panel-force-quit: Error if used when X11 is disabled

mate-panel/panel-force-quit.c

@@ -24,6 +24,10 @@
 
 #include <config.h>
 
+#ifndef HAVE_X11
+#error file should only be built when HAVE_X11 is enabled
+#endif
+
 #include "panel-force-quit.h"
 
 #include <glib/gi18n.h>
@@ -335,6 +339,8 @@ panel_force_quit (GdkScreen *screen,
 	GdkDisplay    *display;
 	GdkSeat       *seat;
 
+	g_return_if_fail (GDK_IS_X11_DISPLAY (gdk_screen_get_display (screen)));
+
 	popup = display_popup_window (screen);
 
 	root = gdk_screen_get_root_window (screen);

mate-panel/panel-force-quit.h

@@ -25,6 +25,12 @@
 #ifndef __PANEL_FORCE_QUIT_H__
 #define __PANEL_FORCE_QUIT_H__
 
+#ifdef PACKAGE_NAME // only check HAVE_X11 if config.h has been included
+#ifndef HAVE_X11
+#error file should only be included when HAVE_X11 is enabled
+#endif
+#endif
+
 #include <gdk/gdk.h>
 
 #ifdef __cplusplus