rust-lang/rust-clippy

Lint for .clone().into_boxed_str()

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#15,951 opened on Oct 25, 2025

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Description

What it does

Suggest turning s.clone().into_boxed_str() into Box::from(s.as_str()).

Possibly could be grouped together with other inefficient string conversions.

Advantage

Removes a call to __rust_realloc

Drawbacks

No response

Example

fn foo(s: &String) -> Box<str> {
    s.clone().into_boxed_str()
}

Could be written as:

fn foo(s: &String) -> Box<str> {
    Box::from(s.as_str())
}

Comparison with existing lints

redundant_clone generally doesn't consider the semantics of the

Additional Context

A GitHub search shows this unoptimal pattern is actually used fairly often.

Contributor guide

Research direction
Study existing Clippy lints related to string conversions, like `redundant clone`. Identify the AST pattern for `.clone().into boxed str()` and write a lint pass that suggests `Box::from(s.as str())`. Consider grouping with other inefficient string conversion lints.
Tech stack
rust
Domain
developer experiencetooling
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
RustClippy lint internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50