If you have an object that's !Unpin, then Miri will not apply uniqueness rules to anything containing it [0], including boxes and &mut references. (In the examp

If you have an object that's !Unpin, then Miri will not apply uniqueness rules to anything containing it [0], including boxes and &mut references. (In the example code, replacing the PhantomPinned with a () will make Miri complain again.) This is considered a temporary (if long-lived) measure to allow async executors to manipulate pinned futures without invalidating all their internal borrows. Thus, it might be seen as undetected UB, in lieu of a permanent solution. [0] https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=56500ae2945bb186030c5e51bda601c6 https://play.rust-lang.org/?version=stable&mode=debug&editio...