zbg nix flake debugging

flake.nix

{
  inputs = {
    flake-utils.url = "github:numtide/flake-utils";
    # nixpkgs.follows = "opam-nix/nixpkgs";
    nixpkgs.url = "github:NixOS/nixpkgs/master";
    # nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
    # opam-nix = {
    #   url = "github:tweag/opam-nix";
    #   inputs.nixpkgs.follows = "nixpkgs";
    # };
  };
  outputs = { self, flake-utils, opam-nix, nixpkgs }@inputs:
    # Don't forget to put the package name instead of `throw':
    let package = "zbg";
    in flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
        on = opam-nix.lib.${system};
        scope =
          on.buildDuneProject { } package ./. { ocaml-base-compiler = "*"; };
        overlay = final: prev:
          {
            # dune = prev.dune.overrideAttrs (_: { nativeBuildInputs = with pkgs; [dune_3]; });
            # Your overrides go here
          };
      in {
        legacyPackages = scope.overrideScope' overlay;

        packages.default = self.legacyPackages.${system}.${package};
      });
}