Recursive function causes undefined behavior in release mode

[Mokuzzai]

In latest rust stable, nightly and beta (tried this in playground) this code causes undefined behavior.

// danger!
fn never() -> String {
    never()
}

fn main() {
    let v = never();
    
    println!("{:?}", v);
}

In debug mode this simply causes a stack overflow, but with optimization on it returns an uninitialized value.

[jonas-schievink]

Duplicate of #28728