Tidy, remove unused function, fix init length

Author: paulhauner

consensus/state_processing/src/per_epoch_processing/altair/participation_cache.rs

@@ -148,7 +148,7 @@ pub struct ParticipationCache {
 }
 
 impl ParticipationCache {
-    /// Instantiate `Self`, returning a cache that is fully initialized and ready-to-go.
+    /// Instantiate `Self`, returning a fully initialized cache.
     ///
     /// ## Errors
     ///
@@ -167,11 +167,20 @@ impl ParticipationCache {
             .get_cached_active_validator_indices(RelativeEpoch::Current)?
             .len();
 
+        // Both the current/previous epoch participations are set to a capacity that is slightly
+        // larger than required. The difference will be due slashed-but-active validators.
         let mut current_epoch_participation =
             SingleEpochParticipationCache::new(num_current_epoch_active_vals, spec);
         let mut previous_epoch_participation =
             SingleEpochParticipationCache::new(num_previous_epoch_active_vals, spec);
-        let mut eligible_indices = Vec::with_capacity(num_previous_epoch_active_vals);
+        // Contains the set of validators which are:
+        //
+        // - Active in the previous epoch.
+        // - Slashed, but not yet withdrawable.
+        //
+        // Using the full length of `state.validators` is almost always overkill, but it ensures no
+        // reallocations.
+        let mut eligible_indices = Vec::with_capacity(state.validators().len());
 
         for (val_index, val) in state.validators().iter().enumerate() {
             if val.is_active_at(current_epoch) {
@@ -195,6 +204,14 @@ impl ParticipationCache {
             }
         }
 
+        eligible_indices.shrink_to_fit();
+        current_epoch_participation
+            .unslashed_participating_indices
+            .shrink_to_fit();
+        previous_epoch_participation
+            .unslashed_participating_indices
+            .shrink_to_fit();
+
         Ok(Self {
             current_epoch,
             current_epoch_participation,

consensus/types/src/beacon_state.rs

@@ -1451,30 +1451,6 @@ impl<T: EthSpec> BeaconState<T> {
         self.clone_with(CloneConfig::committee_caches_only())
     }
 
-    pub fn get_eligible_validator_indices(&self) -> Result<Vec<usize>, Error> {
-        match self {
-            BeaconState::Base(_) => Err(Error::IncorrectStateVariant),
-            BeaconState::Altair(_) => {
-                let previous_epoch = self.previous_epoch();
-                Ok(self
-                    .validators()
-                    .iter()
-                    .enumerate()
-                    .filter_map(|(i, val)| {
-                        if val.is_active_at(previous_epoch)
-                            || (val.slashed
-                                && previous_epoch + Epoch::new(1) < val.withdrawable_epoch)
-                        {
-                            Some(i)
-                        } else {
-                            None
-                        }
-                    })
-                    .collect())
-            }
-        }
-    }
-
     pub fn is_eligible_validator(&self, val_index: usize) -> Result<bool, Error> {
         match self {
             BeaconState::Base(_) => Err(Error::IncorrectStateVariant),