chore: checkpoint before Python removal

vendor/futures/tests/future_join.rs

@@ -0,0 +1,32 @@
+use futures::executor::block_on;
+use futures::future::{self, Future};
+use std::task::Poll;
+
+/// This tests verifies (through miri) that self-referencing
+/// futures are not invalidated when joining them.
+#[test]
+fn futures_join_macro_self_referential() {
+    block_on(async { futures::join!(yield_now(), trouble()) });
+}
+
+async fn trouble() {
+    let lucky_number = 42;
+    let problematic_variable = &lucky_number;
+
+    yield_now().await;
+
+    // problematic dereference
+    let _ = { *problematic_variable };
+}
+
+fn yield_now() -> impl Future<Output = ()> {
+    let mut yielded = false;
+    future::poll_fn(move |cx| {
+        if core::mem::replace(&mut yielded, true) {
+            Poll::Ready(())
+        } else {
+            cx.waker().wake_by_ref();
+            Poll::Pending
+        }
+    })
+}