Revert "Revert "services.xserver: assert that either desktop- or window manager is not "none"""

This reverts commit e64dc2543458b52abcd913bad87851f5d7db435d.

2 files changed, 14 insertions, 2 deletions

diff --git a/nixos/modules/services/x11/desktop-managers/default.nix b/nixos/modules/services/x11/desktop-managers/default.nix
index 13f339e3fbf3..b393167ae2c6 100644
--- a/nixos/modules/services/x11/desktop-managers/default.nix
+++ b/nixos/modules/services/x11/desktop-managers/default.nix
@@ -87,8 +87,8 @@ in
 
       default = mkOption {
         type = types.str;
-        default = "";
-        example = "none";
+        default = "none";
+        example = "plasma5";
         description = "Default desktop manager loaded if none have been chosen.";
         apply = defaultDM:
           if defaultDM == "" && cfg.session.list != [] then
diff --git a/nixos/modules/services/x11/xserver.nix b/nixos/modules/services/x11/xserver.nix
index d4fe475690ce..58dc75bcb4e6 100644
--- a/nixos/modules/services/x11/xserver.nix
+++ b/nixos/modules/services/x11/xserver.nix
@@ -161,6 +161,15 @@ in
         '';
       };
 
+      plainX = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Whether the X11 session can be plain (without DM/WM) and
+          the Xsession script will be used as fallback or not.
+        '';
+      };
+
       autorun = mkOption {
         type = types.bool;
         default = true;
@@ -552,6 +561,9 @@ in
                 + "${toString (length primaryHeads)} heads set to primary: "
                 + concatMapStringsSep ", " (x: x.output) primaryHeads;
       })
+      { assertion = cfg.desktopManager.default == "none" && cfg.windowManager.default == "none" -> cfg.plainX;
+        message = "Either the desktop manager or the window manager shouldn't be `none`! To explicitly allow this, you can also set `services.xserver.plainX` to `true`.";
+      }
     ];
 
     environment.etc =