Confirmation rule prerequisite - fork choice filter change

specs/phase0/fork-choice.md

@@ -16,10 +16,12 @@
     - [`get_forkchoice_store`](#get_forkchoice_store)
     - [`get_slots_since_genesis`](#get_slots_since_genesis)
     - [`get_current_slot`](#get_current_slot)
+    - [`get_current_store_epoch`](#get_current_store_epoch)
     - [`compute_slots_since_epoch_start`](#compute_slots_since_epoch_start)
     - [`get_ancestor`](#get_ancestor)
     - [`calculate_committee_fraction`](#calculate_committee_fraction)
     - [`get_checkpoint_block`](#get_checkpoint_block)
+    - [`get_proposer_score`](#get_proposer_score)
     - [`get_weight`](#get_weight)
     - [`get_voting_source`](#get_voting_source)
     - [`filter_block_tree`](#filter_block_tree)
@@ -140,8 +142,7 @@ class Store(object):
 
 ```python
 def is_previous_epoch_justified(store: Store) -> bool:
-    current_slot = get_current_slot(store)
-    current_epoch = compute_epoch_at_slot(current_slot)
+    current_epoch = get_current_store_epoch(store)
     return store.justified_checkpoint.epoch + 1 == current_epoch
 ```
 
@@ -190,6 +191,13 @@ def get_current_slot(store: Store) -> Slot:
     return Slot(GENESIS_SLOT + get_slots_since_genesis(store))
 ```
 
+#### `get_current_store_epoch`
+
+```python
+def get_current_store_epoch(store: Store) -> Epoch:
+    return compute_epoch_at_slot(get_current_slot(store))
+```
+
 #### `compute_slots_since_epoch_start`
 
 ```python
@@ -226,6 +234,15 @@ def get_checkpoint_block(store: Store, root: Root, epoch: Epoch) -> Root:
     return get_ancestor(store, root, epoch_first_slot)
 ```
 
+#### `get_proposer_score`
+
+```python
+def get_proposer_score(store: Store) -> Gwei:
+    justified_checkpoint_state = store.checkpoint_states[store.justified_checkpoint]
+    committee_weight = get_total_active_balance(justified_checkpoint_state) // SLOTS_PER_EPOCH
+    return (committee_weight * PROPOSER_SCORE_BOOST) // 100
+```
+
 #### `get_weight`
 
 ```python
@@ -249,7 +266,7 @@ def get_weight(store: Store, root: Root) -> Gwei:
     proposer_score = Gwei(0)
     # Boost is applied if ``root`` is an ancestor of ``proposer_boost_root``
     if get_ancestor(store, store.proposer_boost_root, store.blocks[root].slot) == root:
-        proposer_score = calculate_committee_fraction(state, PROPOSER_SCORE_BOOST)
+        proposer_score = get_proposer_score(store)
     return attestation_score + proposer_score
 ```
 
@@ -261,7 +278,7 @@ def get_voting_source(store: Store, block_root: Root) -> Checkpoint:
     Compute the voting source checkpoint in event that block with root ``block_root`` is the head block
     """
     block = store.blocks[block_root]
-    current_epoch = compute_epoch_at_slot(get_current_slot(store))
+    current_epoch = get_current_store_epoch(store)
     block_epoch = compute_epoch_at_slot(block.slot)
     if current_epoch > block_epoch:
         # The block is from a prior epoch, the voting source will be pulled-up
@@ -293,23 +310,17 @@ def filter_block_tree(store: Store, block_root: Root, blocks: Dict[Root, BeaconB
             return True
         return False
 
-    current_epoch = compute_epoch_at_slot(get_current_slot(store))
+    current_epoch = get_current_store_epoch(store)
     voting_source = get_voting_source(store, block_root)
 
-    # The voting source should be at the same height as the store's justified checkpoint
+    # 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
     )
 
-    # If the previous epoch is justified, the block should be pulled-up. In this case, check that unrealized
-    # justification is higher than the store and that the voting source is not more than two epochs ago
-    if not correct_justified and is_previous_epoch_justified(store):
-        correct_justified = (
-            store.unrealized_justifications[block_root].epoch >= store.justified_checkpoint.epoch and
-            voting_source.epoch + 2 >= current_epoch
-        )
-
     finalized_checkpoint_block = get_checkpoint_block(
         store,
         block_root,
@@ -519,7 +530,7 @@ def compute_pulled_up_tip(store: Store, block_root: Root) -> None:
 
     # If the block is from a prior epoch, apply the realized values
     block_epoch = compute_epoch_at_slot(store.blocks[block_root].slot)
-    current_epoch = compute_epoch_at_slot(get_current_slot(store))
+    current_epoch = get_current_store_epoch(store)
     if block_epoch < current_epoch:
         update_checkpoints(store, state.current_justified_checkpoint, state.finalized_checkpoint)
 ```
@@ -556,7 +567,7 @@ def validate_target_epoch_against_current_time(store: Store, attestation: Attest
     target = attestation.data.target
 
     # Attestations must be from the current or previous epoch
-    current_epoch = compute_epoch_at_slot(get_current_slot(store))
+    current_epoch = get_current_store_epoch(store)
     # Use GENESIS_EPOCH for previous when genesis to avoid underflow
     previous_epoch = current_epoch - 1 if current_epoch > GENESIS_EPOCH else GENESIS_EPOCH
     # If attestation target is from a future epoch, delay consideration until the epoch arrives
@@ -653,7 +664,7 @@ def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
         block.parent_root,
         store.finalized_checkpoint.epoch,
     )
-    assert store.finalized_checkpoint.root == finalized_checkpoint_block    
+    assert store.finalized_checkpoint.root == finalized_checkpoint_block
 
     # Check the block is valid and compute the post-state
     state = pre_state.copy()

tests/core/pyspec/eth2spec/test/phase0/fork_choice/test_reorg.py

@@ -286,34 +286,43 @@ def _run_include_votes_of_another_empty_chain(spec, state, enough_ffg, is_justif
     for _ in range(2):
         state, store, _ = yield from apply_next_epoch_with_attestations(
             spec, state, store, True, True, test_steps=test_steps)
+
     if is_justifying_previous_epoch:
+        # build chain with head in epoch 3 and justified checkpoint in epoch 2
         block_a = build_empty_block_for_next_slot(spec, state)
         signed_block_a = state_transition_and_sign_block(spec, state, block_a)
         yield from tick_and_add_block(spec, store, signed_block_a, test_steps)
+        assert spec.compute_epoch_at_slot(spec.get_current_slot(store)) == 3
         assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 2
     else:
-        # fill one more epoch
+        # build chain with head in epoch 4 and justified checkpoint in epoch 3
         state, store, _ = yield from apply_next_epoch_with_attestations(
             spec, state, store, True, True, test_steps=test_steps)
         signed_block_a = state_transition_with_full_block(spec, state, True, True)
         yield from tick_and_add_block(spec, store, signed_block_a, test_steps)
+        assert spec.compute_epoch_at_slot(spec.get_current_slot(store)) == 4
         assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
-
     spec.get_head(store) == signed_block_a.message.hash_tree_root()
-
     state = store.block_states[spec.get_head(store)].copy()
+    state_a = state.copy()
+
     if is_justifying_previous_epoch:
+        assert spec.compute_epoch_at_slot(spec.get_current_slot(store)) == 3
+        assert spec.compute_epoch_at_slot(state.slot) == 3
         assert state.current_justified_checkpoint.epoch == 2
     else:
+        assert spec.compute_epoch_at_slot(spec.get_current_slot(store)) == 4
+        assert spec.compute_epoch_at_slot(state.slot) == 4
         assert state.current_justified_checkpoint.epoch == 3
-    state_a = state.copy()
 
     if is_justifying_previous_epoch:
-        # try to find the block that can justify epoch 3
+        # try to find the block that can justify epoch 3 by including only previous epoch attesations
         _, justifying_slot = find_next_justifying_slot(spec, state, False, True)
+        assert spec.compute_epoch_at_slot(justifying_slot) == 4
     else:
-        # try to find the block that can justify epoch 4
+        # try to find the block that can justify epoch 4 by including current epoch attestations
         _, justifying_slot = find_next_justifying_slot(spec, state, True, True)
+        assert spec.compute_epoch_at_slot(justifying_slot) == 4
 
     last_slot_of_z = justifying_slot if enough_ffg else justifying_slot - 1
     last_slot_of_y = justifying_slot if is_justifying_previous_epoch else last_slot_of_z - 1
@@ -324,15 +333,14 @@ def _run_include_votes_of_another_empty_chain(spec, state, enough_ffg, is_justif
     # build an empty chain to the slot prior epoch boundary
     signed_blocks_of_empty_chain = []
     states_of_empty_chain = []
-
     for slot in range(state.slot + 1, last_slot_of_y + 1):
         block = build_empty_block(spec, state, slot=slot)
         signed_block = state_transition_and_sign_block(spec, state, block)
         signed_blocks_of_empty_chain.append(signed_block)
         states_of_empty_chain.append(state.copy())
         signed_blocks_of_y.append(signed_block)
-
     signed_block_y = signed_blocks_of_empty_chain[-1]
+    assert spec.compute_epoch_at_slot(signed_block_y.message.slot) == 4
 
     # create 2/3 votes for the empty chain
     attestations_for_y = []
@@ -345,7 +353,6 @@ def _run_include_votes_of_another_empty_chain(spec, state, enough_ffg, is_justif
 
     state = state_a.copy()
     signed_block_z = None
-
     for slot in range(state_a.slot + 1, last_slot_of_z + 1):
         # apply chain y, the empty chain
         if slot <= last_slot_of_y and len(signed_blocks_of_y) > 0:
@@ -368,12 +375,21 @@ def _run_include_votes_of_another_empty_chain(spec, state, enough_ffg, is_justif
         if is_ready_to_justify(spec, state):
             break
 
-    assert spec.get_head(store) == signed_block_y.message.hash_tree_root()
+    assert spec.compute_epoch_at_slot(spec.get_current_slot(store)) == 4
+    assert spec.compute_epoch_at_slot(signed_block_y.message.slot) == 4
+    assert spec.compute_epoch_at_slot(signed_block_z.message.slot) == 4
 
+    # y is not filtered out & wins the LMD competition, so y should be the head
+    y_voting_source_epoch = spec.get_voting_source(store, signed_block_y.message.hash_tree_root()).epoch
     if is_justifying_previous_epoch:
         assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 2
+        assert y_voting_source_epoch == 2
+        assert y_voting_source_epoch == store.justified_checkpoint.epoch
     else:
         assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+        assert y_voting_source_epoch == 3
+        assert y_voting_source_epoch == store.justified_checkpoint.epoch
+    assert spec.get_head(store) == signed_block_y.message.hash_tree_root()
 
     if enough_ffg:
         assert is_ready_to_justify(spec, state)
@@ -386,17 +402,57 @@ def _run_include_votes_of_another_empty_chain(spec, state, enough_ffg, is_justif
     on_tick_and_append_step(spec, store, current_time, test_steps)
     assert spec.compute_epoch_at_slot(spec.get_current_slot(store)) == 5
 
-    if enough_ffg:
-        # reorg
+    y_voting_source_epoch = spec.get_voting_source(store, signed_block_y.message.hash_tree_root()).epoch
+    if is_justifying_previous_epoch:
+        # y is filtered out & so z should be the head
+        assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+        assert y_voting_source_epoch == 2
+        assert y_voting_source_epoch != store.justified_checkpoint.epoch
+        assert not (y_voting_source_epoch + 2 >= spec.compute_epoch_at_slot(spec.get_current_slot(store)))
         assert spec.get_head(store) == signed_block_z.message.hash_tree_root()
-        if is_justifying_previous_epoch:
-            assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
-        else:
-            assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 4
     else:
-        # no reorg
-        assert spec.get_head(store) == signed_block_y.message.hash_tree_root()
+        if enough_ffg:
+            # y is not filtered out & wins the LMD competition, so y should be the head
+            assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 4
+            assert y_voting_source_epoch == 3
+            assert y_voting_source_epoch != store.justified_checkpoint.epoch
+            assert y_voting_source_epoch + 2 >= spec.compute_epoch_at_slot(spec.get_current_slot(store))
+            assert spec.get_head(store) == signed_block_y.message.hash_tree_root()
+        else:
+            # y is not filtered out & wins the LMD competition, so y should be the head
+            assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+            assert y_voting_source_epoch == 3
+            assert y_voting_source_epoch == store.justified_checkpoint.epoch
+            assert spec.get_head(store) == signed_block_y.message.hash_tree_root()
+
+    # to next epoch
+    next_epoch(spec, state)
+    current_time = state.slot * spec.config.SECONDS_PER_SLOT + store.genesis_time
+    on_tick_and_append_step(spec, store, current_time, test_steps)
+    assert spec.compute_epoch_at_slot(spec.get_current_slot(store)) == 6
+
+    y_voting_source_epoch = spec.get_voting_source(store, signed_block_y.message.hash_tree_root()).epoch
+    if is_justifying_previous_epoch:
+        # y is filtered out & so z should be the head
         assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+        assert y_voting_source_epoch == 2
+        assert y_voting_source_epoch != store.justified_checkpoint.epoch
+        assert not (y_voting_source_epoch + 2 >= spec.compute_epoch_at_slot(spec.get_current_slot(store)))
+        assert spec.get_head(store) == signed_block_z.message.hash_tree_root()
+    else:
+        if enough_ffg:
+            # y is filtered out & so z should be the head
+            assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 4
+            assert y_voting_source_epoch == 3
+            assert y_voting_source_epoch != store.justified_checkpoint.epoch
+            assert not (y_voting_source_epoch + 2 >= spec.compute_epoch_at_slot(spec.get_current_slot(store)))
+            assert spec.get_head(store) == signed_block_z.message.hash_tree_root()
+        else:
+            # y is not filtered out & wins the LMD competition, so y should be the head
+            assert state.current_justified_checkpoint.epoch == store.justified_checkpoint.epoch == 3
+            assert y_voting_source_epoch == 3
+            assert y_voting_source_epoch == store.justified_checkpoint.epoch
+            assert spec.get_head(store) == signed_block_y.message.hash_tree_root()
 
     yield 'steps', test_steps