Found non-binding `let` on a synchronization lockRS-E1014

A "non-binding" let is one of the form let _ = <expr>. Such statements immediately drop the right-hand side expression. When non-binding let statements are used with synchronization locks, the guard to the lock is immediately dropped instead of living till the end of the scope as expected, which is often not intended. To extend the lifetime of the guard to the end of the scope, use an underscore-prefixed name instead (i.e. _lock). If you want to explicitly drop the lock, std::mem::drop(lock) conveys the intention better and is less error-prone.

Consider revisiting this statement if the intention was not to immediately drop the guard. Otherwise, prefer using std::mem::drop. This issue is tuned to work on synchronization locks from the standard library such as std::sync::Mutex, and those from the parking_lot crate, such as parking_lot::RawMutex.

Bad practice

let guard = std::sync::Mutex::new(data);
let _ = guard.lock();

let rwlock = parking_lot::RwLock::new(data);
let _ = rwlock.read();

Recommended

let guard = std::sync::Mutex::new();
let _lock = guard.lock();

let rwlock = parking_lot::RwLock::new(data);
let _read_lock = rwlock.read();