New lint: `vec_from_literal_array` by DanielEScherzer · Pull Request #17482 · rust-lang/rust-clippy

DanielEScherzer · 2026-07-31T16:41:53Z

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

changelog: [vec_from_literal_array]: add lint

rustbot · 2026-07-31T16:41:57Z

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CommanderStorm

LGTM.
Not sure about pedantic.. could also be stylstic?
This is something for the fcp though.

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y21 · 2026-08-01T20:54:25Z

+    fn check_expr<'tcx>(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
+        if let ExprKind::MethodCall(method_name, receiver, args, _) = expr.kind
+            && method_name.ident.name == sym::to_vec
+            && let ExprKind::Array(_) = receiver.kind


Is it intentional for now that this does not lint array repeat expressions, i.e. [1; 10].to_vec(), which can also be vec![1; 10] (they are a separate ExprKind::Repeat)?

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I figured that the lint name might not make sense for repetition - we could add a repetition lint separately sharing almost all of the logic, vec_from_array_repetition, but I figured I should start with normal arrays

I'd group that under array literal personally still.

If we go by the grammar these are strictly speaking both called ArrayExpressions not literals https://doc.rust-lang.org/reference/grammar.html#railroad-summary-ArrayExpression but [1; 10] feels like a literal to me.

Gri-ffin · 2026-08-05T14:49:37Z

+    /// It is clearer and may be more performant to use the `vec!` macro.
+    /// Calling `.to_vec()` also requires that the array values be clonable;
+    /// `vec!` has no such requirement.


Calling .to_vec() also requires that the array values be clonable;
vec! has no such requirement.

Worth noting this might change behavior for types with custom Clone implementation.

View changes since the review

Do you have an example of where this would matter in practice? Clone implementations with "side effects" in a way that would affect this feel very... cursed and I'm having a hard time coming up with a practical example (in which case I feel like it'd make the description longer for little gain). We have a bunch of similar perf lints that help eliminate clones and they don't explicitly point it out, either (e.g. redundant_iter_cloned).

Hmm, well I believe in practice this wouldn't matter indeed, the "strongest" example I had in mind was related to atomic operations, It's mostly just me being a perfectionist since you never know with these edge cases.

rustbot · 2026-08-11T23:33:07Z

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.

DanielEScherzer · 2026-08-11T23:34:06Z

@Gri-ffin would you mind taking another look so this can hopefully move towards FCP?

Gri-ffin

In the case of [a; n].to_vec(), I think it should be handled by this lint.

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rustbot · 2026-08-12T08:46:07Z

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rustbot · 2026-08-12T14:35:22Z

☔ The latest upstream changes (possibly #17552) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot added the S-waiting-on-community-reviews Status: This is awaiting for positive reviews from the community before a maintainer is assigned. label Jul 31, 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 Jul 31, 2026

CommanderStorm approved these changes Aug 1, 2026

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Comment thread tests/ui/vec_from_literal_array.rs

y21 reviewed Aug 1, 2026

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Comment thread clippy_lints/src/vec_from_literal_array.rs Outdated

y21 reviewed Aug 1, 2026

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DanielEScherzer force-pushed the vec_from_literal_array branch from 206c081 to 9b01938 Compare August 1, 2026 21:30

Gri-ffin reviewed Aug 5, 2026

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DanielEScherzer force-pushed the vec_from_literal_array branch from fcacd0c to 1e9abae Compare August 8, 2026 13:27

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DanielEScherzer added 6 commits August 11, 2026 16:32

New lint: vec_from_literal_array

beaada6

Properly skip to_vec() from a trait

0102fc0

Properly skip arrays from macros

7d93fea

Test that non-arrays do not trigger lint

6c4d883

Note performance

0637aa5

No clone requirement

6bbc7d3

DanielEScherzer force-pushed the vec_from_literal_array branch from 1e9abae to 6bbc7d3 Compare August 11, 2026 23:33

Gri-ffin approved these changes Aug 12, 2026

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rustbot removed the S-waiting-on-community-reviews Status: This is awaiting for positive reviews from the community before a maintainer is assigned. label Aug 12, 2026

rustbot assigned dswij Aug 12, 2026

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