Generated code contains GHC.Internal imports

[turion]

When I run the generator through the nix flake, it creates types like GHC.Internal.Maybe.Maybe GHC.Types.Float, but ghc-internal is not (and IMHO shouldn't be) a dependency of the generated package. So the generated package doesn't build.

[joel-bach]

Could you provide a minimal reproducer for this?

[turion]

Yes.

{
  description = "openapi-bug";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable-small";
    flake-utils.url = "github:numtide/flake-utils";
    openapi3-code-generator.url = "github:Haskell-OpenAPI-Code-Generator/Haskell-OpenAPI-Client-Code-Generator";
  };

  outputs = { self, nixpkgs, flake-utils, openapi3-code-generator }:
    with builtins;
    with nixpkgs.lib;

    flake-utils.lib.eachDefaultSystem
      (system:

        let
          openapi3-code-generator-overlay = openapi3-code-generator.overlays.${system};
          pkgs = import nixpkgs {
            inherit system;
            overlays = [
              openapi3-code-generator-overlay
            ];
          };

          json = toFile "openapi-bug.json" ''
            {
              "openapi": "3.0.1",
              "info": {
                "title": "openapi-bug",
                "version": "v1"
              },
              "paths": {
                  "/foo/bar": {
                  "get": {
                    "responses": {
                      "200": {
                        "description": "OK",
                        "content": {
                          "application/json": {
                            "schema": {
                              "$ref": "#/components/schemas/someenum"
                            }
                          }
                        }
                      }
                    }
                  }
                },
              },
              "components": {
                "schemas": {
                  "someenum": {
                    "enum": [
                      "variant"
                    ],
                    "type": "string"
                  }
                }
              }
            }
          '';

          openapi-bug-src = pkgs.runCommand "openapi-bug-src"
              {
                src = json;
                nativeBuildInputs = [
                  pkgs.openapi3-code-generator
                  pkgs.cabal-install
                ];
              } ''
              openapi3-code-generator-exe ${json} -f -o $out --package-name openapi-bug
              ls -r $out
            '';
        in
        {
          packages.default = pkgs.haskellPackages.callCabal2nix "openapi-bug" openapi-bug-src {};
        });
}

❯ nix flake info
warning: 'nix flake info' is a deprecated alias for 'nix flake metadata'
Resolved URL:  path:/home/turion/haskell/openapi-bug
Locked URL:    path:/home/turion/haskell/openapi-bug?lastModified=1762771795&narHash=sha256-XO%2ByUDnSUfvTDULRC8c62ESk/zjKB3TsB6gDdXEBwVQ%3D
Description:   openapi-bug
Path:          /nix/store/6qxvwh8vc3ikg0wfnk0ipqvq1zsmrhib-source
Last modified: 2025-11-10 11:49:55
Inputs:
├───flake-utils: github:numtide/flake-utils/11707dc2f618dd54ca8739b309ec4fc024de578b
│   Last modified: 2024-11-13 22:27:16
│   └───systems: github:nix-systems/default/da67096a3b9bf56a91d16901293e51ba5b49a27e
│       Last modified: 2023-04-09 10:27:08
├───nixpkgs: github:NixOS/nixpkgs/e5d07586ec39f74b390308f2e00040c23bdef530
│   Last modified: 2025-11-09 21:56:22
└───openapi3-code-generator: github:Haskell-OpenAPI-Code-Generator/Haskell-OpenAPI-Client-Code-Generator/311cf56a736846b4b578f30a9f894fd90ef5dd27
    Last modified: 2025-11-04 15:43:23
    ├───flake-utils: github:numtide/flake-utils/11707dc2f618dd54ca8739b309ec4fc024de578b
    │   Last modified: 2024-11-13 22:27:16
    │   └───systems: github:nix-systems/default/da67096a3b9bf56a91d16901293e51ba5b49a27e
    │       Last modified: 2023-04-09 10:27:08
    ├───nixpkgs: github:NixOS/nixpkgs/7c43f080a7f28b2774f3b3f43234ca11661bf334
    │   Last modified: 2025-05-25 10:38:51
    └───pre-commit-hooks: github:cachix/pre-commit-hooks.nix/dcf5072734cb576d2b0c59b2ac44f5050b5eac82
        Last modified: 2025-03-22 14:26:04
        ├───flake-compat: github:edolstra/flake-compat/0f9255e01c2351cc7d116c072cb317785dd33b33
        │   Last modified: 2023-10-04 15:37:54
        ├───gitignore: github:hercules-ci/gitignore.nix/637db329424fd7e46cf4185293b9cc8c88c95394
        │   Last modified: 2024-02-28 03:28:52
        │   └───nixpkgs follows input 'openapi3-code-generator/pre-commit-hooks/nixpkgs'
        └───nixpkgs: github:NixOS/nixpkgs/a04d33c0c3f1a59a2c1cb0c6e34cd24500e5a1dc
            Last modified: 2024-11-05 02:08:39

❯ nix build -v
fetching path input 'path:/home/turion/haskell/openapi-bug'
building '/nix/store/qy1879sc14dgazjwhm4h5h74zdhygphw-openapi-bug-src.drv'...
building '/nix/store/fmksk95291nx5agb032dh5d7c7pzis1j-cabal2nix-openapi-bug.drv'...
this derivation will be built:
  /nix/store/13jhh23j96plrr2q3h0lkm88s19axv8w-openapi-bug-0.1.0.0.drv
building '/nix/store/13jhh23j96plrr2q3h0lkm88s19axv8w-openapi-bug-0.1.0.0.drv'...
error: builder for '/nix/store/13jhh23j96plrr2q3h0lkm88s19axv8w-openapi-bug-0.1.0.0.drv' failed with exit code 1;
       last 25 log lines:
       > [5 of 9] Compiling OpenAPI.Types.Someenum[boot] ( src/OpenAPI/Types/Someenum.hs-boot, dist/build/OpenAPI/Types/Someenum.o-boot, dist/build/OpenAPI/Types/Someenum.dyn_o-boot )
       > [6 of 9] Compiling OpenAPI.Types.Someenum ( src/OpenAPI/Types/Someenum.hs, dist/build/OpenAPI/Types/Someenum.o, dist/build/OpenAPI/Types/Someenum.dyn_o )
       > src/OpenAPI/Types/Someenum.hs:43:13: error: [8;;https://errors.haskell.org/messages/GHC-76037GHC-760378;;]
       >     Not in scope: type constructor or class ‘GHC.Internal.Show.Show’
       >     NB: no module named ‘GHC.Internal.Show’ is imported.
       >    |
       > 43 |   deriving (GHC.Internal.Show.Show, GHC.Classes.Eq)
       >    |             ^^^^^^^^^^^^^^^^^^^^^^
       >
       > src/OpenAPI/Types/Someenum.hs:49:28: error: [8;;https://errors.haskell.org/messages/GHC-76037GHC-760378;;]
       >     Not in scope: ‘GHC.Internal.Base.pure’
       >     NB: no module named ‘GHC.Internal.Base’ is imported.
       >    |
       > 49 |     where {parseJSON val = GHC.Internal.Base.pure (if | val GHC.Classes.== "variant" -> SomeenumEnumVariant
       >    |                            ^^^^^^^^^^^^^^^^^^^^^^
       >
       > src/OpenAPI/Types/Someenum.hs:50:57: error: [8;;https://errors.haskell.org/messages/GHC-76037GHC-760378;;]
       >     Not in scope: ‘GHC.Internal.Base.otherwise’
       >     NB: no module named ‘GHC.Internal.Base’ is imported.
       >     Suggested fix:
       >       Perhaps use ‘GHC.Integer.Type.otherwise’ (imported from Prelude)
       >    |
       > 50 |                                                       | GHC.Internal.Base.otherwise -> SomeenumOther val)}
       >    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
       >
       For full logs, run 'nix log /nix/store/13jhh23j96plrr2q3h0lkm88s19axv8w-openapi-bug-0.1.0.0.drv'.

[turion]

I'm pretty sure this is due to some change in more recent GHCs and/or more recent nixpkgs. In another project I have these pins:

Inputs:
├───flake-utils: github:numtide/flake-utils/11707dc2f618dd54ca8739b309ec4fc024de578b
│   Last modified: 2024-11-13 22:27:16
│   └───systems: github:nix-systems/default/da67096a3b9bf56a91d16901293e51ba5b49a27e
│       Last modified: 2023-04-09 10:27:08
├───nixpkgs: github:NixOS/nixpkgs/78e2cd1a1590f8c70b329cbc7d13bb2ab5b5a16c
│   Last modified: 2025-04-21 07:57:54
└───openapi3-code-generator: github:Haskell-OpenAPI-Code-Generator/Haskell-OpenAPI-Client-Code-Generator/665374f465f214ffa766b5a43c6a6b8b921e4673
    Last modified: 2025-04-14 13:10:16
    ├───autodocodec: github:NorfairKing/autodocodec/7439601de128dadf562430f4216cbdb28580ed20
    │   Last modified: 2025-02-14 20:54:07
    ├───fast-myers-diff: github:NorfairKing/fast-myers-diff/4a5c31884b8fc399085bffacd15d6cb5624b3177
    │   Last modified: 2025-01-15 14:44:12
    ├───flake-utils: github:numtide/flake-utils/11707dc2f618dd54ca8739b309ec4fc024de578b
    │   Last modified: 2024-11-13 22:27:16
    │   └───systems: github:nix-systems/default/da67096a3b9bf56a91d16901293e51ba5b49a27e
    │       Last modified: 2023-04-09 10:27:08
    ├───nixpkgs: github:NixOS/nixpkgs/26d499fc9f1d567283d5d56fcf367edd815dba1d
    │   Last modified: 2025-04-12 08:55:57
    ├───pre-commit-hooks: github:cachix/pre-commit-hooks.nix/dcf5072734cb576d2b0c59b2ac44f5050b5eac82
    │   Last modified: 2025-03-22 14:26:04
    │   ├───flake-compat: github:edolstra/flake-compat/0f9255e01c2351cc7d116c072cb317785dd33b33
    │   │   Last modified: 2023-10-04 15:37:54
    │   ├───gitignore: github:hercules-ci/gitignore.nix/637db329424fd7e46cf4185293b9cc8c88c95394
    │   │   Last modified: 2024-02-28 03:28:52
    │   │   └───nixpkgs follows input 'openapi3-code-generator/pre-commit-hooks/nixpkgs'
    │   └───nixpkgs: github:NixOS/nixpkgs/a04d33c0c3f1a59a2c1cb0c6e34cd24500e5a1dc
    │       Last modified: 2024-11-05 02:08:39
    ├───safe-coloured-text: github:NorfairKing/safe-coloured-text/9ed65a40b3b2fade447c9d5fcb941d58f6367308
    │   Last modified: 2024-10-13 01:01:46
    ├───sydtest: github:NorfairKing/sydtest/0aad7d9c41a53f5d46694c87dcacc51f6c6063d5
    │   Last modified: 2025-03-20 18:57:10
    └───validity: github:NorfairKing/validity/512aea6e0a112f5df09cc0b08f7fceffb122abc6
        Last modified: 2024-10-13 00:32:57

And there I'm not suffering from the bug.

[joel-bach]

Thank you for the reproducer @turion !
I agree that it looks like the nixpkgs/GHC version is the reason. I've included the new imports as alias (that is how we dealt with this in the past as well) and opened a PR here: #124
The reproducer was able to build for me with this branch, could you check if it works for you as well?

[turion]

Yes, I can verify that the PR solves the problem! Thanks a lot :)

[joel-bach]

Closed by #124