1 error: `extern` block uses type `impl Fn<()>`, which is not FFI-safe
2 --> $DIR/opaque-ty-ffi-unsafe.rs:14:17
7 note: the lint level is defined here
8 --> $DIR/opaque-ty-ffi-unsafe.rs:5:9
10 LL | #![deny(improper_ctypes)]
12 = note: opaque types have no C equivalent
14 error: aborting due to previous error