--- /dev/null
+error: `extern` block uses type `impl Baz`, which is not FFI-safe
+ --> $DIR/lint-ctypes-73251-1.rs:24:25
+ |
+LL | pub fn lint_me() -> <u32 as Foo>::Assoc;
+ | ^^^^^^^^^^^^^^^^^^^ not FFI-safe
+ |
+note: the lint level is defined here
+ --> $DIR/lint-ctypes-73251-1.rs:5:9
+ |
+LL | #![deny(improper_ctypes)]
+ | ^^^^^^^^^^^^^^^
+ = note: opaque types have no C equivalent
+
+error: aborting due to previous error
+