error[E0277]: `PhantomPinned` cannot be unpinned
  --> $DIR/overlapping_unpin_struct.rs:18:5
   |
15 | fn is_unpin<T: Unpin>() {}
   |                ----- required by this bound in `is_unpin`
...
18 |     is_unpin::<S<PhantomPinned>>(); //~ ERROR E0277
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ within `_::__S<'_, PhantomPinned>`, the trait `Unpin` is not implemented for `PhantomPinned`
   |
   = note: consider using `Box::pin`
note: required because it appears within the type `_::__S<'_, PhantomPinned>`
  --> $DIR/overlapping_unpin_struct.rs:6:8
   |
6  | struct S<T> {
   |        ^
   = note: required because of the requirements on the impl of `Unpin` for `S<PhantomPinned>`