error[E0119]: conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>, _)`
  --> $DIR/normalize-for-errors.rs:16:1
   |
LL | impl<T: Copy, S: Iterator> MyTrait<S> for (T, S::Item) {}
   | ------------------------------------------------------ first implementation here
LL |
LL | impl<S: Iterator> MyTrait<S> for (Box<<(MyType,) as Mirror>::Assoc>, S::Item) {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(Box<(MyType,)>, _)`
   |
   = note: upstream crates may add a new impl of trait `std::marker::Copy` for type `std::boxed::Box<(MyType,)>` in future versions

error: aborting due to 1 previous error

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