Original: #3110 (comment)
Without {Read,Write} for Pin<P> implementations, something like Pin<Box<T: Read>> doesn't actually impl Read. It seems like a pretty obvious blanket impl to have (e.g. Future has impl<P> Future for Pin<P> where P: DerefMut<Target: Future>, tokio has impl<P> Async{Read,Write} for Pin<P> where P: DerefMut<Target: Async{Read,Write}> + Unpin), and because Pin is #[fundamental] it would actually be a breaking change to add one in the future.
Original: #3110 (comment)
Without
{Read,Write} for Pin<P>implementations, something likePin<Box<T: Read>>doesn't actually implRead. It seems like a pretty obvious blanket impl to have (e.g. Future hasimpl<P> Future for Pin<P> where P: DerefMut<Target: Future>, tokio hasimpl<P> Async{Read,Write} for Pin<P> where P: DerefMut<Target: Async{Read,Write}> + Unpin), and because Pin is#[fundamental]it would actually be a breaking change to add one in the future.