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do not in-place-iterate over flatmap/flatten #135104

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merged 2 commits into from
Jan 5, 2025

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@the8472 the8472 commented Jan 4, 2025

The implementation is unsound when a partially consumed iterator has some elements buffered in the front/back parts and cloning the Iterator removes the capacity from the backing vec::IntoIter.

This is a fix for #135103 that removes the specialization trait impls without removing some supporting parts. I've kept it small so it can be easily backported. I'll either remove the remaining parts or think of a way to recover the optimization in a separate PR.

The implementation is unsound when a partially consumed iterator has
some elements buffered in the front/back parts and cloning the Iterator
removes the capacity from the backing vec::IntoIter.
@the8472 the8472 added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Jan 4, 2025
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rustbot commented Jan 4, 2025

r? @Mark-Simulacrum

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jan 4, 2025
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@bors r+

I think a backport is not unreasonable (it seems pretty safe and is a clear soundness fix), but it's also been broken for a while so probably not critical.

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bors commented Jan 4, 2025

📌 Commit 1ed0ea4 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

@bors bors 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 Jan 4, 2025
bors added a commit to rust-lang-ci/rust that referenced this pull request Jan 5, 2025
…kingjubilee

Rollup of 4 pull requests

Successful merges:

 - rust-lang#134925 (deny usage of special FileCheck prefixes as revision names)
 - rust-lang#134996 (Add UWP (msvc) target support page)
 - rust-lang#135104 (do not in-place-iterate over flatmap/flatten)
 - rust-lang#135110 (library: fix adler{ -> 2}.debug)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 5be6c9b into rust-lang:master Jan 5, 2025
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@rustbot rustbot added this to the 1.86.0 milestone Jan 5, 2025
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Jan 5, 2025
Rollup merge of rust-lang#135104 - the8472:disable-in-place-iter-for-flatten, r=Mark-Simulacrum

do not in-place-iterate over flatmap/flatten

The implementation is unsound when a partially consumed iterator has some elements buffered in the front/back parts and cloning the Iterator removes the capacity from the backing vec::IntoIter.

This is a fix for rust-lang#135103 that removes the specialization trait impls without removing some supporting parts. I've kept it small so it can be easily backported. I'll either remove the remaining parts or think of a way to recover the optimization in a separate PR.
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bors commented Jan 5, 2025

⌛ Testing commit 1ed0ea4 with merge 8417f83...

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4 participants