#4512 inactivity calculation for Altair (#4807)

## Issue Addressed
#4512 
Which issue # does this PR address?

## Proposed Changes
Add inactivity calculation for Altair

Please list or describe the changes introduced by this PR.
Add inactivity calculation for Altair

## Additional Info

Please provide any additional information. For example, future considerations
or information useful for reviewers.


Co-authored-by: Jimmy Chen <jchen.tc@gmail.com>

beacon_node/beacon_chain/src/attestation_rewards.rs

@@ -5,6 +5,7 @@ use participation_cache::ParticipationCache;
 use safe_arith::SafeArith;
 use serde_utils::quoted_u64::Quoted;
 use slog::debug;
+use state_processing::per_epoch_processing::altair::process_inactivity_updates;
 use state_processing::{
     common::altair::BaseRewardPerIncrement,
     per_epoch_processing::altair::{participation_cache, rewards_and_penalties::get_flag_weight},
@@ -124,6 +125,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
         // Calculate ideal_rewards
         let participation_cache = ParticipationCache::new(&state, spec)?;
+        process_inactivity_updates(&mut state, &participation_cache, spec)?;
 
         let previous_epoch = state.previous_epoch();
 
@@ -190,6 +192,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             let mut head_reward = 0i64;
             let mut target_reward = 0i64;
             let mut source_reward = 0i64;
+            let mut inactivity_penalty = 0i64;
 
             if eligible {
                 let effective_balance = state.get_effective_balance(*validator_index)?;
@@ -215,6 +218,14 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                         head_reward = 0;
                     } else if flag_index == TIMELY_TARGET_FLAG_INDEX {
                         target_reward = *penalty;
+
+                        let penalty_numerator = effective_balance
+                            .safe_mul(state.get_inactivity_score(*validator_index)?)?;
+                        let penalty_denominator = spec
+                            .inactivity_score_bias
+                            .safe_mul(spec.inactivity_penalty_quotient_for_state(&state))?;
+                        inactivity_penalty =
+                            -(penalty_numerator.safe_div(penalty_denominator)? as i64);
                     } else if flag_index == TIMELY_SOURCE_FLAG_INDEX {
                         source_reward = *penalty;
                     }
@@ -226,8 +237,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 target: target_reward,
                 source: source_reward,
                 inclusion_delay: None,
-                // TODO: altair calculation logic needs to be updated to include inactivity penalty
+                inactivity: inactivity_penalty,
-                inactivity: 0,
             });
         }
 
@@ -250,7 +260,6 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                             target: 0,
                             source: 0,
                             inclusion_delay: None,
-                            // TODO: altair calculation logic needs to be updated to include inactivity penalty
                             inactivity: 0,
                         });
                     match *flag_index {

beacon_node/beacon_chain/src/test_utils.rs

@@ -2350,6 +2350,29 @@ where
         .await
     }
 
+    /// Uses `Self::extend_chain` to `num_slots` blocks.
+    ///
+    /// Utilizes:
+    ///
+    ///  - BlockStrategy::OnCanonicalHead,
+    ///  - AttestationStrategy::SomeValidators(validators),
+    pub async fn extend_slots_some_validators(
+        &self,
+        num_slots: usize,
+        validators: Vec<usize>,
+    ) -> Hash256 {
+        if self.chain.slot().unwrap() == self.chain.canonical_head.cached_head().head_slot() {
+            self.advance_slot();
+        }
+
+        self.extend_chain(
+            num_slots,
+            BlockStrategy::OnCanonicalHead,
+            AttestationStrategy::SomeValidators(validators),
+        )
+        .await
+    }
+
     /// Extend the `BeaconChain` with some blocks and attestations. Returns the root of the
     /// last-produced block (the head of the chain).
     ///

beacon_node/beacon_chain/tests/rewards.rs

@@ -14,7 +14,7 @@ use eth2::lighthouse::StandardAttestationRewards;
 use eth2::types::ValidatorId;
 use lazy_static::lazy_static;
 use types::beacon_state::Error as BeaconStateError;
-use types::{BeaconState, ChainSpec};
+use types::{BeaconState, ChainSpec, ForkName, Slot};
 
 pub const VALIDATOR_COUNT: usize = 64;
 
@@ -219,6 +219,100 @@ async fn test_verify_attestation_rewards_base_inactivity_leak() {
     assert_eq!(expected_balances, balances);
 }
 
+#[tokio::test]
+async fn test_verify_attestation_rewards_altair_inactivity_leak() {
+    let spec = ForkName::Altair.make_genesis_spec(E::default_spec());
+    let harness = get_harness(spec.clone());
+
+    let half = VALIDATOR_COUNT / 2;
+    let half_validators: Vec<usize> = (0..half).collect();
+    // target epoch is the epoch where the chain enters inactivity leak
+    let target_epoch = &spec.min_epochs_to_inactivity_penalty + 1;
+
+    // advance until beginning of epoch N + 1 and get balances
+    harness
+        .extend_slots_some_validators(
+            (E::slots_per_epoch() * (target_epoch + 1)) as usize,
+            half_validators.clone(),
+        )
+        .await;
+    let initial_balances: Vec<u64> = harness.get_current_state().balances().clone().into();
+
+    // advance until epoch N + 2 and build proposal rewards map
+    let mut proposal_rewards_map: HashMap<u64, u64> = HashMap::new();
+    let mut sync_committee_rewards_map: HashMap<u64, i64> = HashMap::new();
+    for _ in 0..E::slots_per_epoch() {
+        let state = harness.get_current_state();
+        let slot = state.slot() + Slot::new(1);
+
+        // calculate beacon block rewards / penalties
+        let ((signed_block, _maybe_blob_sidecars), mut state) =
+            harness.make_block_return_pre_state(state, slot).await;
+        let beacon_block_reward = harness
+            .chain
+            .compute_beacon_block_reward(
+                signed_block.message(),
+                signed_block.canonical_root(),
+                &mut state,
+            )
+            .unwrap();
+
+        let total_proposer_reward = proposal_rewards_map
+            .get(&beacon_block_reward.proposer_index)
+            .unwrap_or(&0u64)
+            + beacon_block_reward.total;
+
+        proposal_rewards_map.insert(beacon_block_reward.proposer_index, total_proposer_reward);
+
+        // calculate sync committee rewards / penalties
+        let reward_payload = harness
+            .chain
+            .compute_sync_committee_rewards(signed_block.message(), &mut state)
+            .unwrap();
+
+        reward_payload.iter().for_each(|reward| {
+            let mut amount = *sync_committee_rewards_map
+                .get(&reward.validator_index)
+                .unwrap_or(&0);
+            amount += reward.reward;
+            sync_committee_rewards_map.insert(reward.validator_index, amount);
+        });
+
+        harness
+            .extend_slots_some_validators(1, half_validators.clone())
+            .await;
+    }
+
+    // compute reward deltas for all validators in epoch N
+    let StandardAttestationRewards {
+        ideal_rewards,
+        total_rewards,
+    } = harness
+        .chain
+        .compute_attestation_rewards(Epoch::new(target_epoch), vec![])
+        .unwrap();
+
+    // assert inactivity penalty for both ideal rewards and individual validators
+    assert!(ideal_rewards.iter().all(|reward| reward.inactivity == 0));
+    assert!(total_rewards[..half]
+        .iter()
+        .all(|reward| reward.inactivity == 0));
+    assert!(total_rewards[half..]
+        .iter()
+        .all(|reward| reward.inactivity < 0));
+
+    // apply attestation, proposal, and sync committee rewards and penalties to initial balances
+    let expected_balances = apply_attestation_rewards(&initial_balances, total_rewards);
+    let expected_balances = apply_beacon_block_rewards(&proposal_rewards_map, expected_balances);
+    let expected_balances =
+        apply_sync_committee_rewards(&sync_committee_rewards_map, expected_balances);
+
+    // verify expected balances against actual balances
+    let balances: Vec<u64> = harness.get_current_state().balances().clone().into();
+
+    assert_eq!(expected_balances, balances);
+}
+
 #[tokio::test]
 async fn test_verify_attestation_rewards_base_subset_only() {
     let harness = get_harness(E::default_spec());
@@ -297,3 +391,32 @@ fn get_validator_balances(state: BeaconState<E>, validators: &[usize]) -> Vec<u6
         })
         .collect()
 }
+
+fn apply_beacon_block_rewards(
+    proposal_rewards_map: &HashMap<u64, u64>,
+    expected_balances: Vec<u64>,
+) -> Vec<u64> {
+    let calculated_balances = expected_balances
+        .iter()
+        .enumerate()
+        .map(|(i, balance)| balance + proposal_rewards_map.get(&(i as u64)).unwrap_or(&0u64))
+        .collect();
+
+    calculated_balances
+}
+
+fn apply_sync_committee_rewards(
+    sync_committee_rewards_map: &HashMap<u64, i64>,
+    expected_balances: Vec<u64>,
+) -> Vec<u64> {
+    let calculated_balances = expected_balances
+        .iter()
+        .enumerate()
+        .map(|(i, balance)| {
+            (*balance as i64 + sync_committee_rewards_map.get(&(i as u64)).unwrap_or(&0i64))
+                .unsigned_abs()
+        })
+        .collect();
+
+    calculated_balances
+}