Unsafe trait implementation for IntoBytes is incorrect (and UB)

[gendx]

The IntoBytes implementation is incorrect, as shown when running this program under Miri. The correct syntax is &raw const *self (which returns a *const Self) rather than &raw const self (which returns a *const &Self).

use std::{mem, slice};

/// ...
/// # Safety
/// The type must have a defined representation and no padding.
pub unsafe trait IntoBytes {
    fn as_bytes(&self) -> &[u8] {
        let len = mem::size_of_val(self);
        unsafe { slice::from_raw_parts((&raw const self).cast::<u8>(), len) }
    }
}

// SAFETY: `u32` has a defined representation and no padding.
unsafe impl IntoBytes for u32 {}

fn main() {
    println!("{:?}", 42.as_bytes());
}

error: Undefined Behavior: out-of-bounds pointer use: alloc811 has been freed, so this pointer is dangling
  --> src/main.rs:17:22
   |
17 |     println!("{:?}", 42.as_bytes());
   |                      ^^^^^^^^^^^^^ out-of-bounds pointer use: alloc811 has been freed, so this pointer is dangling
   |
   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
help: alloc811 was allocated here:
  --> src/main.rs:7:17
   |
7  |     fn as_bytes(&self) -> &[u8] {
   |                 ^^^^^
help: alloc811 was deallocated here:
  --> src/main.rs:10:6
   |
10 |     }
   |      ^
   = note: BACKTRACE (of the first span):
   = note: inside `main` at src/main.rs:17:22: 17:35

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

[djmitche]

While looking, I notice that while we are now using the &raw syntax, we don't introduce it anywhere!

That slide was updated in b4f07ba, and it looks like that introduced the bug.

Do you want to make a PR to fix this? Bonus points for adding a quick introduction to the &raw syntax!