error: `extern` fn uses type `[u8]`, which is not FFI-safe
  --> $DIR/extern-C-fnptr-lints-slices.rs:5:14
   |
LL | pub type F = extern "C" fn(&[u8]);
   |              ^^^^^^^^^^^^^^^^^^^^ not FFI-safe
   |
   = help: consider using a raw pointer instead
   = note: slices have no C equivalent
note: the lint level is defined here
  --> $DIR/extern-C-fnptr-lints-slices.rs:1:8
   |
LL | #[deny(improper_ctypes_definitions)]
   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error