error[E0119]: conflicting implementations of trait `Overlap<<Overflow as Trait>::Assoc<Overflow>, _>` for type `Overflow`
  --> $DIR/unproductive-in-coherence.rs:18:1
   |
LL | impl<T: Trait, U: Copy> Overlap<T::Assoc<T>, U> for T {}
   | ----------------------------------------------------- first implementation here
LL | impl<U> Overlap<u32, U> for Overflow {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Overflow`

error: aborting due to 1 previous error

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