error[E0751]: found both positive and negative implementation of trait `std::ops::DerefMut` for type `&MyType<'_>`: --> $DIR/pin-unsound-issue-66544-derefmut.rs:12:1 | LL | impl<'a> DerefMut for &'a MyType<'a> { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ positive implementation here | = note: negative implementation in crate `core` error: aborting due to previous error For more information about this error, try `rustc --explain E0751`.