nixos/modules/options/displayManager.nix

{
  lib,
  ...
}:
with lib;
{
  options.modules.displayManager = {
    displayManager = mkOption {
      type = types.enum [
        "gdm"
        "sddm"
      ];
      default = "sddm";
      description = ''
        The display manager to use.
      '';
    };
  };
}