modules: system: nix: make it configurable

modules/system/nix.nix

@@ -1,10 +1,28 @@
 # Nix related settings
-{ inputs, pkgs, ... }:
-
+{ config, inputs, lib, pkgs, ... }:
+let
+  cfg = config.my.system.nix;
+in
 {
+  options.my.system.nix = with lib; {
+    enable = my.mkDisableOption "nix configuration";
+
+    addToRegistry = my.mkDisableOption "add inputs and self to registry";
+  };
+
+  config = lib.mkIf cfg.enable (lib.mkMerge [
+    {
       nix = {
         package = pkgs.nixFlakes;
-    registry = {
+
+        extraOptions = ''
+          experimental-features = nix-command flakes
+        '';
+      };
+    }
+
+    (lib.mkIf cfg.addToRegistry {
+      nix.registry = {
         # Allow me to use my custom package using `nix run self#pkg`
         self.flake = inputs.self;
         # Use pinned nixpkgs when using `nix run pkgs#<whatever>`
@@ -12,8 +30,6 @@
         # Add NUR to run some packages that are only present there
         nur.flake = inputs.nur;
       };
-    extraOptions = ''
-      experimental-features = nix-command flakes
-    '';
-  };
+    })
+  ]);
 }