A longstanding soundness issue of interpreting a user input type T as
bytes... This goes back to 0.2 at least where we have the following trait:

pub trait ComponentBytes<T> {
  fn as_slice(&self) -> &[T];
  fn as_mut_slice(&mut self) -> &mut [T];

  // Provides: does this obvious transmutation cast of `as_slice` result.
  fn as_bytes(&self) -> &[u8] { ... }
}

This is so unsound, the user can even return an wrong slice of an arbitrary
and just let this trait do the dirty work of inspecting its bytes.

In a more recent version we're allowed to even write into that byte slice!
Let us create null references, invalid enums, whatever your heart desires.