error: `extern` block uses type `A`, which is not FFI-safe
  --> $DIR/issue-14309.rs:30:15
   |
LL |     fn foo(x: A);
   |               ^ not FFI-safe
   |
note: the lint level is defined here
  --> $DIR/issue-14309.rs:1:9
   |
LL | #![deny(improper_ctypes)]
   |         ^^^^^^^^^^^^^^^
   = 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/issue-14309.rs:4:1
   |
LL | struct A {
   | ^^^^^^^^

error: `extern` block uses type `A`, which is not FFI-safe
  --> $DIR/issue-14309.rs:31:15
   |
LL |     fn bar(x: B);
   |               ^ 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/issue-14309.rs:4:1
   |
LL | struct A {
   | ^^^^^^^^

error: `extern` block uses type `A`, which is not FFI-safe
  --> $DIR/issue-14309.rs:33:15
   |
LL |     fn qux(x: A2);
   |               ^^ 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/issue-14309.rs:4:1
   |
LL | struct A {
   | ^^^^^^^^

error: `extern` block uses type `A`, which is not FFI-safe
  --> $DIR/issue-14309.rs:34:16
   |
LL |     fn quux(x: B2);
   |                ^^ 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/issue-14309.rs:4:1
   |
LL | struct A {
   | ^^^^^^^^

error: `extern` block uses type `A`, which is not FFI-safe
  --> $DIR/issue-14309.rs:36:16
   |
LL |     fn fred(x: D);
   |                ^ 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/issue-14309.rs:4:1
   |
LL | struct A {
   | ^^^^^^^^

error: aborting due to 5 previous errors