Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::allow_attributes: #[allow] attribute found

What it meansChecks for usage of the #[allow] attribute and suggests replacing it with the #[expect] attribute (See RFC 2383) This lint only warns outer attributes (#[allow]), as inner attributes (#![allow]) are usually used to enable or disable lints on a global scale. It is in the restriction group and off by default.

What you see

warning: #[allow] attribute found
 --> main.rs:3:3
  |
3 | #[allow(unused_mut)]
  |   ^^^^^ help: replace it with: `expect`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#allow_attributes
  = note: requested on the command line with `-W clippy::allow-attributes`

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

#[expect] attributes suppress the lint emission, but emit a warning, if the expectation is unfulfilled. This can be useful to be notified when the lint is no longer triggered.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

#[allow(unused_mut)]
fn foo() -> usize {
    let mut a = Vec::new();
    a.len()
}

Write this instead

#[expect(unused_mut)]
fn foo() -> usize {
    let mut a = Vec::new();
    a.len()
}

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
allow_attributes = "warn"

In code

#![warn(clippy::allow_attributes)]

One run

cargo clippy -- -W clippy::allow-attributes

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

Restrictiongroup

allowdefault level

yesfixed by cargo clippy --fix

1.70.0added in Rust

Clippy's own documentation

What it does

Checks for usage of the #[allow] attribute and suggests replacing it with the #[expect] attribute (See RFC 2383)

This lint only warns outer attributes (#[allow]), as inner attributes (#![allow]) are usually used to enable or disable lints on a global scale.

Why is this bad?

#[expect] attributes suppress the lint emission, but emit a warning, if the expectation is unfulfilled. This can be useful to be notified when the lint is no longer triggered.

Example

#[allow(unused_mut)]
fn foo() -> usize {
    let mut a = Vec::new();
    a.len()
}

Use instead:

#[expect(unused_mut)]
fn foo() -> usize {
    let mut a = Vec::new();
    a.len()
}

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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