rust-lang/rust-clippy

`or_fun_call` isn't always a performance lint

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#8,574 opened on Mar 22, 2022

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A-categoryL-nurserygood first issue

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Description

Replacing .unwrap_or(Vec::new()) with .unwrap_or_default() doesn't do anything for performance, they produce identical machine code with optimizations: https://rust.godbolt.org/z/hzTdazGqW.

Perhaps the lint category could be changed or it could be changed to not detect cases where it's not actually a performance warning?

Contributor guide

Research direction
Examine the `or fun call` lint implementation in Clippy to understand how it determines performance implications, then consider adjusting the lint category or adding exceptions for cases where the replacement yields identical machine code.
Tech stack
rust
Domain
developer experience
Issue type
Bug
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.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
RustClippy internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60