Subtyping structs from untyped code is unsound

[lexi-lambda]

This program segfaults:

#lang racket

(module untyped racket
  (provide (struct-out foo))
  (struct foo (value)))

(module typed typed/racket
  (require/typed
   (submod ".." untyped)
   [#:struct foo ([value : (-> (List Integer) Integer)])])
  (provide the-bar)
  (struct bar foo ())
  (define the-bar (bar (λ (lst) (car lst)))))

(require 'untyped
         'typed)

((foo-value the-bar) #f)

The the-bar export appears to escape with an any/c contract, since TR believes it has proved the relevant obligations, but as the program demonstrates, that just isn’t true.

[samth]

Looks like the import of struct:foo needs a contract, and chaperone-struct-type seems sufficient to write this, but there's no general struct-type/c and the one in TR is very restrictive.