nixos GDM: fix #19896

- As noted on github, GDM needs different parameters for X.
- Making xserverArgs a true list instead of concat-string helps to
  filter it and it feels more correct anyway.
- Tested: gdm+gnome, lightdm+gnome.  There seems to be no logout option
  in gnome, and gdm doesn't offer other sessions, but maybe these are normal.

nixos/modules/services/x11/display-managers/default.nix

@@ -187,7 +187,6 @@ in
         default = [];
         example = [ "-ac" "-logverbose" "-verbose" "-nolisten tcp" ];
         description = "List of arguments for the X server.";
-        apply = toString;
       };
 
       sessionCommands = mkOption {

nixos/modules/services/x11/display-managers/gdm.nix

@@ -92,10 +92,15 @@ in
 
     users.extraGroups.gdm.gid = config.ids.gids.gdm;
 
+    # GDM needs different xserverArgs, presumable because using wayland by default.
+    services.xserver.tty = null;
+    services.xserver.display = null;
+
     services.xserver.displayManager.job =
       {
         environment = {
-          GDM_X_SERVER_EXTRA_ARGS = "${cfg.xserverArgs}";
+          GDM_X_SERVER_EXTRA_ARGS = toString
+            (filter (arg: arg != "-terminate") cfg.xserverArgs);
           GDM_SESSIONS_DIR = "${cfg.session.desktops}";
           # Find the mouse
           XCURSOR_PATH = "~/.icons:${config.system.path}/share/icons";

nixos/modules/services/x11/display-managers/kdm.nix

@@ -25,7 +25,7 @@ let
       FailsafeClient=${pkgs.xterm}/bin/xterm
 
       [X-:*-Core]
-      ServerCmd=${dmcfg.xserverBin} ${dmcfg.xserverArgs}
+      ServerCmd=${dmcfg.xserverBin} ${toString dmcfg.xserverArgs}
       # KDM calls `rm' somewhere to clean up some temporary directory.
       SystemPath=${pkgs.coreutils}/bin
       # The default timeout (15) is too short in a heavily loaded boot process.

nixos/modules/services/x11/display-managers/lightdm.nix

@@ -23,7 +23,7 @@ let
       else additionalArgs="-logfile /var/log/X.$display.log"
       fi
 
-      exec ${dmcfg.xserverBin} ${dmcfg.xserverArgs} $additionalArgs "$@"
+      exec ${dmcfg.xserverBin} ${toString dmcfg.xserverArgs} $additionalArgs "$@"
     '';
 
   usersConf = writeText "users.conf"

nixos/modules/services/x11/display-managers/sddm.nix

@@ -14,7 +14,7 @@ let
   xserverWrapper = pkgs.writeScript "xserver-wrapper" ''
     #!/bin/sh
     ${concatMapStrings (n: "export ${n}=\"${getAttr n xEnv}\"\n") (attrNames xEnv)}
-    exec systemd-cat ${dmcfg.xserverBin} ${dmcfg.xserverArgs} "$@"
+    exec systemd-cat ${dmcfg.xserverBin} ${toString dmcfg.xserverArgs} "$@"
   '';
 
   Xsetup = pkgs.writeScript "Xsetup" ''

nixos/modules/services/x11/display-managers/slim.nix

@@ -12,7 +12,7 @@ let
     ''
       xauth_path ${dmcfg.xauthBin}
       default_xserver ${dmcfg.xserverBin}
-      xserver_arguments ${dmcfg.xserverArgs}
+      xserver_arguments ${toString dmcfg.xserverArgs}
       sessiondir ${dmcfg.session.desktops}
       login_cmd exec ${pkgs.stdenv.shell} ${dmcfg.session.script} "%session"
       halt_cmd ${config.systemd.package}/sbin/shutdown -h now