Lint against iterator functions that panic when `N` is zero by Urgau · Pull Request #153563 · rust-lang/rust

Urgau · 2026-03-08T12:14:42Z

This PR extends the deny-by-default unconditional_panic lint, by linting on iterator functions that panics when N (chunks/windows size) is zero¹.

Those methods are documented to panic if N is zero.

error: this operation will panic at runtime
  --> $DIR/const-n-is-zero.rs:11:13
   |
LL |     let _ = s.array_windows::<0>();
   |             ^^^^^^^^^^^^^^^^^^^^^^ const parameter `N` is zero
   |
   = note: `#[deny(unconditional_panic)]` on by default

cc @rust-lang/libs-api

this is done by introducing a new internal attribute on the const parameter: #[rustc_panics_when_zero] ↩

rustbot · 2026-03-08T12:14:45Z

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann, @JonathanBrouwer

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @vakaras

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann, @JonathanBrouwer

This PR changes rustc_public

cc @oli-obk, @celinval, @ouz-a, @makai410

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

rustbot · 2026-03-08T12:14:47Z

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RalfJung · 2026-03-08T12:32:40Z

This PR adds new kind of variant to the deny-by-default unconditional_panic lint, by linting on iterator functions that panics when N (chunks/windows size) is zero.

This seems to do much more than that. It adds a new language primitive, a new kind of built-in assertion. Could you motivate that?

Urgau · 2026-03-08T12:41:08Z

This seems to do much more than that. It adds a new language primitive, a new kind of built-in assertion. Could you motivate that?

The code is unfortunately tangled, it doesn't add a new language primitive per se, but report_assert_as_lint requires a AssertKind variant even if it's just for linting in one place.

I could probably modify that function so it doesn't take an AssertKind, but I wasn't sure about that.

RalfJung · 2026-03-08T12:43:44Z

Given that AssertKind is part of the MIR syntax, I feel very strongly that we shouldn't modify it for non-MIR/opsem purposes.

Urgau · 2026-03-08T13:23:56Z

Understandable, I've reworked the PR to avoid touching at AssertKind.

JohnTitor

I love the idea but it should better for someone more familiar with this topic other than me to review. @RalfJung Could you take over? Otherwise I'd reroll.

View changes since this review

RalfJung · 2026-03-09T10:51:27Z

I'm afraid not, I don't have capacity at the moment.

@rustbot reroll

fee1-dead

I think the overall idea is good and I could see myself approving down the line, however I think we should see if we can have an attribute on the generic parameter itself instead of applying rustc_panics_when_n_is_zero to the enclosing function. If not, I'd still want something more verbose, such as #[rustc_panics_when_const_param_is_zero(N)]

I don't think this should be touching AssertLint. I feel like it might be simpler to just add a separate error for this rather than using existing mechanisms.

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Urgau · 2026-03-29T20:43:25Z

I had to add the encoding of const-params in rmeta, but otherwise I've moved the attribute directly to the const generic.

I've also removed any interaction with AssertLint, but kept the reporting behind the unconditional_panic lint.

@rustbot ready

fee1-dead · 2026-04-06T00:03:19Z

overall looks good, would like someone else to sign off with me on this together though

@rustbot reroll

Urgau · 2026-07-23T17:13:48Z

r? compiler

ShoyuVanilla

The implementation looks good to me. Do we need another approval to merge this?

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Urgau · 2026-07-27T06:53:42Z

@fee1-dead also approved it in this comment.

@bors r=fee1-dead,ShoyuVanilla

rust-bors · 2026-07-27T06:53:45Z

📌 Commit 93b8cf2 has been approved by fee1-dead,ShoyuVanilla

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

Reason for tree closure: spurious failures

…r=fee1-dead,ShoyuVanilla Lint against iterator functions that panic when `N` is zero This PR extends the deny-by-default `unconditional_panic` lint, by linting on iterator functions that panics when `N` (chunks/windows size) is zero[^attr]. Those methods are [documented](https://doc.rust-lang.org/std/primitive.slice.html#panics-11) to panic if `N` is zero. ``` error: this operation will panic at runtime --> $DIR/const-n-is-zero.rs:11:13 | LL | let _ = s.array_windows::<0>(); | ^^^^^^^^^^^^^^^^^^^^^^ const parameter `N` is zero | = note: `#[deny(unconditional_panic)]` on by default ``` cc @rust-lang/libs-api [^attr]: this is done by introducing a new internal attribute on the const parameter: `#[rustc_panics_when_zero]`

JonathanBrouwer · 2026-07-27T09:57:20Z

💔 I suspect this PR failed tests as part of a rollup
@bors r-

After fixing the problem, consider running a try job for the failed job before re-approving.

Link to failure: https://github.com/rust-lang/rust/actions/runs/30255157007/job/89942047433?pr=160002

rust-bors · 2026-07-27T09:57:29Z

This pull request was unapproved.

This PR was contained in a rollup (#160002), which was unapproved.

View changes since this unapproval

rustbot · 2026-07-27T20:48:43Z

This PR was rebased onto a different main 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.

ShoyuVanilla · 2026-07-28T02:44:49Z

@bors r=fee1-dead,ShoyuVanilla

rust-bors · 2026-07-28T02:44:51Z

📌 Commit 24e4698 has been approved by fee1-dead,ShoyuVanilla

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

Reason for tree closure: spurious failures

Rollup of 9 pull requests Successful merges: - #153563 (Lint against iterator functions that panic when `N` is zero ) - #159960 (Allow `UnsafeCell` content access without `get` in `invalid_reference_casting` lint) - #158893 (Clarify preconditions of raw size/align methods) - #159220 (Don't optimize across storage markers in SimplifyComparisonIntegral) - #159309 (Move tests batch 18) - #159450 (Add codegen test for enum clone) - #160017 (Make BorrowSet methods public again) - #160022 (Refactor rustc_hir re-exports) - #160041 (Correct tracking issue for `casefold` feature)

Rollup merge of #153563 - Urgau:lint-panics-when-n-is-zero, r=fee1-dead,ShoyuVanilla Lint against iterator functions that panic when `N` is zero This PR extends the deny-by-default `unconditional_panic` lint, by linting on iterator functions that panics when `N` (chunks/windows size) is zero[^attr]. Those methods are [documented](https://doc.rust-lang.org/std/primitive.slice.html#panics-11) to panic if `N` is zero. ``` error: this operation will panic at runtime --> $DIR/const-n-is-zero.rs:11:13 | LL | let _ = s.array_windows::<0>(); | ^^^^^^^^^^^^^^^^^^^^^^ const parameter `N` is zero | = note: `#[deny(unconditional_panic)]` on by default ``` cc @rust-lang/libs-api [^attr]: this is done by introducing a new internal attribute on the const parameter: `#[rustc_panics_when_zero]`

rustbot added the A-attributes Area: Attributes (`#[…]`, `#![…]`) label Mar 8, 2026

rustbot assigned JohnTitor Mar 8, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Mar 8, 2026

Urgau force-pushed the lint-panics-when-n-is-zero branch from ff233d2 to 44380ea Compare March 8, 2026 12:25

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rustbot assigned ShoyuVanilla and unassigned jackh726 Jul 23, 2026

ShoyuVanilla approved these changes Jul 27, 2026

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JonathanBrouwer mentioned this pull request Jul 27, 2026

Rollup of 15 pull requests #160002

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rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jul 27, 2026

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Comment thread compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs Outdated

Urgau added 4 commits July 27, 2026 22:44

Add #[rustc_panics_when_zero] attribute

73d7d8d

Apply #[rustc_panics_when_zero] to the relevant core functions

d67cce7

Encode const params attributes in rmeta

5413066

Lint against iterator functions that panics when N is zero

24e4698

Urgau force-pushed the lint-panics-when-n-is-zero branch from 93b8cf2 to 24e4698 Compare July 27, 2026 20:48

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 28, 2026

jhpratt mentioned this pull request Jul 28, 2026

Rollup of 9 pull requests #160047

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rust-bors Bot merged commit f8ee207 into rust-lang:main Jul 28, 2026
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rustbot added this to the 1.99.0 milestone Jul 28, 2026

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