Make indicies start from 0

Author: Poscat

src/Data/Aeson/TH.hs

@@ -443,7 +443,7 @@ argsToValue target jc tvMap opts multiCons
         let len = length argTys'
         args <- newNameList "arg" len
         let os = zipWith (\arg argTy -> dispatchToJSON target jc conName tvMap argTy `appE` varE arg) args argTys'
-            pairs = zip (fmap (show :: Int -> String) [1..]) os
+            pairs = zip (fmap (show :: Int -> String) [0..]) os
             obj = objectE (tag : pairs)
         match (conP conName $ map varP args)
               (normalB obj)
@@ -526,7 +526,7 @@ argsToValue target jc tvMap opts multiCons
         ar <- newName "argR"
         let tag = (tagFieldName, conStr target opts conName)
             os = zipWith (\arg argTy -> dispatchToJSON target jc conName tvMap argTy `appE` varE arg) [al, ar] [alTy, arTy]
-            pairs = zip (fmap (show :: Int -> String) [1..]) os
+            pairs = zip (fmap (show :: Int -> String) [0..]) os
             obj = objectE (tag : pairs)
         match (infixP (varP al) conName (varP ar))
               (normalB obj)

src/Data/Aeson/Types/FromJSON.hs

@@ -1123,14 +1123,14 @@ parseNonAllNullarySum p@(tname :* opts :* _) =
               ", but found tag " ++ show tag
           cnames_ = unTagged2 (constructorTags (constructorTagModifier opts) :: Tagged2 f [String])
 
-      TaggedFlatObject{..} -> 
+      TaggedFlatObject{..} ->
           withObject tname $ \obj -> do
               let tagKey = pack tagFieldName
                   badTag tag = failWith_ $ \cnames ->
                     "expected tag field to be one of " ++ show cnames ++
                     ", but found tag " ++ show tag
                   cnames_ = unTagged2 (constructorTags (constructorTagModifier opts) :: Tagged2 f [String])
-              tag <- contextType tname . contextTag tagKey cnames_ $ obj .: tagKey 
+              tag <- contextType tname . contextTag tagKey cnames_ $ obj .: tagKey
               fromMaybe (badTag tag <?> Key tagKey) $
                 parseTaggedFlatObject (tag :* p) obj
 
@@ -1454,9 +1454,9 @@ instance (RecordFromJSON arity f, FieldNames f) => FromTaggedFlatObject' arity f
 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 :: Proxy 1) p obj)
- 
+instance OVERLAPPABLE_ PositionFromObject 0 arity f => FromTaggedFlatObject' arity f False where
+    parseTaggedFlatObject' (_ :* p) obj = Tagged (positionFromObject (Proxy :: Proxy 0) p obj)
+
 class KnownNat n => PositionFromObject n arity f where
     positionFromObject :: Proxy n
                        -> TypeName :* Options :* FromArgs arity a

src/Data/Aeson/Types/Internal.hs

@@ -711,7 +711,7 @@ data SumEncoding =
     --      in that data type with an additional field '$tagFieldName'.
     --      For example, given @A@ defined as
     --      @data A = A Int Int | B@,
-    --      this option will encode @A 1 2@ as @{"1": 1, "2": 2, "$tagFieldName": \"A"}@
+    --      this option will encode @A 1 2@ as @{"0": 1, "1": 2, "$tagFieldName": \"A"}@
     --   5. The behavior is undefined when the '$tagFieldName' collides with another field name and should
     --      not be relied upon. It may or may not overwite the field.
     --      It may or may not throw an runtime exception. It may or may not raise an compile time error.

src/Data/Aeson/Types/ToJSON.hs

@@ -954,8 +954,8 @@ instance RecordToPairs pairs enc arity f => TaggedFlatObject' pairs enc arity f
 instance Monoid pairs => TaggedFlatObject' enc pairs arity U1 False where
     taggedFlatObject' _ _ _ = Tagged mempty
 
-instance OVERLAPPABLE_ PositionToPairs 1 pairs enc arity f => TaggedFlatObject' enc pairs arity f False where
-    taggedFlatObject' opts targs a = Tagged $ positionToPairs (Proxy :: Proxy 1) opts targs a
+instance OVERLAPPABLE_ PositionToPairs 0 pairs enc arity f => TaggedFlatObject' enc pairs arity f False where
+    taggedFlatObject' opts targs a = Tagged $ positionToPairs (Proxy :: Proxy 0) opts targs a
 
 class KnownNat n => PositionToPairs n pairs enc arity f where
     positionToPairs :: Proxy n -> Options -> ToArgs enc arity a -> f a -> pairs