src/Tools/jEdit/src/plugin.scala

 object PIDE
 {
   /* plugin instance */
 
   val options = new JEdit_Options
+  val completion_history = new Completion.History_Variable
 
   @volatile var startup_failure: Option[Throwable] = None
   @volatile var startup_notified = false
 
   @volatile var plugin: Plugin = null

       Isabelle_System.init()
       Isabelle_Font.install_fonts()
 
       val init_options = Options.init()
       Swing_Thread.now { PIDE.options.update(init_options)  }
+      PIDE.completion_history.load()
 
       if (Platform.is_macos && PIDE.options.bool("jedit_mac_adapter"))
         OSX_Adapter.set_quit_handler(this, this.getClass.getDeclaredMethod("handle_quit"))
 
       SyntaxUtilities.setStyleExtender(new Token_Markup.Style_Extender)

 
   override def stop()
   {
     JEdit_Lib.jedit_text_areas.foreach(Completion_Popup.Text_Area.exit _)
 
-    if (PIDE.startup_failure.isEmpty)
+    if (PIDE.startup_failure.isEmpty) {
       PIDE.options.value.save_prefs()
+      PIDE.completion_history.value.save()
+    }
 
     PIDE.session.phase_changed -= session_manager
     PIDE.exit_models(JEdit_Lib.jedit_buffers().toList)
     PIDE.session.stop()
   }