Remove overlapping [From,To]JSON instances for NExpr

…for compatibility with aeson-1.5.3.

Closes #690.

hnix.cabal

@@ -384,7 +384,7 @@ library
       src
   ghc-options: -Wall -fprint-potential-instances
   build-depends:
-      aeson >= 1.4.2 && < 1.5.3
+      aeson >= 1.4.2 && < 1.6
     , array >= 0.4 && < 0.6
     , base >= 4.11 && < 5
     , binary >= 0.8.5 && < 0.9

main/Main.hs

@@ -17,7 +17,6 @@ import           Control.Monad.Catch
 import           Control.Monad.Free
 import           Control.Monad.IO.Class
 -- import           Control.Monad.ST
-import qualified Data.Aeson.Text               as A
 import qualified Data.HashMap.Lazy             as M
 import qualified Data.Map                      as Map
 import           Data.List                      ( sortOn )
@@ -25,7 +24,6 @@ import           Data.Maybe                     ( fromJust )
 import           Data.Time
 import qualified Data.Text                     as Text
 import qualified Data.Text.IO                  as Text
-import qualified Data.Text.Lazy.IO             as TL
 import           Nix
 import           Nix.Convert
 import qualified Nix.Eval                      as Eval
@@ -124,7 +122,7 @@ main = do
     | xml opts
     = error "Rendering expression trees to XML is not yet implemented"
     | json opts
-    = liftIO $ TL.putStrLn $ A.encodeToLazyText (stripAnnotation expr)
+    = error "Rendering expression trees to JSON is not implemented"
     | verbose opts >= DebugInfo
     = liftIO $ putStr $ PS.ppShow $ stripAnnotation expr
     | cache opts

src/Nix/Expr/Types.hs

@@ -543,7 +543,6 @@ instance ToJSON NUnaryOp
 instance ToJSON NBinaryOp
 instance ToJSON NRecordType
 instance ToJSON a => ToJSON (NExprF a)
-instance ToJSON NExpr
 
 instance (FromJSON v, FromJSON a) => FromJSON (Antiquoted v a)
 instance FromJSON a => FromJSON (NString a)
@@ -558,7 +557,6 @@ instance FromJSON NUnaryOp
 instance FromJSON NBinaryOp
 instance FromJSON NRecordType
 instance FromJSON a => FromJSON (NExprF a)
-instance FromJSON NExpr
 
 $(makeTraversals ''NExprF)
 $(makeTraversals ''Binding)