail early if targets requested by data provider exceed maximum winners supported.
+		ensure!(desired_targets <= T::MaxWinners::get(), FeasibilityError::TooManyDesiredTargets);
+
+		// Ensure that the solution's score can pass absolute min-score.
+		let submitted_score = raw_solution.score;
+		ensure!(
+			minimum_untrusted_score.map_or(true, |min_score| {
+				submitted_score.strict_threshold_better(min_score, sp_runtime::Perbill::zero())
+			}),
+			FeasibilityError::UntrustedScoreTooLow
+		);
+
+		// ----- Start building. First, we need some closures.
+		let cache = helpers::generate_voter_cache::<T>(&snapshot_voters);
+		let voter_at = helpers::voter_at_fn::<T>(&snapshot_voters);
+		let target_at = helpers::target_at_fn::<T>(&snapshot_targets);
+		let voter_index = helpers::voter_index_fn_usize::<T>(&cache);
+
+		// Then convert solution -> assignment. This will fail if any of the indices are gibberish,
+		// namely any of the voters or targets.
+		let assignments = solution
+			.into_assignment(voter_at, target_at)
+			.map_err::<FeasibilityError, _>(Into::into)?;
+
+		// Ensure that assignments is correct.
+		let _ = assignments.iter().try_for_each(|assignment| {
+			// Check that assignment.who is actually a voter (defensive-only).
+			// NOTE: while using the index map from `voter_index` is better than a blind linear
+			// search, this *still* has room for optimization. Note that we had the index when
+			// we did `solution -> assignment` and we lost it. Ideal is to keep the index
+			// around.
+
+			// Defensive-only: must exist in the snapshot.
+			let snapshot_index =
+				voter_index(&assignment.who).ok_or(FeasibilityError::InvalidVoter)?;
+			// Defensive-only: index comes from the snapshot, must exist.
+			let (_voter, _stake, targets) =
+				snapshot_voters.get(snapshot_index).ok_or(FeasibilityError::InvalidVoter)?;
+
+			// Check that all of the targets are valid based on the snapshot.
+			if assignment.distribution.iter().any(|(d, _)| !targets.contains(d)) {
+				return Err(FeasibilityError::InvalidVote)
+			}
+			Ok(())
+		})?;
+
+		// ----- Start building support. First, we need one more closure.
+		let stake_of = helpers::stake_of_fn::<T>(&snapshot_voters, &cache);
+
+		// This might fail if the normalization fails. Very unlikely. See `integrity_test`.
+		let staked_assignments = assignment_ratio_to_staked_normalized(assignments, stake_of)
+			.map_err::<FeasibilityError, _>(Into::into)?;
+		let supports = sp_npos_elections::to_supports(&staked_assignments);
+
+		// Finally, check that the claimed score was indeed correct.
+		let known_score = supports.evaluate();
+		ensure!(known_score == score, FeasibilityError::InvalidScore);
+
+		// Size of winners in miner solution is equal to `desired_targets` <= `MaxWinners`.
+		let supports = supports
+			.try_into()
+			.defensive_map_err(|_| FeasibilityError::BoundedConversionFailed)?;
+
+		Ok(ReadySolution { supports, compute, score })
+	}
 }
 
 #[cfg(test)]