error[E0277]: the trait bound `Bar: std::hash::Hash` is not satisfied
  --> $DIR/issue-21160.rs:9:12
   |
LL | struct Foo(Bar);
   |            ^^^ the trait `std::hash::Hash` is not implemented for `Bar`
   | 
  ::: $SRC_DIR/libcore/hash/mod.rs:LL:COL
   |
LL |     fn hash<H: Hasher>(&self, state: &mut H);
   |             - required by this bound in `std::hash::Hash::hash`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.