Guess head span of async blocks

Author: oli-obk

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

@@ -1680,6 +1680,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             ));
 
             let original_span = err.span.primary_span().unwrap();
+            let original_span = self.tcx.sess.source_map().guess_head_span(original_span);
             let mut span = MultiSpan::from_span(original_span);
 
             let message = outer_generator

src/test/ui/async-await/issue-64130-4-async-move.stderr

@@ -1,14 +1,8 @@
 error: future cannot be sent between threads safely
   --> $DIR/issue-64130-4-async-move.rs:17:5
    |
-LL | /     async move {
-LL | |
-LL | |         match client.status() {
-LL | |             200 => {
-...  |
-LL | |         }
-LL | |     }
-   | |_____^ future created by async block is not `Send`
+LL |     async move {
+   |     ^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: the trait `Sync` is not implemented for `(dyn Any + Send + 'static)`
 note: future is not `Send` as this value is used across an await

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

@@ -2,7 +2,7 @@ error: future cannot be sent between threads safely
   --> $DIR/issue-70818.rs:5:5
    |
 LL |     async { (ty, ty1) }
-   |     ^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
+   |     ^^^^^ future created by async block is not `Send`
    |
 note: captured value is not `Send`
   --> $DIR/issue-70818.rs:5:18

src/test/ui/async-await/issue-70935-complex-spans.stderr

@@ -1,13 +1,8 @@
 error: future cannot be sent between threads safely
   --> $DIR/issue-70935-complex-spans.rs:11:5
    |
-LL | /     async move {
-LL | |
-LL | |         baz(|| async{
-LL | |             foo(tx.clone());
-LL | |         }).await;
-LL | |     }
-   | |_____^ future created by async block is not `Send`
+LL |     async move {
+   |     ^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: the trait `Sync` is not implemented for `Sender<i32>`
 note: future is not `Send` as this value is used across an await