Fix failing test

Author: roxelo

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1307,6 +1307,26 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         let mut generator = None;
         let mut outer_generator = None;
         let mut next_code = Some(&obligation.cause.code);
+        // By introducing a tuple into the upvar types, the first item in the obligation chain
+        // can be of Tuple type instead of the generator that captured the type. We want to catch for
+        // this case and skip it.
+        if let Some(code) = next_code {
+            match code {
+                ObligationCauseCode::DerivedObligation(derived_obligation)
+                | ObligationCauseCode::BuiltinDerivedObligation(derived_obligation)
+                | ObligationCauseCode::ImplDerivedObligation(derived_obligation) => {
+                    let ty = derived_obligation.parent_trait_ref.skip_binder().self_ty();
+                    match *ty.kind() {
+                        ty::Tuple(_) => {
+                            next_code = Some(derived_obligation.parent_code.as_ref());
+                        }
+                        _ => {}
+                    }
+                }
+                _ => {}
+            }
+        }
+
         while let Some(code) = next_code {
             debug!("maybe_note_obligation_cause_for_async_await: code={:?}", code);
             match code {

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

@@ -1,21 +1,17 @@
-error[E0277]: `U` cannot be sent between threads safely
+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 {
-   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `U` cannot be sent between threads safely
+   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
 LL |
 LL |     async { (ty, ty1) }
    |     ------------------- this returned value is of type `impl Future`
-   | 
-  ::: $SRC_DIR/core/src/future/mod.rs:LL:COL
    |
-LL | pub const fn from_generator<T>(gen: T) -> impl Future<Output = T::Return>
-   |                                           ------------------------------- within this `impl Future`
+note: captured value is not `Send`
+  --> $DIR/issue-70818.rs:6:18
    |
-   = note: required because it appears within the type `(T, U)`
-   = note: required because it appears within the type `[static generator@$DIR/issue-70818.rs:6:11: 6:24 _]`
-   = note: required because it appears within the type `from_generator::GenFuture<[static generator@$DIR/issue-70818.rs:6:11: 6:24 _]>`
-   = note: required because it appears within the type `impl Future`
+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`
    |
@@ -24,4 +20,3 @@ LL | fn foo<T: Send, U: Send>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + S
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0277`.