std::fmt::Pointer should be implemented for pointers to T: ?Sized

[benw]

Example:

fn main() {
    let x: Box<std::fmt::Debug> = Box::new("hello");
    println!("{:p}", x);
    // error: the trait `core::marker::Sized` is not implemented for the type `core::fmt::Debug`
}

I think Pointer should be impled as follows:

impl<T: ?Sized> Pointer for Box<T>

and likewise for borrowed refs, raw pointers, Arc etc.

[sfackler]

Boxed trait objects contain two pointers - one to the object and the other to the vtable. Should only one be printed?

[benw]

Oh, that is a very good point, thanks. This is not nearly as obvious as I thought. I was assuming that the data pointer would be printed, but if you see any possible downside to implementing that, then I'll be entirely satisfied with transmuting to TraitObject and printing the data field for myself.

[bluss]

Considering trait pointers can be cast to thin pointers, whatever pointer that yields is the one.

[durka]

This was fixed by #31479.