error[E0119]: conflicting implementations of trait `Overlap` for type `Box<_>`
  --> $DIR/ambiguity-causes-visitor-hang.rs:53:1
   |
LL | impl<T: RecursiveSuper> Overlap for T {}
   | ------------------------------------- first implementation here
LL | impl<T> Overlap for Box<T> {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<_>`
   |
   = note: downstream crates may implement trait `Super` for type `std::boxed::Box<_>`
   = note: downstream crates may implement trait `RecursiveSuper` for type `std::boxed::Box<_>`

error: aborting due to 1 previous error

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