Conditional Configuration

With options it’s easy to conditionally install something based on if another program is enabled in your configuration.

Hyprland Module

For example, if I have an option to enable or disable hyprland like this:

# hyprland.nix
{
  pkgs,
  lib,
  config,
  inputs,
  ...
}: let
  cfg = config.custom.hyprland;
in {
  options.custom.hyprland = {
    enable = lib.mkOption {
      type = lib.types.bool;
      default = false;
      description = "Enable hyprland module";
    };
  };
   config = lib.mkIf cfg.enable {
    home.packages = with pkgs; [
      # swww
      grim
      slurp
      wl-clipboard-rs
      cliphist
      swappy
      ydotool
      wpaperd
      wofi
      hyprpicker
      pavucontrol
      blueman
      # lxqt.lxqt-policykit
      brightnessctl
      polkit_gnome
      wlr-randr
      wtype
      rose-pine-cursor
      # nwg-look
      # yad
      # gtk-engine-murrine
    ];

# .. snip ..

• Since the above module is set to false, it is necessary to add custom.hyprland.enable = true to my home.nix to have Nix add it to my configuration. And since home.packages is wrapped in config = lib.mkIf cfg.enable Those packages will only be installed if the module is enabled.

• if I used programs.hyprland.enable and added home.packages = [ pkgs.waybar ]; without conditionals, waybar would install even if hyprland was disabled.

Wlogout Module

I can then have my default for something like wlogout be to install only if the custom.hyprland module is enabled:

# wlogout.nix
{
  config,
  lib,
  ...
}: let
  cfg = config.custom.wlogout;
in {
  options.custom.wlogout = {
    enable = lib.mkOption {
      type = lib.types.bool;
      default = config.custom.hyprland.enable;
      description = "Enable wlogout module";
    };
  };
    config = lib.mkIf cfg.enable {
    programs.wlogout = {
      enable = true;
    }
    }
# .. snip ..

• The default value of config.custom.wlogout.enable is set to config.custom.hyprland.enable. Therefore, if config.custom.hyprland.enable evaluates to true, the wlogout module will be enabled by default.

Benefits of this Approach

The lib.mkIf cfg.enable ensures that wlogout’s configuration (e.g., enabling programs.wlogout) is only applied when custom.wlogout.enable = true, which defaults to custom.hyprland.enable. This means wlogout is enabled by default only if Hyprland is enabled, but I can override this (e.g., custom.wlogout.enable = true without Hyprland). This conditional logic prevents wlogout from being installed unnecessarily when Hyprland is disabled, unlike a simpler approach like programs.wlogout. enable = config.programs.hyprland.enable, which hardcodes the dependency and offers less flexibility.