Attempt to fix nix CI

Author: andreasabel

nix/agda2hs.nix

@@ -51,7 +51,10 @@ let
     runCommand "${pname}-${version}"
       {
         inherit pname version;
-        nativeBuildInputs = [ makeWrapper ];
+        nativeBuildInputs = [
+          pkgs.diffutils
+          makeWrapper
+        ];
         passthru = {
           unwrapped = agda2hs;
           inherit withPackages;

nix/shell.nix

@@ -24,5 +24,7 @@ pkgs.haskellPackages.shellFor {
     pkgs.nixfmt-rfc-style
     cabal2nix
     pkgs.haskellPackages.fix-whitespace
+    # The testsuite uses diff, so ensure `diff` is available in the shell/tests
+    pkgs.diffutils
   ];
 }