eval.c:1715
static VALUE
rb_mod_nesting()
{
    NODE *cbase = ruby_cref;
    VALUE ary = rb_ary_new();

    while (cbase && cbase->nd_next) {
	if (!NIL_P(cbase->nd_clss)) rb_ary_push(ary, cbase->nd_clss);
	cbase = cbase->nd_next;
    }
    if (ruby_wrapper && RARRAY(ary)->len == 0) {
	rb_ary_push(ary, ruby_wrapper);
    }
    return ary;
}
