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diff --git a/tests/ui/async-await/async-fn/macro-async-trait-bound-theoretical-regression.rs b/tests/ui/async-await/async-fn/macro-async-trait-bound-theoretical-regression.rs
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+// Demonstrates and records a theoretical regressions / breaking changes caused by the
+// introduction of async trait bounds.
+
+// Setting the edition to 2018 since we don't regress `demo! { dyn async }` in Rust <2018.
+//@ edition:2018
+
+macro_rules! demo {
+    ($ty:ty) => { compile_error!("ty"); };
+    //~^ ERROR ty
+    //~| ERROR ty
+    (impl $c:ident Trait) => {};
+    (dyn $c:ident Trait) => {};
+}
+
+demo! { impl async Trait }
+//~^ ERROR `async` trait bounds are unstable
+
+demo! { dyn async Trait }
+//~^ ERROR `async` trait bounds are unstable
+
+fn main() {}