error[E0200]: the trait `Bar` requires an `unsafe impl` declaration --> $DIR/E0200.rs:5:1 | LL | impl Bar for Foo { } | ^^^^^^^^^^^^^^^^ | = note: the trait `Bar` enforces invariants that the compiler can't check. Review the trait documentation and make sure this implementation upholds those invariants before adding the `unsafe` keyword help: add `unsafe` to this trait implementation | LL | unsafe impl Bar for Foo { } | ++++++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0200`.