Clippy lint · Complexity · checked with Clippy 0.1.99

clippy::manual_noop_waker: Checks for manual implementations of std::task::Wake that are empty

What it meansChecks for manual implementations of std::task::Wake that are empty. It is in the complexity group and warns by default.

Does it matter?

Waker::noop() provides a more performant and cleaner way to create a waker that does nothing, avoiding unnecessary Arc allocations and reference count increments.

Code that does something simple in a complicated way. Warns by default.

How to fix it

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

Flagged

struct MyWaker;
impl Wake for MyWaker {
    fn wake(self: Arc<Self>) {}
    fn wake_by_ref(self: &Arc<Self>) {}
}

Write this instead

use std::task::Waker;
let waker = Waker::noop();

Turn it off, or on

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

On one item

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

Whole crate (Cargo.toml)

[lints.clippy]
manual_noop_waker = "allow"

One run

cargo clippy -- -A clippy::manual-noop-waker

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.

Settings in clippy.toml

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

Complexitygroup

warndefault level

nofixed by cargo clippy --fix

1.96.0added in Rust

Clippy's own documentation

What it does

Checks for manual implementations of std::task::Wake that are empty.

Why is this bad?

Waker::noop() provides a more performant and cleaner way to create a waker that does nothing, avoiding unnecessary Arc allocations and reference count increments.

Example

struct MyWaker;
impl Wake for MyWaker {
    fn wake(self: Arc<Self>) {}
    fn wake_by_ref(self: &Arc<Self>) {}
}

Use instead:

use std::task::Waker;
let waker = Waker::noop();

Configuration

msrv: The minimum rust version that the project supports. Defaults to the rust-version field in Cargo.toml

(default: current version)

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

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