add EIP-7251 initialize_beacon_state_from_eth1 function

Author: ralexstokes

specs/_features/eip7251/beacon-chain.md

@@ -77,6 +77,7 @@
         - [New `process_consolidation`](#new-process_consolidation)
       - [Voluntary exits](#voluntary-exits)
         - [Updated `process_voluntary_exit`](#updated-process_voluntary_exit)
+- [Testing](#testing)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 <!-- /TOC -->
@@ -1063,3 +1064,61 @@ def process_voluntary_exit(state: BeaconState, signed_voluntary_exit: SignedVolu
     # Initiate exit
     initiate_validator_exit(state, voluntary_exit.validator_index)
 ```
+
+## Testing
+
+*Note*: The function `initialize_beacon_state_from_eth1` is modified for pure EIP-7251 testing only.
+
+```python
+def initialize_beacon_state_from_eth1(eth1_block_hash: Hash32,
+                                      eth1_timestamp: uint64,
+                                      deposits: Sequence[Deposit],
+                                      execution_payload_header: ExecutionPayloadHeader=ExecutionPayloadHeader()
+                                      ) -> BeaconState:
+    fork = Fork(
+        previous_version=EIP7251_FORK_VERSION,  # [Modified in EIP-7251] for testing only
+        current_version=EIP7251_FORK_VERSION,  # [Modified in EIP-7251]
+        epoch=GENESIS_EPOCH,
+    )
+    state = BeaconState(
+        genesis_time=eth1_timestamp + GENESIS_DELAY,
+        fork=fork,
+        eth1_data=Eth1Data(block_hash=eth1_block_hash, deposit_count=uint64(len(deposits))),
+        latest_block_header=BeaconBlockHeader(body_root=hash_tree_root(BeaconBlockBody())),
+        randao_mixes=[eth1_block_hash] * EPOCHS_PER_HISTORICAL_VECTOR,  # Seed RANDAO with Eth1 entropy
+    )
+
+    # Process deposits
+    leaves = list(map(lambda deposit: deposit.data, deposits))
+    for index, deposit in enumerate(deposits):
+        deposit_data_list = List[DepositData, 2**DEPOSIT_CONTRACT_TREE_DEPTH](*leaves[:index + 1])
+        state.eth1_data.deposit_root = hash_tree_root(deposit_data_list)
+        process_deposit(state, deposit)
+
+    # Process deposit balance updates
+    for deposit in state.pending_balance_deposits:
+        increase_balance(state, deposit.index, deposit.amount)
+    state.pending_balance_deposits = []
+
+    # Process activations
+    for index, validator in enumerate(state.validators):
+        balance = state.balances[index]
+        validator.effective_balance = min(balance - balance % EFFECTIVE_BALANCE_INCREMENT, MAX_EFFECTIVE_BALANCE)
+        if validator.effective_balance == MAX_EFFECTIVE_BALANCE:
+            validator.activation_eligibility_epoch = GENESIS_EPOCH
+            validator.activation_epoch = GENESIS_EPOCH
+
+    # Set genesis validators root for domain separation and chain versioning
+    state.genesis_validators_root = hash_tree_root(state.validators)
+
+    # Fill in sync committees
+    # Note: A duplicate committee is assigned for the current and next committee at genesis
+    state.current_sync_committee = get_next_sync_committee(state)
+    state.next_sync_committee = get_next_sync_committee(state)
+
+    # Initialize the execution payload header
+    # If empty, will initialize a chain that has not yet gone through the Merge transition
+    state.latest_execution_payload_header = execution_payload_header
+
+    return state
+```