error: #[pin_project] attribute may not be used on structs with zero fields
  --> tests/ui/cfg/unsupported.rs:6:10
   |
6  |   struct S {
   |  __________^
7  | |     //~^ ERROR may not be used on structs with zero fields
8  | |     #[cfg(any())]
9  | |     #[pin]
10 | |     f: u8,
11 | | }
   | |_^