add a test

tests/ui/consts/const_waker.rs

@@ -0,0 +1,28 @@
+//@ check-pass
+#![allow(dead_code)]
+
+use core::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
+};
+
+const NOP_RAWWAKER: RawWaker = {
+    fn nop(_: *const ()) {}
+    const VTAB: RawWakerVTable = RawWakerVTable::new(|_| NOP_RAWWAKER, nop, nop, nop);
+    RawWaker::new(&() as *const (), &VTAB)
+};
+
+const NOP_WAKER: &Waker = &unsafe { Waker::from_raw(NOP_RAWWAKER) };
+
+const NOP_CONTEXT: Context<'static> = Context::from_waker(NOP_WAKER);
+
+fn poll_once<T, F>(f: &mut F) -> Poll<T>
+where
+    F: Future<Output = T> + ?Sized + Unpin,
+{
+    let mut cx = NOP_CONTEXT;
+    Pin::new(f).as_mut().poll(&mut cx)
+}
+
+fn main() {}