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

nixos/doc/manual/configuration/profiles/perlless.section.md

@@ -1,11 +1,5 @@
 # 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".

nixos/doc/manual/release-notes/rl-2411.section.md

@@ -34,6 +34,10 @@
   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).

nixos/modules/profiles/perlless.nix

@@ -2,13 +2,6 @@
 
 {
 
-  # 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;

nixos/modules/system/activation/switchable-system.nix

@@ -4,14 +4,6 @@ let
 
   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
 
 {
@@ -20,7 +12,11 @@ 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.
@@ -29,23 +25,17 @@ in
 
     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 \

nixos/tests/switch-test.nix

@@ -48,10 +48,7 @@ in {
 
   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;