Test dyn Trait containing async fn

Author: dtolnay

tests/ui/no-attribute-macro.rs

@@ -8,4 +8,6 @@ impl Trait for Struct {
     async fn method(&self) {}
 }
 
-fn main() {}
+fn main() {
+    let _: &dyn Trait;
+}

tests/ui/no-attribute-macro.stderr

@@ -23,3 +23,18 @@ error[E0706]: functions in traits cannot be declared `async`
   = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
   = note: see issue #91611 <https://github.com/rust-lang/rust/issues/91611> for more information
   = help: add `#![feature(async_fn_in_trait)]` to the crate attributes to enable
+
+error[E0038]: the trait `Trait` cannot be made into an object
+  --> tests/ui/no-attribute-macro.rs:12:12
+   |
+12 |     let _: &dyn Trait;
+   |            ^^^^^^^^^^ `Trait` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> tests/ui/no-attribute-macro.rs:2:14
+   |
+1  | pub trait Trait {
+   |           ----- this trait cannot be made into an object...
+2  |     async fn method(&self);
+   |              ^^^^^^ ...because method `method` is `async`
+   = help: consider moving `method` to another trait