xwayland: set meta.mainProgram

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

···
     (lib.mesonBool "test-junit-xml" false)
     (lib.mesonBool "xwayland" xwaylandSupport)
   ] ++ lib.optionals xwaylandSupport [
-    (lib.mesonOption "xwayland-path" "${xwayland.out}/bin/Xwayland")
+    (lib.mesonOption "xwayland-path" (lib.getExe xwayland))
   ];
 
   passthru.providedSessions = [ "weston" ];

pkgs/desktops/gnome/core/mutter/43/default.nix

···
     "-Dinstalled_tests=false" # TODO: enable these
     "-Dwayland_eglstream=true"
     "-Dprofiler=true"
-    "-Dxwayland_path=${xwayland}/bin/Xwayland"
+    "-Dxwayland_path=${lib.getExe xwayland}"
     # This should be auto detected, but it looks like it manages a false
     # positive.
     "-Dxwayland_initfd=disabled"

pkgs/desktops/gnome/core/mutter/default.nix

···
     "-Dtests=false"
     "-Dwayland_eglstream=true"
     "-Dprofiler=true"
-    "-Dxwayland_path=${xwayland}/bin/Xwayland"
+    "-Dxwayland_path=${lib.getExe xwayland}"
     # This should be auto detected, but it looks like it manages a false
     # positive.
     "-Dxwayland_initfd=disabled"

pkgs/desktops/plasma-5/kwin/default.nix

···
   ];
 
   CXXFLAGS = [
-    ''-DNIXPKGS_XWAYLAND=\"${lib.getBin xwayland}/bin/Xwayland\"''
+    ''-DNIXPKGS_XWAYLAND=\"${lib.getExe xwayland}\"''
   ];
 
   postInstall = ''

pkgs/servers/mir/default.nix

···
 
     # Fix Xwayland default
     substituteInPlace src/miral/x11_support.cpp \
-      --replace '/usr/bin/Xwayland' '${xwayland}/bin/Xwayland'
+      --replace '/usr/bin/Xwayland' '${lib.getExe xwayland}'
 
     # Fix paths for generating drm-formats
     substituteInPlace src/platform/graphics/CMakeLists.txt \

pkgs/servers/x11/xorg/xwayland.nix

···
     description = "An X server for interfacing X11 apps with the Wayland protocol";
     homepage = "https://wayland.freedesktop.org/xserver.html";
     license = licenses.mit;
+    mainProgram = "Xwayland";
     maintainers = with maintainers; [ emantor ];
     platforms = platforms.linux;
   };