Warning.categories

static VALUE
rb_warning_s_categories(VALUE mod)
{
    st_index_t num = warning_categories.id2enum->num_entries;
    ID *ids = ALLOCA_N(ID, num);
    num = st_keys(warning_categories.id2enum, ids, num);
    VALUE ary = rb_ary_new_capa(num);
    for (st_index_t i = 0; i < num; ++i) {
        rb_ary_push(ary, ID2SYM(ids[i]));
    }
    return rb_ary_freeze(ary);
}