`derive(CoercePointee)` accepts `?Sized + Sized`

derive(CoercePointee) checks whether the generic type is ?Sized, and rejects the code if it is not marked as ?Sized. However, making it ?Sized + Sized is still accepted by the macro. That is, the following code compiles:

#![feature(derive_coerce_pointee)]

use std::marker::CoercePointee;

#[derive(CoercePointee)]
#[repr(transparent)]
struct Foo<T: ?Sized + Sized>(*const T);

Is the fact that ?Sized is required effectively just a lint, or is it important for some other reason? Currently, the check doesn't actually enforce anything, and it's possible to accidentally require Sized with something like T: ?Sized + Clone.

Meta

Reproducible on the playground with version 1.93.0-nightly (2025-11-01 bd3ac0330018c23b111b)

Start by reproducing the issue's Rust snippet with the nightly compiler and inspect the derive(CoercePointee) validation that checks ?Sized bounds. Determine whether ?Sized + Sized and bounds such as ?Sized + Clone should be rejected, then add regression coverage showing the intended diagnostic or acceptance behavior.