Add Vec<T> into Arc/Rc<[T]> lint by landaire · Pull Request #16790 · rust-lang/rust-clippy

landaire · 2026-04-02T06:05:51Z

Followed [lint naming conventions][lint_naming]
Added passing UI tests (including committed .stderr file)
cargo test passes locally
Executed cargo dev update_lints
Added lint documentation
Run cargo dev fmt

Adds a lint detecting conversions from Vec<T> into Arc<[T]> and Rc<[T]>. When doing this conversion, the source Vec<T> allocation cannot be re-used because of incompatible layout with Arc<[T]> and Rc<[T]>, which may be a fairly expensive reallocation depending on the source vector's size.

In most cases, it's probably better to convert to an Arc<Box<[T]>> instead.

See discussion here for rationale: https://users.rust-lang.org/t/could-arc-t-from-vec-t-be-optimized-to-remove-the-copy/137532

changelog: [vec_to_rc_slice]: add perf lint for converting from Vec<[T]> to Arc<[T]>/Rc<[T]>

rustbot · 2026-04-02T06:05:57Z

r? @dswij

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github-actions · 2026-04-02T06:15:28Z

Lintcheck changes for a6eec8f

Lint	Added	Removed	Changed
`clippy::vec_to_rc_slice`	4	0	0

This comment will be updated if you push new changes

ada4a · 2026-04-05T17:22:08Z

the changelog message doesn't need to be enclosed in a code block:) I think the default PR comment is confusing people into thinking that, because you're not the first one to have done this^^

ada4a

This is already looking very good -- just a few comments

View changes since this review

rustbot · 2026-04-05T17:56:02Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

landaire · 2026-04-06T17:49:10Z

@rustbot ready

I use jj and was trying to avoid force-pushing to preserve the original review but realized a bit too late I was applying changes on top of the existing commit rather than a new one. My apologies.

ada4a · 2026-04-06T20:04:42Z

I use jj and was trying to avoid force-pushing to preserve the original review but realized a bit too late I was applying changes on top of the existing commit rather than a new one. My apologies.

Hello fellow jj user:) I mean force-pushing is usually okay if you're only addressing smaller comments, but yeah in this case a separate commit would've been nice. Oh well^^

ada4a · 2026-04-06T20:05:09Z

@rustbot author

landaire · 2026-04-06T21:29:43Z

@rustbot ready

landaire · 2026-04-14T16:40:57Z

@rustbot ready

@ada4a I ended up not rolling back the ascryption change. I think you're right it's a losing battle but the context I have it in working with atm is probably still useful. Sorry for the delay on this.

I also noted the conflict -- I'll wait until this is approved to avoid the force push.

ada4a · 2026-04-19T17:50:47Z

I'll wait until this is approved to avoid the force push.

Oh don't worry, that should be fine -- when you do a rebase, rustbot shows this nice range-diff thing, which hides the "all the new stuff from main" part of the changes and allows concentrating on the "the things that the rebase changed in this PR" part.

Sorry for the delay on this.

That's no problem either:) As you can see, I'm not perfect myself^^ In general you're more likely to need to wait for a reviewer than vice versa...

Adds a lint detecting conversions from `Vec<T>` into `Arc<[T]>` and `Rc<[T]>`. When doing this conversion, the source `Vec<T>` allocation cannot be re-used because of incompatible layout with `Arc<[T]>` and `Rc<[T]>`, which may be a fairly expensive reallocation depending on the source vector's size. In most cases, it's probably better to convert to an `Arc<Box<[T]>>` instead. See discussion here for rationale: https://users.rust-lang.org/t/could-arc-t-from-vec-t-be-optimized-to-remove-the-copy/137532

….rs`

…e scenarios

rustbot · 2026-04-19T18:19:58Z

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.

landaire · 2026-04-20T17:19:50Z

@rustbot ready

rustbot · 2026-04-20T17:26:05Z

This lint has been nominated for inclusion.

A FCP topic has been created on Zulip.

rustbot · 2026-04-24T15:54:06Z

☔ The latest upstream changes (possibly #16025) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot assigned dswij Apr 2, 2026

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 Apr 2, 2026

landaire force-pushed the push-ywunxyxovqyn branch from 7e67b53 to fac19f9 Compare April 2, 2026 06:16

landaire commented Apr 2, 2026

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landaire force-pushed the push-ywunxyxovqyn branch from fac19f9 to 5d5596e Compare April 6, 2026 17:38

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landaire added 7 commits April 19, 2026 11:08

make Vec<T> into {wrapper}<[T]> lint an autofix lint

578e8d2

address unfixiable lints by moving them to `vec_to_rc_slice_unfixable…

24fcb66

….rs`

add support for rewriting Arc<[T]> into Arc<Box<[T]>> for more fixabl…

77d1c54

…e scenarios

fix var name failure

4db5b40

fix accidentally rolled back changes + update lint text

6f2e208

don't focus on into_boxed_slice() in error message

41904d2

ada4a requested changes Apr 19, 2026

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Comment thread clippy_lints/src/vec_to_rc_slice.rs Outdated

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Comment thread clippy_lints/src/vec_to_rc_slice.rs Outdated

Comment thread clippy_lints/src/vec_to_rc_slice.rs

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 Apr 19, 2026

landaire force-pushed the push-ywunxyxovqyn branch from e79c36a to 41904d2 Compare April 19, 2026 18:19

reduce work done before applying lint + reduce control flow

bf4b9f7

ada4a requested changes Apr 20, 2026

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Comment thread clippy_lints/src/vec_to_rc_slice.rs Outdated

make intent of inner_slice_span more clear/better code locality

a6eec8f

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties and removed S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) labels Apr 20, 2026

ada4a added lint-nominated Create an FCP-thread on Zulip for this PR and removed needs-fcp PRs that add, remove, or rename lints and need an FCP labels Apr 20, 2026

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