Merge #5061: add xwayland

Also resolve minor nitpicks -- *during* the merge commit.

pkgs/applications/window-managers/weston/default.nix

@@ -1,7 +1,8 @@
 { stdenv, fetchurl, pkgconfig, wayland, mesa, libxkbcommon, cairo, libxcb
 , libXcursor, x11, udev, libdrm, mtdev, libjpeg, pam, dbus, libinput
 , pango ? null, libunwind ? null, freerdp ? null, vaapi ? null, libva ? null
-, libwebp ? null
+, libwebp ? null, xwayland ? null
+# beware of null defaults, as the parameters *are* supplied by callPackage by default
 }:
 
 let version = "1.6.0"; in
@@ -21,7 +22,6 @@ stdenv.mkDerivation rec {
   ];
 
   configureFlags = [
-    "--enable-xwayland"
     "--enable-x11-compositor"
     "--enable-drm-compositor"
     "--enable-wayland-compositor"
@@ -32,7 +32,11 @@ stdenv.mkDerivation rec {
     "--enable-weston-launch"
     "--disable-setuid-install" # prevent install target to chown root weston-launch, which fails
   ] ++ stdenv.lib.optional (freerdp != null) "--enable-rdp-compositor"
-    ++ stdenv.lib.optional (vaapi != null) "--enabe-vaapi-recorder";
+    ++ stdenv.lib.optional (vaapi != null) "--enabe-vaapi-recorder"
+    ++ stdenv.lib.optionals (xwayland != null) [
+        "--enable-xwayland"
+        "--with-xserver-path=${xwayland}/bin/Xwayland"
+      ];
 
   meta = with stdenv.lib; {
     description = "Reference implementation of a Wayland compositor";