Fix compatibility with older ghc versions

Author: Poscat

Data/Aeson/Types/FromJSON.hs

@@ -4,13 +4,13 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE InstanceSigs #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE UndecidableInstances #-}
@@ -159,8 +159,7 @@ import qualified Data.Primitive.Types as PM
 import qualified Data.Primitive.PrimArray as PM
 
 import Data.Coerce (Coercible, coerce)
-import GHC.TypeNats
-import Data.Kind (Type)
+import GHC.TypeLits
 
 parseIndexedJSON :: (Value -> Parser a) -> Int -> Value -> Parser a
 parseIndexedJSON p idx value = p value <?> Index idx
@@ -1434,12 +1433,15 @@ instance ( IsRecord f isRecord
          , FromTaggedFlatObject' arity f isRecord
          , Constructor c
          ) => FromTaggedFlatObject arity (C1 c f) where
+    parseTaggedFlatObject :: Text :* TypeName :* Options :* FromArgs arity a
+                          -> Object
+                          -> Maybe (Parser (C1 c f a))
     parseTaggedFlatObject (tag :* p@(_ :* opts :* _)) obj
-       | tag == tag' = Just $ fmap M1 $ (unTagged @Type @isRecord) $ parseTaggedFlatObject' (cname :* p) obj
+       | tag == tag' = Just $ fmap M1 $ (unTagged :: Tagged isRecord (Parser (f a)) -> Parser (f a)) $ parseTaggedFlatObject' (cname :* p) obj
        | otherwise = Nothing
      where
         tag' = pack $ constructorTagModifier opts cname
-        cname = conName (undefined :: M1 i c a p)
+        cname = conName (undefined :: M1 i c f p)
 
 class FromTaggedFlatObject' arity f isRecord where
     parseTaggedFlatObject' :: ConName :* TypeName :* Options :* FromArgs arity a
@@ -1453,7 +1455,7 @@ instance FromTaggedFlatObject' arity U1 False where
     parseTaggedFlatObject' _ _ = Tagged (pure U1)
 
 instance OVERLAPPABLE_ (PositionFromObject 1 arity f) => FromTaggedFlatObject' arity f False where
-    parseTaggedFlatObject' (_ :* p) obj = Tagged (positionFromObject (Proxy @1) p obj)
+    parseTaggedFlatObject' (_ :* p) obj = Tagged (positionFromObject (Proxy :: Proxy 1) p obj)
 
 class KnownNat n => PositionFromObject n arity f where
     positionFromObject :: Proxy n
@@ -1463,15 +1465,15 @@ class KnownNat n => PositionFromObject n arity f where
 
 instance (KnownNat n, GFromJSON arity a) => PositionFromObject n arity (S1 m a) where
     positionFromObject _ (_ :* opts :* fargs) obj =
-       explicitParseField (gParseJSON opts fargs) obj $ pack $ show $ natVal $ Proxy @n
+       explicitParseField (gParseJSON opts fargs) obj $ pack $ show $ natVal (Proxy :: Proxy n)
 
 instance ( PositionFromObject n arity f
          , PositionFromObject (n+1) arity g
          ) => PositionFromObject n arity (f :*: g) where
     positionFromObject _ p obj =
       (:*:)
-        <$> positionFromObject (Proxy @n) p obj
-        <*> positionFromObject (Proxy @(n+1)) p obj
+        <$> positionFromObject (Proxy :: Proxy n) p obj
+        <*> positionFromObject (Proxy :: Proxy (n+1)) p obj
 
 --------------------------------------------------------------------------------
 

Data/Aeson/Types/ToJSON.hs

@@ -142,7 +142,7 @@ import qualified Data.Primitive.Array as PM
 import qualified Data.Primitive.SmallArray as PM
 import qualified Data.Primitive.Types as PM
 import qualified Data.Primitive.PrimArray as PM
-import GHC.TypeNats
+import GHC.TypeLits
 
 toJSONPair :: (a -> Value) -> (b -> Value) -> (a, b) -> Value
 toJSONPair a b = liftToJSON2 a (listValue a) b (listValue b)