EIP-7547: Inclusion Lists

specs/_features/eip7547/fork-choice.md

@@ -8,6 +8,7 @@
 - [Introduction](#introduction)
 - [Helpers](#helpers)
   - [New `is_inclusion_list_available`](#new-is_inclusion_list_available)
+  - [Modified `filter_block_tree`](#modified-filter_block_tree)
 - [New fork-choice handlers](#new-fork-choice-handlers)
   - [New `on_inclusion_list`](#new-on_inclusion_list)
 
@@ -23,13 +24,67 @@ This is the modification of the fork choice accompanying EIP-7547.
 ### New `is_inclusion_list_available`
 
 ```python
-def is_inclusion_list_available(self: ExecutionEngine, new_payload_request: NewPayloadRequest) -> bool:
+def is_inclusion_list_available(block_root: Root) -> bool:
     """
     Return ``True`` if and only if the payload has a corresponding inclusion list.
     """
     ...
 ```
 
+### Modified `filter_block_tree`
+
+Add filter for if the inclusion list is available.
+
+```python
+def filter_block_tree(store: Store, block_root: Root, blocks: Dict[Root, BeaconBlock]) -> bool:
+    block = store.blocks[block_root]
+    # [Modified in EIP-7547] Check that IL is available when considering heads.
+    children = [
+        root for (root, block) in blocks.items()
+        if block.parent_root == block_root
+        and is_inclusion_list_available(root)
+    ]
+
+    # If any children branches contain expected finalized/justified checkpoints,
+    # add to filtered block-tree and signal viability to parent.
+    if any(children):
+        filter_block_tree_result = [filter_block_tree(store, child, blocks) for child in children]
+        if any(filter_block_tree_result):
+            blocks[block_root] = block
+            return True
+        return False
+
+    current_epoch = get_current_store_epoch(store)
+    voting_source = get_voting_source(store, block_root)
+
+    # The voting source should be either at the same height as the store's justified checkpoint or
+    # not more than two epochs ago
+    correct_justified = (
+        store.justified_checkpoint.epoch == GENESIS_EPOCH
+        or voting_source.epoch == store.justified_checkpoint.epoch
+        or voting_source.epoch + 2 >= current_epoch
+    )
+
+    finalized_checkpoint_block = get_checkpoint_block(
+        store,
+        block_root,
+        store.finalized_checkpoint.epoch,
+    )
+
+    correct_finalized = (
+        store.finalized_checkpoint.epoch == GENESIS_EPOCH
+        or store.finalized_checkpoint.root == finalized_checkpoint_block
+    )
+
+    # If expected finalized/justified, add to viable block-tree and signal viability to parent.
+    if correct_justified and correct_finalized:
+        blocks[block_root] = block
+        return True
+
+    # Otherwise, branch not viable
+    return False
+```
+
 ## New fork-choice handlers
 
 ### New `on_inclusion_list`