rust-lang/rust-clippy

New lint: clone on arguments taken by reference

Open

#2074 opened on Sep 19, 2017

View on GitHub
 (7 comments) (0 reactions) (1 assignee)Rust (10,406 stars) (1,391 forks)batch import
A-lintL-unnecessaryT-middlegood first issue

Description

If a function takes an argument by reference, but later calls .clone() on it (or otherwise requires an impl Clone or impl Copy from it), lint that taking it by ownership allows the caller to pass in its memory rather than forcing a clone on the data.

I don't know if this is possible, but can it default to allow on public functions and deny on crate-private functions (due to the API change)?

Contributor guide

Tech stack
rust
Domain
toolingdeveloper 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.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Rust programmingclippy internalsRust ownership model
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
To implement this lint, the contributor should first understand clippy's lint infrastructure by examining existing lints in the `clippy lints` crate. They should look at how other lints detect patterns in function signatures and bodies. The issue's comment thread may provide additional clarification. The functionality should detect functions that accept a reference and later call `.clone()` on it, and suggest changing to ownership. The distinction between public and crate private functions should be considered, possibly using the `is in unconfigured public` or similar attribute.