Use a label instead of a note for the drop site to create denser diagnostics

Author: oli-obk

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

@@ -2212,17 +2212,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, '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));
-                    }
+                    span.push_span_label(scope_span, msg);
                 }
                 err.span_note(
                     span,
@@ -2231,9 +2225,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         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 {
             GeneratorInteriorOrUpvar::Interior(interior_span, interior_extra_info) => {

src/test/ui/async-await/async-await-let-else.drop-tracking.stderr

@@ -68,14 +68,10 @@ note: future is not `Send` as this value is used across an await
   --> $DIR/async-await-let-else.rs:33:28
    |
 LL |         (Rc::new(()), bar().await);
-   |          -----------       ^^^^^^ await occurs here, with `Rc::new(())` maybe used later
-   |          |
+   |          -----------       ^^^^^^ - `Rc::new(())` is later dropped here
+   |          |                 |
+   |          |                 await occurs here, with `Rc::new(())` maybe used later
    |          has type `Rc<()>` which is not `Send`
-note: `Rc::new(())` is later dropped here
-  --> $DIR/async-await-let-else.rs:33:35
-   |
-LL |         (Rc::new(()), bar().await);
-   |                                   ^
 note: required by a bound in `is_send`
   --> $DIR/async-await-let-else.rs:19:15
    |

src/test/ui/async-await/async-await-let-else.no-drop-tracking.stderr

@@ -53,14 +53,10 @@ note: future is not `Send` as this value is used across an await
   --> $DIR/async-await-let-else.rs:33:28
    |
 LL |         (Rc::new(()), bar().await);
-   |          -----------       ^^^^^^ await occurs here, with `Rc::new(())` maybe used later
-   |          |
+   |          -----------       ^^^^^^ - `Rc::new(())` is later dropped here
+   |          |                 |
+   |          |                 await occurs here, with `Rc::new(())` maybe used later
    |          has type `Rc<()>` which is not `Send`
-note: `Rc::new(())` is later dropped here
-  --> $DIR/async-await-let-else.rs:33:35
-   |
-LL |         (Rc::new(()), bar().await);
-   |                                   ^
 note: required by a bound in `is_send`
   --> $DIR/async-await-let-else.rs:19:15
    |

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

@@ -12,14 +12,10 @@ LL |           baz(|| async{
    |  _____________-
 LL | |             foo(tx.clone());
 LL | |         }).await;
-   | |         - ^^^^^^ await occurs here, with the value maybe used later
-   | |_________|
+   | |         - ^^^^^^- the value is later dropped here
+   | |         | |
+   | |_________| await occurs here, with the value maybe used later
    |           has type `[closure@$DIR/issue-70935-complex-spans.rs:17:13: 17:15]` which is not `Send`
-note: the value is later dropped here
-  --> $DIR/issue-70935-complex-spans.rs:19:17
-   |
-LL |         }).await;
-   |                 ^
 
 error: aborting due to previous error
 

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

@@ -13,14 +13,10 @@ note: future is not `Send` as this value is used across an await
   --> $DIR/issue-65436-raw-ptr-not-send.rs:18:35
    |
 LL |         bar(Foo(std::ptr::null())).await;
-   |                 ----------------  ^^^^^^ await occurs here, with `std::ptr::null()` maybe used later
-   |                 |
+   |                 ----------------  ^^^^^^- `std::ptr::null()` is later dropped here
+   |                 |                 |
+   |                 |                 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:18:41
-   |
-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:18:13
    |

src/test/ui/async-await/issues/issue-67893.stderr

@@ -9,14 +9,10 @@ note: future is not `Send` as this value is used across an await
   --> $DIR/auxiliary/issue_67893.rs:9:26
    |
 LL |     f(*x.lock().unwrap()).await;
-   |        ----------------- ^^^^^^ await occurs here, with `x.lock().unwrap()` maybe used later
-   |        |
+   |        ----------------- ^^^^^^- `x.lock().unwrap()` is later dropped here
+   |        |                 |
+   |        |                 await occurs here, with `x.lock().unwrap()` maybe used later
    |        has type `MutexGuard<'_, ()>` which is not `Send`
-note: `x.lock().unwrap()` is later dropped here
-  --> $DIR/auxiliary/issue_67893.rs:9:32
-   |
-LL |     f(*x.lock().unwrap()).await;
-   |                                ^
 note: required by a bound in `g`
   --> $DIR/issue-67893.rs:6:14
    |