rust-lang/rust-clippy

Suggestion: borrowing a RefCell in funarg position

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#4632 opened on Oct 4, 2019

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 (2 comments) (3 reactions) (0 assignees)Rust (10,406 stars) (1,391 forks)batch import
A-lintT-middlegood first issue

Description

I recently came across this fun correctness bug in my code: https://github.com/rust-lang/rust/issues/65086.

I’m not sure how I could have known this without asking a compiler developer. Can we add a lint prohibiting RefCell borrows in funarg position since they prevent mutable borrows further down the stack?

Contributor guide

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.
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
RustBorrow checker basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
This feature requests a new Clippy lint to detect RefCell borrows in function argument positions. To implement, study existing Clippy lints related to borrows (e.g., borrow deref ref). The lint will need to analyze function call expressions in the HIR or MIR, checking if any argument is a borrow from a RefCell. Also review the linked Rust issue (https://github.com/rust lang/rust/issues/65086) for understanding the problem. The implementation should produce a warning with a clear message explaining why the pattern is problematic.