While this sounds contra-intuitive, there are std/core-library functions where I can/have to assume that they are correct and won't panic (e.g. str::from_utf8). However since the compiler is unable to prove for some functions that they are panic-free, I cannot use them.

Is there a way to "trust" such a function that it will never panic? Since due to the huge amounts of unsafe code in std/core, I have to rely on their correctness anyway; so it would make no difference for my crate's correctness assumptions…