Fix semigroup

Author: Poscat

flake.nix

@@ -0,0 +1,31 @@
+{
+  inputs.nixpkgs.url = github:NixOS/nixpkgs/nixos-unstable;
+  inputs.flake-utils.url = github:poscat0x04/flake-utils;
+
+  outputs = { self, nixpkgs, flake-utils, ... }: with flake-utils;
+    eachDefaultSystem (
+      system:
+        let
+          pkgs = import nixpkgs { inherit system; overlays = [ self.overlay ]; };
+        in
+          with pkgs;
+          {
+            devShell = aeson-dev.envFunc { withHoogle = true; };
+            defaultPackage = aeson;
+          }
+    ) // {
+      overlay = self: super:
+        let
+          hpkgs = super.haskellPackages;
+          aeson = hpkgs.callCabal2nix "aeson" ./. {};
+        in
+          with super; with haskell.lib;
+          {
+            inherit aeson;
+            aeson-dev = addBuildTools aeson [
+              haskell-language-server
+              cabal-install
+            ];
+          };
+    };
+}

src/Data/Aeson/TH.hs

@@ -510,7 +510,7 @@ argsToValue target jc tvMap opts multiCons
                            ()
                             | TaggedFlatObject {tagFieldName} <- sumEncoding opts -> do
                                let tag = pairE tagFieldName (conStr target opts conName)
-                               fromPairsE $ infixApp tag [|(<>)|] pairs
+                               fromPairsE $ infixApp tag [|(Monoid.<>)|] pairs
                             | otherwise -> recordSumToValue target opts multiCons (null argTys) conName pairs)
               []
 
@@ -763,7 +763,7 @@ consFromJSON jc tName opts instTys cons = do
         case sumEncoding opts of
           TaggedObject {tagFieldName, contentsFieldName} ->
             parseObject $ parseTaggedObject tvMap tagFieldName contentsFieldName
-          TaggedFlatObject {tagFieldName} -> 
+          TaggedFlatObject {tagFieldName} ->
             parseObject $ parseTaggedFlatObject tvMap tagFieldName
           UntaggedValue -> error "UntaggedValue: Should be handled already"
           ObjectWithSingleField ->