services.xserver: fix `apply` of default DM/WM

This is needed to pick the first enabled DM/WM
if the default is `none`

1 files changed, 3 insertions, 1 deletions

diff --git a/nixos/modules/services/x11/xserver.nix b/nixos/modules/services/x11/xserver.nix
index 58dc75bcb4e6..7d544e153e9a 100644
--- a/nixos/modules/services/x11/xserver.nix
+++ b/nixos/modules/services/x11/xserver.nix
@@ -562,7 +562,9 @@ in
                 + 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`.";
+        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`. "
+                + "The `default` value looks for enabled WMs/DMs and select the first one.";
       }
     ];