added note/help about iterator invalidation when mutating a collection inside a for loop by ssenthilnathan3 · Pull Request #159816 · rust-lang/rust

ssenthilnathan3 · 2026-07-24T06:53:25Z

when the borrow checker detects a mutable borrow of a collection that is also immutably borrowed by a for loop,

this emits a note explaining that the for loop holds the borrow for its entire iteration, and a help
message suggesting alternatives like index-based loops.

rustbot · 2026-07-24T06:53:30Z

Thanks for the pull request, and welcome! The Rust Project is excited to review your changes, and you should hear from @camelid (or someone else) some time within the next two weeks.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

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camelid · 2026-07-24T15:37:23Z

Thanks! Looks pretty good overall, but I left a few comments.

ssenthilnathan3 · 2026-07-27T07:01:34Z

@rustbot review

rustbot · 2026-07-27T19:00:58Z

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

ssenthilnathan3 · 2026-07-28T08:06:24Z

@rustbot review

camelid

Thanks! One last nit then r=me

View changes since this review

camelid · 2026-08-06T16:18:47Z

        let issued_span = issued_spans.args_or_use();

        let borrow_spans = self.borrow_spans(span, location);
+        let gen_span = span;


Please remove this unnecessary let. Just use span at the two spots later in the function. It's confusing otherwise.

camelid · 2026-08-06T16:21:59Z

Please squash your commits into one, as well.

ssenthilnathan3 · 2026-08-07T05:17:34Z

@rustbot review

camelid · 2026-08-07T15:59:09Z

Thanks again! @bors r+ rollup

rust-bors · 2026-08-07T15:59:11Z

📌 Commit 8b5cad1 has been approved by camelid

It is now in the queue for this repository.

… r=camelid added note/help about iterator invalidation when mutating a collection inside a for loop closes: rust-lang#159489 when the borrow checker detects a mutable borrow of a collection that is also immutably borrowed by a for loop, this emits a note explaining that the for loop holds the borrow for its entire iteration, and a help message suggesting alternatives like index-based loops.

…uwer Rollup of 28 pull requests Successful merges: - #159784 (Hint that memchr returns an in-bounds index) - #160673 (Improve `canonical_param_env_cache`) - #150885 (Revive L4Re target) - #159643 (Add support for splatted function pointers) - #160433 (delegation: add support for wrapping of the return value with `From::from`) - #160530 (refactor handling of target features in Session) - #160606 (bootstrap: Store and use an explicit CheckKind in `check::Rustc`) - #160628 (fix ICE in `suggest_add_reference_to_arg` for non-callable items) - #160683 (Add regression test for unknown feaeture name reported with other errors) - #157641 (Do not promote extern statics) - #158904 (Fix FutureDropPoll shim for by-move async closures) - #159816 (added note/help about iterator invalidation when mutating a collection inside a for loop) - #160103 (Add regression test for GAT bound mismatched type error) - #160335 (dlopen offload) - #160445 (codegen: classify localized MSVC linker progress as linker_info) - #160499 (rustc_resolve: move diagnostic attribute linting to attr parsing) - #160504 (cleanup borrowck, improve c-variadic handling) - #160577 (expand: Feature gate AST-based attribute macros on expressions and statements) - #160587 (Add regression test for associated type outlives bound at call site) - #160625 (platform-support/netbsd.md: No longer mention 8.x, due to EoL.) - #160633 (delegation: fix determining wrong `FnKind` when delegation is inside const arg) - #160636 (derive(Diagnostic): link to proper docs) - #160644 (Clean up some manual debug impls) - #160649 (move naked function ui tests) - #160672 (Improve `MaybeLiveLocals`) - #160693 (Add branch config for perf. unrolling in bors) - #160696 (rustc_codegen_llvm: handle sm_101* features being an alias) - #160706 (renovate: clarify that vulnerability PRs are opened automatically)

Rollup merge of #159816 - ssenthilnathan3:e0502-loop-mutate, r=camelid added note/help about iterator invalidation when mutating a collection inside a for loop closes: #159489 when the borrow checker detects a mutable borrow of a collection that is also immutably borrowed by a for loop, this emits a note explaining that the for loop holds the borrow for its entire iteration, and a help message suggesting alternatives like index-based loops.

…uwer Rollup of 28 pull requests Successful merges: - rust-lang/rust#159784 (Hint that memchr returns an in-bounds index) - rust-lang/rust#160673 (Improve `canonical_param_env_cache`) - rust-lang/rust#150885 (Revive L4Re target) - rust-lang/rust#159643 (Add support for splatted function pointers) - rust-lang/rust#160433 (delegation: add support for wrapping of the return value with `From::from`) - rust-lang/rust#160530 (refactor handling of target features in Session) - rust-lang/rust#160606 (bootstrap: Store and use an explicit CheckKind in `check::Rustc`) - rust-lang/rust#160628 (fix ICE in `suggest_add_reference_to_arg` for non-callable items) - rust-lang/rust#160683 (Add regression test for unknown feaeture name reported with other errors) - rust-lang/rust#157641 (Do not promote extern statics) - rust-lang/rust#158904 (Fix FutureDropPoll shim for by-move async closures) - rust-lang/rust#159816 (added note/help about iterator invalidation when mutating a collection inside a for loop) - rust-lang/rust#160103 (Add regression test for GAT bound mismatched type error) - rust-lang/rust#160335 (dlopen offload) - rust-lang/rust#160445 (codegen: classify localized MSVC linker progress as linker_info) - rust-lang/rust#160499 (rustc_resolve: move diagnostic attribute linting to attr parsing) - rust-lang/rust#160504 (cleanup borrowck, improve c-variadic handling) - rust-lang/rust#160577 (expand: Feature gate AST-based attribute macros on expressions and statements) - rust-lang/rust#160587 (Add regression test for associated type outlives bound at call site) - rust-lang/rust#160625 (platform-support/netbsd.md: No longer mention 8.x, due to EoL.) - rust-lang/rust#160633 (delegation: fix determining wrong `FnKind` when delegation is inside const arg) - rust-lang/rust#160636 (derive(Diagnostic): link to proper docs) - rust-lang/rust#160644 (Clean up some manual debug impls) - rust-lang/rust#160649 (move naked function ui tests) - rust-lang/rust#160672 (Improve `MaybeLiveLocals`) - rust-lang/rust#160693 (Add branch config for perf. unrolling in bors) - rust-lang/rust#160696 (rustc_codegen_llvm: handle sm_101* features being an alias) - rust-lang/rust#160706 (renovate: clarify that vulnerability PRs are opened automatically)

rustbot assigned camelid Jul 24, 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. labels Jul 24, 2026

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camelid 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-review Status: Awaiting review from the assignee but also interested parties. labels Jul 24, 2026

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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 (such as code changes or more information) from the author. labels Jul 28, 2026

ssenthilnathan3 requested a review from camelid August 1, 2026 07:25

camelid approved these changes Aug 6, 2026

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camelid 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-review Status: Awaiting review from the assignee but also interested parties. labels Aug 6, 2026

Add note to invalidate iterator when mutating inside a for-loop

8b5cad1

ssenthilnathan3 force-pushed the e0502-loop-mutate branch from 33252b5 to 8b5cad1 Compare August 7, 2026 05:16

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Aug 7, 2026

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ssenthilnathan3 requested a review from camelid August 7, 2026 05:20

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 Aug 7, 2026

jhpratt mentioned this pull request Aug 7, 2026

Rollup of 30 pull requests #160721

Closed

JonathanBrouwer mentioned this pull request Aug 7, 2026

Rollup of 28 pull requests #160725

Merged

rust-bors Bot merged commit 386fb4e into rust-lang:main Aug 8, 2026
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rustbot added this to the 1.99.0 milestone Aug 8, 2026

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