kick_stale_signatures() returns Vec<> instead of Option<Vec<>>

Author: Adam Reif

pallets/collator-selection/src/lib.rs

@@ -560,25 +560,25 @@ pub mod pallet {
 		/// Returns the removed AccountIds
 		pub fn kick_stale_candidates(
 			candidates: Vec<CandidateInfo<T::AccountId, BalanceOf<T>>>,
-		) -> Option<Vec<T::AccountId>> {
+		) -> Vec<T::AccountId> {
 			use sp_runtime::PerThing;
 
 			// 0. Storage reads and precondition checks
 			if candidates.is_empty() {
-				return None; // No candidates means we're running invulnerables only
+				return Vec::new(); // No candidates means we're running invulnerables only
 			}
 			let percentile_for_kick = Self::eviction_percentile();
 			if percentile_for_kick == Percent::zero() {
-				return None; // Selecting 0-th percentile disables kicking. Upper bound check in fn build()
+				return Vec::new(); // Selecting 0-th percentile disables kicking. Upper bound check in fn build()
 			}
 			let underperformance_threshold_percent = Self::eviction_threshold();
 			if underperformance_threshold_percent == Percent::one() {
-				return None; // tolerating 100% underperformance disables kicking
+				return Vec::new(); // tolerating 100% underperformance disables kicking
 			}
 			let mut collator_perf_this_session =
 				<BlocksPerCollatorThisSession<T>>::iter().collect::<Vec<_>>();
 			if collator_perf_this_session.is_empty() {
-				return None; // no validator performance recorded ( should not happen )
+				return Vec::new(); // no validator performance recorded ( should not happen )
 			}
 
 			// 1. Ascending sort of collator performance list by number of produced blocks
@@ -625,11 +625,7 @@ pub mod pallet {
 					}
 				}
 			});
-			if removed_account_ids.is_empty() {
-				None
-			} else {
-				Some(removed_account_ids)
-			}
+			removed_account_ids
 		}
 
 		/// Reset the performance map to the currently active validators at 0 blocks
@@ -687,19 +683,16 @@ pub mod pallet {
 			let candidates = Self::candidates();
 			let candidates_len_before = candidates.len();
 			let removed_candidate_ids = Self::kick_stale_candidates(candidates.clone());
-			let active_candidate_ids: Vec<_> = match removed_candidate_ids {
-				None => candidates.iter().map(|x| x.who.clone()).collect(),
-				Some(removed_candidate_ids) => candidates
-					.iter()
-					.filter_map(|x| {
-						if removed_candidate_ids.contains(&x.who) {
-							None
-						} else {
-							Some(x.who.clone())
-						}
-					})
-					.collect(),
-			};
+			let active_candidate_ids = candidates
+				.iter()
+				.filter_map(|x| {
+					if removed_candidate_ids.contains(&x.who) {
+						None
+					} else {
+						Some(x.who.clone())
+					}
+				})
+				.collect::<Vec<_>>();
 			let result = Self::assemble_collators(active_candidate_ids);
 
 			frame_system::Pallet::<T>::register_extra_weight_unchecked(

pallets/collator-selection/src/tests.rs

@@ -428,7 +428,7 @@ fn kick_algorithm_manta() {
 		BlocksPerCollatorThisSession::<Test>::insert(4u64, 9);
 		BlocksPerCollatorThisSession::<Test>::insert(5u64, 0);
 		assert_eq!(
-			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()).unwrap(),
+			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()),
 			vec![5, 3]
 		);
 
@@ -443,11 +443,12 @@ fn kick_algorithm_manta() {
 		BlocksPerCollatorThisSession::<Test>::insert(4u64, 9);
 		BlocksPerCollatorThisSession::<Test>::insert(5u64, 0);
 		assert_eq!(
-			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()).unwrap(),
+			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()),
 			vec![5, 3]
 		);
 
 		// Test boundary conditions
+		let empty_vec = Vec::<<Test as frame_system::Config>::AccountId>::new();
 		// Kick anyone not at perfect performance
 		EvictionPercentile::<Test>::put(Percent::from_percent(100));
 		EvictionThreshold::<Test>::put(Percent::from_percent(0));
@@ -456,21 +457,21 @@ fn kick_algorithm_manta() {
 		BlocksPerCollatorThisSession::<Test>::insert(4u64, 10);
 		assert_eq!(
 			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()),
-			Some(vec![3])
+			vec![3]
 		);
 		assert_ok!(CollatorSelection::register_as_candidate(Origin::signed(3)));
 		// Allow any underperformance => eviction disabled
 		EvictionThreshold::<Test>::put(Percent::from_percent(100));
 		assert_eq!(
 			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()),
-			None
+			empty_vec
 		);
 		// 0-th percentile = use worst collator as benchmark => eviction disabled
 		EvictionPercentile::<Test>::put(Percent::from_percent(0));
 		EvictionThreshold::<Test>::put(Percent::from_percent(0));
 		assert_eq!(
 			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()),
-			None
+			empty_vec
 		);
 		// Same performance => no kick
 		EvictionPercentile::<Test>::put(Percent::from_percent(100));
@@ -479,7 +480,7 @@ fn kick_algorithm_manta() {
 		BlocksPerCollatorThisSession::<Test>::insert(4u64, 10);
 		assert_eq!(
 			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()),
-			None
+			empty_vec
 		);
 		// Exactly on threshold => no kick
 		EvictionPercentile::<Test>::put(Percent::from_percent(100));
@@ -488,7 +489,7 @@ fn kick_algorithm_manta() {
 		BlocksPerCollatorThisSession::<Test>::insert(4u64, 9);
 		assert_eq!(
 			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()),
-			None
+			empty_vec
 		);
 		// Rational threshold = 8.1, kick 8 and below
 		EvictionPercentile::<Test>::put(Percent::from_percent(100));
@@ -497,7 +498,7 @@ fn kick_algorithm_manta() {
 		BlocksPerCollatorThisSession::<Test>::insert(4u64, 10);
 		assert_eq!(
 			CollatorSelection::kick_stale_candidates(CollatorSelection::candidates()),
-			Some(vec![3])
+			vec![3]
 		);
 	});
 }