Hard fork history

[edsko]

This introduces the hard fork history, with records changing slot lengths and epoch sizes across hard fork boundaries, and derives EpochInfo and BlockchainTime from this.

This PR paves the way for (but does not yet close) #1637 and #1205.

[edsko]

I don't know why I closed this, this is not the branch that I'm replacing.

[edsko]

#1700 is the one I intended to close.

[mrBliss]

Reviewed in a meet.

[edsko]

Ok, this took way too long (nearly midnight now), but really rather happy with the result, quite proud of it. Both the implementation and its tests are quite nice: we generate a random Shape (number of eras, era parameters), then generate a random Chain (model), derive the Transitions from that Chain, summarize those transitions using the shape, and then use that summary to do translation between SlotNo and EpochNo/UTCTime for any event within the scope of the chain. The only thing that is still missing is to test that we can also predict the future; the is not hard to test anymore: take a prefix of the chain, and then do conversions for the events that follow it, up to the safe zone. However, I'm now well and truly fried; opened #1807 to track that last remaining piece of work.

[edsko]

@nfrisby , just a heads up, this removes the generalization to multiple slot lengths from everywhere, in preparation for #1637 (slot lengths can only change at hard fork boundaries).

[edsko]

bors r+

[edsko]

Incidentally, here are the tests running 100k tests, first generating an arbitrary Summary and then doing roundtrip translations for arbitrary SlotNo/EpochNo/UTCTime, and then doing the full test setup using chain-derived Summary:

ouroboros-consensus
  HardForkHistory
    Summary
      Sanity
        generator:              OK (1.23s)
          +++ OK, passed 100000 tests.
        shrinker:               OK (4.78s)
          +++ OK, passed 100000 tests.
      Conversions
        roundtripWallclockSlot: OK (1.84s)
          +++ OK, passed 100000 tests.
        roundtripSlotWallclock: OK (1.47s)
          +++ OK, passed 100000 tests.
        roundtripSlotEpoch:     OK (0.53s)
          +++ OK, passed 100000 tests.
        roundtripEpochSlot:     OK (0.61s)
          +++ OK, passed 100000 tests.
        reportsPastHorizon:     OK (1.60s)
          +++ OK, passed 100000 tests.
    Chain
      Sanity
        generator:              OK (0.39s)
          +++ OK, passed 100000 tests.
        shrinker:               OK (4.57s)
          +++ OK, passed 100000 tests.
      Conversions
        summarizeInvariant:     OK (5.08s)
          +++ OK, passed 100000 tests.
        eventSlotToEpoch:       OK (4.26s)
          +++ OK, passed 100000 tests.
        eventEpochToSlot:       OK (4.13s)
          +++ OK, passed 100000 tests.
        eventSlotToWallclock:   OK (6.08s)
          +++ OK, passed 100000 tests.
        eventWallclockToSlot:   OK (6.46s)
          +++ OK, passed 100000 tests.

All 14 tests passed (43.07s)

[iohk-bors]

Build succeeded

• buildkite/ouroboros-network
• ci/hydra:Cardano:ouroboros-network:required