rust-lang/rust-clippy

Rewrite `arithmetic_side_effects` to not use matching on string representation of types

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#16359 opened on Jan 8, 2026

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C-enhancementgood first issue

Description

Description

arithmetic_side_effects uses the string representation of types to compare them. This will miss aliases (including core/alloc → std), takes longer to compare, etc.

It should use a method similar to what is done in the disallowed_types lint, where maps of DefId or PrimTy are built at lint initialization time and then used throughout the tree walk. Some type lookup code could probably even be shared (including the part where unloaded crates don't cause errors).

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Contributor guide

Tech stack
rust
Domain
developer experiencetooling
Issue type
refactor
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.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
RustClippy internalsDefId and PrimTyLint initialization
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Study the implementation of the `disallowed types` lint in the clippy codebase to understand how maps of DefId or PrimTy are built at initialization. Look at files like `clippy lints/src/disallowed types.rs` and the associated type lookup code. The goal is to replicate that pattern in `arithmetic side effects` located in `clippy lints/src/arithmetic side effects.rs`. Ensure that the new approach handles type aliases and avoids string representation comparisons.