Add tests for moving data across await point

tests/pass/move-data-across-await-point.rs

@@ -0,0 +1,81 @@
+use std::future::Future;
+use std::ptr;
+
+// This test:
+// - Compares addresses of non-Copy data before and after moving it
+// - Writes to the pointer after it has moved across the await point
+//
+// This is only meant to assert current behavior, not guarantee that this is
+// how it should work in the future. In fact, upcoming changes to rustc
+// *should* break these tests.
+// See: https://github.com/rust-lang/rust/issues/62958
+async fn data_moved_async() {
+    async fn helper(mut data: Vec<u8>, raw_pointer: *mut Vec<u8>) {
+        let raw_pointer2 = ptr::addr_of_mut!(data);
+        // `raw_pointer` points to the original location where the Vec was stored in the caller.
+        // `data` is where that Vec (to be precise, its ptr+capacity+len on-stack data)
+        // got moved to. Those will usually not be the same since the Vec got moved twice
+        // (into the function call, and then into the generator upvar).
+        assert_ne!(raw_pointer, raw_pointer2);
+        unsafe {
+            // This writes into the `x` in `data_moved_async`, re-initializing it.
+            std::ptr::write(raw_pointer, vec![3]);
+        }
+    }
+    // Vec<T> is not Copy
+    let mut x: Vec<u8> = vec![2];
+    let raw_pointer = ptr::addr_of_mut!(x);
+    helper(x, raw_pointer).await;
+    unsafe {
+        assert_eq!(*raw_pointer, vec![3]);
+        // Drop to prevent leak.
+        std::ptr::drop_in_place(raw_pointer);
+    }
+}
+
+// Same thing as above, but non-async.
+fn data_moved() {
+    fn helper(mut data: Vec<u8>, raw_pointer: *mut Vec<u8>) {
+        let raw_pointer2 = ptr::addr_of_mut!(data);
+        assert_ne!(raw_pointer, raw_pointer2);
+        unsafe {
+            std::ptr::write(raw_pointer, vec![3]);
+        }
+    }
+
+    let mut x: Vec<u8> = vec![2];
+    let raw_pointer = ptr::addr_of_mut!(x);
+    helper(x, raw_pointer);
+    unsafe {
+        assert_eq!(*raw_pointer, vec![3]);
+        std::ptr::drop_in_place(raw_pointer);
+    }
+}
+
+fn run_fut<T>(fut: impl Future<Output = T>) -> T {
+    use std::sync::Arc;
+    use std::task::{Context, Poll, Wake, Waker};
+
+    struct MyWaker;
+    impl Wake for MyWaker {
+        fn wake(self: Arc<Self>) {
+            unimplemented!()
+        }
+    }
+
+    let waker = Waker::from(Arc::new(MyWaker));
+    let mut context = Context::from_waker(&waker);
+
+    let mut pinned = Box::pin(fut);
+    loop {
+        match pinned.as_mut().poll(&mut context) {
+            Poll::Pending => continue,
+            Poll::Ready(v) => return v,
+        }
+    }
+}
+
+fn main() {
+    run_fut(data_moved_async());
+    data_moved();
+}