public ButtonsType buttons { construct; }

The Gtk.ButtonsType value to display a set of buttons in the dialog.

By design, some actions are not acceptable and such action values will not be added to the dialog, these include:

If you wish to provide more specific actions for your dialog pass a Gtk.ButtonsType.NONE to Granite.MessageDialog.MessageDialog and manually add those actions with Gtk.Dialog.add_buttons or Gtk.Dialog.add_action_widget.