Assumptions that the genesis slot is zero

[paulhauner]

Description

There are some places in the code where we are either faulty or misleading in the case where the genesis slot is non-zero.

Encountering a non-zero genesis slot in phase 0 seems negligible. However, we can reasonably expect non-zero genesis slots for the shard chains, once they arrive.

In the short term, I think it's acceptable for LH to be faulty for a non-zero genesis slot. But I don't think that's the case in the long term.

Known Issues

"Oldest roots" getters

lighthouse/consensus/types/src/beacon_state.rs

Lines 670 to 685 in 28b6d92

	/// Gets the oldest (earliest slot) state root.
	///
	/// Spec v0.12.1
	pub fn get_oldest_state_root(&self) -> Result<&Hash256, Error> {
	let i =
	self.get_latest_state_roots_index(self.slot - Slot::from(self.state_roots.len()))?;
	Ok(&self.state_roots[i])
	}
	/// Gets the oldest (earliest slot) block root.
	///
	/// Spec v0.12.1
	pub fn get_oldest_block_root(&self) -> Result<&Hash256, Error> {
	let i = self.get_latest_block_roots_index(self.slot - self.block_roots.len() as u64)?;
	Ok(&self.block_roots[i])
	}

Relative epoch

lighthouse/consensus/types/src/relative_epoch.rs

Line 35 in 28b6d92

RelativeEpoch::Previous => base - 1,

[paulhauner]

I'm closing this since it's stale and irrelevant now.