Reduce Electra boilerplate

[dapplion]

Description

Electra's new attestation type has introduced a match boilerplate.

lighthouse/consensus/types/src/beacon_block_body.rs

Lines 236 to 243 in c4f2284

	match self {
	Self::Base(body) => body.attestations.len(),
	Self::Altair(body) => body.attestations.len(),
	Self::Bellatrix(body) => body.attestations.len(),
	Self::Capella(body) => body.attestations.len(),
	Self::Deneb(body) => body.attestations.len(),
	Self::Electra(body) => body.attestations.len(),
	}

lighthouse/beacon_node/beacon_chain/tests/block_verification.rs

Lines 727 to 757 in 9a01b6b

	BeaconBlockBodyRefMut::Base(ref mut blk) => {
	blk.attester_slashings
	.push(attester_slashing.as_base().unwrap().clone())
	.expect("should update attester slashing");
	}
	BeaconBlockBodyRefMut::Altair(ref mut blk) => {
	blk.attester_slashings
	.push(attester_slashing.as_base().unwrap().clone())
	.expect("should update attester slashing");
	}
	BeaconBlockBodyRefMut::Bellatrix(ref mut blk) => {
	blk.attester_slashings
	.push(attester_slashing.as_base().unwrap().clone())
	.expect("should update attester slashing");
	}
	BeaconBlockBodyRefMut::Capella(ref mut blk) => {
	blk.attester_slashings
	.push(attester_slashing.as_base().unwrap().clone())
	.expect("should update attester slashing");
	}
	BeaconBlockBodyRefMut::Deneb(ref mut blk) => {
	blk.attester_slashings
	.push(attester_slashing.as_base().unwrap().clone())
	.expect("should update attester slashing");
	}
	BeaconBlockBodyRefMut::Electra(ref mut blk) => {
	blk.attester_slashings
	.push(attester_slashing.as_electra().unwrap().clone())
	.expect("should update attester slashing");
	}
	}

In previous issues, I stressed how we want fork addition to be as easy as possible to foster innovation. Having to add 1000 lines of mindless code just to develop a new feature is not optimal.

We can use some macro magic to prevent a new ForkName::EIP9999 variant from having to modify all these statements.

[michaelsproul]

The example shown could use a superstruct mapping macro

[michaelsproul]

    pub fn attestations_len(self) -> usize {
        map_beacon_block_body_ref!(&'a _, self, |inner, cons| {
            let n = inner.attestations.len();
            cons(inner);
            n
        })
    }

Needs the cons(inner) trick to do type hinting. That's an open issue: sigp/superstruct#31