flake.nix

{ inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";

    utils.url = "github:numtide/flake-utils";

    flake-compat = {
      url = "github:edolstra/flake-compat";
      flake = false;
    };
  };

  outputs = { nixpkgs, utils, ... }:
    let
      compiler = "ghc94";

      overlay = final: prev: {
        cabal2nix-unwrapped =
          final.haskell.lib.justStaticExecutables
            final.haskell.packages."${compiler}".cabal2nix;

        haskell = prev.haskell // {
          packages = prev.haskell.packages // {
            "${compiler}" = prev.haskell.packages."${compiler}".override (old: {
              overrides =
                final.lib.fold final.lib.composeExtensions (old.overrides or (_: _: { })) [
                  (final.haskell.lib.packageSourceOverrides {
                    nix-serve-ng = ./.;

                    base16 = "1.0";
                  })
                  (haskellPackagesNew: haskellPackagesOld: {
                    nix-serve-ng =
                      final.haskell.lib.overrideCabal
                        haskellPackagesOld.nix-serve-ng
                        (old: {
                          executableSystemDepends = (old.executableSystemDepends or []) ++ [
                            final.boost.dev
                            final.nixVersions.nix_2_24
                          ];
                        });
                  })
                ];
            });
          };
        };

        nix-serve-ng =
          final.haskell.lib.justStaticExecutables
            final.haskell.packages."${compiler}".nix-serve-ng;
      };

    in
      utils.lib.eachDefaultSystem (system:
        let
          pkgs = import nixpkgs {
            config = { };

            overlays = [ overlay ];

            inherit system;
          };

          inherit (pkgs) nix-serve-ng;

        in
          rec {
            packages.default = nix-serve-ng;

            defaultPackage = packages.default;

            apps.default = {
              type = "app";

              program = "${nix-serve-ng}/bin/nix-serve";
            };

            defaultApp = apps.default;

            devShells.default =
              (pkgs.haskell.lib.doBenchmark
                pkgs.haskell.packages."${compiler}".nix-serve-ng
              ).env;

            devShell = devShells.default;
          }) // rec {
        overlays = {
          # The default overlay only adds the exports for
          # `pkgs.haskell.packages."${compiler}".nix-serve-ng` and
          # `pkgs.nix-serve-ng`
          default = overlay;

          # This overlay additionally overrides `pkgs.nix-serve` to refer to
          # `pkgs.nix-serve-ng`
          override = final: prev: {
            nix-serve = final.nix-serve-ng;
          };
        };

        # The NixOS module is a thin wrapper around the overlay to replace
        # `nix-serve` with `nix-serve-ng`
        #
        # You can continue to use the old `services.nix-serve` NixOS options.
        nixosModules.default = {
          nixpkgs.overlays = [ overlays.default overlays.override ];
        };
      };
}