de-non_const `Iterator` trait methods#153708

Lars-Schumann · 2026-03-11T10:11:53Z

constifying Iterators methods that don't immediately or transitively need const closures or ugly hacks.

rustbot · 2026-03-11T10:11:59Z

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library/core/src/iter/adapters/flatten.rs

oli-obk · 2026-03-11T19:34:59Z

library/core/src/iter/traits/iterator.rs

+        {
            default fn spec_advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
-                for i in 0..n {
+                // FIXME(const-hack): this should be `for i in 0..n`


Maybe we should figure that one out first 😅

As far as const-hacks go, this is very tame, and I didn't want to make this pr too big by constifying the Range Iterator impl as well (if that's even possible right now)

yea, def don't do range iterators this in this one, I was wondering if we'd just delay on touching this one. But it is tame, and I do worry that by not doing progress here we end up in a deadlock somewhere with other iterator constifications.

oli-obk · 2026-03-12T08:42:18Z

@bors r+ rollup

rust-bors · 2026-03-12T08:42:21Z

📌 Commit 2960e3a has been approved by oli-obk

It is now in the queue for this repository.

…r-trait-methods, r=oli-obk de-non_const `Iterator` trait methods rust-lang#92476 constifying Iterators methods that don't immediately or transitively need const closures or ugly hacks.

Rollup of 11 pull requests Successful merges: - #153726 (Add optional CI job to build the compiler with the parallel frontend) - #153763 (Don't add empty target features for target-cpu=native on macOS) - #153432 (Fix some comments about dataflow analysis.) - #153529 (Fix LegacyKeyValueFormat report from docker build: pr) - #153694 (fix(query): Pass Query Key to `value_from_cycle_error`) - #153708 (de-non_const `Iterator` trait methods) - #153717 (unused_macro_rules switched used and unused comments) - #153736 (add test that an incomplete feature emits a warning) - #153748 (editorconfig: css uses tabs) - #153750 (rustc-dev-guide subtree update) - #153762 (actually make the is-fn test test what it says it tests)

Zalathar · 2026-03-12T11:29:00Z

Investigating Rollup of 11 pull requests #153767 (comment)

@bors try jobs=x86_64-rust-for-linux

…hods, r=<try> de-non_const `Iterator` trait methods try-job: x86_64-rust-for-linux

Zalathar · 2026-03-12T11:31:13Z

On closer inspection the error mentions Iterator, so I’ll assume that this PR Is the most likely cause.

@bors r-

rust-bors · 2026-03-12T11:31:20Z

This pull request was unapproved.

This PR was contained in a rollup (#153767), which was unapproved.

JonathanBrouwer · 2026-03-12T11:31:26Z

@bors r-
@bors try jobs=x86_64-rust-for-linux
#153767 (comment)

…hods, r=<try> de-non_const `Iterator` trait methods try-job: x86_64-rust-for-linux

rust-bors · 2026-03-12T12:24:31Z

💔 Test for 4b830c9 failed: CI. Failed job:

try - x86_64-rust-for-linux (web logs, enhanced plaintext logs)

rustbot · 2026-03-29T23:25:57Z

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.

Lars-Schumann · 2026-03-30T00:45:35Z

@bors try jobs=x86_64-rust-for-linux

rust-bors · 2026-03-30T00:45:40Z

@Lars-Schumann: 🔑 Insufficient privileges: not in try users

oli-obk · 2026-03-30T05:11:41Z

@bors try jobs=x86_64-rust-for-linux

…hods, r=<try> de-non_const `Iterator` trait methods try-job: x86_64-rust-for-linux

rust-bors · 2026-03-30T05:57:59Z

💔 Test for ea2c265 failed: CI. Failed job:

Calculate job matrix (web logs, enhanced plaintext logs)

Zalathar · 2026-03-30T06:16:54Z

@bors try jobs=x86_64-rust-for-linux

…hods, r=<try> de-non_const `Iterator` trait methods try-job: x86_64-rust-for-linux

rust-bors · 2026-03-30T07:11:15Z

💔 Test for f003781 failed: CI. Failed job:

try - x86_64-rust-for-linux (web logs, enhanced plaintext logs)

…r, r=oli-obk de-non_const some `Iterator` methods rust-lang#92476 r? oli-obk this is essentially just rust-lang#153708 again (which I accidentally closed...), but with the changes to `advance_by` omitted, since that seems to have caused the ICE.

Rollup merge of #154729 - Lars-Schumann:de-non_const-iterator, r=oli-obk de-non_const some `Iterator` methods #92476 r? oli-obk this is essentially just #153708 again (which I accidentally closed...), but with the changes to `advance_by` omitted, since that seems to have caused the ICE.

rustbot assigned scottmcm Mar 11, 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 11, 2026

Lars-Schumann changed the title ~~de-non_const Iterator trait methods~~ de-non_const Iterator trait methods Mar 11, 2026

Lars-Schumann force-pushed the de-non_const-iterator-trait-methods branch from 5e438b4 to 2960e3a Compare March 11, 2026 13:22

oli-obk assigned oli-obk and fee1-dead and unassigned scottmcm Mar 11, 2026

oli-obk reviewed Mar 11, 2026

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oli-obk reviewed Mar 11, 2026

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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-review Status: Awaiting review from the assignee but also interested parties. labels Mar 12, 2026

Zalathar mentioned this pull request Mar 12, 2026

Rollup of 11 pull requests #153767

Closed