https://doc.rust-lang.org/std/boxed/struct.Box.html#method.into_raw
The pointer will be properly aligned and non-null.
Sometimes we take its return value for use in a NonNull. But NonNull::new returns an Option which needs an extra unwrap. I'm against unwrap in general, and in this example, it's like we are converting NonNull to * mut to NonNull itself. Is there any consideration against returning NonNull for functions like Box::into_raw that we know return a non-null pointer?
The only thing I can think of is NonNull is covariant while * mut is invariant. This raises a related question whether NonNull is losing orthogonality by combining non-null and covariance in one data structure. Is there a need for something like RawNonNull which only exhibits non-null and nothing else?