Replace unsafe usage of `NonNull::new_unchecked` with `Box::into_non_null` by ArhanChaudhary · Pull Request #160251 · rust-lang/rust

ArhanChaudhary · 2026-07-31T07:05:25Z

We can avoid unsafe by replacing unsafe { NonNull::new_unchecked(Box::into_raw(..)) } with NonNull::from_mut(Self::leak(..)). A simple test to demonstrate the code generation is equivalent: https://godbolt.org/z/P5q9bzPPK

We can avoid unsafe by replacing unsafe { NonNull::new_unchecked(Box::into_raw(..)) } with the (soon-to-be-stable) Box::into_non_null(..)

Additionally, slightly tweak documentation.

rustbot · 2026-07-31T07:05:31Z

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JohnTitor · 2026-07-31T11:49:07Z

@rustbot reroll

asquared31415 · 2026-07-31T15:56:17Z

Unfortunately, all four cases here must be Box::into_raw, because they are all intended to be used to reconstruct the Box later using Box::from_raw or Box::from_non_null. "un-leaking" a Box is not permitted.

asquared31415 · 2026-07-31T16:09:26Z

oh, it might not be forbidden entirely? it appears to be an open question: rust-lang/unsafe-code-guidelines#316

I think that the consensus from that issue is that it has to be sound for the global allocator, but might not be for custom allocators? I'm unsure, someone from opsem should probably weigh in on this.

jhpratt · 2026-08-01T02:37:28Z

cc @rust-lang/opsem ^^

Personally, the PR looks fine as far as semantics, but that's not my area of expertise. I have to say that I do find the unsafe version clearer, as leak feels a bit odd here.

saethlin · 2026-08-01T03:41:45Z

In addition to the above, there was recent discussion about this topic on Zulip: #t-opsem > Custom allocators vs Box::leak and "unleaking"

saethlin · 2026-08-01T03:45:56Z

It's pretty scary that clippy is now suggesting the more dangerous pattern. I would much prefer the lint be removed from clippy until the open questions are settled.

ArhanChaudhary · 2026-08-01T04:00:36Z

It's pretty scary that clippy is now suggesting the more dangerous pattern. I would much prefer the lint be removed from clippy until the open questions are settled.

Haha... I know right. Whoever contributed that lint clearly should have thought about it more.

( it was me :3 )

saethlin · 2026-08-01T04:35:36Z

Yeah, the lint looks reasonable and I did see you cite a comment that predates rust-lang/unsafe-code-guidelines#316, and the opsem implications aren't obvious from the code because the impact isn't local. And we don't backlink to all previous discussions of a topic when we find a lurking problem.

RalfJung · 2026-08-01T07:12:41Z

Agreed with @saethlin . Please use Box::into_non_null.

ArhanChaudhary · 2026-08-01T07:26:07Z

Thank you advising. How does this look?

jhpratt · 2026-08-01T07:29:04Z

r=me if there's no opsem concerns.

ArhanChaudhary · 2026-08-01T07:40:30Z

Thank you! How about now?

RalfJung · 2026-08-01T09:45:13Z

LGTM, thanks!
@bors squash

…null` * replace unsafe usage of `NonNull::new_unchecked` with `NonNull::from_mut` * apply review feedback * apply review feedback again!

rust-bors · 2026-08-01T09:45:34Z

🔨 3 commits were squashed into c2d84bc.

RalfJung · 2026-08-01T09:46:33Z

@bors r=jhpratt,RalfJung rollup

rust-bors · 2026-08-01T09:46:36Z

📌 Commit c2d84bc has been approved by jhpratt,RalfJung

It is now in the queue for this repository.

…=jhpratt,RalfJung Replace unsafe usage of `NonNull::new_unchecked` with `Box::into_non_null` ~~We can avoid unsafe by replacing `unsafe { NonNull::new_unchecked(Box::into_raw(..)) }` with `NonNull::from_mut(Self::leak(..))`. A simple test to demonstrate the code generation is equivalent: https://godbolt.org/z/P5q9bzPPK~~ We can avoid unsafe by replacing `unsafe { NonNull::new_unchecked(Box::into_raw(..)) }` with the (soon-to-be-stable) `Box::into_non_null(..)` Additionally, slightly tweak documentation.

…uwer Rollup of 10 pull requests Successful merges: - #157572 (stabilize size_of_val_raw, align_of_val_raw, Layout::for_value_raw) - #160012 (miri: ensure validity of references and pointers we dereference and cast) - #160294 (Update Enzyme to resolve one of the open bugs) - #159503 (allocations: document that they can be read-only) - #160250 (When issuing suggestions for missing trait items, label unstable items) - #160251 (Replace unsafe usage of `NonNull::new_unchecked` with `Box::into_non_null`) - #160311 (Remove final use of sealed traits from stdlib) - #160313 (Make the noundef-on-Cast size guard explicit) - #160323 (Box::leak: tell people to avoid unleaking) - #160328 (Move `check_track_caller` into the attribute parser)

…uwer Rollup of 12 pull requests Successful merges: - #157572 (stabilize size_of_val_raw, align_of_val_raw, Layout::for_value_raw) - #160012 (miri: ensure validity of references and pointers we dereference and cast) - #160294 (Update Enzyme to resolve one of the open bugs) - #159503 (allocations: document that they can be read-only) - #160179 (std: Update `wasip3` crate dependency) - #160250 (When issuing suggestions for missing trait items, label unstable items) - #160251 (Replace unsafe usage of `NonNull::new_unchecked` with `Box::into_non_null`) - #160311 (Remove final use of sealed traits from stdlib) - #160313 (Make the noundef-on-Cast size guard explicit) - #160323 (Box::leak: tell people to avoid unleaking) - #160328 (Move `check_track_caller` into the attribute parser) - #160333 (Remove itertools dependency from `rustc_ast_pretty`)

Rollup merge of #160251 - ArhanChaudhary:nonnull-from-mut, r=jhpratt,RalfJung Replace unsafe usage of `NonNull::new_unchecked` with `Box::into_non_null` ~~We can avoid unsafe by replacing `unsafe { NonNull::new_unchecked(Box::into_raw(..)) }` with `NonNull::from_mut(Self::leak(..))`. A simple test to demonstrate the code generation is equivalent: https://godbolt.org/z/P5q9bzPPK~~ We can avoid unsafe by replacing `unsafe { NonNull::new_unchecked(Box::into_raw(..)) }` with the (soon-to-be-stable) `Box::into_non_null(..)` Additionally, slightly tweak documentation.

…uwer Rollup of 12 pull requests Successful merges: - rust-lang/rust#157572 (stabilize size_of_val_raw, align_of_val_raw, Layout::for_value_raw) - rust-lang/rust#160012 (miri: ensure validity of references and pointers we dereference and cast) - rust-lang/rust#160294 (Update Enzyme to resolve one of the open bugs) - rust-lang/rust#159503 (allocations: document that they can be read-only) - rust-lang/rust#160179 (std: Update `wasip3` crate dependency) - rust-lang/rust#160250 (When issuing suggestions for missing trait items, label unstable items) - rust-lang/rust#160251 (Replace unsafe usage of `NonNull::new_unchecked` with `Box::into_non_null`) - rust-lang/rust#160311 (Remove final use of sealed traits from stdlib) - rust-lang/rust#160313 (Make the noundef-on-Cast size guard explicit) - rust-lang/rust#160323 (Box::leak: tell people to avoid unleaking) - rust-lang/rust#160328 (Move `check_track_caller` into the attribute parser) - rust-lang/rust#160333 (Remove itertools dependency from `rustc_ast_pretty`)

rustbot assigned JohnTitor Jul 31, 2026

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 Jul 31, 2026

rustbot assigned jhpratt and unassigned JohnTitor Jul 31, 2026

ArhanChaudhary changed the title ~~Replace unsafe usage of NonNull::new_unchecked with NonNull::from_mut~~Replace unsafe usage of NonNull::new_unchecked with Box::into_non_nullAug 1, 2026

RalfJung reviewed Aug 1, 2026
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Comment threadlibrary/alloc/src/boxed.rs Outdated

RalfJung reviewed Aug 1, 2026
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Comment threadlibrary/core/src/ptr/non_null.rs Outdated

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Comment threadlibrary/core/src/ptr/non_null.rs Outdated

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Replace unsafe usage of NonNull::new_unchecked with `Box::into_non_…
c2d84bc
…null` * replace unsafe usage of `NonNull::new_unchecked` with `NonNull::from_mut` * apply review feedback * apply review feedback again!

rust-borsBotforce-pushed the nonnull-from-mut branch from 0151071 to c2d84bcCompare August 1, 2026 09:45

rust-borsBot added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Aug 1, 2026

rust-borsBot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 1, 2026

ArhanChaudhary mentioned this pull request Aug 1, 2026
Rename and reimplement nonnull_unchecked_on_box_ptrrust-lang/rust-clippy#17485
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JonathanBrouwer mentioned this pull request Aug 1, 2026
Rollup of 10 pull requests #160332
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JonathanBrouwer mentioned this pull request Aug 1, 2026
Rollup of 12 pull requests #160339
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rust-borsBot merged commit ac499eb into rust-lang:mainAug 1, 2026
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rustbot added this to the 1.99.0 milestone Aug 1, 2026

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