The case of the missing ada #1598
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This commit reworks the "preservation of ADA" test to more accurately reflect what it's testing (CHAIN level rather than NEWEPOCH). In addition, it adds an extra ada preservation property, which confirms that outside of an epoch boundary, the change in rewards is equal to the sum of withdrawls.
This will fix the problem, but does not reveal the underlying cause.
This commit fixes the underlying issue behind the missing ADA. When we create a reward update, we only grant rewards to registered stake keys. However, it's possible to deregister them after the update is created but before it's applied. In such a case, `applyRUpd` was adding them to a reward map anyway. When the key got re-registered, the reward account was being reset to 0, and hence money was being destroyed. This commit adds a check to `applyRUpd` that verifies whether a key is still registered and, if not, returns the funds to the reserves.
| @@ -222,6 +232,7 @@ delegationTransition = do | |||
| -- note that pattern match is used instead of regCred, as in the spec | |||
| -- hk ∉ dom (_stkCreds ds) -- Specification code translates below | |||
| not (haskey hk (_stkCreds ds)) ?! StakeKeyAlreadyRegisteredDELEG hk | |||
| not (haskey (RewardAcnt network hk) (_rewards ds)) ?! StakeKeyInRewardsDELEG hk | |||
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want to add this change to the spec too? I can do it if that would be helpful.
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I think this change isn't too important (it's a sanity check), but if you felt like adding the applyRUpd changes to the spec that would be great!
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A fun one, this.
The scenario:
In one of our tests, 163,000 ADA vanished, violating the preservation of ADA property. How did this happen? The sequence of events was something like this:
_rewardsmap, but not the_stkCredsmap._stkCredsmap, this is allowed. However, the registration zeros its rewards, resulting in the destruction of those 163,000 ADA.Why did we not spot this sooner? Well, because previously we had:
during certificate registration. But during the performance upgrades (in d716ad) this was changes to
_rewards = addpair (RewardAcnt network hk) (Coin 0) (_rewards ds),Union is left-biased, and hence will not overwrite. addpair is implemented to ignore the old value and overwrite it with the new. Hence before d716ad, the reward account still contained funds, albeit inaccessible ones.
This PR does a number of things:
stkCredsandrewardsmaps stay in sync (e.g. that they have the same domain).rewards.applyRUpdby checking whether the keys are still registered. Any funds allocated to deregistered keys are now returned to the reserves.