Rollup merge of #90939 - estebank:wg-af-polish, r=tmandry

Tweak errors coming from `for`-loop, `?` and `.await` desugaring

 * Suggest removal of `.await` on non-`Future` expression
 * Keep track of obligations introduced by desugaring
 * Remove span pointing at method for obligation errors coming from desugaring
 * Point at called local sync `fn` and suggest making it `async`

```
error[E0277]: `()` is not a future
  --> $DIR/unnecessary-await.rs:9:10
   |
LL |     boo().await;
   |     -----^^^^^^ `()` is not a future
   |     |
   |     this call returns `()`
   |
   = help: the trait `Future` is not implemented for `()`
help: do not `.await` the expression
   |
LL -     boo().await;
LL +     boo();
   |
help: alternatively, consider making `fn boo` asynchronous
   |
LL | async fn boo () {}
   | +++++
```

Fix #66731.

1 files changed, 7 insertions, 4 deletions

diff --git a/compiler/rustc_passes/src/region.rs b/compiler/rustc_passes/src/region.rs
index ae423070392..8968c163987 100644
--- a/compiler/rustc_passes/src/region.rs
+++ b/compiler/rustc_passes/src/region.rs
@@ -421,11 +421,14 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
         // Mark this expr's scope and all parent scopes as containing `yield`.
         let mut scope = Scope { id: expr.hir_id.local_id, data: ScopeData::Node };
         loop {
-            let data = YieldData {
-                span: expr.span,
-                expr_and_pat_count: visitor.expr_and_pat_count,
-                source: *source,
+            let span = match expr.kind {
+                hir::ExprKind::Yield(expr, hir::YieldSource::Await { .. }) => {
+                    expr.span.shrink_to_hi().to(expr.span)
+                }
+                _ => expr.span,
             };
+            let data =
+                YieldData { span, expr_and_pat_count: visitor.expr_and_pat_count, source: *source };
             visitor.scope_tree.yield_in_scope.insert(scope, data);
             if visitor.pessimistic_yield {
                 debug!("resolve_expr in pessimistic_yield - marking scope {:?} for fixup", scope);