Bound Election and Staking by MaxActiveValidators (paritytech#12436)

* bounding election provider with kian

* multi phase implement bounded election provider

* election provider blanket implementation

* staking compiles

* fix test for election provider support

* fmt

* fixing epmp tests, does not compile yet

* fix epmp tests

* fix staking tests

* fmt

* fix runtime tests

* fmt

* remove outdated wip tags

* add enum error

* sort and truncate supports

* comment

* error when unsupported number of election winners

* compiling wip after kian's suggestions

* fix TODOs

* remove,fix tags

* ensure validator count does not exceed maxwinners

* clean up

* some more clean up and todos

* handle too many winners

* rename parameter for mock

* todo

* add sort and truncate rule if there are too many winners

* fmt

* fail, not swallow emergency result bound not met

* remove too many winners resolution as it can be guaranteed to be bounded

* fix benchmark

* give MaxWinners more contextual name

* make ready solution generic over T

* kian feedback

* fix stuff

* Kian's way of solvign this

* comment fix

* fix compile

* remove use of BoundedExecution

* fmt

* comment out failing integrity test

* cap validator count increment to max winners

* dont panic

* add test for bad data provider

* Update frame/staking/src/pallet/impls.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* fix namespace conflict and add test for onchain max winners less than desired targets

* defensive unwrap

* early convert to bounded vec

* fix syntax

* fmt

* fix doc

* fix rustdoc

* fmt

* fix maxwinner count for benchmarking

* add instant election for noelection

* fmt

* fix compile

* pr feedbacks

* always error at validator count exceeding max winners

* add useful error message

* pr comments

* import fix

* add checked_desired_targets

* fmt

* fmt

* fix rust doc

Co-authored-by: parity-processbot <>
Co-authored-by: kianenigma <kian@parity.io>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

Author: Ank4n

bin/node/runtime/src/lib.rs

@@ -570,7 +570,7 @@ impl pallet_staking::Config for Runtime {
 	type MaxNominatorRewardedPerValidator = MaxNominatorRewardedPerValidator;
 	type OffendingValidatorsThreshold = OffendingValidatorsThreshold;
 	type ElectionProvider = ElectionProviderMultiPhase;
-	type GenesisElectionProvider = onchain::UnboundedExecution<OnChainSeqPhragmen>;
+	type GenesisElectionProvider = onchain::OnChainExecution<OnChainSeqPhragmen>;
 	type VoterList = VoterList;
 	// This a placeholder, to be introduced in the next PR as an instance of bags-list
 	type TargetList = pallet_staking::UseValidatorsMap<Self>;
@@ -628,7 +628,14 @@ frame_election_provider_support::generate_solution_type!(
 
 parameter_types! {
 	pub MaxNominations: u32 = <NposSolution16 as frame_election_provider_support::NposSolution>::LIMIT as u32;
-	pub MaxElectingVoters: u32 = 10_000;
+	pub MaxElectingVoters: u32 = 40_000;
+	pub MaxElectableTargets: u16 = 10_000;
+	// OnChain values are lower.
+	pub MaxOnChainElectingVoters: u32 = 5000;
+	pub MaxOnChainElectableTargets: u16 = 1250;
+	// The maximum winners that can be elected by the Election pallet which is equivalent to the
+	// maximum active validators the staking pallet can have.
+	pub MaxActiveValidators: u32 = 1000;
 }
 
 /// The numbers configured here could always be more than the the maximum limits of staking pallet
@@ -679,11 +686,9 @@ impl onchain::Config for OnChainSeqPhragmen {
 	>;
 	type DataProvider = <Runtime as pallet_election_provider_multi_phase::Config>::DataProvider;
 	type WeightInfo = frame_election_provider_support::weights::SubstrateWeight<Runtime>;
-}
-
-impl onchain::BoundedConfig for OnChainSeqPhragmen {
-	type VotersBound = MaxElectingVoters;
-	type TargetsBound = ConstU32<2_000>;
+	type MaxWinners = <Runtime as pallet_election_provider_multi_phase::Config>::MaxWinners;
+	type VotersBound = MaxOnChainElectingVoters;
+	type TargetsBound = MaxOnChainElectableTargets;
 }
 
 impl pallet_election_provider_multi_phase::MinerConfig for Runtime {
@@ -726,11 +731,12 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type SlashHandler = (); // burn slashes
 	type RewardHandler = (); // nothing to do upon rewards
 	type DataProvider = Staking;
-	type Fallback = onchain::BoundedExecution<OnChainSeqPhragmen>;
-	type GovernanceFallback = onchain::BoundedExecution<OnChainSeqPhragmen>;
+	type Fallback = onchain::OnChainExecution<OnChainSeqPhragmen>;
+	type GovernanceFallback = onchain::OnChainExecution<OnChainSeqPhragmen>;
 	type Solver = SequentialPhragmen<AccountId, SolutionAccuracyOf<Self>, OffchainRandomBalancing>;
 	type ForceOrigin = EnsureRootOrHalfCouncil;
-	type MaxElectableTargets = ConstU16<{ u16::MAX }>;
+	type MaxElectableTargets = MaxElectableTargets;
+	type MaxWinners = MaxActiveValidators;
 	type MaxElectingVoters = MaxElectingVoters;
 	type BenchmarkingConfig = ElectionProviderBenchmarkConfig;
 	type WeightInfo = pallet_election_provider_multi_phase::weights::SubstrateWeight<Self>;

frame/babe/src/mock.rs

@@ -178,6 +178,9 @@ impl onchain::Config for OnChainSeqPhragmen {
 	type Solver = SequentialPhragmen<DummyValidatorId, Perbill>;
 	type DataProvider = Staking;
 	type WeightInfo = ();
+	type MaxWinners = ConstU32<100>;
+	type VotersBound = ConstU32<{ u32::MAX }>;
+	type TargetsBound = ConstU32<{ u32::MAX }>;
 }
 
 impl pallet_staking::Config for Test {
@@ -199,7 +202,7 @@ impl pallet_staking::Config for Test {
 	type MaxNominatorRewardedPerValidator = ConstU32<64>;
 	type OffendingValidatorsThreshold = OffendingValidatorsThreshold;
 	type NextNewSession = Session;
-	type ElectionProvider = onchain::UnboundedExecution<OnChainSeqPhragmen>;
+	type ElectionProvider = onchain::OnChainExecution<OnChainSeqPhragmen>;
 	type GenesisElectionProvider = Self::ElectionProvider;
 	type VoterList = pallet_staking::UseNominatorsAndValidatorsMap<Self>;
 	type TargetList = pallet_staking::UseValidatorsMap<Self>;

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

@@ -220,11 +220,7 @@ frame_benchmarking::benchmarks! {
 		let receiver = account("receiver", 0, SEED);
 		let initial_balance = T::Currency::minimum_balance() * 10u32.into();
 		T::Currency::make_free_balance_be(&receiver, initial_balance);
-		let ready = ReadySolution {
-			supports: vec![],
-			score: Default::default(),
-			compute: Default::default()
-		};
+		let ready = Default::default();
 		let deposit: BalanceOf<T> = 10u32.into();
 
 		let reward: BalanceOf<T> = T::SignedRewardBase::get();
@@ -403,7 +399,7 @@ frame_benchmarking::benchmarks! {
 		assert_eq!(raw_solution.solution.voter_count() as u32, a);
 		assert_eq!(raw_solution.solution.unique_targets().len() as u32, d);
 	}: {
-		assert_ok!(<MultiPhase<T>>::feasibility_check(raw_solution, ElectionCompute::Unsigned));
+		assert!(<MultiPhase<T>>::feasibility_check(raw_solution, ElectionCompute::Unsigned).is_ok());
 	}
 
 	// NOTE: this weight is not used anywhere, but the fact that it should succeed when execution in