rust-lang/rust-clippy

Lint for Iterator + Copy

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#1534 opened on Feb 13, 2017

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A-lintE-mediumL-correctnessgood first issue

Description

Implementing Copy for iterators makes footguns, and the standard library settled not to do so for now.

let mut it = /* a Copy + Iterator */;
for x in it { if cond { break; } } // `it` copied here (forgot to `&mut it`)
let x = it.next(); // `it` is in the initial state

Clippy should have a lint that warns if "use of the original iterator after copied" is detected.

Contributor guide

Tech stack
rust
Domain
tooling
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.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Rust programmingClippy lint developmentGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Study existing Clippy lints for pattern of detecting Copy types on iterators. The referenced rust lang/rust PR #21846 provides context. Implement a lint using the `declare clippy lint!` macro and check for Copy + Iterator trait bounds in function parameters or loop expressions.