Clippy lint · Correctness · checked with Clippy 0.1.99

clippy::if_let_mutex: Checks for Mutex::lock calls in if let expression with lock calls in any of the else blocks

What it meansChecks for Mutex::lock calls in if let expression with lock calls in any of the else blocks. It is in the correctness group and denied by default (the build fails).

Does it matter?

The Mutex lock remains held for the whole if let ... else block and deadlocks.

Code that is almost certainly wrong. Denied by default: the build fails until you fix it or allow it.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

if let Ok(thing) = mutex.lock() {
    do_thing();
} else {
    mutex.lock();
}

Write this instead

let locked = mutex.lock();
if let Ok(thing) = locked {
    do_thing(thing);
} else {
    use_locked(locked);
}

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::if_let_mutex)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
if_let_mutex = "allow"

One run

cargo clippy -- -A clippy::if-let-mutex

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Correctnessgroup

denydefault level

nofixed by cargo clippy --fix

1.45.0added in Rust

Clippy's own documentation

What it does

Checks for Mutex::lock calls in if let expression with lock calls in any of the else blocks.

Disabled starting in Edition 2024

This lint is effectively disabled starting in Edition 2024 as if let ... else scoping was reworked such that this is no longer an issue. See Proposal: stabilize if_let_rescope for Edition 2024

Why is this bad?

The Mutex lock remains held for the whole if let ... else block and deadlocks.

Example

if let Ok(thing) = mutex.lock() {
    do_thing();
} else {
    mutex.lock();
}

Should be written

let locked = mutex.lock();
if let Ok(thing) = locked {
    do_thing(thing);
} else {
    use_locked(locked);
}

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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