nixosOptionsDoc generates config for the built-in module system option _module.args.

[frederictobiasc]

Describe the bug

Generating module options documentation with nixosOptionsDoc generates config for the built-in module system option _module.args since b9756b4.

Steps To Reproduce

Steps to reproduce the behavior:

1. Create minimal example:

# generate-doc.nix
with import <nixpkgs> {};
  {}: let
    eval = lib.evalModules {
      specialArgs = {inherit pkgs;};
      modules = [(_: {_module.check = false;})];
    };
    optionsDoc = nixosOptionsDoc {
      inherit (eval) options;
    };
  in
    runCommand "options-doc.md" {} ''
      cat ${optionsDoc.optionsCommonMark} > $out
    ''

2. Run nix-build generate-doc.nix
3. Observe that result contains a chapter about _module.args

Expected behavior

An empty result, like prior to b9756b4.

Alternatively documentation at nixosOptionsDoc about how to disable generating documentation for built-in options.

Additional context

I wonder what is the best way of hiding the built-in module system options from docs.

Ways I came up with:

User filters the eval result

  eval = lib.evalModules {
    specialArgs = {inherit pkgs;};
    modules = [ (_: {_module.check = false;}) ];
  };

  cleanEval = lib.filterAttrsRecursive (n: v: n != "_module") eval;

User makes _module.args internal

# my-module.nix
{ ... }: {
  options._module.args = lib.mkOption {
    internal = true;
  };
  ...
}

Extend nixosOptionsDoc with a filter

See #293494

Notify maintainers

@asymmetric @ryantm

Metadata

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.1.79, NixOS, 24.05 (Uakari), 24.05pre-git`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.18.1`
 - channels(root): `"home-manager, nixos"`
 - channels(istobic): `""`
 - nixpkgs: `/home/istobic/.nix-defexpr/channels/nixpkgs`

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