error[E0119]: conflicting implementations of trait `Foo` for type `&_` --> $DIR/feature-gate-with_negative_coherence.rs:5:1 | LL | impl<T: std::ops::DerefMut> Foo for T { } | ------------------------------------- first implementation here LL | LL | impl<T> Foo for &T { } | ^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_` error: aborting due to previous error For more information about this error, try `rustc --explain E0119`.