Fix nightly breakage

Generators now use `Pin` to make `resume` safe: rust-lang/rust#55704

Author: phil-opp

core/src/lib.rs

@@ -37,11 +37,11 @@ pub mod future {
     impl<T: Generator<Yield = ()>> Future for GenFuture<T> {
         type Output = T::Return;
         fn poll(self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Self::Output> {
-            set_task_waker(lw, || {
-                match unsafe { Pin::get_unchecked_mut(self).0.resume() } {
-                    GeneratorState::Yielded(()) => Poll::Pending,
-                    GeneratorState::Complete(x) => Poll::Ready(x),
-                }
+            // Safe because we're !Unpin + !Drop mapping to a ?Unpin value
+            let gen = unsafe { Pin::map_unchecked_mut(self, |s| &mut s.0) };
+            set_task_waker(lw, || match gen.resume() {
+                GeneratorState::Yielded(()) => Poll::Pending,
+                GeneratorState::Complete(x) => Poll::Ready(x),
             })
         }
     }