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Add undocumented_as_casts lint - #16682

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Add undocumented_as_casts lint#16682
charlieHsiuC wants to merge 4 commits into
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@charlieHsiuC charlieHsiuC commented Mar 7, 2026 •
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Checks for as casts that do not have a preceding // CAST: comment.

fixes #15963

changelog: new lint: [undocumented_as_casts]

@rustbot rustbot added needs-fcp PRs that add, remove, or rename lints and need an FCP S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Mar 7, 2026
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r? @samueltardieu

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github-actions Bot commented Mar 7, 2026 •
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Lintcheck changes for 99f42bd

Lint Added Removed Changed
clippy::undocumented_as_casts 6979 0 0

This comment will be updated if you push new changes

@ojeda ojeda mentioned this pull request Mar 7, 2026
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samueltardieu requested changes Mar 7, 2026
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@samueltardieu samueltardieu left a comment •
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Initial review.

Also, please add tests where parts of the cast expression come from a declarative macro. For example, a cast!(expr, type) which expands to (expr) as type, or a copy!(expr as type).

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Comment thread clippy_lints/src/undocumented_as_casts.rs Outdated
Comment thread clippy_lints/src/undocumented_as_casts.rs Outdated
Comment thread clippy_lints/src/undocumented_as_casts.rs Outdated
@rustbot rustbot added S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Mar 7, 2026
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Reminder, once the PR becomes ready for a review, use @rustbot ready.

@samueltardieu samueltardieu added the lint-nominated Create an FCP-thread on Zulip for this PR label Mar 7, 2026
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This lint has been nominated for inclusion.

A FCP topic has been created on Zulip.

@charlieHsiuC

charlieHsiuC commented Mar 11, 2026

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Hi, @samueltardieu
I've updated the code based on your suggestions.

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charlieHsiuC commented Apr 12, 2026

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To allow the existing projects to gradually adopt this lint, I have added configurations to enable checks for specific scenarios that users may be most concerned about.

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@charlieHsiuC
Add undocumented_as_casts lint to enforce comments on as casts
926bc91
@charlieHsiuC
Fix doctest fail on example code
ddc9c34
@charlieHsiuC
Share check marked comment logic with undocumented_unsafe_blocks, a…
7479907 
…dd test case for declared macro
@charlieHsiuC
Enhance undocumented_as_casts lint to improve comment checks
99f42bd 
- Refactored the linting logic to utilize `span_lint_and_then` for better suggestion handling.
- Updated the comment checking mechanism to ensure `// CAST:` comments are properly validated, including for casts originating from macro expansions.
- Improved documentation within the lint to clarify the requirements for cast comments.
- Adjusted test cases to cover new scenarios and ensure compliance with the updated linting rules.
- Refine `undocumented_as_casts` lint error messages for clarity
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This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

@charlieHsiuC

charlieHsiuC commented Sep 15, 2026

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Hi @samueltardieu,

Could you review this PR when you have a chance? I'm looking for some feedback to get it ready for merging.

Based on your suggestions, I added support for macros. I also updated the lint to show different messages when it triggers inside a macro, which is why I think using span_lint_and_then is better here.

I initially tried to reuse the logic from undocumented_unsafe_block, but I felt it gave the comments too much flexibility in terms of placement. Instead, I kept it simple and changed it to only expect comments right before the linted span.

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rustbot commented Oct 11, 2026

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☔ The latest upstream changes (possibly #13598) made this pull request unmergeable. Please resolve the merge conflicts.

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// CAST: ... comment on as casts

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