Crosslink in AttestationData

[JustinDrake]

Substantive change:

• Batch fields in AttestationData into a Crosslink
  • better encapsulation and reuse of Crosslink type
  • cleaner presentation (remove an awkward helper function, simpler code, 15 lines removed).

Cosmetic changes:

• rename MAX_CROSSLINK_EPOCHS to MAX_EPOCHS_PER_CROSSLINK
• avoid long lines (over 120 characters) in process_attestation

[djrtwo]

I like this! One suggestion before approve

I've always kind of wanted shard inside Crosslink even though they are ordered in state. Makes Crosslink more useful in other contexts.

yay

[hwwhww]

Since crosslink_data_root only be used in Crosslink, what do you think about renaming it to data_root? (I'm fine with both)

[JustinDrake]

Since crosslink_data_root only be used in Crosslink, what do you think about renaming it to data_root?

data_root is also used in the custody bit, but I think that's the right thing to do regardless :) I also think we should rename previous_crosslink_root to parent_crosslink_root. The reason is that there is a naming clash now with state.previous_crosslink_roots. For consistency this means reverting back to parent_block_root (as opposed to previous_block_root).

[hwwhww]

LGTM! 👍

Maybe wait for more 👍 on renamings?

[djrtwo]

yeah, let me do one more pass

[djrtwo]

I cleaned up the validator guide (and fixed a couple of things there). Would appreciated a once over before we merge

[JustinDrake]

Side note: making the validator guide executable may be useful, if anything to help with testing.

[djrtwo]

Yeah, I've been thinking it would help keep things in sync for sure