1 files changed, 71 insertions, 0 deletions
diff --git a/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs b/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs
new file mode 100644
index 000000000..afd3db5e0
--- /dev/null
+++ b/tests/ui/async-await/in-trait/dont-project-to-specializable-projection.rs
@@ -0,0 +1,71 @@
+// edition: 2021
+// known-bug: #108309
+
+#![feature(async_fn_in_trait)]
+#![feature(min_specialization)]
+
+struct MyStruct;
+
+trait MyTrait<T> {
+    async fn foo(_: T) -> &'static str;
+}
+
+impl<T> MyTrait<T> for MyStruct {
+    default async fn foo(_: T) -> &'static str {
+        "default"
+    }
+}
+
+impl MyTrait<i32> for MyStruct {
+    async fn foo(_: i32) -> &'static str {
+        "specialized"
+    }
+}
+
+async fn async_main() {
+    assert_eq!(MyStruct::foo(42).await, "specialized");
+    assert_eq!(indirection(42).await, "specialized");
+}
+
+async fn indirection<T>(x: T) -> &'static str {
+    //explicit type coercion is currently necessary
+    // because of https://github.com/rust-lang/rust/issues/67918
+    <MyStruct as MyTrait<T>>::foo(x).await
+}
+
+// ------------------------------------------------------------------------- //
+// Implementation Details Below...
+
+use std::future::Future;
+use std::pin::Pin;
+use std::task::*;
+
+pub fn noop_waker() -> Waker {
+    let raw = RawWaker::new(std::ptr::null(), &NOOP_WAKER_VTABLE);
+
+    // SAFETY: the contracts for RawWaker and RawWakerVTable are upheld
+    unsafe { Waker::from_raw(raw) }
+}
+
+const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
+
+unsafe fn noop_clone(_p: *const ()) -> RawWaker {
+    RawWaker::new(std::ptr::null(), &NOOP_WAKER_VTABLE)
+}
+
+unsafe fn noop(_p: *const ()) {}
+
+fn main() {
+    let mut fut = async_main();
+
+    // Poll loop, just to test the future...
+    let waker = noop_waker();
+    let ctx = &mut Context::from_waker(&waker);
+
+    loop {
+        match unsafe { Pin::new_unchecked(&mut fut).poll(ctx) } {
+            Poll::Pending => {}
+            Poll::Ready(()) => break,
+        }
+    }
+}