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.

[source]