Recursive election provider as fallback

bin/node/runtime/src/lib.rs

@@ -42,7 +42,6 @@ use frame_system::{
 pub use node_primitives::{AccountId, Signature};
 use node_primitives::{AccountIndex, Balance, BlockNumber, Hash, Index, Moment};
 use pallet_contracts::weights::WeightInfo;
-use pallet_election_provider_multi_phase::FallbackStrategy;
 use pallet_grandpa::{
 	fg_primitives, AuthorityId as GrandpaId, AuthorityList as GrandpaAuthorityList,
 };
@@ -487,6 +486,11 @@ parameter_types! {
 }
 
 use frame_election_provider_support::onchain;
+impl onchain::Config for Runtime {
+	type Accuracy = Perbill;
+	type DataProvider = Staking;
+}
+
 impl pallet_staking::Config for Runtime {
 	const MAX_NOMINATIONS: u32 = MAX_NOMINATIONS;
 	type Currency = Balances;
@@ -510,9 +514,7 @@ impl pallet_staking::Config for Runtime {
 	type NextNewSession = Session;
 	type MaxNominatorRewardedPerValidator = MaxNominatorRewardedPerValidator;
 	type ElectionProvider = ElectionProviderMultiPhase;
-	type GenesisElectionProvider = onchain::OnChainSequentialPhragmen<
-		pallet_election_provider_multi_phase::OnChainConfig<Self>,
-	>;
+	type GenesisElectionProvider = onchain::OnChainSequentialPhragmen<Self>;
 	type WeightInfo = pallet_staking::weights::SubstrateWeight<Runtime>;
 }
 
@@ -527,9 +529,6 @@ parameter_types! {
 	pub const SignedDepositBase: Balance = 1 * DOLLARS;
 	pub const SignedDepositByte: Balance = 1 * CENTS;
 
-	// fallback: no on-chain fallback.
-	pub const Fallback: FallbackStrategy = FallbackStrategy::Nothing;
-
 	pub SolutionImprovementThreshold: Perbill = Perbill::from_rational(1u32, 10_000);
 
 	// miner configs
@@ -591,10 +590,9 @@ impl pallet_election_provider_multi_phase::Config for Runtime {
 	type SlashHandler = (); // burn slashes
 	type RewardHandler = (); // nothing to do upon rewards
 	type DataProvider = Staking;
-	type OnChainAccuracy = Perbill;
 	type Solution = NposSolution16;
-	type Fallback = Fallback;
-	type WeightInfo = pallet_election_provider_multi_phase::weights::SubstrateWeight<Runtime>;
+	type Fallback = pallet_election_provider_multi_phase::NoFallback<Self>;
+	type WeightInfo = pallet_election_provider_multi_phase::weights::SubstrateWeight<Self>;
 	type ForceOrigin = EnsureRootOrHalfCouncil;
 	type BenchmarkingConfig = BenchmarkConfig;
 }
@@ -1672,6 +1670,7 @@ impl_runtime_apis! {
 mod tests {
 	use super::*;
 	use frame_system::offchain::CreateSignedTransaction;
+	use sp_runtime::UpperOf;
 
 	#[test]
 	fn validate_transaction_submitter_bounds() {
@@ -1684,6 +1683,16 @@ mod tests {
 		is_submit_signed_transaction::<Runtime>();
 	}
 
+	#[test]
+	fn perbill_as_onchain_accuracy() {
+		type OnChainAccuracy = <Runtime as onchain::Config>::Accuracy;
+		let maximum_chain_accuracy: Vec<UpperOf<OnChainAccuracy>> = (0..MAX_NOMINATIONS)
+			.map(|_| <UpperOf<OnChainAccuracy>>::from(OnChainAccuracy::one().deconstruct()))
+			.collect();
+		let _: UpperOf<OnChainAccuracy> =
+			maximum_chain_accuracy.iter().fold(0, |acc, x| acc.checked_add(*x).unwrap());
+	}
+
 	#[test]
 	fn call_size() {
 		assert!(