"Infinite recursion encountered" by making module configurable

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I’ve been changing my NixOS config to parameterize my config modules using options declarations. This has been working fine, except for my XServer config. The below is a minimal version of the offending module:

{ config, pkgs, lib, ... }:

with lib;
{
  options.os.xorg = {
    enable = pkgs.lib.mkOption {
      default = false;
      type = types.bool;
    };
  };

  config = mkIf config.os.xorg.enable {
    services.xserver = {
      enable = true;

      displayManager.lightdm = {
        enable = true;
        greeters.enso = {
          enable = true;
          blur = true;
        };
      };

      displayManager.defaultSession = "xsession";
      displayManager.session = [
        {
          manage = "desktop";
          name = "xsession";
          start = ''exec $HOME/.xsession'';
        }
      ];
    };
  };
}

When I include that module from my NixOS config, and set os.xorg.enable = true; from another module, I get the following error when I sudo nixos-rebuild test --flake '.':

error: infinite recursion encountered

       at /nix/store/kmy3yfc596gvfm5lkxzbq37kxizdj78r-source/lib/types.nix:461:58:

          460|         # Push down position info.
          461|         (map (def: mapAttrs (n: v: { inherit (def) file; value = v; }) def.value) defs);
             |                                                          ^
          462|       emptyValue = { value = {}; };

--show-trace does not seem to produce any useful results; I can attach those if wanted.

If I comment out enable = true and the LightDM config block, it seems to move forwards. Similarly, if I comment out the options block, the config = mkIf ... line, and the corresponding ending curly brace, it works fine.

Expected outcome

I’d expect to be able to parameterize this module, like I’ve done with others.

Other information

  • NixOS 22.05
  • Nix v2.8.1
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