Instances for Sum and Product monoid wrappers

src/Data/Aeson/Types/FromJSON.hs

@@ -2334,6 +2334,34 @@ instance FromJSON1 Monoid.Dual where
 instance FromJSON a => FromJSON (Monoid.Dual a) where
     parseJSON = parseJSON1
 
+instance FromJSON1 Monoid.Sum where
+    liftParseJSON _ p _ a = coerce (p a)
+
+    liftParseJSONList _ _ p a = coerce (p a)
+
+    liftOmittedField = coerce
+
+instance (FromJSON a) => FromJSON (Monoid.Sum a) where
+    parseJSON = parseJSON1
+
+    parseJSONList = liftParseJSONList omittedField parseJSON parseJSONList
+
+    omittedField = omittedField1
+
+instance FromJSON1 Monoid.Product where
+    liftParseJSON _ p _ a = coerce (p a)
+
+    liftParseJSONList _ _ p a = coerce (p a)
+
+    liftOmittedField = coerce
+
+instance (FromJSON a) => FromJSON (Monoid.Product a) where
+    parseJSON = parseJSON1
+
+    parseJSONList = liftParseJSONList omittedField parseJSON parseJSONList
+
+    omittedField = omittedField1
+
 
 instance FromJSON1 Monoid.First where
     liftParseJSON o = coerce (liftParseJSON @Maybe o)

src/Data/Aeson/Types/ToJSON.hs

@@ -364,7 +364,7 @@ instance (key ~ Key, value ~ Value) => KeyValue Value (key, value) where
 instance value ~ Value => KeyValue Value (KM.KeyMap value) where
     (.=) = explicitToField toJSON
     {-# INLINE (.=) #-}
-    
+
     explicitToField f name value = KM.singleton name (f value)
     {-# INLINE explicitToField #-}
 
@@ -2100,12 +2100,32 @@ instance ToJSON a => ToJSON (Monoid.Dual a) where
     toEncoding = toEncoding1
     omitField = omitField1
 
+instance ToJSON1 Monoid.Sum where
+    liftToJSON _ t _ = t . Monoid.getSum
+    liftToEncoding _ t _ = t . Monoid.getSum
+    liftOmitField = coerce
+
+instance ToJSON a => ToJSON (Monoid.Sum a) where
+    toJSON = toJSON1
+    toEncoding = toEncoding1
+    omitField = omitField1
+
+instance ToJSON1 Monoid.Product where
+    liftToJSON _ t _ = t . Monoid.getProduct
+    liftToEncoding _ t _ = t . Monoid.getProduct
+    liftOmitField = coerce
+
+instance ToJSON a => ToJSON (Monoid.Product a) where
+    toJSON = toJSON1
+    toEncoding = toEncoding1
+    omitField = omitField1
+
 instance ToJSON1 Monoid.First where
     liftToJSON o t to' = liftToJSON o t to' . Monoid.getFirst
     liftToEncoding o t to' = liftToEncoding o t to' . Monoid.getFirst
     liftOmitField :: forall a. (a -> Bool) -> Monoid.First a -> Bool
     liftOmitField _ = coerce (isNothing @a)
-    
+
 instance ToJSON a => ToJSON (Monoid.First a) where
     toJSON = toJSON1
     toEncoding = toEncoding1
@@ -2168,7 +2188,7 @@ instance ToJSON1 Semigroup.WrappedMonoid where
     liftToJSON _ t _ (Semigroup.WrapMonoid x) = t x
     liftToEncoding _ t _ (Semigroup.WrapMonoid x) = t x
     liftOmitField = coerce
-    
+
 instance ToJSON a => ToJSON (Semigroup.WrappedMonoid a) where
     toJSON = toJSON1
     toEncoding = toEncoding1

tests/PropertyRoundTrip.hs

@@ -87,6 +87,8 @@ roundTripTests =
     , testProperty "Nu" $ roundTripEq @(F.Nu (These Char))
     , testProperty "Maybe" $ roundTripEq @(Maybe Int)
     , testProperty "Monoid.First" $ roundTripEq @(Monoid.First Int)
+    , testProperty "Monoid.Sum" $ roundTripEq @(Monoid.Sum Int)
+    , testProperty "Monoid.Product" $ roundTripEq @(Monoid.Product Int)
     , testProperty "Strict Pair" $ roundTripEq @(S.Pair Int Char)
     , testProperty "Strict Either" $ roundTripEq @(S.Either Int Char)
     , testProperty "Strict These" $ roundTripEq @(S.These Int Char)