Broken Unsize bound in generic function in nightly-2026-08-22.

The following code snippet compiled with nightly-2026-08-21 but does not since 2026-08-22.

In the std::ptr::write() line, the compiler pretends it gets a U while o is a T.
There is no error without the Unsize<> bound on from_sized.

#![feature(unsize)]

use std::marker::{PhantomData, Unsize};

pub struct Ptr<T: ?Sized> {
    _phantom: PhantomData<T>,
}

impl<U: ?Sized> Ptr<U> {
    unsafe fn get(&self) -> *mut () {
        unimplemented!()
    }

    pub fn from_sized<T: Unsize<U>>(self, o: T) -> Self {
        unsafe {
            let data = self.get() as *mut T;
            std::ptr::write(data, o);
            todo!()
        }
    }
}

Start with the provided minimal reproducer, comparing nightly-2026-08-21 and nightly-2026-08-22, and inspect the handling of the Unsize bound around std::ptr::write(). Trace why the compiler treats the pointer as U while the value is T. Done means the reproducer has consistent, correct type checking and a regression test covers the behavior.