Don't drop uninit memory when `MapWindows::clone` panics by Jules-Bertholet · Pull Request #156588 · rust-lang/rust

Jules-Bertholet · 2026-05-14T23:37:32Z

Fixes #156501, using the approach suggested in @bjorn3's comment #156517 (comment)

rustbot · 2026-05-14T23:37:36Z

The Miri subtree was changed

cc @rust-lang/miri

rustbot · 2026-05-14T23:37:38Z

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scottmcm · 2026-05-18T06:27:43Z

I'm leaving libs reviews.
@rustbot reroll

rustbot · 2026-05-21T15:46:26Z

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

Jules-Bertholet · 2026-05-31T14:27:45Z

@rustbot ready

rustbot · 2026-05-31T14:31:55Z

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.

Mark-Simulacrum

@bors squash msg="Don't drop uninit memory when MapWindows::clone panics"

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Mark-Simulacrum · 2026-06-01T12:24:17Z

    fn clone(&self) -> Self {
-        let mut buffer = Buffer {
+        // Use `ManuallyDrop` until buffer is fully written to avoid dropping uninitialized elements on panic.
+        // (See `Buffer` rustdoc for safety invariant)


Hm, I guess this works, but it seems like it might be easier to just delay initializing self.start until after the write / clone complete?

But either way seems fine.

rust-bors · 2026-06-01T12:25:37Z

🔨 2 commits were squashed into 4a647a5.

Mark-Simulacrum · 2026-06-01T12:33:26Z

@bors r+ rollup

rust-bors · 2026-06-01T12:33:29Z

📌 Commit 4a647a5 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

@bjorn3

…dows-clone, r=Mark-Simulacrum Don't drop uninit memory when `MapWindows::clone` panics Fixes rust-lang#156501, using the approach suggested in @bjorn3's comment rust-lang#156517 (comment)

@bjorn3

…dows-clone, r=Mark-Simulacrum Don't drop uninit memory when `MapWindows::clone` panics Fixes rust-lang#156501, using the approach suggested in @bjorn3's comment rust-lang#156517 (comment)

@bjorn3

…dows-clone, r=Mark-Simulacrum Don't drop uninit memory when `MapWindows::clone` panics Fixes rust-lang#156501, using the approach suggested in @bjorn3's comment rust-lang#156517 (comment)

…uwer Rollup of 13 pull requests Successful merges: - #156085 (miri: require (almost) all 1-ZST arguments to be actually passed) - #155193 (Check arguments of attributes where no arguments are expected) - #156516 (nix: remove some unneeded variables) - #156562 (Resolving Windows environment test failures) - #156588 (Don't drop uninit memory when `MapWindows::clone` panics) - #156673 (Privacy: small cleanups) - #156817 (Add `#[unsafe_eii]` to unsafe EII UI tests) - #156924 (Use #[panic_handler] rather than #[lang = "panic_impl"]) - #157055 (LLVM 23: Run AssignGUIDPass in some places) - #157108 (Add Xtensa va_arg assembly coverage) - #157220 (cg_ssa: a bit less `immediate_or_packed_pair`) - #157241 (Trace `?id.local_def_index` instead of `id` in `def_path_hash`) - #157242 (Tune backport Zulip messages)

@bjorn3

Rollup merge of #156588 - Jules-Bertholet:fix-panicky-mapwindows-clone, r=Mark-Simulacrum Don't drop uninit memory when `MapWindows::clone` panics Fixes #156501, using the approach suggested in @bjorn3's comment #156517 (comment)

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 May 14, 2026

rustbot assigned scottmcm May 14, 2026

RalfJung reviewed May 15, 2026

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Comment thread src/tools/miri/tests/pass/issues/issue-156501-mapwindows-panicking-clone.rs Outdated

RalfJung reviewed May 15, 2026

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Comment thread library/core/src/iter/adapters/map_windows.rs Outdated

RalfJung reviewed May 15, 2026

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Comment thread library/core/src/iter/adapters/map_windows.rs Outdated

rustbot assigned Mark-Simulacrum and unassigned scottmcm May 18, 2026

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joboet requested changes May 21, 2026

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Comment thread library/core/src/iter/adapters/map_windows.rs Outdated

Comment thread library/coretests/tests/iter/adapters/map_windows.rs Outdated

rustbot 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 May 21, 2026

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 May 31, 2026

Jules-Bertholet force-pushed the fix-panicky-mapwindows-clone branch from 9d22610 to 4d2dcb9 Compare May 31, 2026 14:31

Mark-Simulacrum approved these changes Jun 1, 2026

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Don't drop uninit memory when panics

4a647a5

rust-bors Bot force-pushed the fix-panicky-mapwindows-clone branch from 92b3b09 to 4a647a5 Compare June 1, 2026 12:25

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 Jun 1, 2026

JonathanBrouwer mentioned this pull request Jun 1, 2026

Rollup of 10 pull requests #157246

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JonathanBrouwer mentioned this pull request Jun 1, 2026

Rollup of 10 pull requests #157253

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This was referenced Jun 1, 2026

Rollup of 13 pull requests #157261

Closed

Rollup of 13 pull requests #157266

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rust-bors Bot merged commit 8c1c6c1 into rust-lang:main Jun 2, 2026
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rustbot added this to the 1.98.0 milestone Jun 2, 2026

Jules-Bertholet deleted the fix-panicky-mapwindows-clone branch June 2, 2026 02:35

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