pr feedback

specs/core/0_beacon-chain.md

@@ -68,6 +68,7 @@
         - [`get_crosslink_committees_at_slot`](#get_crosslink_committees_at_slot)
         - [`get_block_root_at_slot`](#get_block_root_at_slot)
         - [`get_block_root`](#get_block_root)
+        - [`get_state_root`](#get_state_root)
         - [`get_randao_mix`](#get_randao_mix)
         - [`get_active_index_root`](#get_active_index_root)
         - [`generate_seed`](#generate_seed)
@@ -877,6 +878,18 @@ def get_block_root(state: BeaconState,
     return get_block_root_at_slot(state, get_epoch_start_slot(epoch))
 ```
 
+### `get_state_root`
+
+```python
+def get_state_root(state: BeaconState,
+                   slot: Slot) -> Bytes32:
+    """
+    Return the state root at a recent ``slot``.
+    """
+    assert slot < state.slot <= slot + SLOTS_PER_HISTORICAL_ROOT
+    return state.latest_state_roots[slot % SLOTS_PER_HISTORICAL_ROOT]
+```
+
 ### `get_randao_mix`
 
 ```python
@@ -1519,12 +1532,12 @@ def process_justification_and_finalization(state: BeaconState) -> None:
     state.justification_bitfield = (state.justification_bitfield << 1) % 2**64
     previous_epoch_matching_target_balance = get_attesting_balance(state, get_matching_target_attestations(state, previous_epoch))
     if previous_epoch_matching_target_balance * 3 >= get_total_active_balance(state) * 2:
-        state.current_justified_epoch = get_previous_epoch(state)
+        state.current_justified_epoch = previous_epoch
         state.current_justified_root = get_block_root(state, state.current_justified_epoch)
         state.justification_bitfield |= (1 << 1)
     current_epoch_matching_target_balance = get_attesting_balance(state, get_matching_target_attestations(state, current_epoch))
     if current_epoch_matching_target_balance * 3 >= get_total_active_balance(state) * 2:
-        state.current_justified_epoch = get_current_epoch(state)
+        state.current_justified_epoch = current_epoch
         state.current_justified_root = get_block_root(state, state.current_justified_epoch)
         state.justification_bitfield |= (1 << 0)
 

specs/validator/0_beacon-chain-validator.md

@@ -138,7 +138,7 @@ A validator has two primary responsibilities to the beacon chain -- [proposing b
 
 ### Block proposal
 
-A validator is expected to propose a [`BeaconBlock`](../core/0_beacon-chain.md#beaconblock) at the beginning of any slot during which `get_beacon_proposer_index(state, slot)` returns the validator's `validator_index`. To propose, the validator selects the `BeaconBlock`, `parent`, that in their view of the fork choice is the head of the chain during `slot - 1`. The validator is to create, sign, and broadcast a `block` that is a child of `parent` and that executes a valid [beacon chain state transition](../core/0_beacon-chain.md#beacon-chain-state-transition-function).
+A validator is expected to propose a [`BeaconBlock`](../core/0_beacon-chain.md#beaconblock) at the beginning of any slot during which `get_beacon_proposer_index(state)` returns the validator's `validator_index`. To propose, the validator selects the `BeaconBlock`, `parent`, that in their view of the fork choice is the head of the chain during `slot - 1`. The validator is to create, sign, and broadcast a `block` that is a child of `parent` and that executes a valid [beacon chain state transition](../core/0_beacon-chain.md#beacon-chain-state-transition-function).
 
 There is one proposer per slot, so if there are N active validators any individual validator will on average be assigned to propose once per N slots (e.g. at 312500 validators = 10 million ETH, that's once per ~3 weeks).
 
@@ -368,7 +368,7 @@ def get_committee_assignment(
             return assignment
 ```
 
-A validator can use the following function to see if they are supposed to propose during their assigned committee slot. This function can only be run during the slot in question and can not reliably be used to predict in advance.
+A validator can use the following function to see if they are supposed to propose during their assigned committee slot. This function can only be run during the slot in question. Proposer selection is only stable within the context of the current epoch.
 
 ```python
 def is_proposer_at_slot(state: BeaconState,

test_libs/pyspec/tests/test_sanity.py

@@ -9,7 +9,6 @@ from eth2spec.utils.minimal_ssz import signing_root
 from eth2spec.phase0.spec import (
     # constants
     ZERO_HASH,
-    SLOTS_PER_HISTORICAL_ROOT,
     # SSZ
     Deposit,
     Transfer,
@@ -17,13 +16,12 @@ from eth2spec.phase0.spec import (
     # functions
     get_active_validator_indices,
     get_beacon_proposer_index,
-    get_block_root,
     get_block_root_at_slot,
+    get_state_root,
     get_current_epoch,
     get_domain,
     advance_slot,
     cache_state,
-    slot_to_epoch,
     verify_merkle_branch,
     hash,
 )
@@ -49,13 +47,6 @@ from .helpers import (
 )
 
 
-def get_state_root(state, slot) -> bytes:
-    """
-    Return the state root at a recent ``slot``.
-    """
-    assert slot < state.slot <= slot + SLOTS_PER_HISTORICAL_ROOT
-    return state.latest_state_roots[slot % SLOTS_PER_HISTORICAL_ROOT]
-
 # mark entire file as 'sanity'
 pytestmark = pytest.mark.sanity
 

tests/phase0/helpers.py

@@ -142,7 +142,7 @@ def build_attestation_data(state, slot, shard):
     if epoch_start_slot == slot:
         epoch_boundary_root = block_root
     else:
-        get_block_root(state, get_current_epoch(state))
+        epoch_boundary_root = get_block_root(state, get_current_epoch(state))
 
     if slot < epoch_start_slot:
         justified_block_root = state.previous_justified_root