Adding `Fallback` on election failure (#5093)

* Adding `Fallback` on election failure
Use the newly introduced `BoundedOnChainSequentialPhragmen`
and `UnboundedOnChainSequentialPhragmen`

* Adding `BoundedOnchainExecution`
after changes in substrate

* Introducing `ExecutionConfig`
from `frame_election_provider_support::onchain`

* `OnChainSequentialPhragmen` > `OnChainSeqPhragmen`
Renaming to have a shorter name

* `BoundedOnchainExecution` -> `BoundedExecution`
And `UnboundedOnchainExecution` -> `UnboundedExecution`

* `Fallback` back to `NoFallback`
`UnboundedExecution` for `GovernanceFallback`

* Update runtime/test-runtime/src/lib.rs

* update lockfile for {"substrate"}

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

polkadot/runtime/common/src/elections.rs

@@ -16,7 +16,10 @@
 
 //! Code for elections.
 
-use frame_election_provider_support::SortedListProvider;
+use frame_election_provider_support::{
+	onchain::{ExecutionConfig, UnboundedExecution},
+	ElectionDataProvider, SequentialPhragmen, SortedListProvider,
+};
 use sp_std::{boxed::Box, marker::PhantomData};
 
 /// Implements the weight types for the elections module and a specific
@@ -64,9 +67,20 @@ impl pallet_election_provider_multi_phase::BenchmarkingConfig for BenchmarkConfi
 /// The accuracy type used for genesis election provider;
 pub type OnOnChainAccuracy = sp_runtime::Perbill;
 
+/// Election Configuration parameters
+pub struct OnChainSeqPhragmen<T: frame_system::Config, S>(PhantomData<(T, S)>);
+impl<
+		T: frame_system::Config,
+		S: ElectionDataProvider<AccountId = T::AccountId, BlockNumber = T::BlockNumber>,
+	> ExecutionConfig for OnChainSeqPhragmen<T, S>
+{
+	type System = T;
+	type Solver = SequentialPhragmen<T::AccountId, OnOnChainAccuracy>;
+	type DataProvider = S;
+}
+
 /// The election provider of the genesis
-pub type GenesisElectionOf<T> =
-	frame_election_provider_support::onchain::OnChainSequentialPhragmen<T>;
+pub type GenesisElectionOf<T, S> = UnboundedExecution<OnChainSeqPhragmen<T, S>>;
 
 /// Implementation of `frame_election_provider_support::SortedListProvider` that updates the
 /// bags-list but uses [`pallet_staking::Nominators`] for `iter`. This is meant to be a transitionary

polkadot/runtime/kusama/src/lib.rs

@@ -29,8 +29,9 @@ use primitives::v2::{
 	SessionInfo, Signature, ValidationCode, ValidationCodeHash, ValidatorId, ValidatorIndex,
 };
 use runtime_common::{
-	auctions, claims, crowdloan, impl_runtime_weights, impls::DealWithFees, paras_registrar,
-	prod_or_fast, slots, BlockHashCount, BlockLength, CurrencyToVote, SlowAdjustingFeeUpdate,
+	auctions, claims, crowdloan, elections::OnChainSeqPhragmen, impl_runtime_weights,
+	impls::DealWithFees, paras_registrar, prod_or_fast, slots, BlockHashCount, BlockLength,
+	CurrencyToVote, SlowAdjustingFeeUpdate,
 };
 use sp_std::{cmp::Ordering, collections::btree_map::BTreeMap, prelude::*};
 
@@ -45,6 +46,9 @@ use runtime_parachains::{
 
 use authority_discovery_primitives::AuthorityId as AuthorityDiscoveryId;
 use beefy_primitives::crypto::AuthorityId as BeefyId;
+use frame_election_provider_support::{
+	generate_solution_type, onchain::UnboundedExecution, NposSolution, SequentialPhragmen,
+};
 use frame_support::{
 	construct_runtime, parameter_types,
 	traits::{
@@ -413,7 +417,7 @@ parameter_types! {
 	pub const MaxElectableTargets: u16 = u16::MAX;
 }
 
-frame_election_provider_support::generate_solution_type!(
+generate_solution_type!(
 	#[compact]
 	pub struct NposCompactSolution24::<
 		VoterIndex = u32,
@@ -445,9 +449,8 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type DataProvider = Staking;
 	type Solution = NposCompactSolution24;
 	type Fallback = pallet_election_provider_multi_phase::NoFallback<Self>;
-	type GovernanceFallback =
-		frame_election_provider_support::onchain::OnChainSequentialPhragmen<Self>;
-	type Solver = frame_election_provider_support::SequentialPhragmen<
+	type GovernanceFallback = UnboundedExecution<OnChainSeqPhragmen<Self, Staking>>;
+	type Solver = SequentialPhragmen<
 		AccountId,
 		pallet_election_provider_multi_phase::SolutionAccuracyOf<Self>,
 		(),
@@ -546,7 +549,7 @@ parameter_types! {
 	pub const MaxNominatorRewardedPerValidator: u32 = 256;
 	pub const OffendingValidatorsThreshold: Perbill = Perbill::from_percent(17);
 	// 24
-	pub const MaxNominations: u32 = <NposCompactSolution24 as frame_election_provider_support::NposSolution>::LIMIT as u32;
+	pub const MaxNominations: u32 = <NposCompactSolution24 as NposSolution>::LIMIT as u32;
 }
 
 type SlashCancelOrigin = EnsureOneOf<
@@ -554,18 +557,13 @@ type SlashCancelOrigin = EnsureOneOf<
 	pallet_collective::EnsureProportionAtLeast<AccountId, CouncilCollective, 1, 2>,
 >;
 
-impl frame_election_provider_support::onchain::Config for Runtime {
-	type Accuracy = runtime_common::elections::OnOnChainAccuracy;
-	type DataProvider = Staking;
-}
-
 impl pallet_staking::Config for Runtime {
 	type MaxNominations = MaxNominations;
 	type Currency = Balances;
 	type UnixTime = Timestamp;
 	type CurrencyToVote = CurrencyToVote;
 	type ElectionProvider = ElectionProviderMultiPhase;
-	type GenesisElectionProvider = runtime_common::elections::GenesisElectionOf<Self>;
+	type GenesisElectionProvider = runtime_common::elections::GenesisElectionOf<Self, Staking>;
 	type RewardRemainder = Treasury;
 	type Event = Event;
 	type Slash = Treasury;

polkadot/runtime/polkadot/src/lib.rs

@@ -22,8 +22,9 @@
 
 use pallet_transaction_payment::CurrencyAdapter;
 use runtime_common::{
-	auctions, claims, crowdloan, impl_runtime_weights, impls::DealWithFees, paras_registrar,
-	prod_or_fast, slots, BlockHashCount, BlockLength, CurrencyToVote, SlowAdjustingFeeUpdate,
+	auctions, claims, crowdloan, elections::OnChainSeqPhragmen, impl_runtime_weights,
+	impls::DealWithFees, paras_registrar, prod_or_fast, slots, BlockHashCount, BlockLength,
+	CurrencyToVote, SlowAdjustingFeeUpdate,
 };
 
 use runtime_parachains::{
@@ -37,6 +38,9 @@ use runtime_parachains::{
 
 use authority_discovery_primitives::AuthorityId as AuthorityDiscoveryId;
 use beefy_primitives::crypto::AuthorityId as BeefyId;
+use frame_election_provider_support::{
+	generate_solution_type, onchain::UnboundedExecution, SequentialPhragmen,
+};
 use frame_support::{
 	construct_runtime, parameter_types,
 	traits::{
@@ -456,7 +460,7 @@ parameter_types! {
 	pub const MaxElectableTargets: u16 = u16::MAX;
 }
 
-frame_election_provider_support::generate_solution_type!(
+generate_solution_type!(
 	#[compact]
 	pub struct NposCompactSolution16::<
 		VoterIndex = u32,
@@ -488,9 +492,8 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type DataProvider = Staking;
 	type Solution = NposCompactSolution16;
 	type Fallback = pallet_election_provider_multi_phase::NoFallback<Self>;
-	type GovernanceFallback =
-		frame_election_provider_support::onchain::OnChainSequentialPhragmen<Self>;
-	type Solver = frame_election_provider_support::SequentialPhragmen<
+	type GovernanceFallback = UnboundedExecution<OnChainSeqPhragmen<Self, Staking>>;
+	type Solver = SequentialPhragmen<
 		AccountId,
 		pallet_election_provider_multi_phase::SolutionAccuracyOf<Self>,
 		(),
@@ -551,11 +554,6 @@ type SlashCancelOrigin = EnsureOneOf<
 	pallet_collective::EnsureProportionAtLeast<AccountId, CouncilCollective, 3, 4>,
 >;
 
-impl frame_election_provider_support::onchain::Config for Runtime {
-	type Accuracy = runtime_common::elections::OnOnChainAccuracy;
-	type DataProvider = Staking;
-}
-
 impl pallet_staking::Config for Runtime {
 	type MaxNominations = MaxNominations;
 	type Currency = Balances;
@@ -576,7 +574,7 @@ impl pallet_staking::Config for Runtime {
 	type OffendingValidatorsThreshold = OffendingValidatorsThreshold;
 	type NextNewSession = Session;
 	type ElectionProvider = ElectionProviderMultiPhase;
-	type GenesisElectionProvider = runtime_common::elections::GenesisElectionOf<Self>;
+	type GenesisElectionProvider = runtime_common::elections::GenesisElectionOf<Self, Staking>;
 	type VoterList = BagsList;
 	type MaxUnlockingChunks = frame_support::traits::ConstU32<32>;
 	type BenchmarkingConfig = runtime_common::StakingBenchmarkingConfig;

polkadot/runtime/test-runtime/src/lib.rs

@@ -318,11 +318,6 @@ parameter_types! {
 	pub const MaxAuthorities: u32 = 100_000;
 }
 
-impl frame_election_provider_support::onchain::Config for Runtime {
-	type Accuracy = runtime_common::elections::OnOnChainAccuracy;
-	type DataProvider = Staking;
-}
-
 impl pallet_staking::Config for Runtime {
 	type MaxNominations = frame_support::pallet_prelude::ConstU32<16>;
 	type Currency = Balances;
@@ -342,10 +337,14 @@ impl pallet_staking::Config for Runtime {
 	type MaxNominatorRewardedPerValidator = MaxNominatorRewardedPerValidator;
 	type OffendingValidatorsThreshold = OffendingValidatorsThreshold;
 	type NextNewSession = Session;
-	type ElectionProvider =
-		frame_election_provider_support::onchain::OnChainSequentialPhragmen<Self>;
-	type GenesisElectionProvider =
-		frame_election_provider_support::onchain::OnChainSequentialPhragmen<Self>;
+	type ElectionProvider = frame_election_provider_support::onchain::UnboundedExecution<
+		runtime_common::elections::OnChainSeqPhragmen<Self, Staking>,
+	>;
+	type GenesisElectionProvider = frame_election_provider_support::onchain::UnboundedExecution<
+		runtime_common::elections::OnChainSeqPhragmen<Self, Staking>,
+	>;
+	// Use the nominator map to iter voter AND no-ops for all SortedListProvider hooks. The migration
+	// to bags-list is a no-op, but the storage version will be updated.
 	type VoterList = pallet_staking::UseNominatorsAndValidatorsMap<Runtime>;
 	type MaxUnlockingChunks = frame_support::traits::ConstU32<32>;
 	type BenchmarkingConfig = runtime_common::StakingBenchmarkingConfig;

polkadot/runtime/westend/src/lib.rs

@@ -22,6 +22,7 @@
 
 use authority_discovery_primitives::AuthorityId as AuthorityDiscoveryId;
 use beefy_primitives::crypto::AuthorityId as BeefyId;
+use frame_election_provider_support::{onchain::UnboundedExecution, SequentialPhragmen};
 use frame_support::{
 	construct_runtime, parameter_types,
 	traits::{Contains, InstanceFilter, KeyOwnerProofSystem, OnRuntimeUpgrade},
@@ -42,8 +43,9 @@ use primitives::v2::{
 	ValidatorIndex, ValidatorSignature,
 };
 use runtime_common::{
-	assigned_slots, auctions, crowdloan, impl_runtime_weights, impls::ToAuthor, paras_registrar,
-	paras_sudo_wrapper, slots, BlockHashCount, BlockLength, CurrencyToVote, SlowAdjustingFeeUpdate,
+	assigned_slots, auctions, crowdloan, elections::OnChainSeqPhragmen, impl_runtime_weights,
+	impls::ToAuthor, paras_registrar, paras_sudo_wrapper, slots, BlockHashCount, BlockLength,
+	CurrencyToVote, SlowAdjustingFeeUpdate,
 };
 use runtime_parachains::{
 	configuration as parachains_configuration, disputes as parachains_disputes,
@@ -390,9 +392,8 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type DataProvider = Staking;
 	type Solution = NposCompactSolution16;
 	type Fallback = pallet_election_provider_multi_phase::NoFallback<Self>;
-	type GovernanceFallback =
-		frame_election_provider_support::onchain::OnChainSequentialPhragmen<Self>;
-	type Solver = frame_election_provider_support::SequentialPhragmen<
+	type GovernanceFallback = UnboundedExecution<OnChainSeqPhragmen<Self, Staking>>;
+	type Solver = SequentialPhragmen<
 		AccountId,
 		pallet_election_provider_multi_phase::SolutionAccuracyOf<Self>,
 		(),
@@ -440,11 +441,6 @@ parameter_types! {
 	pub const MaxNominations: u32 = <NposCompactSolution16 as frame_election_provider_support::NposSolution>::LIMIT as u32;
 }
 
-impl frame_election_provider_support::onchain::Config for Runtime {
-	type Accuracy = runtime_common::elections::OnOnChainAccuracy;
-	type DataProvider = Staking;
-}
-
 impl pallet_staking::Config for Runtime {
 	type MaxNominations = MaxNominations;
 	type Currency = Balances;
@@ -465,7 +461,7 @@ impl pallet_staking::Config for Runtime {
 	type OffendingValidatorsThreshold = OffendingValidatorsThreshold;
 	type NextNewSession = Session;
 	type ElectionProvider = ElectionProviderMultiPhase;
-	type GenesisElectionProvider = runtime_common::elections::GenesisElectionOf<Self>;
+	type GenesisElectionProvider = runtime_common::elections::GenesisElectionOf<Self, Staking>;
 	type VoterList = BagsList;
 	type MaxUnlockingChunks = frame_support::traits::ConstU32<32>;
 	type BenchmarkingConfig = runtime_common::StakingBenchmarkingConfig;