Uplifts and extends `clippy::needless-maybe-sized` into rustc #145924

CrooseGit · 2025-08-27T11:13:11Z

Uplift the clippy::needless_maybe_sized lint into rustc as redundant_sizedness_bounds. This is useful for #144404 as it deals with redundant bound that would need to be addressed during migration.

`redundant_sizedness_bounds`

(warn-by-default)

The needless_maybe_sized lint checks that ?Sized bounds aren't redundant. This lint is extended to do the equivalent checks for the sizedness traits introduced by #144404 and thus renamed from needless_maybe_sized.

Example

// `T` cannot relaxed the `Size` bound because `Clone` requires it to be `Sized`.
fn f<T: Clone + ?Sized>(t: &T) {}
// `T` must already be `Sized`, so the bound is redundant.
fn g<T: Clone + Sized>() {}

Explanation

Relaxing a default Sized bound with ?Sized does nothing when there's another bound with a Sized supertrait (Clone in the example above)

@rustbot label: +I-lang-nominated
r? @lcnr
cc @flip1995

For Clippy:

changelog: Moves: Uplifted clippy::needless_maybe_sized into rustc as redundant_sizedness_bounds

rustbot · 2025-08-27T11:13:19Z

This PR modifies tests/ui/issues/. If this PR is adding new tests to tests/ui/issues/,
please refrain from doing so, and instead add it to more descriptive subdirectories.

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

CrooseGit · 2025-08-27T11:13:56Z

@davidtwco

samueltardieu

Reviewed only the Clippy part.

View changes since this review

src/tools/clippy/tests/ui/needless_maybe_sized.fixed

src/tools/clippy/tests/ui/derive.rs

src/tools/clippy/tests/ui/needless_doc_main.rs

src/tools/clippy/clippy_lints/src/deprecated_lints.rs

src/tools/clippy/clippy_lints/src/disallowed_macros.rs

src/tools/clippy/clippy_lints/src/needless_maybe_sized.rs

CrooseGit · 2025-08-27T17:34:32Z

Thank you @samueltardieu for your feedback. Regarding the small changes to unrelated files, I believe that was my auto-formatter doing me a disservice, and I believe I have removed said changes from the commits.
I also believe I have addressed the other points you made, but do let me know if anything is amiss.
Thanks again.

samueltardieu

I also believe I have addressed the other points you made, but do let me know if anything is amiss.

I think you still have to remove src/tools/clippy/tests/ui/needless_maybe_sized.rs and src/tools/clippy/tests/ui/needless_maybe_sized.stderr.

View changes since this review

CrooseGit · 2025-08-28T08:42:31Z

As far as I can tell those files have already been removed, let me know if I'm missing anything. Thank you

needless_maybe_sized.stderr
needless_maybe_sized.rs

davidtwco · 2025-08-28T08:53:54Z

I think you still have to remove src/tools/clippy/tests/ui/needless_maybe_sized.rs and src/tools/clippy/tests/ui/needless_maybe_sized.stderr.

These have been removed as far as I can tell, they're just showing as moves in Git as similar tests have been added to the rustc ui test suite w/ some changes.

samueltardieu · 2025-08-28T09:03:26Z

I think you still have to remove src/tools/clippy/tests/ui/needless_maybe_sized.rs and src/tools/clippy/tests/ui/needless_maybe_sized.stderr.

These have been removed as far as I can tell, they're just showing as moves in Git as similar tests have been added to the rustc ui test suite w/ some changes.

Oh yes, the subpar GitHub diff UI shows this only at the point of destination, not at the point of origin.

CrooseGit · 2025-08-28T09:58:26Z

I have added a .fixed file to the tests

tmandry · 2025-09-24T15:43:25Z

@rfcbot fcp merge

nikomatsakis · 2025-09-30T14:01:00Z

@rfcbot reviewed

new name lgtm

compiler/rustc_lint/src/redundant_sizedness_bounds.rs

tmandry · 2025-09-30T19:39:40Z

@rfcbot reviewed

rust-rfcbot · 2025-09-30T19:39:47Z

🔔 This is now entering its final comment period, as per the review above. 🔔

- Copies the lint and test (+ stderr) from clippy into rustc_lint/src and tests/ui/lint respectively. - Makes necessary changes to uplifted lint to work correctly in rustc. - Removes needless `?Sized` bounds from 3 files as detected and suggested by the lint.

- Changes name from needless-maybe-sized to redundant-sizedness-bound to reflect extended functionality.

- Extends the test to include tests covering the lint's soon to be extended functionality. - Adds `//@ run-rustfix` to test and creates corresponding .fixed file.

- Extends lint to check for redundant sizedness bounds. - Applies the extended lint's suggestions to `clone.rs` as flagged by the lint.

- Uses clippy dev tool to rename and deprecate needless-maybe-sized in clippy. - Removes needless-maybe-sized from late pass lint register.

rustbot · 2025-10-08T09:15:39Z

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.

camsteffen · 2025-10-10T07:32:38Z

I think the two cases should not be the same lint, and we should probably only uplift the first case. One case is ”bound is overridden by other bound" and the other case is "bound is implied by other bound". Ostensibly the latter case is more controversial of a lint since you may wish to make an implicit bound explicit for readability. Additionally, the latter case is generalizable for cases like Clone + Copy or ExactSizedIterator + Iterator, so we may want to leave an opening for such a more general lint.

rust-rfcbot · 2025-10-10T19:41:53Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

rustbot assigned lcnr Aug 27, 2025

rustbot added the I-lang-nominated Nominated for discussion during a lang team meeting. label Aug 27, 2025

CrooseGit changed the title ~~Dev/reucru01/needless maybe sized~~ Uplifts and extends needless-maybe-sized Aug 27, 2025

CrooseGit changed the title ~~Uplifts and extends needless-maybe-sized~~ Uplifts and extends clippy::needless-maybe-sized into rustc Aug 27, 2025

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CrooseGit force-pushed the dev/reucru01/needless-maybe-sized branch from 6f856bf to fe3f26f Compare August 27, 2025 12:33

samueltardieu reviewed Aug 27, 2025

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traviscross added the P-lang-drag-2 Lang team prioritization drag level 2.https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang. label Aug 27, 2025

CrooseGit force-pushed the dev/reucru01/needless-maybe-sized branch from fe3f26f to 7306887 Compare August 27, 2025 17:24

samueltardieu reviewed Aug 27, 2025

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samueltardieu mentioned this pull request Aug 27, 2025

triagebot: Amend a review to include a link to what was changed since rust-lang/rust-clippy#15580

Merged

CrooseGit force-pushed the dev/reucru01/needless-maybe-sized branch from 7306887 to 8446c5a Compare August 28, 2025 09:54

rust-rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Sep 26, 2025

CrooseGit force-pushed the dev/reucru01/needless-maybe-sized branch from a02ff43 to 00b61bb Compare September 26, 2025 16:24

rustbot added the T-clippy Relevant to the Clippy team. label Sep 26, 2025

traviscross reviewed Sep 30, 2025

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rust-rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Sep 30, 2025

CrooseGit force-pushed the dev/reucru01/needless-maybe-sized branch from 00b61bb to 302136b Compare October 1, 2025 09:33

Urgau added S-waiting-on-t-lang Status: Awaiting decision from T-lang and removed S-waiting-on-team DEPRECATED: Use the team-based variants `S-waiting-on-t-lang`, `S-waiting-on-t-compiler`, ... labels Oct 6, 2025

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bors added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Oct 7, 2025

CrooseGit added 6 commits October 7, 2025 17:02

Renames lint to redundant-sizedness-bound

06b467a

- Changes name from needless-maybe-sized to redundant-sizedness-bound to reflect extended functionality.

Extends tests

ae6c9cc

- Extends the test to include tests covering the lint's soon to be extended functionality. - Adds `//@ run-rustfix` to test and creates corresponding .fixed file.

Extends lint

8a05d4d

- Extends lint to check for redundant sizedness bounds. - Applies the extended lint's suggestions to `clone.rs` as flagged by the lint.

Deprecates needless-maybe-sized in clippy

d846194

- Uses clippy dev tool to rename and deprecate needless-maybe-sized in clippy. - Removes needless-maybe-sized from late pass lint register.

Applies changes suggested by reviewers

66f91da

CrooseGit force-pushed the dev/reucru01/needless-maybe-sized branch from 302136b to 66f91da Compare October 8, 2025 09:15

rustbot mentioned this pull request Oct 10, 2025

Tracking issue for release notes of #145924: Uplifts and extends clippy::needless-maybe-sized into rustc #147567

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Uplifts and extends clippy::needless-maybe-sized into rustc #145924

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Uplifts and extends clippy::needless-maybe-sized into rustc #145924

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redundant_sizedness_bounds

Example

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Uplifts and extends `clippy::needless-maybe-sized` into rustc #145924

Uplifts and extends `clippy::needless-maybe-sized` into rustc #145924

CrooseGit commented Aug 27, 2025 •

edited by traviscross

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