Review comment: remove mention of `move` closure

src/libcore/marker.rs

@@ -344,18 +344,20 @@ pub trait Copy : Clone {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[lang = "sync"]
 #[rustc_on_unimplemented(
-    on(
-        _Self="std::sync::mpsc::Receiver<T>",
-        label="`{Self}` cannot be shared safely, consider marking the closure `move`"
-    ),
-    on(
-        _Self="std::sync::mpsc::Sender<T>",
-        label="`{Self}` cannot be shared safely, consider marking the closure `move`"
-    ),
     message="`{Self}` cannot be shared between threads safely",
     label="`{Self}` cannot be shared between threads safely"
 )]
 pub unsafe auto trait Sync {
+    // FIXME(estebank): once support to add notes in `rustc_on_unimplemented`
+    // lands in beta, and it has been extended to check whether a closure is
+    // anywhere in the requirement chain, extend it as such (#48534):
+    // ```
+    // on(
+    //     closure,
+    //     note="`{Self}` cannot be shared safely, consider marking the closure `move`"
+    // ),
+    // ```
+
     // Empty
 }
 

src/test/ui/closure-move-sync.stderr

 error[E0277]: `std::sync::mpsc::Receiver<()>` cannot be shared between threads safely
   --> $DIR/closure-move-sync.rs:16:13
    |
-16 |     let t = thread::spawn(|| {
-   |             ^^^^^^^^^^^^^ `std::sync::mpsc::Receiver<()>` cannot be shared safely, consider marking the closure `move`
+LL |     let t = thread::spawn(|| {
+   |             ^^^^^^^^^^^^^ `std::sync::mpsc::Receiver<()>` cannot be shared between threads safely
    |
    = help: the trait `std::marker::Sync` is not implemented for `std::sync::mpsc::Receiver<()>`
    = note: required because of the requirements on the impl of `std::marker::Send` for `&std::sync::mpsc::Receiver<()>`
@@ -12,8 +12,8 @@ error[E0277]: `std::sync::mpsc::Receiver<()>` cannot be shared between threads s
 error[E0277]: `std::sync::mpsc::Sender<()>` cannot be shared between threads safely
   --> $DIR/closure-move-sync.rs:28:5
    |
-28 |     thread::spawn(|| tx.send(()).unwrap());
-   |     ^^^^^^^^^^^^^ `std::sync::mpsc::Sender<()>` cannot be shared safely, consider marking the closure `move`
+LL |     thread::spawn(|| tx.send(()).unwrap());
+   |     ^^^^^^^^^^^^^ `std::sync::mpsc::Sender<()>` cannot be shared between threads safely
    |
    = help: the trait `std::marker::Sync` is not implemented for `std::sync::mpsc::Sender<()>`
    = note: required because of the requirements on the impl of `std::marker::Send` for `&std::sync::mpsc::Sender<()>`
@@ -22,3 +22,4 @@ error[E0277]: `std::sync::mpsc::Sender<()>` cannot be shared between threads saf
 
 error: aborting due to 2 previous errors
 
+If you want more information on this error, try using "rustc --explain E0277"