Enable Offchain Equalise (#5683)

* Master.into()

* Remove debug stuff

* Better license

* Migrate away from SimpleDispatchInfo

* Fix test

* Revert "Migrate away from SimpleDispatchInfo"

This reverts commit dbdd27fa19948f16bd17defdc01d3dd32986df11.

* Move to offchain randomness

* Fix tests

* Fix tests more

substrate/frame/staking/src/offchain_election.rs

@@ -16,17 +16,18 @@
 
 //! Helpers for offchain worker election.
 
+use codec::Decode;
 use crate::{
 	Call, CompactAssignments, Module, NominatorIndex, OffchainAccuracy, Trait, ValidatorIndex,
 };
 use frame_system::offchain::SubmitTransaction;
 use sp_phragmen::{
 	build_support_map, evaluate_support, reduce, Assignment, ExtendedBalance, PhragmenResult,
-	PhragmenScore,
+	PhragmenScore, equalize,
 };
 use sp_runtime::offchain::storage::StorageValueRef;
-use sp_runtime::PerThing;
-use sp_runtime::RuntimeDebug;
+use sp_runtime::{PerThing, RuntimeDebug, traits::{TrailingZeroInput, Zero}};
+use frame_support::{debug, traits::Get};
 use sp_std::{convert::TryInto, prelude::*};
 
 /// Error types related to the offchain election machinery.
@@ -159,10 +160,7 @@ pub fn prepare_submission<T: Trait>(
 	};
 
 	// Clean winners.
-	let winners = winners
-		.into_iter()
-		.map(|(w, _)| w)
-		.collect::<Vec<T::AccountId>>();
+	let winners = sp_phragmen::to_without_backing(winners);
 
 	// convert into absolute value and to obtain the reduced version.
 	let mut staked = sp_phragmen::assignment_ratio_to_staked(
@@ -170,10 +168,33 @@ pub fn prepare_submission<T: Trait>(
 		<Module<T>>::slashable_balance_of_vote_weight,
 	);
 
+	// reduce
 	if do_reduce {
 		reduce(&mut staked);
 	}
 
+	let (mut support_map, _) = build_support_map::<T::AccountId>(&winners, &staked);
+
+	// equalize a random number of times.
+	let iterations_executed = match T::MaxIterations::get() {
+		0 => {
+			// Don't run equalize at all
+			0
+		}
+		iterations @ _ => {
+			let seed = sp_io::offchain::random_seed();
+			let iterations = <u32>::decode(&mut TrailingZeroInput::new(seed.as_ref()))
+				.expect("input is padded with zeroes; qed") % iterations.saturating_add(1);
+			equalize(
+				&mut staked,
+				&mut support_map,
+				Zero::zero(),
+				iterations as usize,
+			)
+		}
+	};
+
+
 	// Convert back to ratio assignment. This takes less space.
 	let low_accuracy_assignment = sp_phragmen::assignment_staked_to_ratio(staked);
 
@@ -215,5 +236,12 @@ pub fn prepare_submission<T: Trait>(
 		}
 	}
 
+	debug::native::debug!(
+		target: "staking",
+		"prepared solution after {} equalization iterations with score {:?}",
+		iterations_executed,
+		score,
+	);
+
 	Ok((winners_indexed, compact, score))
 }