From 1a913a634721d3a69f3b41a638d605812aca8d5a Mon Sep 17 00:00:00 2001
From: Eric Holk <ericholk@microsoft.com>
Date: Thu, 17 Nov 2022 16:03:55 -0800
Subject: [PATCH] Add a test case for async dyn* traits

---
 src/test/ui/dyn-star/dyn-async-trait.rs | 36 +++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 src/test/ui/dyn-star/dyn-async-trait.rs

diff --git a/src/test/ui/dyn-star/dyn-async-trait.rs b/src/test/ui/dyn-star/dyn-async-trait.rs
new file mode 100644
index 00000000000..a8c5a1dbf66
--- /dev/null
+++ b/src/test/ui/dyn-star/dyn-async-trait.rs
@@ -0,0 +1,36 @@
+// check-pass
+// edition: 2021
+
+// This test case is meant to demonstrate how close we can get to async
+// functions in dyn traits with the current level of dyn* support.
+
+#![feature(dyn_star)]
+#![allow(incomplete_features)]
+
+use std::future::Future;
+
+trait DynAsyncCounter {
+    fn increment<'a>(&'a mut self) -> dyn* Future<Output = usize> + 'a;
+}
+
+struct MyCounter {
+    count: usize,
+}
+
+impl DynAsyncCounter for MyCounter {
+    fn increment<'a>(&'a mut self) -> dyn* Future<Output = usize> + 'a {
+        Box::pin(async {
+            self.count += 1;
+            self.count
+        }) as dyn* Future<Output = _> // FIXME(dyn-star): coercion doesn't work here yet
+    }
+}
+
+async fn do_counter(counter: &mut dyn DynAsyncCounter) -> usize {
+    counter.increment().await
+}
+
+fn main() {
+    let mut counter = MyCounter { count: 0 };
+    let _ = do_counter(&mut counter);
+}