Tame TransitionImpossible et al #364
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nfrisby
commented
Sep 23, 2023
| oneForecast sno pairs (Current start AnnForecast{..}) = | ||
| case annForecastEnd of | ||
| oneForecast sno staticTransitions crosses (Current start AnnForecast{..}) = | ||
| (\k -> maybe (neverEnd <$> forecastFor annForecast sno) k annForecastEnd) $ \case |
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Accept the additional index indent for the unchanged lines instead of golfing.
| @@ -583,7 +624,8 @@ inspectHardForkLedger = go | |||
| map liftEvent $ | |||
| inspectLedger c (currentState before) (currentState after) | |||
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| , case (pss, confirmedBefore, confirmedAfter) of | |||
| -- TODO assert currentStart before == currentStart after? | |||
| , (\k -> case singleEraTransition' pc ps (currentStart before) of FixedTransition{} -> []; EventualTransition f -> k f) $ \f -> case (pss, f (currentState before), f (currentState after)) of | |||
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Accept the additional index indent for the unchanged lines instead of golfing.
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This commit renames TransitionImpossible to TransitionNever for two reasons. First, this is a more precise name. Second, this commit refines the singleEraTransition method so that TransitionNever is actually an absorbing state. Before this commit, TransitionImpossible could arise under certain circumstances but then the TransitionInfo for _the same era_ could later become TransitionUnknown. But now it is invariant that once the TransitionInfo for an era is ever TransitionNever then it always will be and moreover that era will indeed never end. This invariant is enforced in two ways. singleEraTransition can now induce TransitionNever, but only when that decision is independent of the ledger state, ie it must be a function only of inputs that the HFC does not vary (ledger config, EraParams, start of the era). The only other place TransitionNever arises is in the Unary.Isomorphism class, and it now has a law requiring that singleEraTransition only induce TransitionNever.
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nfrisby
commented
Sep 25, 2023
| TriggerHardForkNever -> Nothing | ||
| TriggerHardForkAtEpoch epoch -> Just epoch | ||
| TriggerHardForkAtVersion shelleyMajorVersion -> | ||
| TriggerHardForkNever -> FixedTransition Nothing |
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Bah! This line would reintroduce the bug fixed by IntersectMBO/ouroboros-network#3754
For example, I think TriggerHardForkNever should be renamed to TriggerHardForkCannotBeKnown. Either that, or protocolInfoCardano should use TriggerHardForkAtVersion (maxBound?) even for the last era. 🤔
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Single commit PR; see the message.