(module borrow_return_reject

  (data Box
    (doc "Heap cell holding one Int.")
    (ctor Box (con Int)))

  (fn peek
    (doc "MUST FAIL post-cutover: borrow-return is refcount-invisible and can outlive its source; re-enabling needs the escape axis.")
    (type
      (fn-type
        (params (own (con Box)))
        (ret (borrow (con Box)))))
    (params b)
    (body b)))
