error[E0277]: `std::marker::PhantomPinned` cannot be unpinned
   --> $DIR/trivial_bounds-bug.rs:13:43
    |
13  |     impl Unpin for A where PhantomPinned: Unpin {} //~ ERROR E0277
    |                                           ^^^^^ the trait `std::marker::Unpin` is not implemented for `std::marker::PhantomPinned`
    |
   ::: /Users/taiki/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/src/libcore/marker.rs:736:1
    |
736 | pub auto trait Unpin {}
    | -------------------- required by this bound in `std::marker::Unpin`