First of all, you need some space character in string to use autowrap.
SuperLabel.gd
extends Label
func _ready():
connect("item_rect_changed", self, "on_item_rect_changed")
func on_item_rect_changed():
set_custom_minimum_size(Vector2(0, (get_line_height()+get_constant("line_spacing")) * get_line_count()))
Root.gd
LabelContainer.get_children()[1].set_text("AABCAB CABCA BCABC ABCABC ....")