if I declare an ActionEntry array as:

  const ActionEntry[] entries = {
    { "Open", Gtk.STOCK_OPEN, "Open files", (GLib.Callback) on_open, "<control>O" },
    ...
  };

and on_open is:

  [Callback]
  void on_open (Gtk.Action action) {
    ...
  }

the "on_open" callback is correctly translated to namespace_class_on_open, but since it's private it will not be declared before the entries array, thus producing a warning.