error[E0119]: conflicting implementations of trait `Trait<Bar, _>`
  --> $DIR/issue-84660-unsoundness.rs:23:1
   |
LL | impl<In, Out> Trait<Bar, In> for Out {
   | ------------------------------------ first implementation here
...
LL | impl<In, Out> Trait<(), In> for Out {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation

error: aborting due to previous error

For more information about this error, try `rustc --explain E0119`.