bless issue-70818 test case

src/test/ui/async-await/issue-70818.rs

@@ -1,7 +1,9 @@
-// edition 2018
+// edition:2018
 
-fn foo<T: Sized>(ty: T) -> impl std::future::Future<Output = T> + Send { //~ Error `T` cannot be sent between threads safely
-    async { ty }
+use std::future::Future;
+fn foo<T: Send, U>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + Send {
+//~^ Error future cannot be sent between threads safely
+    async { (ty, ty1) }
 }
 
 fn main() {}

src/test/ui/async-await/issue-70818.stderr

@@ -0,0 +1,23 @@
+error: future cannot be sent between threads safely
+  --> $DIR/issue-70818.rs:4:38
+   |
+LL | fn foo<T: Send, U>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + Send {
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
+LL |
+LL |     async { (ty, ty1) }
+   |     ------------------- this returned value is of type `impl std::future::Future`
+   |
+   = help: within `impl std::future::Future`, the trait `std::marker::Send` is not implemented for `U`
+note: captured outer value is not `Send`
+  --> $DIR/issue-70818.rs:6:18
+   |
+LL |     async { (ty, ty1) }
+   |                  ^^^ has type `U` which is not `Send`
+   = note: the return type of a function must have a statically known size
+help: consider restricting type parameter `U`
+   |
+LL | fn foo<T: Send, U: std::marker::Send>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + Send {
+   |                  ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+