error: #[pin_project] attribute may not be used on structs with zero fields
 --> $DIR/unsupported.rs:4:1
  |
4 | / struct S {
5 | |     //~^ ERROR may not be used on structs with zero fields
6 | |     #[cfg(any())]
7 | |     #[pin]
8 | |     f: u8,
9 | | }
  | |_^