review comments

Author: estebank

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

@@ -1735,16 +1735,13 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 //    | |
                 // LL | |              foo(tx.clone());
                 // LL | |          }).await;
-                //    | |          - ^^^^^^- value is later dropped here
-                //    | |          | |
-                //    | |__________| await occurs here, with value maybe used later
+                //    | |          - ^^^^^^ await occurs here, with value maybe used later
+                //    | |__________|
                 //    |            has type `closure` which is not `Send`
+                // note: value is later dropped here
+                // LL | |          }).await;
+                //    | |                  ^
                 //
-                // If available, use the scope span to annotate the drop location.
-                if let Some(scope_span) = scope_span {
-                    let scope_span = source_map.end_point(scope_span);
-                    span.push_span_label(scope_span, format!("{} is later dropped here", snippet));
-                }
                 span.push_span_label(
                     yield_span,
                     format!("{} occurs here, with {} maybe used later", await_or_yield, snippet),
@@ -1753,13 +1750,28 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     interior_span,
                     format!("has type `{}` which {}", target_ty, trait_explanation),
                 );
+                // If available, use the scope span to annotate the drop location.
+                let mut scope_note = None;
+                if let Some(scope_span) = scope_span {
+                    let scope_span = source_map.end_point(scope_span);
+
+                    let msg = format!("{} is later dropped here", snippet);
+                    if source_map.is_multiline(yield_span.between(scope_span)) {
+                        span.push_span_label(scope_span, msg);
+                    } else {
+                        scope_note = Some((scope_span, msg));
+                    }
+                }
                 err.span_note(
                     span,
                     &format!(
                         "{} {} as this value is used across {}",
                         future_or_generator, trait_explanation, an_await_or_yield
                     ),
                 );
+                if let Some((span, msg)) = scope_note {
+                    err.span_note(span, &msg);
+                }
             }
         };
         match interior_or_upvar_span {

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

@@ -12,10 +12,14 @@ LL |           baz(|| async{
    |  _____________-
 LL | |             foo(tx.clone());
 LL | |         }).await;
-   | |         - ^^^^^^- the value is later dropped here
-   | |         | |
-   | |_________| await occurs here, with the value maybe used later
+   | |         - ^^^^^^ await occurs here, with the value maybe used later
+   | |_________|
    |           has type `[closure@$DIR/issue-70935-complex-spans.rs:13:13: 15:10]` which is not `Send`
+note: the value is later dropped here
+  --> $DIR/issue-70935-complex-spans.rs:15:17
+   |
+LL |         }).await;
+   |                 ^
 
 error: aborting due to previous error
 

src/test/ui/async-await/issues/issue-65436-raw-ptr-not-send.stderr

@@ -9,10 +9,14 @@ note: future is not `Send` as this value is used across an await
   --> $DIR/issue-65436-raw-ptr-not-send.rs:14:35
    |
 LL |         bar(Foo(std::ptr::null())).await;
-   |                 ----------------  ^^^^^^- `std::ptr::null()` is later dropped here
-   |                 |                 |
-   |                 |                 await occurs here, with `std::ptr::null()` maybe used later
+   |                 ----------------  ^^^^^^ await occurs here, with `std::ptr::null()` maybe used later
+   |                 |
    |                 has type `*const u8` which is not `Send`
+note: `std::ptr::null()` is later dropped here
+  --> $DIR/issue-65436-raw-ptr-not-send.rs:14:41
+   |
+LL |         bar(Foo(std::ptr::null())).await;
+   |                                         ^
 help: consider moving this into a `let` binding to create a shorter lived borrow
   --> $DIR/issue-65436-raw-ptr-not-send.rs:14:13
    |

src/test/ui/async-await/unnecessary-await.rs

@@ -1,8 +1,8 @@
 // edition:2018
 
 async fn foo () { }
-fn bar () -> impl std::future::Future { async {} }
-fn boo () {}
+fn bar() -> impl std::future::Future { async {} }
+fn boo() {}
 
 async fn baz() -> std::io::Result<()> {
     foo().await;

src/test/ui/async-await/unnecessary-await.stderr

@@ -16,7 +16,7 @@ LL +     boo();
    | 
 help: alternatively, consider making `fn boo` asynchronous
    |
-LL | async fn boo () {}
+LL | async fn boo() {}
    | +++++
 
 error: aborting due to previous error