Add test

tests/ui/async-await/in-trait/async-default-fn-overridden.rs

@@ -0,0 +1,66 @@
+// run-pass
+// edition:2021
+
+#![feature(async_fn_in_trait)]
+//~^ WARN the feature `async_fn_in_trait` is incomplete and may not be safe to use
+
+use std::future::Future;
+
+trait AsyncTrait {
+    async fn default_impl() {
+        assert!(false);
+    }
+
+    async fn call_default_impl() {
+        Self::default_impl().await
+    }
+}
+
+struct AsyncType;
+
+impl AsyncTrait for AsyncType {
+    async fn default_impl() {
+        // :)
+    }
+}
+
+async fn async_main() {
+    // Should not assert false
+    AsyncType::call_default_impl().await;
+}
+
+// ------------------------------------------------------------------------- //
+// Implementation Details Below...
+
+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,
+        }
+    }
+}

tests/ui/async-await/in-trait/async-default-fn-overridden.stderr

@@ -0,0 +1,11 @@
+warning: the feature `async_fn_in_trait` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/async-default-fn-overridden.rs:4:12
+   |
+LL | #![feature(async_fn_in_trait)]
+   |            ^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+