Refine error message for thread-safe usage of std::sync::Arc<{Self}>

library/core/src/marker.rs

@@ -79,7 +79,7 @@ macro marker_impls {
     on(_Self = "std::rc::Rc<T, A>", note = "use `std::sync::Arc` instead of `std::rc::Rc`"),
     message = "`{Self}` cannot be sent between threads safely",
     label = "`{Self}` cannot be sent between threads safely",
-    note = "consider using `std::sync::Arc<{Self}>`; for more information visit \
+    note = "consider whether `std::sync::Arc<{Self}>` could be incorporated to share this value between threads; for more information visit \
             <https://doc.rust-lang.org/book/ch16-03-shared-state.html>"
 )]
 pub unsafe auto trait Send {
@@ -634,7 +634,7 @@ impl<T: ?Sized> Copy for &T {}
     on(_Self = "std::rc::Rc<T, A>", note = "use `std::sync::Arc` instead of `std::rc::Rc`"),
     message = "`{Self}` cannot be shared between threads safely",
     label = "`{Self}` cannot be shared between threads safely",
-    note = "consider using `std::sync::Arc<{Self}>`; for more information visit \
+    note = "consider whether `std::sync::Arc<{Self}>` could be incorporated to share this value between threads; for more information visit \
             <https://doc.rust-lang.org/book/ch16-03-shared-state.html>"
 )]
 pub unsafe auto trait Sync {

tests/ui/associated-type-bounds/bad-bounds-on-assoc-in-trait.stderr

@@ -5,7 +5,7 @@ LL |     type C: Clone + Iterator<Item: Send + Iterator<Item: for<'a> Lam<&'a u8
    |                                    ^^^^ `<<Self as Case1>::C as Iterator>::Item` cannot be sent between threads safely
    |
    = help: the trait `Send` is not implemented for `<<Self as Case1>::C as Iterator>::Item`
-   = note: consider using `std::sync::Arc<<<Self as Case1>::C as Iterator>::Item>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<<<Self as Case1>::C as Iterator>::Item>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 help: consider further restricting the associated type
    |
 LL | trait Case1 where <<Self as Case1>::C as Iterator>::Item: Send {
@@ -30,7 +30,7 @@ LL |     type C: Clone + Iterator<Item: Send + Iterator<Item: for<'a> Lam<&'a u8
    |                                                                                             ^^^^ `<<Self as Case1>::C as Iterator>::Item` cannot be shared between threads safely
    |
    = help: the trait `Sync` is not implemented for `<<Self as Case1>::C as Iterator>::Item`
-   = note: consider using `std::sync::Arc<<<Self as Case1>::C as Iterator>::Item>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<<<Self as Case1>::C as Iterator>::Item>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 help: consider further restricting the associated type
    |
 LL | trait Case1 where <<Self as Case1>::C as Iterator>::Item: Sync {

tests/ui/associated-type-bounds/return-type-notation/basic.without.stderr

@@ -14,7 +14,7 @@ LL |     is_send(foo::<T>());
    |             ^^^^^^^^^^ future returned by `foo` is not `Send`
    |
    = help: within `impl Future<Output = Result<(), ()>>`, the trait `Send` is not implemented for `impl Future<Output = Result<(), ()>>`
-   = note: consider using `std::sync::Arc<impl Future<Output = Result<(), ()>>>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<impl Future<Output = Result<(), ()>>>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as it awaits another future which is not `Send`
   --> $DIR/basic.rs:13:5
    |

tests/ui/async-await/async-fn-nonsend.drop_tracking.stderr

@@ -29,7 +29,7 @@ LL |     assert_send(non_sync_with_method_call());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `non_sync_with_method_call` is not `Send`
    |
    = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `dyn std::fmt::Write`
-   = note: consider using `std::sync::Arc<dyn std::fmt::Write>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<dyn std::fmt::Write>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/async-fn-nonsend.rs:49:15
    |

tests/ui/async-await/async-fn-nonsend.drop_tracking_mir.stderr

@@ -26,7 +26,7 @@ LL |     assert_send(non_sync_with_method_call());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `non_sync_with_method_call` is not `Send`
    |
    = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `dyn std::fmt::Write`
-   = note: consider using `std::sync::Arc<dyn std::fmt::Write>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<dyn std::fmt::Write>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/async-fn-nonsend.rs:49:15
    |

tests/ui/async-await/async-fn-nonsend.no_drop_tracking.stderr

@@ -53,7 +53,7 @@ LL |     assert_send(non_sync_with_method_call());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `non_sync_with_method_call` is not `Send`
    |
    = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `dyn std::fmt::Write`
-   = note: consider using `std::sync::Arc<dyn std::fmt::Write>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<dyn std::fmt::Write>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/async-fn-nonsend.rs:49:15
    |
@@ -78,7 +78,7 @@ LL |     assert_send(non_sync_with_method_call_panic());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `non_sync_with_method_call_panic` is not `Send`
    |
    = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `dyn std::fmt::Write`
-   = note: consider using `std::sync::Arc<dyn std::fmt::Write>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<dyn std::fmt::Write>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/async-fn-nonsend.rs:56:15
    |
@@ -103,7 +103,7 @@ LL |     assert_send(non_sync_with_method_call_infinite_loop());
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future returned by `non_sync_with_method_call_infinite_loop` is not `Send`
    |
    = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `dyn std::fmt::Write`
-   = note: consider using `std::sync::Arc<dyn std::fmt::Write>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<dyn std::fmt::Write>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/async-fn-nonsend.rs:63:15
    |

tests/ui/async-await/in-trait/missing-send-bound.stderr

@@ -5,7 +5,7 @@ LL |     assert_is_send(test::<T>());
    |                    ^^^^^^^^^^^ future returned by `test` is not `Send`
    |
    = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `impl Future<Output = ()>`
-   = note: consider using `std::sync::Arc<impl Future<Output = ()>>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<impl Future<Output = ()>>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as it awaits another future which is not `Send`
   --> $DIR/missing-send-bound.rs:10:5
    |

tests/ui/async-await/issue-64130-1-sync.drop_tracking.stderr

@@ -5,7 +5,7 @@ LL |     is_sync(bar());
    |             ^^^^^ future returned by `bar` is not `Sync`
    |
    = help: within `impl Future<Output = ()>`, the trait `Sync` is not implemented for `Foo`
-   = note: consider using `std::sync::Arc<Foo>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<Foo>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Sync` as this value is used across an await
   --> $DIR/issue-64130-1-sync.rs:18:11
    |

tests/ui/async-await/issue-64130-1-sync.drop_tracking_mir.stderr

@@ -5,7 +5,7 @@ LL |     is_sync(bar());
    |             ^^^^^ future returned by `bar` is not `Sync`
    |
    = help: within `impl Future<Output = ()>`, the trait `Sync` is not implemented for `Foo`
-   = note: consider using `std::sync::Arc<Foo>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<Foo>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Sync` as this value is used across an await
   --> $DIR/issue-64130-1-sync.rs:18:11
    |

tests/ui/async-await/issue-64130-1-sync.no_drop_tracking.stderr

@@ -5,7 +5,7 @@ LL |     is_sync(bar());
    |             ^^^^^ future returned by `bar` is not `Sync`
    |
    = help: within `impl Future<Output = ()>`, the trait `Sync` is not implemented for `Foo`
-   = note: consider using `std::sync::Arc<Foo>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<Foo>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Sync` as this value is used across an await
   --> $DIR/issue-64130-1-sync.rs:18:11
    |

tests/ui/async-await/issue-64130-4-async-move.no_drop_tracking.stderr

@@ -5,7 +5,7 @@ LL | pub fn foo() -> impl Future + Send {
    |                 ^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: the trait `Sync` is not implemented for `(dyn Any + Send + 'static)`
-   = note: consider using `std::sync::Arc<(dyn Any + Send + 'static)>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<(dyn Any + Send + 'static)>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/issue-64130-4-async-move.rs:27:23
    |

tests/ui/async-await/issue-64130-non-send-future-diags.stderr

@@ -5,7 +5,7 @@ LL |     is_send(foo());
    |             ^^^^^ future returned by `foo` is not `Send`
    |
    = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `MutexGuard<'_, u32>`
-   = note: consider using `std::sync::Arc<MutexGuard<'_, u32>>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<MutexGuard<'_, u32>>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/issue-64130-non-send-future-diags.rs:17:11
    |

tests/ui/async-await/issue-67252-unnamed-future.drop_tracking.stderr

@@ -10,7 +10,7 @@ LL | |     });
    | |_____^ future created by async block is not `Send`
    |
    = help: within `[async block@$DIR/issue-67252-unnamed-future.rs:21:11: 25:6]`, the trait `Send` is not implemented for `*mut ()`
-   = note: consider using `std::sync::Arc<*mut ()>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<*mut ()>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/issue-67252-unnamed-future.rs:23:17
    |

tests/ui/async-await/issue-67252-unnamed-future.drop_tracking_mir.stderr

@@ -5,7 +5,7 @@ LL |     spawn(async {
    |     ^^^^^ future created by async block is not `Send`
    |
    = help: within `[async block@$DIR/issue-67252-unnamed-future.rs:21:11: 25:6]`, the trait `Send` is not implemented for `*mut ()`
-   = note: consider using `std::sync::Arc<*mut ()>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<*mut ()>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/issue-67252-unnamed-future.rs:23:17
    |

tests/ui/async-await/issue-67252-unnamed-future.no_drop_tracking.stderr

@@ -10,7 +10,7 @@ LL | |     });
    | |_____^ future created by async block is not `Send`
    |
    = help: within `[async block@$DIR/issue-67252-unnamed-future.rs:21:11: 25:6]`, the trait `Send` is not implemented for `*mut ()`
-   = note: consider using `std::sync::Arc<*mut ()>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<*mut ()>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/issue-67252-unnamed-future.rs:23:17
    |

tests/ui/async-await/issue-70818.drop_tracking.stderr

@@ -4,7 +4,7 @@ error: future cannot be sent between threads safely
 LL | fn foo<T: Send, U>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + Send {
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
    |
-   = note: consider using `std::sync::Arc<U>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<U>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: captured value is not `Send`
   --> $DIR/issue-70818.rs:9:18
    |

tests/ui/async-await/issue-70818.drop_tracking_mir.stderr

@@ -4,7 +4,7 @@ error: future cannot be sent between threads safely
 LL | fn foo<T: Send, U>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + Send {
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
    |
-   = note: consider using `std::sync::Arc<U>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<U>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: captured value is not `Send`
   --> $DIR/issue-70818.rs:9:18
    |

tests/ui/async-await/issue-70818.no_drop_tracking.stderr

@@ -4,7 +4,7 @@ error: future cannot be sent between threads safely
 LL | fn foo<T: Send, U>(ty: T, ty1: U) -> impl Future<Output = (T, U)> + Send {
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
    |
-   = note: consider using `std::sync::Arc<U>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<U>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: captured value is not `Send`
   --> $DIR/issue-70818.rs:9:18
    |

tests/ui/async-await/issue-70935-complex-spans.drop_tracking.stderr

@@ -5,7 +5,7 @@ LL | fn foo(x: NotSync) -> impl Future + Send {
    |                       ^^^^^^^^^^^^^^^^^^ `*mut ()` cannot be shared between threads safely
    |
    = help: within `NotSync`, the trait `Sync` is not implemented for `*mut ()`
-   = note: consider using `std::sync::Arc<*mut ()>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<*mut ()>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: required because it appears within the type `PhantomData<*mut ()>`
   --> $SRC_DIR/core/src/marker.rs:LL:COL
 note: required because it appears within the type `NotSync`

tests/ui/async-await/issue-70935-complex-spans.drop_tracking_mir.stderr

@@ -5,7 +5,7 @@ LL | fn foo(x: NotSync) -> impl Future + Send {
    |                       ^^^^^^^^^^^^^^^^^^ `*mut ()` cannot be shared between threads safely
    |
    = help: within `NotSync`, the trait `Sync` is not implemented for `*mut ()`
-   = note: consider using `std::sync::Arc<*mut ()>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<*mut ()>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: required because it appears within the type `PhantomData<*mut ()>`
   --> $SRC_DIR/core/src/marker.rs:LL:COL
 note: required because it appears within the type `NotSync`

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

@@ -5,7 +5,7 @@ LL | fn foo(x: NotSync) -> impl Future + Send {
    |                       ^^^^^^^^^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: within `NotSync`, the trait `Sync` is not implemented for `*mut ()`
-   = note: consider using `std::sync::Arc<*mut ()>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<*mut ()>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/issue-70935-complex-spans.rs:24:12
    |

tests/ui/async-await/issue-71137.stderr

@@ -5,7 +5,7 @@ LL |   fake_spawn(wrong_mutex());
    |              ^^^^^^^^^^^^^ future returned by `wrong_mutex` is not `Send`
    |
    = help: within `impl Future<Output = ()>`, the trait `Send` is not implemented for `MutexGuard<'_, i32>`
-   = note: consider using `std::sync::Arc<MutexGuard<'_, i32>>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<MutexGuard<'_, i32>>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: future is not `Send` as this value is used across an await
   --> $DIR/issue-71137.rs:14:26
    |

tests/ui/async-await/issue-86507.drop_tracking.stderr

@@ -8,7 +8,7 @@ LL | |                 }
 LL | |             )
    | |_____________^ future created by async block is not `Send`
    |
-   = note: consider using `std::sync::Arc<T>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<T>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: captured value is not `Send` because `&` references cannot be sent unless their referent is `Sync`
   --> $DIR/issue-86507.rs:22:29
    |

tests/ui/async-await/issue-86507.drop_tracking_mir.stderr

@@ -8,7 +8,7 @@ LL | |                 }
 LL | |             )
    | |_____________^ future created by async block is not `Send`
    |
-   = note: consider using `std::sync::Arc<T>`; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
+   = note: consider whether `std::sync::Arc<T>` could be incorporated to share this value between threads; for more information visit <https://doc.rust-lang.org/book/ch16-03-shared-state.html>
 note: captured value is not `Send` because `&` references cannot be sent unless their referent is `Sync`
   --> $DIR/issue-86507.rs:22:29
    |