rust-lang/rust-clippy

Lint for unused empty function value

Open

#15957 opened on Oct 26, 2025

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 (10 comments) (0 reactions) (1 assignee)Rust (10,406 stars) (1,391 forks)batch import
C-bugI-false-negativegood first issue

Description

What it does

Suggests turning let _unused = returns_nothing(); to returns_nothing();

Advantage

Increases code hygiene

Drawbacks

None

Example

let _unused: () = returns_nothing();

Could be written as:

returns_nothing();

Comparison with existing lints

No similar lints were found

Additional Context

A quick Github search shows around 116 thousand instances of the aforementioned example

Contributor guide

Tech stack
rust
Domain
developer experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Rust programmingclippy internalsAST manipulation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
To implement this lint, study existing lints in clippy lints/src/ for patterns, especially those related to unused variables or expressions. The example shows a let binding with type (), so you need to detect let statements where the initializer's type is unit and the binding is unused (e.g., name starts with underscore). Check the Clippy documentation for adding a new lint and look at similar lints like 'let unit value'. The issue also provides a GitHub search showing many instances, which can help test the lint.