error: `extern` fn uses type `Option<&T>`, which is not FFI-safe
  --> $DIR/lint-ctypes-option-nonnull-unsized.rs:3:45
   |
LL | extern "C" fn foo<T: ?Sized + 'static>() -> Option<&'static T> {
   |                                             ^^^^^^^^^^^^^^^^^^ not FFI-safe
   |
   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
   = note: enum has no representation hint
note: the lint level is defined here
  --> $DIR/lint-ctypes-option-nonnull-unsized.rs:1:9
   |
LL | #![deny(improper_ctypes_definitions)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error