modify fork choice to utilize epochs properly #1198
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Started reviewing. Suggest merging #1185 soon regardless of this PR :)
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djrtwo
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| ```python | ||
| @dataclass | ||
| class Target(object): | ||
| @dataclass(eq=True, frozen=True) |
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This is temporary to make Checkpoint usable as a lookup key in a dictionary.
In #1210, we elevate Checkpoint to an SSZ type in beacon chain spec and this is removed
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| children = [root for root in store.blocks.keys() if store.blocks[root].parent_root == head] | ||
| children = [ | ||
| root for root in store.blocks.keys() | ||
| if store.blocks[root].parent_root == head and store.blocks[root].slot > justified_slot |
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Just checking parent_root should be enough. But if we are doing both, maybe swap the slot check to be first (much faster)?
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It isn't actually enough. There is a case where the block is in the block tree since latest justified block but is from an epoch prior to latest justified epoch.
Example:
- Block A at slot 60
- Block B (parent A) at slot 61
- Block A is justified at epoch 1 (slot 64)
- The block tree under consideration is now descendants of Block A but exclusively after the epoch boundary slot of epoch 1.
- Thus Block B should not be in consideration.
That said, we can flip the two bool checks for speed
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This is a full adaptation of the issue discussed in #768 and is a crucial component of how state must be utilized in a slot/epoch based fork choice. note that this is a PR to the current fork choice PR #1185
When justifying and finalizing a block, we are actually justifying/finalize a
(block, epoch)tuple (Checkpoint). This represents the block at the 0th slot of the epoch and we must use the associated state from here. In the normal case, this is at parity but in the case of skipped slots, the finalized block must be transitions up to the start of the epoch it was finalized in.