An unsafe trait was implemented without an unsafe implementation.
Erroneous code example:
struct Foo;
unsafe trait Bar { }
impl Bar for Foo { } // error!
Unsafe traits must have unsafe implementations. This error occurs when an implementation for an unsafe trait isn't marked as unsafe. This may be resolved by marking the unsafe implementation as unsafe.
struct Foo;
unsafe trait Bar { }
unsafe impl Bar for Foo { } // ok!