Remove isUnary

Instead decide at compile time whether a record is unary

Author: Lysxia

Data/Aeson/Types/FromJSON.hs

@@ -1004,7 +1004,7 @@ instance ( IsRecord            f isRecord
 
 instance OVERLAPPING_
          ( GFromJSON arity a, FromRecord arity (S1 s a)
-         ) => ConsFromJSON' arity (S1 s a) 'True where
+         ) => ConsFromJSON' arity (S1 s a) True where
     consParseJSON' opts fargs
       | unwrapUnaryRecords opts = Tagged . gParseJSON opts fargs
       | otherwise = Tagged . withObject "unary record" (parseRecord opts fargs)
@@ -1013,7 +1013,7 @@ instance FromRecord arity f => ConsFromJSON' arity f True where
     consParseJSON' opts fargs =
       Tagged . withObject "record (:*:)" (parseRecord opts fargs)
 
-instance (GFromJSON arity f) => ConsFromJSON' arity f False where
+instance GFromJSON arity f => ConsFromJSON' arity f False where
     consParseJSON' opts fargs = Tagged . gParseJSON opts fargs
 
 --------------------------------------------------------------------------------

Data/Aeson/Types/Generic.hs

@@ -44,12 +44,8 @@ import GHC.Generics
 --------------------------------------------------------------------------------
 
 class IsRecord (f :: * -> *) isRecord | f -> isRecord
-  where
-    isUnary :: f a -> Bool
-    isUnary = const True
 
 instance (IsRecord f isRecord) => IsRecord (f :*: g) isRecord
-  where isUnary = const False
 #if MIN_VERSION_base(4,9,0)
 instance OVERLAPPING_ IsRecord (M1 S ('MetaSel 'Nothing u ss ds) f) False
 #else
@@ -61,7 +57,6 @@ instance IsRecord Par1 True
 instance IsRecord (Rec1 f) True
 instance IsRecord (f :.: g) True
 instance IsRecord U1 False
-  where isUnary = const False
 
 --------------------------------------------------------------------------------
 

Data/Aeson/Types/ToJSON.hs

@@ -956,7 +956,6 @@ class ConsToJSON enc arity f where
 
 class ConsToJSON' enc arity f isRecord where
     consToJSON'     :: Options -> ToArgs enc arity a
-                    -> Bool -- ^ Are we a record with one field?
                     -> f a -> Tagged isRecord enc
 
 instance ( IsRecord                f isRecord
@@ -965,23 +964,28 @@ instance ( IsRecord                f isRecord
   where
     consToJSON opts targs =
         (unTagged :: Tagged isRecord enc -> enc)
-      . consToJSON' opts targs (isUnary (undefined :: f a))
+      . consToJSON' opts targs
     {-# INLINE consToJSON #-}
 
-instance ( RecordToPairs enc pairs arity f
+instance OVERLAPPING_
+         ( RecordToPairs enc pairs arity (S1 s f)
          , FromPairs enc pairs
          , GToJSON enc arity f
-         ) => ConsToJSON' enc arity f True
+         ) => ConsToJSON' enc arity (S1 s f) True
   where
-    consToJSON' opts targs isUn =
-      Tagged .
-        case (isUn, unwrapUnaryRecords opts) of
-          (True, True) -> gToJSON opts targs
-          _ -> fromPairs . recordToPairs opts targs
+    consToJSON' opts targs
+      | unwrapUnaryRecords opts = Tagged . gToJSON opts targs
+      | otherwise = Tagged . fromPairs . recordToPairs opts targs
     {-# INLINE consToJSON' #-}
 
+instance ( RecordToPairs enc pairs arity f
+         , FromPairs enc pairs
+         ) => ConsToJSON' enc arity f True
+  where
+    consToJSON' opts targs = Tagged . fromPairs . recordToPairs opts targs
+
 instance GToJSON enc arity f => ConsToJSON' enc arity f False where
-    consToJSON' opts targs _ = Tagged . gToJSON opts targs
+    consToJSON' opts targs = Tagged . gToJSON opts targs
     {-# INLINE consToJSON' #-}
 
 --------------------------------------------------------------------------------