Make ready and lazy's panic messages easy to understand

Author: taiki-e

futures-util/src/future/lazy.rs

@@ -49,6 +49,6 @@ impl<F, R> Future for Lazy<F>
     type Output = R;
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<R> {
-        Poll::Ready((self.f.take().unwrap())(cx))
+        Poll::Ready((self.f.take().expect("Lazy polled after completion"))(cx))
     }
 }

futures-util/src/future/ready.rs

@@ -28,7 +28,7 @@ impl<T> Future for Ready<T> {
 
     #[inline]
     fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<T> {
-        Poll::Ready(self.0.take().unwrap())
+        Poll::Ready(self.0.take().expect("Ready polled after completion"))
     }
 }