Add #[must_use] to types and methods#3395
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mladedav merged 8 commits intotokio-rs:mainfrom Jul 5, 2025
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July 3, 2025 13:58
Methods returning `Self` often create new instances of a type without causing any side-effects (such as interacting with other types). Unlike for `must_use_candidate`, it is almost guaranteed that the user intended to use the newly created value, and simply just forgot. This fixes the `return_self_not_must_use` clippy lint.
Add `#[must_use]` attribute to public functions that return something not already marked must-use, have no mutable arg and mutate no statics. This fixes the `must_use_candidate` clippy lint.
Adding `#[must_use]` to each of a type's method is overly verbose and cluttery. This commit moves some of these `#[must_use]` calls to the type definitions instead.
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I wonder if 8a561f3 would make the |
jplatte
reviewed
Jul 4, 2025
Adding `#[must_use]` to each of a type's method is overly verbose and cluttery. This commit moves some of these `#[must_use]` calls to the type definitions instead. This is the second time doing this. See fdc0147 for the first commit doing this.
mladedav
reviewed
Jul 5, 2025
Improve the compilation error messages when never using a returned `CookieJar` (or similar structs) Also add `#[must_use]` to the `CookieJarIter` versions of those structs, with custom error messages.
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I agree. Any reason this is still marked as draft? |
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Sorry, forgot to convert it to a PR. |
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I'm on GitHub mobile right now, I can't find a way to convert it... Are any of you able to convert it for me? Otherwise I'll convert it in a few hours when I get home. |
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Ready to merge now 👌 |
jplatte
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Sep 28, 2025
Co-authored-by: Theodore Bjernhed <fosseder@danwin1210.de>
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Motivation
This PR is part of the broader PR #3394 (Activate more lints)
Sometimes, users forget to use their newly created values after calling certain methods. To make Axum more user-friendly, we should help them remember to use these values.
Solution
The
#[must_use]attribute does exactly that. It causes a warning if the resulting value is never used.This PR also adds 3 lints to
Cargo.toml.Blockers
What types should receive the
#[must_use]attribute? More importantly, which ones should not? I imagine a GitHub search might help.