4768638 · typeable/aeson

git.iko.soy/typeable/aeson

IncoherentInstances needed to derive some instances

* Add IncoherentInstances to Data.Aeson.TH and Data.Aeson.FromJSON * Add data type with test that demonstrates the need for IncoherentInstances in TH and Generic deriving (specifically for the classes LookupField and FromRecord) * Fix #468

commit4768638cbbaefcb9e5e4f96cabb33a4f9960caac authorSean Leather <sean.leather@gmail.com> dateThu 29 Sep 2016, 09:33 (10 years ago) parent8044d1a

6 files changed+45−5

compare with master

unifiedsplit

Data/Aeson/TH.hs+2−1 Data/Aeson/Types/FromJSON.hs+4−4 aeson.cabal+1 include/incoherent-compat.h+7 tests/Encoders.hs+19 tests/Types.hs+12

Data/Aeson/TH.hs+2−1

@@ -13,6 +13,7 @@

1313{-# LANGUAGE TemplateHaskell #-}

1414#endif

1515

16+#include "incoherent-compat.h"

1617#include "overlapping-compat.h"

1718

1819{-|

@@ -1222,7 +1223,7 @@ class LookupField a where

12221223instance OVERLAPPABLE_ LookupField a where

12231224 lookupField = lookupFieldWith

12241225

1225−instance LookupField (Maybe a) where

1226+instance INCOHERENT_ LookupField (Maybe a) where

12261227 lookupField pj _ _ = parseOptionalFieldWith pj

12271228

12281229lookupFieldWith :: (Value -> Parser a) -> String -> String

Data/Aeson/Types/FromJSON.hs+4−4

@@ -18,6 +18,7 @@

1818{-# LANGUAGE PolyKinds #-}

1919#endif

2020

21+#include "incoherent-compat.h"

2122#include "overlapping-compat.h"

2223

2324-- TODO: Drop this when we remove support for Data.Attoparsec.Number

@@ -942,9 +943,8 @@ instance ( FromRecord arity a

942943 (:*:) <$> parseRecord opts fargs Nothing obj

943944 <*> parseRecord opts fargs Nothing obj

944945

945−instance ( Selector s

946− , GFromJSON arity a

947− ) => FromRecord arity (S1 s a) where

946+instance OVERLAPPABLE_ (Selector s, GFromJSON arity a) =>

947+ FromRecord arity (S1 s a) where

948948 parseRecord opts fargs lab =

949949 (<?> Key label) . gParseJSON opts fargs <=< (.: label)

950950 where

@@ -952,7 +952,7 @@ instance ( Selector s

952952 defLabel = pack . fieldLabelModifier opts $

953953 selName (undefined :: t s a p)

954954

955−instance OVERLAPPING_ (Selector s, FromJSON a) =>

955+instance INCOHERENT_ (Selector s, FromJSON a) =>

956956 FromRecord arity (S1 s (K1 i (Maybe a))) where

957957 parseRecord _ _ (Just lab) obj = (M1 . K1) <$> obj .:? lab

958958 parseRecord opts _ Nothing obj = (M1 . K1) <$> obj .:? pack label

aeson.cabal+1

@@ -47,6 +47,7 @@ extra-source-files:

4747 benchmarks/Typed/*.hs

4848 benchmarks/json-data/*.json

4949 include/overlapping-compat.h

50+ include/incoherent-compat.h

5051 changelog.md

5152 examples/*.cabal

5253 examples/*.hs

include/incoherent-compat.hnew file+7

@@ -0,0 +1,7 @@

1+#if __GLASGOW_HASKELL__ >= 710

2+#define INCOHERENT_ {-# INCOHERENT #-}

3+#else

4+-- This causes some type class instances to break:

5+-- {-# LANGUAGE IncoherentInstances #-}

6+#define INCOHERENT_

7+#endif

tests/Encoders.hs+19

@@ -235,6 +235,25 @@ gSomeTypeToJSONOmitNothingFields = genericToJSON optsOmitNothingFields

235235gSomeTypeToEncodingOmitNothingFields :: SomeType Int -> Encoding

236236gSomeTypeToEncodingOmitNothingFields = genericToEncoding optsOmitNothingFields

237237

238+--------------------------------------------------------------------------------

239+-- IncoherentInstancesNeeded

240+--------------------------------------------------------------------------------

241+

242+-- | This test demonstrates the need for IncoherentInstances. See the definition

243+-- of 'IncoherentInstancesNeeded' for a discussion of the issue.

244+--

245+-- NOTE 1: We only need to compile this test. We do not need to run it.

246+--

247+-- NOTE 2: We actually only use the INCOHERENT pragma on specific instances

248+-- instead of the IncoherentInstances language extension. Therefore, this is

249+-- only supported on GHC versions >= 7.10.

250+#if __GLASGOW_HASKELL__ >= 710

251+incoherentInstancesNeededParseJSONString :: FromJSON a => Value -> Parser (IncoherentInstancesNeeded a)

252+incoherentInstancesNeededParseJSONString = case () of

253+ _ | True -> $(mkParseJSON defaultOptions ''IncoherentInstancesNeeded)

254+ | False -> genericParseJSON defaultOptions

255+#endif

256+

238257-------------------------------------------------------------------------------

239258-- EitherTextInt encoders/decodes

240259-------------------------------------------------------------------------------

tests/Types.hs+12

@@ -70,6 +70,18 @@ data SomeType a = Nullary

7070 | List [a]

7171 deriving (Eq, Show)

7272

73+-- | This type requires IncoherentInstances for the instances of the type

74+-- classes Data.Aeson.TH.LookupField and Data.Aeson.Types.FromJSON.FromRecord.

75+--

76+-- The minimum known requirements for this type are:

77+-- * Record type with at least two fields

78+-- * One field type is either a type parameter or a type/data family

79+-- * Another field type is a @Maybe@ of the above field type

80+data IncoherentInstancesNeeded a = IncoherentInstancesNeeded

81+ { incoherentInstancesNeededMaybeNot :: a

82+ , incoherentInstancesNeededMaybeYes :: Maybe a

83+ } deriving Generic

84+

7385-- Used for testing UntaggedValue SumEncoding

7486data EitherTextInt

7587 = LeftBool Bool