Added FromJSON instance for PParamUpdates

Author: Soupstraw

libs/cardano-ledger-core/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## 1.18.0.0
 
+* Add `FromJSON` instance for `PParamUpdate`
 * Changed the type of `AtMostEra` and `AtLeastEra` to accept a type level string instead of an actual era type.
 * Add `EraName` type family to the `Era` type class and use it for default implementation of
   `eraName` type class function.

libs/cardano-ledger-core/src/Cardano/Ledger/Core/PParams.hs

@@ -108,7 +108,7 @@ import Cardano.Ledger.HKD (HKD, HKDApplicative, HKDFunctor (..), NoUpdate (..))
 import Cardano.Ledger.Plutus.ToPlutusData (ToPlutusData (..))
 import Control.DeepSeq (NFData)
 import Control.Monad.Identity (Identity)
-import Data.Aeson (FromJSON (..), ToJSON (..), withObject, (.:), (.=))
+import Data.Aeson (FromJSON (..), ToJSON (..), withObject, (.:), (.:!), (.=))
 import qualified Data.Aeson.Key as Aeson (fromText)
 import Data.Default (Default (..))
 import qualified Data.Foldable as F (foldMap', foldl', foldlM)
@@ -249,6 +249,18 @@ deriving via
   instance
     EraPParams era => ToJSON (PParamsUpdate era)
 
+instance EraPParams era => FromJSON (PParamsUpdate era) where
+  parseJSON =
+    withObject (show . typeRep $ Proxy @(PParamsUpdate era)) $ \obj ->
+      let go acc PParam {ppName, ppUpdate} =
+            maybe id setPpu <$> obj .:! Aeson.fromText ppName <*> pure acc
+            where
+              setPpu = maybe (const id) (\PParamUpdate {ppuLens} -> set ppuLens . SJust) ppUpdate
+       in F.foldlM
+            go
+            (emptyPParamsUpdate @era)
+            (eraPParams @era)
+
 deriving instance Generic (PParamsUpdate era)
 
 -- Generic derivation of `applyPPUpdates`

libs/cardano-ledger-core/testlib/Test/Cardano/Ledger/Core/JSON.hs

@@ -62,6 +62,7 @@ roundTripJsonEraSpec =
   describe (eraName @era) $ do
     describe "RoundTrip JSON" $ do
       roundTripJsonSpec @(PParams era)
+      roundTripJsonSpec @(PParamsUpdate era)
       roundTripJsonSpec @(TranslationContext era)
 
 goldenJsonPParamsSpec ::