rust-lang/rust-clippy

Lint for .clone().into_boxed_str()

Open

#15951 opened on Oct 25, 2025

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 (4 comments) (0 reactions) (1 assignee)Rust (10,406 stars) (1,391 forks)batch import
A-lintgood first issue

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

Tech stack
rust
Domain
toolingperformance
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.
1-2 days
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
Basic RustClippy lint developmentRust AST inspection
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Examine existing lints like `redundant clone` in the clippy source at `clippy lints/src/` to understand the pattern. Look at how similar conversions are handled. The issue provides a clear pattern to detect: `x.clone().into boxed str()`. Check if there is an active assignee (the issue shows one assignee) and coordinate accordingly. The implementation should add a new lint or extend an existing one, with proper tests and documentation.