Implementing `Reborrow` on invariant type has strange behavior.

The following code fails to compile, giving a strange error. This seems to be a strange point to error out.

#![feature(reborrow)]

use std::marker::Reborrow;

struct MyMut<'a>(*mut &'a ());

impl Reborrow for MyMut<'_> {}

fn foo(x: MyMut) {
    let _y: MyMut = x;
}

error[E0597]: `x` does not live long enough
  --> src/lib.rs:10:21
   |
 9 | fn foo(x: MyMut) {
   |        -
   |        |
   |        binding `x` declared here
   |        has type `MyMut<'1>`
10 |     let _y: MyMut = x;
   |                     ^
   |                     |
   |                     borrowed value does not live long enough
   |                     requires that `x` is borrowed for `'1`
11 | }
   |  - `x` dropped here while still borrowed

For more information about this error, try `rustc --explain E0597`.

Possibly related to #156310.

cc @aapoalas @P8L1

Meta

Reproducible on the playground with version 1.98.0-nightly (2026-06-01 6bdf43094fae65d298bc)

Start with the Rust playground reproducer using the nightly version noted in the issue, and inspect the Reborrow behavior around the MyMut assignment and E0597 diagnostic. Compare the report with related issue #156310 to establish the intended compiler result; done means this example receives the agreed behavior rather than the reported unexpected borrow error.