fix [allow_undo] in menu event commands

This was disabled in a previous commit

src/actions/undo.cpp

@@ -162,6 +162,14 @@ void undo_list::add_auto_shroud(bool turned_on)
 	add(new undo::auto_shroud_action(turned_on));
 }
 
+void undo_list::add_dummy()
+{
+	/// @todo: Consecutive shroud actions can be collapsed into one.
+
+	// Do not call add(), as this should not clear the redo stack.
+	add(new undo_dummy_action());
+}
+
 /**
  * Adds a dismissal to the undo stack.
  */

src/actions/undo.hpp

@@ -51,6 +51,8 @@ public:
 
 	/// Adds an auto-shroud toggle to the undo stack.
 	void add_auto_shroud(bool turned_on);
+	/// Adds an auto-shroud toggle to the undo stack.
+	void add_dummy();
 	/// Adds a dismissal to the undo stack.
 	void add_dismissal(const unit_const_ptr u);
 	/// Adds a move to the undo stack.

src/actions/undo_action.hpp

@@ -74,4 +74,30 @@ namespace actions {
 
 		int unit_id_diff;
 	};
+
+	/// entry for player actions that do not need any special code to be performed when undoing such as right-click menu items.
+	struct undo_dummy_action : undo_action
+	{
+		undo_dummy_action ()
+			: undo_action()
+		{
+		}
+		explicit undo_dummy_action (const config & cfg)
+			: undo_action(cfg)
+		{
+		}
+		virtual const char* get_type() const { return "dummy"; }
+		virtual ~undo_dummy_action () {};
+		/// Undoes this action.
+		virtual bool undo(int side)
+		{
+			return true;
+		}
+		/// Redoes this action.
+		virtual bool redo(int side)
+		{
+			return true;
+		}
+	};
+
 }

src/synced_commands.cpp

@@ -318,7 +318,7 @@ SYNCED_COMMAND_HANDLER_FUNCTION(move, child,  use_undo, show, error_handler)
 	return true;
 }
 
-SYNCED_COMMAND_HANDLER_FUNCTION(fire_event, child,  /*use_undo*/, /*show*/, /*error_handler*/)
+SYNCED_COMMAND_HANDLER_FUNCTION(fire_event, child,  use_undo, /*show*/, /*error_handler*/)
 {
 	bool undoable = true;
 
@@ -333,9 +333,15 @@ SYNCED_COMMAND_HANDLER_FUNCTION(fire_event, child,  /*use_undo*/, /*show*/, /*er
 	} else {
 		undoable = undoable & !resources::game_events->pump().fire(event_name);
 	}
+
 	// Not clearing the undo stack here casues OOS because we added an entry to the replay but no entry to the undo stack.
-	// if ( !undoable)
-		resources::undo_stack->clear();
+	if(use_undo) {
+		if(!undoable) {
+			resources::undo_stack->clear();
+		} else {
+			resources::undo_stack->add_dummy();
+		}
+	}
 	return true;
 }