error[E0277]: `Cell` cannot be shared between threads safely --> $DIR/mutexguard-sync.rs:11:15 | LL | test_sync(guard); | --------- ^^^^^ `Cell` cannot be shared between threads safely | | | required by a bound introduced by this call | = help: the trait `Sync` is not implemented for `Cell` = note: required for `MutexGuard<'_, Cell>` to implement `Sync` note: required by a bound in `test_sync` --> $DIR/mutexguard-sync.rs:5:17 | LL | fn test_sync(_t: T) {} | ^^^^ required by this bound in `test_sync` error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.