nixos/tools: add desktopConfiguration option

We now have a GNOME ISO so it would be nice to seed that one
with configuration on how to enable it.

nixos/modules/installer/tools/nixos-generate-config.pl

@@ -625,6 +625,10 @@ EOF
 
         my $networkingDhcpConfig = generateNetworkingDhcpConfig();
 
+        (my $desktopConfiguration = <<EOF)=~s/^/  /gm;
+@desktopConfiguration@
+EOF
+
         write_file($fn, <<EOF);
 @configuration@
 EOF

nixos/modules/installer/tools/tools.nix

@@ -45,7 +45,7 @@ let
     src = ./nixos-generate-config.pl;
     path = lib.optionals (lib.elem "btrfs" config.boot.supportedFilesystems) [ pkgs.btrfs-progs ];
     perl = "${pkgs.perl}/bin/perl -I${pkgs.perlPackages.FileSlurp}/${pkgs.perl.libPrefix}";
-    inherit (config.system.nixos-generate-config) configuration;
+    inherit (config.system.nixos-generate-config) configuration desktopConfiguration;
   };
 
   nixos-option =
@@ -78,7 +78,8 @@ in
 
 {
 
-  options.system.nixos-generate-config.configuration = mkOption {
+  options.system.nixos-generate-config = {
+    configuration = mkOption {
       internal = true;
       type = types.str;
       description = ''
@@ -94,8 +95,25 @@ in
       '';
     };
 
-  config = {
+    desktopConfiguration = mkOption {
+      internal = true;
+      type = types.str;
+      default = "";
+      description = ''
+        Text to preseed the desktop configuration that <literal>nixos-generate-config</literal>
+        saves to <literal>/etc/nixos/configuration.nix</literal>.
 
+        This is an internal option. No backward compatibility is guaranteed.
+        Use at your own risk!
+
+        Note that this string gets spliced into a Perl script. The perl
+        variable <literal>$bootLoaderConfig</literal> can be used to
+        splice in the boot loader configuration.
+      '';
+    };
+  };
+
+  config = {
     system.nixos-generate-config.configuration = mkDefault ''
       # Edit this configuration file to define what should be installed on
       # your system.  Help is available in the configuration.nix(5) man page
@@ -113,6 +131,9 @@ in
         # networking.hostName = "nixos"; # Define your hostname.
         # networking.wireless.enable = true;  # Enables wireless support via wpa_supplicant.
 
+        # Set your time zone.
+        # time.timeZone = "Europe/Amsterdam";
+
       $networkingDhcpConfig
         # Configure network proxy if necessary
         # networking.proxy.default = "http://user:password\@proxy:port/";
@@ -125,8 +146,26 @@ in
         #   keyMap = "us";
         # };
 
-        # Set your time zone.
-        # time.timeZone = "Europe/Amsterdam";
+      $desktopConfiguration
+        # Configure keymap in X11
+        # services.xserver.layout = "us";
+        # services.xserver.xkbOptions = "eurosign:e";
+
+        # Enable CUPS to print documents.
+        # services.printing.enable = true;
+
+        # Enable sound.
+        # sound.enable = true;
+        # hardware.pulseaudio.enable = true;
+
+        # Enable touchpad support (enabled default in most desktopManager).
+        # services.xserver.libinput.enable = true;
+
+        # Define a user account. Don't forget to set a password with ‘passwd’.
+        # users.users.jane = {
+        #   isNormalUser = true;
+        #   extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
+        # };
 
         # List packages installed in system profile. To search, run:
         # \$ nix search wget
@@ -154,31 +193,6 @@ in
         # Or disable the firewall altogether.
         # networking.firewall.enable = false;
 
-        # Enable CUPS to print documents.
-        # services.printing.enable = true;
-
-        # Enable sound.
-        # sound.enable = true;
-        # hardware.pulseaudio.enable = true;
-
-        # Enable the X11 windowing system.
-        # services.xserver.enable = true;
-        # services.xserver.layout = "us";
-        # services.xserver.xkbOptions = "eurosign:e";
-
-        # Enable touchpad support (enabled default in most desktopManager).
-        # services.xserver.libinput.enable = true;
-
-        # Enable the Plasma 5 Desktop Environment.
-        # services.xserver.displayManager.sddm.enable = true;
-        # services.xserver.desktopManager.plasma5.enable = true;
-
-        # Define a user account. Don't forget to set a password with ‘passwd’.
-        # users.users.jane = {
-        #   isNormalUser = true;
-        #   extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
-        # };
-
         # This value determines the NixOS release from which the default
         # settings for stateful data, like file locations and database versions
         # on your system were taken. It‘s perfectly fine and recommended to leave

nixos/modules/services/x11/desktop-managers/gnome3.nix

@@ -179,6 +179,14 @@ in
 
   config = mkMerge [
     (mkIf (cfg.enable || flashbackEnabled) {
+      # Seed our configuration into nixos-generate-config
+      system.nixos-generate-config.desktopConfiguration = ''
+        # Enable the GNOME 3 Desktop Environment.
+        services.xserver.enable = true;
+        services.xserver.displayManager.gdm.enable = true;
+        services.xserver.desktopManager.gnome3.enable = true;
+      '';
+
       services.gnome3.core-os-services.enable = true;
       services.gnome3.core-shell.enable = true;
       services.gnome3.core-utilities.enable = mkDefault true;

nixos/modules/services/x11/desktop-managers/plasma5.nix

@@ -184,6 +184,14 @@ in
 
   config = mkMerge [
     (mkIf cfg.enable {
+      # Seed our configuration into nixos-generate-config
+      system.nixos-generate-config.desktopConfiguration = ''
+        # Enable the Plasma 5 Desktop Environment.
+        services.xserver.enable = true;
+        services.xserver.displayManager.sddm.enable = true;
+        services.xserver.desktopManager.plasma5.enable = true;
+      '';
+
       services.xserver.desktopManager.session = singleton {
         name = "plasma5";
         bgSupport = true;

nixos/tests/nixos-generate-config.nix

@@ -7,8 +7,16 @@ import ./make-test-python.nix ({ lib, ... } : {
       { config, pkgs, ... }: {
         imports = [ ./hardware-configuration.nix ];
       $bootLoaderConfig
+      $desktopConfiguration
       }
     '';
+
+    system.nixos-generate-config.desktopConfiguration = ''
+      # DESKTOP
+      # services.xserver.enable = true;
+      # services.xserver.displayManager.gdm.enable = true;
+      # services.xserver.desktopManager.gnome3.enable = true;
+    '';
   };
   testScript = ''
     start_all()
@@ -18,9 +26,17 @@ import ./make-test-python.nix ({ lib, ... } : {
     # Test if the configuration really is overridden
     machine.succeed("grep 'OVERRIDDEN' /etc/nixos/configuration.nix")
 
+    # Test if desktop configuration really is overridden
+    machine.succeed("grep 'DESKTOP' /etc/nixos/configuration.nix")
+
     # Test of if the Perl variable $bootLoaderConfig is spliced correctly:
     machine.succeed(
         "grep 'boot\\.loader\\.grub\\.enable = true;' /etc/nixos/configuration.nix"
     )
+
+    # Test if the Perl variable $desktopConfiguration is spliced correctly
+    machine.succeed(
+        "grep 'services\\.xserver\\.desktopManager\\.gnome3\\.enable = true;' /etc/nixos/configuration.nix"
+    )
   '';
 })