Rename and reimplement `nonnull_unchecked_on_box_ptr` by ArhanChaudhary · Pull Request #17485 · rust-lang/rust-clippy

ArhanChaudhary · 2026-08-01T10:12:06Z

changelog: rename and reimplement nonnull_unchecked_on_box_ptr lint.

Address the discussion in rust-lang/rust#160251 with @RalfJung's recommendation of a re-implementation of the nonnull_unchecked_on_box_ptr lint. Now that rust-lang/rust#130364 was very recently stabilized, we can ship this lint with 1.98.

A question: because the old lint had not yet been released, do I need to follow cargo dev rename_lint? If so, do I need to specify #[clippy::version = "1.99.0"] (which doesn't make sense because 1.98 hasn't been released yet) or leave it as #[clippy::version = ""]? Currently, I have ran cargo dev rename_lint and specified #[clippy::version = ""].

rustbot · 2026-08-01T10:12:09Z

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ArhanChaudhary · 2026-08-01T10:13:28Z

+    /// Checks for unsafe usage of `NonNull::new_unchecked(Box::into_raw(x))` or dangerous usage of `NonNull::from_mut(Box::leak(x))` and suggests calling `Box::into_non_null(x)` instead.
+    ///
+    /// ### Why is this bad?
+    /// First, `NonNull::new_unchecked` is an unsafe function, which we don't need to call at all. Second, at the time of writing, whether or not you are allowed to reconstruct the `Box` from the mutable reference returned by `Box::leak` is an [open question](https://doc.rust-lang.org/std/boxed/struct.Box.html#method.leak). Thus, this lint helps prevent future dangerous calls to `Box::from_non_null`.


The hyperlink will eventually point to the updated documentation in this PR: rust-lang/rust#160323

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ArhanChaudhary · 2026-08-01T10:39:07Z

Also, I'm not sure what category this lint falls into anymore, since the from_mut transformation is a correctness transformation but the new_unchecked transformation is a complexity transformation. We could separate these into two different lints, but that would feel weird. Let me know your thoughts.

github-actions · 2026-08-01T10:43:19Z

Lintcheck changes for 3d65490

Lint	Added	Removed	Changed
`clippy::nonnull_unchecked_on_box_ptr`	0	1	0

This comment will be updated if you push new changes

CommanderStorm

community review: LGTM, mostly a move with the minor changes already discussed 👍🏻

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CommanderStorm

as above:
Community review LGTM

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rustbot · 2026-08-08T09:17:57Z

This PR was rebased onto a different master 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.

Jarcho · 2026-08-09T18:20:03Z

Nothing about NonNull::from(Box::leak(_)) is undefined or even wrong so it doesn't belong in correctness. This also makes improper_nonnull_from_box a very misleading name.

ArhanChaudhary · 2026-08-09T19:00:45Z

There was recently discussion where the compiler people agreed that this is, in general dangerous, specifically with custom allocators. rust-lang/rust#160251 (comment)

See the PR description for more

Jarcho · 2026-08-09T19:12:50Z

I read the thread. The issue there is unleaking the pointer created, not creating the pointer in general.

ArhanChaudhary · 2026-08-09T19:18:06Z

The idea is to prevent future unleaking of the pointer, despite creating the pointer is safe.

ArhanChaudhary · 2026-08-09T19:27:48Z

Or, apologies I mischaracterized what you were responding to. Did you bring that up to answer which lint category this should be in, or do you disagree with the rewrite?

Jarcho · 2026-08-09T19:28:10Z

That neither justifies the rename nor claiming that it's a correctness issue. I have no issue linting on it.

Jarcho

This feels like it should be two different lints. Linting NonNull::from(Box::leak()) is only done due to unresolved provenance questions if that pointer is later unleaked. That definitely doesn't fit a complexity lint, but it could be either suspicious or pedantic depending on what the lint catches in practice.

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Jarcho · 2026-08-09T19:35:37Z

+                && expr2
+                    .ty_rel_def_if_named(cx, sym::leak)
+                    .opt_parent(cx)
+                    .opt_impl_ty(cx)
+                    .is_lang_item(cx, LangItem::OwnedBox)


This needs to check specifically for Box<T, Global>. You can suggest into_non_null_with_allocator for any other allocator.

Jarcho · 2026-08-09T19:36:45Z

+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for unsafe usage of `NonNull::new_unchecked(Box::into_raw(x))` or dangerous usage of `NonNull::from_mut(Box::leak(x))` and suggests calling `Box::into_non_null(x)` instead.


This can't be called a dangerous use since we didn't (and can't reasonably) check if it was unleaked.

rustbot · 2026-08-09T19:44:01Z

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

rustbot · 2026-08-11T23:28:21Z

☔ The latest upstream changes (possibly #17538) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot added the S-waiting-on-community-reviews Status: This is awaiting for positive reviews from the community before a maintainer is assigned. label Aug 1, 2026

rustbot added needs-fcp PRs that add, remove, or rename lints and need an FCP S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Aug 1, 2026

ArhanChaudhary commented Aug 1, 2026

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ArhanChaudhary mentioned this pull request Aug 1, 2026

Box::leak: tell people to avoid unleaking rust-lang/rust#160323

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CommanderStorm approved these changes Aug 1, 2026

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Comment thread tests/ui/improper_nonnull_from_box.rs Outdated

ArhanChaudhary requested a review from CommanderStorm August 1, 2026 19:40

CommanderStorm approved these changes Aug 1, 2026

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ArhanChaudhary force-pushed the revamp-my-lint branch from dabffc8 to 4f084a7 Compare August 1, 2026 19:50

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ArhanChaudhary added 9 commits August 8, 2026 02:17

rename lint

a18fe6e

revamp implementation

8c55bbb

rewords

144fa90

dont need feature flag anymore

60dae62

try to pass ci challenge

0c2f6ab

try to pass ci challenge (difficulty level: extreme)

966fc92

apply review feedback again

e1c787f

forgor uibless

356161b

update msrvs.rs

fd1eedc

ArhanChaudhary force-pushed the revamp-my-lint branch from ed8acfe to fd1eedc Compare August 8, 2026 09:17

remove old lint

3d65490

Jarcho requested changes Aug 9, 2026

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rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Aug 9, 2026

rustbot added the S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) label Aug 9, 2026

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