Rust -- violation of Rust's safety guarantees

Sean McArthur reports:

    The Rust Programming Language Standard Library 1.34.x
    before 1.34.2 contains a stabilized method which, if
    overridden, can violate Rust's safety guarantees and
    cause memory unsafety.  If the Error::type_id method
    is overridden then any type can be safely cast to any
    other type, causing memory safety vulnerabilities in
    safe code (e.g., out-of-bounds write or read).  Code
    that does not manually implement Error::type_id is
    unaffected.