`NonNull` vs `*const` in Repr

[overlookmotel]

This is a question more than a bug report, but just asking in case it reveals something more useful...

• Repr's 1st field is a *const ().
• HeapBuffer's 1st field is a ptr::NonNull<u8>.
• StaticStr's 1st field is a ptr::NonNull<u8>.

HeapBuffer and StaticStr are both transmuted to Repr.

Is there a benefit to HeapBuffer and StaticStr using NonNull<u8> rather than *const? Does it matter that a value with a niche is transmuted to one without?

Second smaller question: Why *const () in Repr instead of *const u8? Only place which accesses this field seems to be as_slice, where it's immediately cast to *const u8. Probably it makes no difference to codegen, but I'm wondering if there's a subtlety I'm missing.