Fix transTxCert always setting deposit to Nothing for TxCertRegStaking & TxCertUnRegStaking

[KtorZ]

Doing some testing on my end, I noticed that deposits were always missing from TxCertRegStaking & TxCertUnRegStaking. However, they ought to be Just something when present; or more specifically when mapping a ConwayRegCert or ConwayUnRegCert to their Plutus counterpart.

The deposit should, in principle, only be set to zero when presented with a legacy certificate format. However, if we take the following certificate:

ConwayTxCertDeleg (ConwayRegCert
  (KeyHashObj (KeyHash {unKeyHash = "00000000000000000000000000000000000000000000000000000000"}))
  (SJust (Coin 3000000))
)

Using transTxCert we obtain:

TxCertRegStaking
  (PubKeyCredential 00000000000000000000000000000000000000000000000000000000)
  Nothing

And similarly for ConwayUnRegCert. This seems due to the order of clauses in the pattern match inside transTxCert which causes RegTxCert andUnRegTxCert to be matched even in the presence of a deposit. Swapping the pattern match clauses fixes the issue and return:

TxCertRegStaking
  (PubKeyCredential 00000000000000000000000000000000000000000000000000000000)
  (Just 3000000)

The writing of a regression test to capture this is left as an excercise for the maintainers 😬

Description

Checklist

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[lehins]

Auch. That is an ugly bug. I guess we could fix it with an intra-era hard fork that should happen later on this year.
The actual bug is not in the TxInfo translation, but in the pattern synonym. these two guys should not have ignored the deposit field:

cardano-ledger/eras/conway/impl/src/Cardano/Ledger/Conway/TxCert.hs

Lines 150 to 156 in adb63e0

	getRegTxCert (ConwayTxCertDeleg (ConwayRegCert c _)) = Just c
	getRegTxCert _ = Nothing
	mkUnRegTxCert c = ConwayTxCertDeleg $ ConwayUnRegCert c SNothing
	getUnRegTxCert (ConwayTxCertDeleg (ConwayUnRegCert c _)) = Just c
	getUnRegTxCert _ = Nothing

It should have been:

  getRegTxCert (ConwayTxCertDeleg (ConwayRegCert c SNothing)) = Just c
  getUnRegTxCert (ConwayTxCertDeleg (ConwayUnRegCert c SNothing)) = Just c

[lehins]

Thank you for reporting this @KtorZ
We'll fix it properly at the intra-era hard fork. Here is the ticket for this bug: #4571