Reimplement DRep threshold computation

This is an alternative approach to figuring out thresholds. Original
approach was buggy and did not work correctly, which resulted in #3835

eras/alonzo/impl/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## 1.5.1.0
 
+* Swap the order of arguments for `updateCostModels`
+
 ### `testlib`
 
 * Provide CDDL spec files with `readAlonzoCddlFileNames` and `readAlonzoCddlFiles` from

eras/alonzo/impl/src/Cardano/Ledger/Alonzo/Scripts.hs

@@ -547,13 +547,13 @@ data CostModels = CostModels
 emptyCostModels :: CostModels
 emptyCostModels = CostModels mempty mempty mempty
 
--- | Updates the first @CostModels@ with the second one so that only the
--- cost models that are present in the second one get updated while all the
+-- | Updates the second @CostModels@ with the first one so that only the
+-- cost models that are present in the first one get updated while all the
 -- others stay unchanged
 updateCostModels :: CostModels -> CostModels -> CostModels
 updateCostModels
-  (CostModels oldValid oldErrors oldUnk)
-  (CostModels newValid newErrors newUnk) =
+  (CostModels newValid newErrors newUnk)
+  (CostModels oldValid oldErrors oldUnk) =
     CostModels
       (Map.union newValid oldValid)
       (Map.union newErrors oldErrors)

eras/conway/impl/src/Cardano/Ledger/Conway/Governance.hs

@@ -115,8 +115,9 @@ module Cardano.Ledger.Conway.Governance (
   psDRepDistrL,
   psDRepStateL,
   RunConwayRatify (..),
+
   -- * Exported for testing
-  pparamsUpdateThreshold
+  pparamsUpdateThreshold,
 ) where
 
 import Cardano.Ledger.BaseTypes (
@@ -188,11 +189,10 @@ import Cardano.Ledger.Conway.Governance.Snapshots (
   snapshotRemoveIds,
  )
 import Cardano.Ledger.Conway.PParams (
-  ConwayEraPParams,
+  ConwayEraPParams (..),
   DRepVotingThresholds (..),
-  PParamGroup (..),
+  PPGroup (..),
   PoolVotingThresholds (..),
-  modifiedGroups,
   ppCommitteeMinSizeL,
   ppDRepVotingThresholdsL,
   ppPoolVotingThresholdsL,
@@ -690,14 +690,14 @@ pparamsUpdateThreshold ::
 pparamsUpdateThreshold pp ppu =
   let thresholdLens = \case
         NetworkGroup -> dvtPPNetworkGroupL
-        GovernanceGroup -> dvtPPGovGroupL
+        GovGroup -> dvtPPGovGroupL
         TechnicalGroup -> dvtPPTechnicalGroupL
         EconomicGroup -> dvtPPEconomicGroupL
       lookupGroupThreshold grp =
         pp ^. ppDRepVotingThresholdsL . thresholdLens grp
    in Set.foldr' max minBound $
         Set.map lookupGroupThreshold $
-          modifiedGroups @era ppu
+          modifiedPPGroups @era ppu
 
 data VotingThreshold
   = -- | This is the actual threshold. It is lazy, because upon proposal we only care if