nixos: switch to `switch-to-configuration-ng` by default (#339727)

# Perlless {#sec-perlless}

::: {.warning}

If you enable this profile, you will NOT be able to switch to a new

configuration and thus you will not be able to rebuild your system with

nixos-rebuild!

:::

Render your system completely perlless (i.e. without the perl interpreter). This

includes a mechanism so that your build fails if it contains a Nix store path

that references the string "perl".

  Users that want to keep PulseAudio will want to set `services.pipewire.enable = false;` and `hardware.pulseaudio.enable = true;`.

  There is currently no plan to fully deprecate and remove PulseAudio, however, PipeWire should generally be preferred for new installs.

- The Rust rewrite of the `switch-to-configuration` program is now used for system activation by default.

  If you experience any issues, please report them.

  The original Perl script can still be used for now by setting `system.switch.enableNg` to `false`.

## New Modules {#sec-release-24.11-new-modules}

- [TaskChampion Sync-Server](https://github.com/GothenburgBitFactory/taskchampion-sync-server), a [Taskwariror 3](https://taskwarrior.org/docs/upgrade-3/) sync server, replacing Taskwarrior 2's sync server named [`taskserver`](https://github.com/GothenburgBitFactory/taskserver).

{

  # switch-to-configuration-ng reimplements switch-to-configuration, but

  # without perl.

  system.switch = lib.mkDefault {

    enable = false;

    enableNg = true;

  };

  # Remove perl from activation

  boot.initrd.systemd.enable = lib.mkDefault true;

  system.etc.overlay.enable = lib.mkDefault true;

  perlWrapped = pkgs.perl.withPackages (p: with p; [ ConfigIniFiles FileSlurp ]);

  description = extra: ''

    Whether to include the capability to switch configurations.

    Disabling this makes the system unable to be reconfigured via `nixos-rebuild`.

    ${extra}

  '';

in

{

    enable = lib.mkOption {

      type = lib.types.bool;

      default = true;

      description = description ''

      description = ''

        Whether to include the capability to switch configurations.

        Disabling this makes the system unable to be reconfigured via `nixos-rebuild`.

        This is good for image based appliances where updates are handled

        outside the image. Reducing features makes the image lighter and

        slightly more secure.

    enableNg = lib.mkOption {

      type = lib.types.bool;

      default = false;

      description = description ''

        Whether to use `switch-to-configuration-ng`, an experimental

        re-implementation of `switch-to-configuration` with the goal of

        replacing the original.

      default = config.system.switch.enable;

      defaultText = lib.literalExpression "config.system.switch.enable";

      description = ''

        Whether to use `switch-to-configuration-ng`, the Rust-based

        re-implementation of the original Perl `switch-to-configuration`.

      '';

    };

  };

  config = lib.mkMerge [

    {

      assertions = [{

        assertion = with config.system.switch; enable -> !enableNg;

        message = "Only one of system.switch.enable and system.switch.enableNg may be enabled at a time";

      }];

    }

    (lib.mkIf config.system.switch.enable {

    (lib.mkIf (config.system.switch.enable && !config.system.switch.enableNg) {

      system.activatableSystemBuilderCommands = ''

        mkdir $out/bin

        substitute ${./switch-to-configuration.pl} $out/bin/switch-to-configuration \

  nodes = {

    machine = { pkgs, lib, ... }: {

      system.switch = {

        enable = !ng;

        enableNg = ng;

      };

      system.switch.enableNg = ng;

      environment.systemPackages = [ pkgs.socat ]; # for the socket activation stuff

      users.mutableUsers = false;