Apply proposer boost to first block in case of equivocation

specs/bellatrix/fork-choice.md

@@ -194,7 +194,8 @@ def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
     # Add proposer score boost if the block is timely
     time_into_slot = (store.time - store.genesis_time) % SECONDS_PER_SLOT
     is_before_attesting_interval = time_into_slot < SECONDS_PER_SLOT // INTERVALS_PER_SLOT
-    if get_current_slot(store) == block.slot and is_before_attesting_interval:
+    is_first_block = store.proposer_boost_root == Root()
+    if get_current_slot(store) == block.slot and is_before_attesting_interval and is_first_block:
         store.proposer_boost_root = hash_tree_root(block)
 
     # Update checkpoints in store if necessary

specs/capella/fork-choice.md

@@ -106,7 +106,8 @@ def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
     # Add proposer score boost if the block is timely
     time_into_slot = (store.time - store.genesis_time) % SECONDS_PER_SLOT
     is_before_attesting_interval = time_into_slot < SECONDS_PER_SLOT // INTERVALS_PER_SLOT
-    if get_current_slot(store) == block.slot and is_before_attesting_interval:
+    is_first_block = store.proposer_boost_root == Root()
+    if get_current_slot(store) == block.slot and is_before_attesting_interval and is_first_block:
         store.proposer_boost_root = hash_tree_root(block)
 
     # Update checkpoints in store if necessary

specs/deneb/fork-choice.md

@@ -106,7 +106,8 @@ def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
     # Add proposer score boost if the block is timely
     time_into_slot = (store.time - store.genesis_time) % SECONDS_PER_SLOT
     is_before_attesting_interval = time_into_slot < SECONDS_PER_SLOT // INTERVALS_PER_SLOT
-    if get_current_slot(store) == block.slot and is_before_attesting_interval:
+    is_first_block = store.proposer_boost_root == Root()
+    if get_current_slot(store) == block.slot and is_before_attesting_interval and is_first_block:
         store.proposer_boost_root = hash_tree_root(block)
 
     # Update checkpoints in store if necessary

specs/phase0/fork-choice.md

@@ -539,7 +539,8 @@ def on_block(store: Store, signed_block: SignedBeaconBlock) -> None:
     # Add proposer score boost if the block is timely
     time_into_slot = (store.time - store.genesis_time) % SECONDS_PER_SLOT
     is_before_attesting_interval = time_into_slot < SECONDS_PER_SLOT // INTERVALS_PER_SLOT
-    if get_current_slot(store) == block.slot and is_before_attesting_interval:
+    is_first_block = store.proposer_boost_root == Root()
+    if get_current_slot(store) == block.slot and is_before_attesting_interval and is_first_block:
         store.proposer_boost_root = hash_tree_root(block)
 
     # Update checkpoints in store if necessary

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

@@ -539,6 +539,56 @@ def test_proposer_boost_root_same_slot_untimely_block(spec, state):
     yield 'steps', test_steps
 
 
+@with_altair_and_later
+@spec_state_test
+def test_proposer_boost_is_first_block(spec, state):
+    test_steps = []
+    genesis_state = state.copy()
+
+    # Initialization
+    store, anchor_block = get_genesis_forkchoice_store_and_block(spec, state)
+    yield 'anchor_state', state
+    yield 'anchor_block', anchor_block
+
+    # Build block that serves as head ONLY on timely arrival, and ONLY in that slot
+    state = genesis_state.copy()
+    next_slots(spec, state, 3)
+    pre_state = state.copy()
+    block_a = build_empty_block_for_next_slot(spec, state)
+    signed_block_a = state_transition_and_sign_block(spec, state, block_a)
+
+    # Process block on timely arrival just before end of boost interval
+    time = (store.genesis_time + block_a.slot * spec.config.SECONDS_PER_SLOT +
+            spec.config.SECONDS_PER_SLOT // spec.INTERVALS_PER_SLOT - 1)
+    on_tick_and_append_step(spec, store, time, test_steps)
+    yield from add_block(spec, store, signed_block_a, test_steps)
+    # `proposer_boost_root` is now `block_a`
+    assert store.proposer_boost_root == spec.hash_tree_root(block_a)
+    assert spec.get_weight(store, spec.hash_tree_root(block_a)) > 0
+    test_steps.append({
+        'checks': {
+            'proposer_boost_root': encode_hex(store.proposer_boost_root),
+        }
+    })
+
+    # make a different block at the same slot
+    state = pre_state.copy()
+    block_b = block_a.copy()
+    block_b.body.graffiti = b'\x34' * 32
+    signed_block_b = state_transition_and_sign_block(spec, state, block_b)
+    yield from add_block(spec, store, signed_block_b, test_steps)
+    # `proposer_boost_root` is still `block_a`
+    assert store.proposer_boost_root == spec.hash_tree_root(block_a)
+    assert spec.get_weight(store, spec.hash_tree_root(block_b)) == 0
+    test_steps.append({
+        'checks': {
+            'proposer_boost_root': encode_hex(store.proposer_boost_root),
+        }
+    })
+
+    yield 'steps', test_steps
+
+
 @with_altair_and_later
 @spec_state_test
 @with_presets([MINIMAL], reason="too slow")