error: `extern` fn uses type `NotSafe`, which is not FFI-safe
  --> $DIR/lint-ctypes-113436-1.rs:22:22
   |
LL | extern "C" fn bar(x: Bar) -> Bar {
   |                      ^^^ not FFI-safe
   |
   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
   = note: this struct has unspecified layout
note: the type is defined here
  --> $DIR/lint-ctypes-113436-1.rs:13:1
   |
LL | struct NotSafe(u32);
   | ^^^^^^^^^^^^^^
note: the lint level is defined here
  --> $DIR/lint-ctypes-113436-1.rs:1:9
   |
LL | #![deny(improper_ctypes_definitions)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: `extern` fn uses type `NotSafe`, which is not FFI-safe
  --> $DIR/lint-ctypes-113436-1.rs:22:30
   |
LL | extern "C" fn bar(x: Bar) -> Bar {
   |                              ^^^ not FFI-safe
   |
   = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
   = note: this struct has unspecified layout
note: the type is defined here
  --> $DIR/lint-ctypes-113436-1.rs:13:1
   |
LL | struct NotSafe(u32);
   | ^^^^^^^^^^^^^^

error: aborting due to 2 previous errors