Put JSON support behind a flag

graphql.cabal

@@ -28,6 +28,11 @@ source-repository head
   type: git
   location: git://caraus.tech/pub/graphql.git
 
+flag Json
+  description: Whether to build against @aeson 1.x@
+  default: True
+  manual: True
+
 library
   exposed-modules:
     Language.GraphQL
@@ -57,8 +62,8 @@ library
   hs-source-dirs:
     src
   ghc-options: -Wall
+
   build-depends:
-    aeson >= 1.5.6 && < 1.6,
     base >= 4.7 && < 5,
     conduit >= 1.3.4 && < 1.4,
     containers >= 0.6.2 && < 0.7,
@@ -66,12 +71,17 @@ library
     hspec-expectations >= 0.8.2 && < 0.9,
     megaparsec >= 9.0.1 && < 9.1,
     parser-combinators >= 1.3.0 && < 1.4,
-    scientific >= 0.3.7 && < 0.4,
     template-haskell >= 2.16 && < 2.18,
     text >= 1.2.4 && < 1.3,
     transformers >= 0.5.6 && < 0.6,
     unordered-containers >= 0.2.14 && < 0.3,
     vector >= 0.12.3 && < 0.13
+  if flag(Json)
+    build-depends:
+      aeson >= 1.5.6 && < 1.6,
+      scientific >= 0.3.7 && < 0.4
+    cpp-options: -DWITH_JSON
+
   default-language: Haskell2010
 
 test-suite graphql-test
@@ -91,9 +101,9 @@ test-suite graphql-test
   hs-source-dirs:
     tests
   ghc-options: -threaded -rtsopts -with-rtsopts=-N -Wall
+
   build-depends:
     QuickCheck >= 2.14.1 && < 2.15,
-    aeson,
     base >= 4.8 && < 5,
     conduit,
     exceptions,
@@ -101,7 +111,6 @@ test-suite graphql-test
     hspec >= 2.9.1 && < 3,
     hspec-megaparsec >= 2.2.0 && < 2.3,
     megaparsec,
-    scientific,
     text,
     unordered-containers
   default-language: Haskell2010