Make docker optional

machines/nunotaba/configuration.nix

@@ -9,6 +9,7 @@
 
   sbruder = {
     cpu.intel.enable = true;
+    docker.enable = true;
     games.enable = true;
     gpu.intel.enable = true;
     gui.enable = true;

machines/sayuri/configuration.nix

@@ -9,6 +9,7 @@
 
   sbruder = {
     cpu.intel.enable = true;
+    docker.enable = true;
     games.enable = true;
     gpu.amd.enable = true;
     gui.enable = true;

modules/docker.nix

@@ -1,6 +1,12 @@
-{ config, pkgs, ... }:
+{ config, lib, pkgs, ... }:
 
 {
+  # This uses a custom option (instead of `virtualisation.docker.enable`) since
+  # `virtualisation.oci-containers` conditionally sets
+  # `virtualisation.docker.enable` and therefore causes an infinite recursion.
+  options.sbruder.docker.enable = lib.mkEnableOption "docker with ipv6nat";
+
+  config = lib.mkIf config.sbruder.docker.enable {
     environment.systemPackages = with pkgs; [
       docker-compose
       docker-credential-helpers
@@ -33,4 +39,5 @@
     };
 
     environment.etc."modules-load.d/ipv6nat.conf".text = "ip6_tables\n";
+  };
 }