Include recently slashed churn in exit churn queue

specs/core/0_beacon-chain.md

@@ -2089,16 +2089,21 @@ def update_validator_registry(state: BeaconState) -> None:
             activate_validator(state, index, is_genesis=False)
 
     # Exit validators within the allowable balance churn
-    balance_churn = 0
-    for index, validator in enumerate(state.validator_registry):
-        if validator.exit_epoch == FAR_FUTURE_EPOCH and validator.initiated_exit:
-            # Check the balance churn would be within the allowance
-            balance_churn += get_effective_balance(state, index)
-            if balance_churn > max_balance_churn:
-                break
+    if current_epoch < state.validator_registry_update_epoch + LATEST_SLASHED_EXIT_LENGTH:
+        balance_churn = (
+            state.latest_slashed_balances[state.validator_registry_update_epoch % LATEST_SLASHED_EXIT_LENGTH] -
+            state.latest_slashed_balances[current_epoch % LATEST_SLASHED_EXIT_LENGTH]
+        )
+
+        for index, validator in enumerate(state.validator_registry):
+            if validator.exit_epoch == FAR_FUTURE_EPOCH and validator.initiated_exit:
+                # Check the balance churn would be within the allowance
+                balance_churn += get_effective_balance(state, index)
+                if balance_churn > max_balance_churn:
+                    break
 
-            # Exit validator
-            exit_validator(state, index)
+                # Exit validator
+                exit_validator(state, index)
 
     state.validator_registry_update_epoch = current_epoch
 ```

tests/phase0/test_sanity.py

@@ -316,12 +316,18 @@ def test_attestation(state, pubkeys, privkeys):
 
 def test_voluntary_exit(state, pubkeys, privkeys):
     pre_state = deepcopy(state)
-    validator_index = get_active_validator_indices(pre_state.validator_registry, get_current_epoch(pre_state))[-1]
+    validator_index = get_active_validator_indices(
+        pre_state.validator_registry,
+        get_current_epoch(pre_state)
+    )[-1]
 
     # move state forward PERSISTENT_COMMITTEE_PERIOD epochs to allow for exit
     pre_state.slot += spec.PERSISTENT_COMMITTEE_PERIOD * spec.SLOTS_PER_EPOCH
     # artificially trigger registry update at next epoch transition
-    pre_state.validator_registry_update_epoch -= 1
+    pre_state.finalized_epoch = get_current_epoch(pre_state) - 1
+    for crosslink in pre_state.latest_crosslinks:
+        crosslink.epoch = pre_state.finalized_epoch
+    pre_state.validator_registry_update_epoch = pre_state.finalized_epoch - 1
 
     post_state = deepcopy(pre_state)
 
@@ -363,6 +369,44 @@ def test_voluntary_exit(state, pubkeys, privkeys):
     return pre_state, [initiate_exit_block, exit_block], post_state
 
 
+def test_no_exit_too_long_since_change(state):
+    pre_state = deepcopy(state)
+    validator_index = get_active_validator_indices(
+        pre_state.validator_registry,
+        get_current_epoch(pre_state)
+    )[-1]
+
+    #
+    # setup pre_state
+    #
+    # move state forward PERSISTENT_COMMITTEE_PERIOD epochs to allow for exit
+    pre_state.slot += spec.PERSISTENT_COMMITTEE_PERIOD * spec.SLOTS_PER_EPOCH
+    # artificially trigger registry update at next epoch transition
+    pre_state.finalized_epoch = get_current_epoch(pre_state) - 1
+    for crosslink in pre_state.latest_crosslinks:
+        crosslink.epoch = pre_state.finalized_epoch
+    # make epochs since registry update greater than LATEST_SLASHED_EXIT_LENGTH
+    pre_state.validator_registry_update_epoch = (
+        get_current_epoch(pre_state) - spec.LATEST_SLASHED_EXIT_LENGTH
+    )
+    # set validator to have previously initiated exit
+    pre_state.validator_registry[validator_index].initiated_exit = True
+
+    post_state = deepcopy(pre_state)
+
+    #
+    # Process registry change but ensure no exit
+    #
+    block = build_empty_block_for_next_slot(post_state)
+    block.slot += spec.SLOTS_PER_EPOCH
+    state_transition(post_state, block)
+
+    assert post_state.validator_registry_update_epoch == get_current_epoch(post_state) - 1
+    assert post_state.validator_registry[validator_index].exit_epoch == spec.FAR_FUTURE_EPOCH
+
+    return pre_state, [block], post_state
+
+
 def test_transfer(state, pubkeys, privkeys):
     pre_state = deepcopy(state)
     current_epoch = get_current_epoch(pre_state)