From 3b4cbe9095d83d13feb13060cc66f3e50bd75350 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sat, 3 Dec 2022 18:38:04 +0100
Subject: [PATCH] add test for self-referential future
---
.../future-self-referential.rs | 102 ++++++++++++++++++
1 file changed, 102 insertions(+)
create mode 100644 src/tools/miri/tests/pass/stacked-borrows/future-self-referential.rs
diff --git a/src/tools/miri/tests/pass/stacked-borrows/future-self-referential.rs b/src/tools/miri/tests/pass/stacked-borrows/future-self-referential.rs
new file mode 100644
index 00000000000..3ba21552fd3
--- /dev/null
+++ b/src/tools/miri/tests/pass/stacked-borrows/future-self-referential.rs
@@ -0,0 +1,102 @@
+#![feature(pin_macro)]
+
+use std::future::*;
+use std::marker::PhantomPinned;
+use std::pin::*;
+use std::ptr;
+use std::task::*;
+
+struct Delay {
+ delay: usize,
+}
+
+impl Delay {
+ fn new(delay: usize) -> Self {
+ Delay { delay }
+ }
+}
+
+impl Future for Delay {
+ type Output = ();
+ fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<()> {
+ if self.delay > 0 {
+ self.delay -= 1;
+ Poll::Pending
+ } else {
+ Poll::Ready(())
+ }
+ }
+}
+
+async fn do_stuff() {
+ (&mut Delay::new(1)).await;
+}
+
+// Same thing implemented by hand
+struct DoStuff {
+ state: usize,
+ delay: Delay,
+ delay_ref: *mut Delay,
+ _marker: PhantomPinned,
+}
+
+impl DoStuff {
+ fn new() -> Self {
+ DoStuff {
+ state: 0,
+ delay: Delay::new(1),
+ delay_ref: ptr::null_mut(),
+ _marker: PhantomPinned,
+ }
+ }
+}
+
+impl Future for DoStuff {
+ type Output = ();
+ fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+ unsafe {
+ let this = self.get_unchecked_mut();
+ match this.state {
+ 0 => {
+ // Set up self-ref.
+ this.delay_ref = &mut this.delay;
+ // Move to next state.
+ this.state = 1;
+ Poll::Pending
+ }
+ 1 => {
+ let delay = &mut *this.delay_ref;
+ Pin::new_unchecked(delay).poll(cx)
+ }
+ _ => unreachable!(),
+ }
+ }
+ }
+}
+
+fn run_fut<T>(fut: impl Future<Output = T>) -> T {
+ use std::sync::Arc;
+
+ 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 = pin!(fut);
+ loop {
+ match pinned.as_mut().poll(&mut context) {
+ Poll::Pending => continue,
+ Poll::Ready(v) => return v,
+ }
+ }
+}
+
+fn main() {
+ run_fut(do_stuff());
+ run_fut(DoStuff::new());
+}