[racket-dev] Triggered a macro system internal error

Hi all,

I accidentally triggered what appears to be an internal error message
from the macro expander (to do with syntax taints).

Unfortunately, I have no idea how to come up with a narrow test case
since it happens due to changing Typed Racket's `struct:` expansion.
I've attached a short patch below that shows what's needed to trigger it
though.

Here's the interaction I get with the patch applied:
  $ racket -I typed/racket
  Welcome to Racket v5.3.900.1.
  -> (struct: Foo ([x : Integer]))
  ; internal error: cannot copy taint armings from tainted source [,bt for
  ;   context]

Any ideas on how I can get a better test case?

Cheers,
Asumu