error[E0597]: `counter` does not live long enough --> $DIR/issue-54556-niconii.rs:22:20 | LL | let counter = Mutex; | ------- binding `counter` declared here LL | LL | if let Ok(_) = counter.lock() { } | ^^^^^^^------- | | | borrowed value does not live long enough | a temporary with access to the borrow is created here ... ... LL | } | - | | | `counter` dropped here while still borrowed | ... and the borrow might be used here, when that temporary is dropped and runs the destructor for type `Result, ()>` | help: consider adding semicolon after the expression so its temporaries are dropped sooner, before the local variables declared by the block are dropped | LL | if let Ok(_) = counter.lock() { }; | + error: aborting due to previous error For more information about this error, try `rustc --explain E0597`.