rust-lang/rust-clippy

Politely mention that `Box<&T>` is almost the most useless type you can have

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#2394 opened on Jan 23, 2018

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 (25 comments) (21 reactions) (1 assignee)Rust (10,406 stars) (1,391 forks)batch import
A-lintT-middlegood first issue

Description

Found in the wild: https://stackoverflow.com/questions/48406077/mutation-of-a-variable-inside-while-loop

List of types that make no sense that we should be linting about:

  • Box<&T>
  • Box::new(SomeT) where sizeof::<T>() <= sizeof::<usize>()
    • unless there are Box::into_raw calls within the function
  • Rc<Box<T>>
  • Rc<Rc<T>>
  • Rc<&T>
  • more...?

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.
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
Rust programmingClippy lintingType system basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Examine the clippy lint infrastructure in `clippy lints/src/`. Look at existing lints like `box vec` or `rc buffer` for patterns. Investigate how to detect generic type arguments and type sizes using Rust's type system. The issue has an assignee (whirm), so coordinate with them before starting work.