module-list.nix

let
  pkgs = import <nixpkgs> {};
  inherit (pkgs) lib;
  evalModules = with lib; { modules
                , prefix ? []
                , # This should only be used for special arguments that need to be evaluated
                  # when resolving module structure (like in imports). For everything else,
                  # there's _module.args. If specialArgs.modulesPath is defined it will be
                  # used as the base path for disabledModules.
                  specialArgs ? {}
                , # This would be remove in the future, Prefer _module.args option instead.
                  args ? {}
                , # This would be remove in the future, Prefer _module.check option instead.
                  check ? true
                }:
    let
      # This internal module declare internal options under the `_module'
      # attribute.  These options are fragile, as they are used by the
      # module system to change the interpretation of modules.
      internalModule = rec {
        _file = ./modules.nix;

        key = _file;

        options = {
          _module.args = mkOption {
            type = types.attrsOf types.unspecified;
            internal = true;
            description = "Arguments passed to each module.";
          };

          _module.check = mkOption {
            type = types.bool;
            internal = true;
            default = check;
            description = "Whether to check whether all option definitions have matching declarations.";
          };
        };

        config = {
          _module.args = args;
        };
      };

      closed = lib.closeModules (modules ++ [ internalModule ]) ({ inherit
      config options lib; } // specialArgs);

      options = mergeModules prefix (reverseList (filterModules (specialArgs.modulesPath or "") closed));

      # Traverse options and extract the option values into the final
      # config set.  At the same time, check whether all option
      # definitions have matching declarations.
      # !!! _module.check's value can't depend on any other config values
      # without an infinite recursion. One way around this is to make the
      # 'config' passed around to the modules be unconditionally unchecked,
      # and only do the check in 'result'.
      config = yieldConfig prefix options;
      yieldConfig = prefix: set:
        let res = removeAttrs (mapAttrs (n: v:
          if isOption v then v.value
          else yieldConfig (prefix ++ [n]) v) set) ["_definedNames"];
        in
        if options._module.check.value && set ? _definedNames then
          foldl' (res: m:
            foldl' (res: name:
              if set ? ${name} then res else throw "The option `${showOption (prefix ++ [name])}' defined in `${m.file}' does not exist.")
              res m.names)
            res set._definedNames
        else
          res;
      result = { inherit options config; };
    in closed;
  in map (x: x.key) (evalModules {
    prefix = [];
    check = true;
    modules = import <nixpkgs/nixos/modules/module-list.nix>;
    args = {};
    specialArgs = { modulesPath = <nixpkgs/nixos/modules>; };
  })