Clippy lint · Pedantic · checked with Clippy 0.1.99

clippy::used_underscore_items: used underscore-prefixed item

What it meansChecks for the use of item with a single leading underscore. It is in the pedantic group and off by default.

What you see

warning: used underscore-prefixed item
 --> main.rs:6:5
  |
6 |     _foo();
  |     ^^^^^^
  |
note: item is defined here
 --> main.rs:1:1
  |
1 | fn _foo() {}
  | ^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#used_underscore_items
  = note: `-W clippy::used-underscore-items` implied by `-W clippy::pedantic`

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?

A single leading underscore is usually used to indicate that a item will not be used. Using such a item breaks this expectation.

Stricter lints with some false positives. Off by default; opt in with clippy::pedantic.

How to fix it

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

Flagged

fn _foo() {}

struct _FooStruct {}

fn main() {
    _foo();
    let _ = _FooStruct{};
}

Write this instead

fn foo() {}

struct FooStruct {}

fn main() {
    foo();
    let _ = FooStruct{};
}

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]
used_underscore_items = "warn"

In code

#![warn(clippy::used_underscore_items)]

One run

cargo clippy -- -W clippy::used-underscore-items

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.

Pedanticgroup

allowdefault level

nofixed by cargo clippy --fix

1.83.0added in Rust

Clippy's own documentation

What it does

Checks for the use of item with a single leading underscore.

Why is this bad?

A single leading underscore is usually used to indicate that a item will not be used. Using such a item breaks this expectation.

Example

fn _foo() {}

struct _FooStruct {}

fn main() {
    _foo();
    let _ = _FooStruct{};
}

Use instead:

fn foo() {}

struct FooStruct {}

fn main() {
    foo();
    let _ = FooStruct{};
}

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

Up next

Also worth your time

Did this answer your question?