RS.CLIPPY.UNUSED_TRAIT_NAMES

Use items that import a trait but only use it anonymously

This checker is a Clippy lint created by The Rust Project Contributors. The documentation shown here is a copy of the original documentation for: unused_trait_names. Copyright ©2025 The Rust Team. All rights reserved.

What it does

Checks for use Trait where the Trait is only used for its methods and not referenced by a path directly.

Why is this bad?

Traits imported that aren't used directly can be imported anonymously with use Trait as _. It is more explicit, avoids polluting the current scope with unused names and can be useful to show which imports are required for traits.

Example

use std::fmt::Write;

fn main() {
    let mut s = String::new();
    let _ = write!(s, "hello, world!");
    println!("{s}");
}

Use instead:

use std::fmt::Write as _;

fn main() {
    let mut s = String::new();
    let _ = write!(s, "hello, world!");
    println!("{s}");
}

Configuration

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

(default: current version)