+#![feature(unsize, dispatch_from_dyn, never_type)]
+
+#![allow(dead_code)]
+
+use std::{
+ ops::DispatchFromDyn,
+ marker::{Unsize, PhantomData},
+};
+
+struct Zst;
+struct NestedZst(PhantomData<()>, Zst);
+
+
+struct WithUnit<T: ?Sized>(Box<T>, ());
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithUnit<U>> for WithUnit<T>
+ where T: Unsize<U> {}
+
+struct WithPhantom<T: ?Sized>(Box<T>, PhantomData<()>);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithPhantom<U>> for WithPhantom<T>
+ where T: Unsize<U> {}
+
+struct WithNever<T: ?Sized>(Box<T>, !);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithNever<U>> for WithNever<T>
+ where T: Unsize<U> {}
+
+struct WithZst<T: ?Sized>(Box<T>, Zst);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithZst<U>> for WithZst<T>
+ where T: Unsize<U> {}
+
+struct WithNestedZst<T: ?Sized>(Box<T>, NestedZst);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<WithNestedZst<U>> for WithNestedZst<T>
+ where T: Unsize<U> {}
+
+
+struct Generic<T: ?Sized, A>(Box<T>, A);
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, ()>> for Generic<T, ()>
+ where T: Unsize<U> {}
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, PhantomData<()>>>
+ for Generic<T, PhantomData<()>>
+ where T: Unsize<U> {}
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, !>> for Generic<T, !>
+ where T: Unsize<U> {}
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, Zst>> for Generic<T, Zst>
+ where T: Unsize<U> {}
+impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Generic<U, NestedZst>> for Generic<T, NestedZst>
+ where T: Unsize<U> {}
+
+
+fn main() {}