rust-lang/rust-clippy

New lint: Use `Into`/`TryInto` in bounds as opposed to `From`/`TryFrom`

Open

#4,894 opened on Dec 10, 2019

View on GitHub
 (29 comments) (1 reaction) (0 assignees)Rust (1,391 forks)batch import
A-lintL-stylegood first issue

Repository metrics

Stars
 (10,406 stars)
PR merge metrics
 (Avg merge 19d 22h) (113 merged PRs in 30d)

Description

When writing generic bounds such as:

fn foo<T>(a: T) where u32: From<T>;

Into should be preferred, like this:

fn foo<T>(a: T) where T: Into<u32>;

Why the former is bad: Into is a superset of From. In some cases coherence rules prevent implementing From but do allow implementing Into. As a result Into is more generic bound than From.

Category: Style, I guess?

Contributor guide

Research direction
Study existing lint examples in Clippy, then implement a new lint that detects `From`/`TryFrom` bounds and suggests replacing with `Into`/`TryInto`.
Tech stack
rust
Domain
developer 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.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Rust
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70