Make a span more useful

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

@@ -1328,6 +1328,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             ty::Generator(..) => "generator",
             _ => "function",
         };
+        let span = self.tcx.sess.source_map().guess_head_span(span);
         let mut err = struct_span_err!(
             self.tcx.sess,
             span,

src/test/ui/generator/issue-88653.stderr

@@ -1,18 +1,11 @@
 error[E0631]: type mismatch in generator arguments
   --> $DIR/issue-88653.rs:9:5
    |
-LL |       |bar| {
-   |       ^----
-   |       |
-   |  _____found signature of `fn(bool) -> _`
-   | |
-LL | |
-LL | |
-LL | |
-...  |
-LL | |         }
-LL | |     }
-   | |_____^ expected signature of `fn((bool,)) -> _`
+LL |     |bar| {
+   |     ^^^^^
+   |     |
+   |     expected signature of `fn((bool,)) -> _`
+   |     found signature of `fn(bool) -> _`
 
 error: aborting due to previous error