* ShufflingRef approach to next-epoch validator duty calculation/prediction
* refactor action_tracker.updateActions to take ShufflingRef + beacon_proposers; refactor maybeUpdateActionTrackerNextEpoch to be separate and reused function; add actual fallback logic
* document one possible set of conditions
* check epoch participation flags and inactivity scores to ensure no penalties and MAX_EFFECTIVE_BALANCE to ensure rewards don't matter
* correctly (un)shuffle each proposer index
* remove debugging assertion
When an uncached `ShufflingRef` is requested, we currently replay state
which can take several seconds. Acceleration is possible by:
1. Start from any state with locked-in `get_active_validator_indices`.
Any blocks / slots applied to such a state can only affect that
result for future epochs, so are viable for querying target epoch.
`compute_activation_exit_epoch(state.slot.epoch) > target.epoch`
2. Determine highest common ancestor among `state` and `target.blck`.
At the ancestor slot, same rules re `get_active_validator_indices`.
`compute_activation_exit_epoch(ancestorSlot.epoch) > target.epoch`
3. We now have a `state` that shares history with `target.blck` up
through a common ancestor slot. Any blocks / slots that the `state`
contains, which are not part of the `target.blck` history, affect
`get_active_validator_indices` at epochs _after_ `target.epoch`.
4. Select `state.randao_mixes[N]` that is closest to common ancestor.
Either direction is fine (above / below ancestor).
5. From that RANDAO mix, mix in / out all RANDAO reveals from blocks
in-between. This is just an XOR operation, so fully reversible.
`mix = mix xor SHA256(blck.message.body.randao_reveal)`
6. Compute the attester dependent slot from `target.epoch`.
`if epoch >= 2: (target.epoch - 1).start_slot - 1 else: GENESIS_SLOT`
7. Trace back from `target.blck` to the attester dependent slot.
We now have the destination for which we want to obtain RANDAO.
8. Mix in all RANDAO reveals from blocks up through the `dependentBlck`.
Same method, no special handling necessary for epoch transitions.
9. Combine `get_active_validator_indices` from `state` at `target.epoch`
with the recovered RANDAO value at `dependentBlck` to obtain the
requested shuffling, and construct the `ShufflingRef` without replay.
* more tests and simplify logic
* test with different number of deposits per branch
* Update beacon_chain/consensus_object_pools/blockchain_dag.nim
Co-authored-by: Jacek Sieka <jacek@status.im>
* `commonAncestor` tests
* lint
---------
Co-authored-by: Jacek Sieka <jacek@status.im>
* final portion of non-trivial v1.3.0 bumps
Updates unchanged logic to latest v1.3.0 consensus-specs refs,
and cleans up surrounding sections / syncs comments, and so on.
```
https://github.com/ethereum/consensus-specs/(blob|tree)/(?!v1\.3\.0/)
```
* lint
* linebreak
The justified and finalized `Checkpoint` are frequently passed around
together. This introduces a new `FinalityCheckpoint` data structure that
combines them into one.
Due to the large usage of this structure in fork choice, also took this
opportunity to update fork choice tests to the latest v1.2.0-rc.1 spec.
Many additional tests enabled, some need more work, e.g. EL mock blocks.
Also implemented `discard_equivocations` which was skipped in #3661,
and improved code reuse across fork choice logic while at it.
