eth2.0-specs/specs/electra/fork.md

# Electra -- Fork Logic

**Notice**: This document is a work-in-progress for researchers and implementers.

## Table of contents

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- [Introduction](#introduction)
- [Configuration](#configuration)
- [Helper functions](#helper-functions)
  - [Misc](#misc)
    - [Modified `compute_fork_version`](#modified-compute_fork_version)
- [Fork to Electra](#fork-to-electra)
  - [Fork trigger](#fork-trigger)
  - [Upgrading the state](#upgrading-the-state)

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## Introduction

This document describes the process of the Electra upgrade.

## Configuration

Warning: this configuration is not definitive.

| Name | Value |
| - | - |
| `ELECTRA_FORK_VERSION` | `Version('0x05000000')` |
| `ELECTRA_FORK_EPOCH` | `Epoch(18446744073709551615)` **TBD** |

## Helper functions

### Misc

#### Modified `compute_fork_version`

```python
def compute_fork_version(epoch: Epoch) -> Version:
    """
    Return the fork version at the given ``epoch``.
    """
    if epoch >= ELECTRA_FORK_EPOCH:
        return ELECTRA_FORK_VERSION
    if epoch >= DENEB_FORK_EPOCH:
        return DENEB_FORK_VERSION
    if epoch >= CAPELLA_FORK_EPOCH:
        return CAPELLA_FORK_VERSION
    if epoch >= BELLATRIX_FORK_EPOCH:
        return BELLATRIX_FORK_VERSION
    if epoch >= ALTAIR_FORK_EPOCH:
        return ALTAIR_FORK_VERSION
    return GENESIS_FORK_VERSION
```

## Fork to Electra

### Fork trigger

TBD. This fork is defined for testing purposes, the EIP may be combined with other consensus-layer upgrade.
For now, we assume the condition will be triggered at epoch `ELECTRA_FORK_EPOCH`.

Note that for the pure Electra networks, we don't apply `upgrade_to_electra` since it starts with Electra version logic.

### Upgrading the state

If `state.slot % SLOTS_PER_EPOCH == 0` and `compute_epoch_at_slot(state.slot) == ELECTRA_FORK_EPOCH`,
an irregular state change is made to upgrade to Electra.

```python
def upgrade_to_electra(pre: deneb.BeaconState) -> BeaconState:
    epoch = deneb.get_current_epoch(pre)
    latest_execution_payload_header = pre.latest_execution_payload_header

    exit_epochs = [v.exit_epoch for v in pre.validators if v.exit_epoch != FAR_FUTURE_EPOCH]
    if not exit_epochs:
        exit_epochs = [get_current_epoch(pre)]
    earliest_exit_epoch = max(exit_epochs) + 1

    post = BeaconState(
        # Versioning
        genesis_time=pre.genesis_time,
        genesis_validators_root=pre.genesis_validators_root,
        slot=pre.slot,
        fork=Fork(
            previous_version=pre.fork.current_version,
            current_version=ELECTRA_FORK_VERSION,  # [Modified in Electra:EIP6110]
            epoch=epoch,
        ),
        # History
        latest_block_header=pre.latest_block_header,
        block_roots=pre.block_roots,
        state_roots=pre.state_roots,
        historical_roots=pre.historical_roots,
        # Eth1
        eth1_data=pre.eth1_data,
        eth1_data_votes=pre.eth1_data_votes,
        eth1_deposit_index=pre.eth1_deposit_index,
        # Registry
        validators=pre.validators,
        balances=pre.balances,
        # Randomness
        randao_mixes=pre.randao_mixes,
        # Slashings
        slashings=pre.slashings,
        # Participation
        previous_epoch_participation=pre.previous_epoch_participation,
        current_epoch_participation=pre.current_epoch_participation,
        # Finality
        justification_bits=pre.justification_bits,
        previous_justified_checkpoint=pre.previous_justified_checkpoint,
        current_justified_checkpoint=pre.current_justified_checkpoint,
        finalized_checkpoint=pre.finalized_checkpoint,
        # Inactivity
        inactivity_scores=pre.inactivity_scores,
        # Sync
        current_sync_committee=pre.current_sync_committee,
        next_sync_committee=pre.next_sync_committee,
        # Execution-layer
        latest_execution_payload_header=latest_execution_payload_header,  # [Modified in Electra:EIP6110:EIP7002]
        # Withdrawals
        next_withdrawal_index=pre.next_withdrawal_index,
        next_withdrawal_validator_index=pre.next_withdrawal_validator_index,
        # Deep history valid from Capella onwards
        historical_summaries=pre.historical_summaries,
        # [New in Electra:EIP6110]
        deposit_requests_start_index=UNSET_DEPOSIT_REQUESTS_START_INDEX,
        # [New in Electra:EIP7251]
        deposit_balance_to_consume=0,
        exit_balance_to_consume=0,
        earliest_exit_epoch=earliest_exit_epoch,
        consolidation_balance_to_consume=0,
        earliest_consolidation_epoch=compute_activation_exit_epoch(get_current_epoch(pre)),
        pending_deposits=[],
        pending_partial_withdrawals=[],
        pending_consolidations=[],
    )

    post.exit_balance_to_consume = get_activation_exit_churn_limit(post)
    post.consolidation_balance_to_consume = get_consolidation_churn_limit(post)

    # [New in Electra:EIP7251]
    # add validators that are not yet active to pending balance deposits
    pre_activation = sorted([
        index for index, validator in enumerate(post.validators)
        if validator.activation_epoch == FAR_FUTURE_EPOCH
    ], key=lambda index: (
        post.validators[index].activation_eligibility_epoch,
        index
    ))

    for index in pre_activation:
        balance = post.balances[index]
        post.balances[index] = 0
        validator = post.validators[index]
        validator.effective_balance = 0
        validator.activation_eligibility_epoch = FAR_FUTURE_EPOCH
        # Use bls.G2_POINT_AT_INFINITY as a signature field placeholder
        # and GENESIS_SLOT to distinguish from a pending deposit request
        post.pending_deposits.append(PendingDeposit(
            pubkey=validator.pubkey,
            withdrawal_credentials=validator.withdrawal_credentials,
            amount=balance,
            signature=bls.G2_POINT_AT_INFINITY,
            slot=GENESIS_SLOT,
        ))

    # Ensure early adopters of compounding credentials go through the activation churn
    for index, validator in enumerate(post.validators):
        if has_compounding_withdrawal_credential(validator):
            queue_excess_active_balance(post, ValidatorIndex(index))

    return post
```