More accurately check for interior mutability in `invalid_reference_casting` lint - #160159

Urgau · 2026-07-29T15:14:28Z

This PR replaces the Freeze trait check in the invalid_reference_casting lint by a recursive type check.

The check was not enough to determine if a type has "interior mutability", as Freeze is proxy for "has some interior mutability", not "fully covered by interior mutability".

As requested in #159960 (comment)

r? mejrs

Urgau · 2026-07-29T15:16:56Z

@bors try @rust-timer queue

More accurately check for interior mutability in `invalid_reference_casting` lint

rust-bors · 2026-07-29T17:23:05Z

☀️ Try build successful (CI)
Build commit: b235b37 (b235b372268a906fe0e2f0deabfe4fbb2889d954)
Base parent: d366396 (d3663963ca08f465d01d283a7199778902623bb9)

rust-timer · 2026-07-29T18:07:56Z

Finished benchmarking commit (b235b37): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-2.6%, -2.6%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -3.9%, secondary -5.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.9%	[-5.3%, -3.0%]	3
Improvements ✅ (secondary)	-5.6%	[-5.6%, -5.6%]	1
All ❌✅ (primary)	-3.9%	[-5.3%, -3.0%]	3

Cycles

Results (primary -0.1%, secondary 0.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.5%, 1.3%]	6
Regressions ❌ (secondary)	1.6%	[0.4%, 4.6%]	15
Improvements ✅ (primary)	-0.9%	[-2.4%, -0.4%]	6
Improvements ✅ (secondary)	-1.9%	[-4.1%, -0.5%]	4
All ❌✅ (primary)	-0.1%	[-2.4%, 1.3%]	12

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 489.658s -> 495.449s (1.18%)
Artifact size: 390.17 MiB -> 390.19 MiB (0.01%)

mejrs

@bors r+ rollup

View changes since this review

rust-bors · 2026-07-31T09:21:52Z

📌 Commit 0c2035c has been approved by mejrs

It is now in the queue for this repository.

…l, r=mejrs More accurately check for interior mutability in `invalid_reference_casting` lint This PR replaces the `Freeze` trait check in the `invalid_reference_casting` lint by a recursive type check. The check was not enough to determine if a type has "interior mutability", as `Freeze` is proxy for "has *some* interior mutability", not "fully covered by interior mutability". As requested in rust-lang#159960 (comment)

…uwer Rollup of 21 pull requests Successful merges: - #160100 (Add "system" option to `override-allocator` directive) - #159675 (rustc: Support `--jobs` options for limiting parallelism in various parts of the compiler) - #159999 (Fix invalidation of stdlib in bootstrap when using non-LLVM codegen backends) - #160233 (Bubble bad path error while parsing field to avoid unecessary second error) - #160272 (rustc_metadata: Move native library search code to `rustc_codegen_ssa`) - #154202 (rustfmt: Format `cfg_select!`) - #158835 (rustc_passes: lint unused `#[path]` attributes on inline modules) - #159520 (Suggest `Vec<T>` instead of `[T]`) - #160034 (Move "macro only" check for `#[allow_internal_unsafe/unstable]` to attribute parser) - #160066 (rustc_middle: lint attribute cleanups) - #160085 (Remove various superfluous lint attributes) - #160113 (Coalesce `rustc_on_unimplemented` attributes and lint malformed filters) - #160119 (fix query cycle in `coroutine_hidden_types` for the next solver) - #160147 (tests: Remove `-Zthreads` options from tests in `ui/parallel-rustc`) - #160157 (Remove outdated comments from `va_list.rs`) - #160159 (More accurately check for interior mutability in `invalid_reference_casting` lint) - #160208 (rustdoc: Fix crash when trying to list attributes on an opaque type) - #160244 (Rename splat to rustc_splat in error messages) - #160246 (dont fire `unused_mut` on `&pin mut self`) - #160247 (Configure backport nominations for rustfmt) - #160274 (renovate: update lock files weekly)

…uwer Rollup of 22 pull requests Successful merges: - #160100 (Add "system" option to `override-allocator` directive) - #160220 (Refactor: shrink region ext traits) - #159675 (rustc: Support `--jobs` options for limiting parallelism in various parts of the compiler) - #159999 (Fix invalidation of stdlib in bootstrap when using non-LLVM codegen backends) - #160233 (Bubble bad path error while parsing field to avoid unecessary second error) - #160272 (rustc_metadata: Move native library search code to `rustc_codegen_ssa`) - #154202 (rustfmt: Format `cfg_select!`) - #159520 (Suggest `Vec<T>` instead of `[T]`) - #159710 (Add rustdoc/cargo PGO profiles to reproducible artifacts) - #160034 (Move "macro only" check for `#[allow_internal_unsafe/unstable]` to attribute parser) - #160066 (rustc_middle: lint attribute cleanups) - #160085 (Remove various superfluous lint attributes) - #160113 (Coalesce `rustc_on_unimplemented` attributes and lint malformed filters) - #160119 (fix query cycle in `coroutine_hidden_types` for the next solver) - #160147 (tests: Remove `-Zthreads` options from tests in `ui/parallel-rustc`) - #160157 (Remove outdated comments from `va_list.rs`) - #160159 (More accurately check for interior mutability in `invalid_reference_casting` lint) - #160208 (rustdoc: Fix crash when trying to list attributes on an opaque type) - #160244 (Rename splat to rustc_splat in error messages) - #160246 (dont fire `unused_mut` on `&pin mut self`) - #160247 (Configure backport nominations for rustfmt) - #160274 (renovate: update lock files weekly)

Rollup merge of #160159 - Urgau:invalid_ref_casts-unsafe-cell, r=mejrs More accurately check for interior mutability in `invalid_reference_casting` lint This PR replaces the `Freeze` trait check in the `invalid_reference_casting` lint by a recursive type check. The check was not enough to determine if a type has "interior mutability", as `Freeze` is proxy for "has *some* interior mutability", not "fully covered by interior mutability". As requested in #159960 (comment)

…uwer Rollup of 22 pull requests Successful merges: - rust-lang/rust#160100 (Add "system" option to `override-allocator` directive) - rust-lang/rust#160220 (Refactor: shrink region ext traits) - rust-lang/rust#159675 (rustc: Support `--jobs` options for limiting parallelism in various parts of the compiler) - rust-lang/rust#159999 (Fix invalidation of stdlib in bootstrap when using non-LLVM codegen backends) - rust-lang/rust#160233 (Bubble bad path error while parsing field to avoid unecessary second error) - rust-lang/rust#160272 (rustc_metadata: Move native library search code to `rustc_codegen_ssa`) - rust-lang/rust#154202 (rustfmt: Format `cfg_select!`) - rust-lang/rust#159520 (Suggest `Vec<T>` instead of `[T]`) - rust-lang/rust#159710 (Add rustdoc/cargo PGO profiles to reproducible artifacts) - rust-lang/rust#160034 (Move "macro only" check for `#[allow_internal_unsafe/unstable]` to attribute parser) - rust-lang/rust#160066 (rustc_middle: lint attribute cleanups) - rust-lang/rust#160085 (Remove various superfluous lint attributes) - rust-lang/rust#160113 (Coalesce `rustc_on_unimplemented` attributes and lint malformed filters) - rust-lang/rust#160119 (fix query cycle in `coroutine_hidden_types` for the next solver) - rust-lang/rust#160147 (tests: Remove `-Zthreads` options from tests in `ui/parallel-rustc`) - rust-lang/rust#160157 (Remove outdated comments from `va_list.rs`) - rust-lang/rust#160159 (More accurately check for interior mutability in `invalid_reference_casting` lint) - rust-lang/rust#160208 (rustdoc: Fix crash when trying to list attributes on an opaque type) - rust-lang/rust#160244 (Rename splat to rustc_splat in error messages) - rust-lang/rust#160246 (dont fire `unused_mut` on `&pin mut self`) - rust-lang/rust#160247 (Configure backport nominations for rustfmt) - rust-lang/rust#160274 (renovate: update lock files weekly)

Add test with fake and wrapped UnsafeCells

278132c

rustbot assigned mejrs Jul 29, 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 29, 2026

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rust-bors Bot pushed a commit that referenced this pull request Jul 29, 2026

Auto merge of #160159 - Urgau:invalid_ref_casts-unsafe-cell, r=<try>

b235b37

More accurately check for interior mutability in `invalid_reference_casting` lint

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Urgau force-pushed the invalid_ref_casts-unsafe-cell branch from a769af4 to 4b7cb31 Compare July 29, 2026 16:40

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 29, 2026

mejrs requested changes Jul 30, 2026

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Comment thread compiler/rustc_lint/src/reference_casting.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 Jul 30, 2026

Add recursive check for UnsafeCell-ness in invalid ref casting lint

0c2035c

Urgau force-pushed the invalid_ref_casts-unsafe-cell branch from 4b7cb31 to 0c2035c Compare July 31, 2026 09:14

Urgau 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 31, 2026

mejrs approved these changes Jul 31, 2026

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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 Jul 31, 2026

JonathanBrouwer mentioned this pull request Jul 31, 2026

Rollup of 11 pull requests #160273

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JonathanBrouwer mentioned this pull request Jul 31, 2026

Rollup of 17 pull requests #160278

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JonathanBrouwer mentioned this pull request Jul 31, 2026

Rollup of 21 pull requests #160283

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JonathanBrouwer mentioned this pull request Jul 31, 2026

Rollup of 22 pull requests #160284

Merged

rust-bors Bot merged commit c70f022 into rust-lang:main Jul 31, 2026
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rustbot added this to the 1.99.0 milestone Jul 31, 2026

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More accurately check for interior mutability in `invalid_reference_casting` lint - #160159