rust-lang/rust-clippy

Lint suggesting from_fn instead of while let Some(x)

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#3940 opened on Apr 11, 2019

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A-lintL-styleL-suggestiongood first issue

Description

With the release of 1.34 with the from_fn function, I'd like to propose a new lint that matches: while let Some(x) = expr and suggests replacing it with for x in from_fn(|| expr). (With a special-case for while let Some(x) = fn() that suggests for x in from_fn(fn) if possible.)

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.
1-3 hours
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 contributing guide
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Examine existing clippy lints in the clippy lints crate to understand the structure for adding a new lint. The pattern to match is `while let Some(x) = expr` where `expr` is a function call. Refer to the std::iter::from fn documentation and clippy's developer guide for adding lints.