Cleanup validator change fetching (#7506)

When building a block, allow BLS to Execution change to be included
for a validator that exits in the same block. Credential changes can
happen together with (or even after) an exit.

Author: etan-status

beacon_chain/consensus_object_pools/validator_change_pool.nim

@@ -259,11 +259,11 @@ proc getValidatorChangeMessagesForBlock(
     if not validateValidatorChangeMessage(cfg, state, validator_change_message):
       continue
 
-    var skip = false
+    # Filter messages that don't affect any new validators
+    var skip = true
     for slashed_index in getValidatorIndices(validator_change_message):
-      if seen.containsOrIncl(slashed_index):
-        skip = true
-        break
+      if not seen.containsOrIncl(slashed_index):
+        skip = false
     if skip:
       continue
 
@@ -273,31 +273,34 @@ proc getValidatorChangeMessagesForBlock(
 proc getBeaconBlockValidatorChanges*(
     pool: var ValidatorChangePool, cfg: RuntimeConfig, state: ForkyBeaconState):
     BeaconBlockValidatorChanges =
-  var
-    indices: HashSet[uint64]
-    res: BeaconBlockValidatorChanges
-
-  getValidatorChangeMessagesForBlock(
-    pool.phase0_attester_slashings, cfg, state, indices,
-    res.phase0_attester_slashings)
-  getValidatorChangeMessagesForBlock(
-    pool.proposer_slashings, cfg, state, indices, res.proposer_slashings)
-  getValidatorChangeMessagesForBlock(
-    pool.voluntary_exits, cfg, state, indices, res.voluntary_exits)
-
-  when typeof(state).kind >= ConsensusFork.Capella:
-    # Prioritize these
+  var res: BeaconBlockValidatorChanges
+
+  # Exits (with priority on slashings)
+  block:
+    var indices: HashSet[uint64]
+    when typeof(state).kind >= ConsensusFork.Electra:
+      getValidatorChangeMessagesForBlock(
+        pool.electra_attester_slashings, cfg, state, indices,
+        res.electra_attester_slashings)
+    else:
+      getValidatorChangeMessagesForBlock(
+        pool.phase0_attester_slashings, cfg, state, indices,
+        res.phase0_attester_slashings)
     getValidatorChangeMessagesForBlock(
-      pool.bls_to_execution_changes_api, cfg, state, indices,
-      res.bls_to_execution_changes)
-
+      pool.proposer_slashings, cfg, state, indices, res.proposer_slashings)
     getValidatorChangeMessagesForBlock(
-      pool.bls_to_execution_changes_gossip, cfg, state, indices,
-      res.bls_to_execution_changes)
+      pool.voluntary_exits, cfg, state, indices, res.voluntary_exits)
 
-  when typeof(state).kind >= ConsensusFork.Electra:
-    getValidatorChangeMessagesForBlock(
-      pool.electra_attester_slashings, cfg, state, indices,
-      res.electra_attester_slashings)
+  # Credential changes (can be combined with exit)
+  when typeof(state).kind >= ConsensusFork.Capella:
+    block:
+      var indices: HashSet[uint64]
+      # Prioritize those from API
+      getValidatorChangeMessagesForBlock(
+        pool.bls_to_execution_changes_api, cfg, state, indices,
+        res.bls_to_execution_changes)
+      getValidatorChangeMessagesForBlock(
+        pool.bls_to_execution_changes_gossip, cfg, state, indices,
+        res.bls_to_execution_changes)
 
   res