Forbid manual `Unpin` impls for structurally pinned types by frank-king · Pull Request #149263 · rust-lang/rust

frank-king · 2025-11-24T09:13:23Z

Part of pin_ergonomics. It forbids to impl Unpin for T where T is an ADT marked with #[pin_v2].

rustbot · 2025-11-24T09:13:28Z

rustbot has assigned @madsmtm.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

madsmtm · 2025-12-04T11:06:34Z

The change itself seems simple, but I'd prefer to have someone from t-types review it.
r? types

If no-one there feels like they have the capacity, feel free to assign it back to me.

bors · 2025-12-14T08:50:22Z

☔ The latest upstream changes (presumably #146348) made this pull request unmergeable. Please resolve the merge conflicts.

BoxyUwU · 2026-01-07T14:04:10Z

r? BoxyUwU

compiler/rustc_hir_analysis/src/coherence/mod.rs

BoxyUwU · 2026-01-07T14:12:30Z

What's the reason for wanting to forbid such impls? Is it just because it's probably pointless to have pin_v2 on an Unpin type, or is there some soundness concern here?

frank-king · 2026-01-07T14:29:57Z

It is for soundness concern.

For a type T annotated with #[pin_v2], it is allowed to project Pin<&mut T> to its field Pin<&mut U> safely (even if U: !Unpin). If T is allowed to impl Unpin manually, then &mut U could be obtained from &mut T that dereferenced by Pin<&mut T>, which breaks the safety contract of Pin<&mut U> for U: !Unpin.

BoxyUwU · 2026-01-07T14:54:05Z

If its soundness critical, I would add tests for impls of unpin for type aliases for adts marked pin_v2, e.g. impl Unpin for <Foo as Identity>::Assoc impl Unpin for Identity<Foo> (with lazy_type_alias feature enabled) and impl Unpin for TAIT (where TAIT is Foo).

rn your logic implicitly ignores all the cases where the self type is a non-adt 🤔 which I think is fine because we enforce that impls of Unpin are always for ADTs? But having tests is good :) It would probably also be good to explicitly match on the TyKind and in non Adt cases (which we expect to be unreachable) delay a bug maybe 🤔 that way you don't get unsoundness here if it goes wrong just an ICE

BoxyUwU · 2026-01-19T11:55:52Z

@rustbot author

rustbot · 2026-01-19T11:55:56Z

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

rustbot · 2026-01-30T06:15:18Z

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.

frank-king · 2026-01-31T23:28:09Z

@rustbot ready

BoxyUwU · 2026-02-03T13:14:16Z

@bors r+ rollup

rust-bors · 2026-02-03T13:14:19Z

📌 Commit e12acb9 has been approved by BoxyUwU

It is now in the queue for this repository.

…BoxyUwU Forbid manual `Unpin` impls for structurally pinned types Part of [`pin_ergonomics`](rust-lang#130494). It forbids to `impl Unpin for T` where `T` is an ADT marked with `#[pin_v2]`.

…uwer Rollup of 13 pull requests Successful merges: - #152034 (Show largest job duration changes in hours and minutes in the post-merge report) - #152039 (coverage: Add a test case for a previously-unknown span mismatch) - #152045 (Convert to inline diagnostics in `rustc_infer`) - #149263 (Forbid manual `Unpin` impls for structurally pinned types) - #151754 (Check proj's parent is trait or not when checking dyn compatibility) - #151848 (Port `rustc_mir` to attribute parser) - #151874 (error on unsized AnonConsts) - #151944 (Convert to inline diagnostics in `rustc_attr_parsing`) - #152012 (Use `DEVELOPER_DIR` instead of a custom `xcode-select` script) - #152019 (`NativeLib` cleanups) - #152029 (disable socket tests in Miri) - #152041 (Convert to inline diagnostics in `rustc_query_system`) - #152050 (Try to fix `rustdoc-gui/globals.goml` flakyness) Failed merges: - #152046 (Use glob imports for attribute parsers)

…uwer Rollup of 12 pull requests Successful merges: - #152034 (Show largest job duration changes in hours and minutes in the post-merge report) - #152039 (coverage: Add a test case for a previously-unknown span mismatch) - #152045 (Convert to inline diagnostics in `rustc_infer`) - #149263 (Forbid manual `Unpin` impls for structurally pinned types) - #151754 (Check proj's parent is trait or not when checking dyn compatibility) - #151848 (Port `rustc_mir` to attribute parser) - #151874 (error on unsized AnonConsts) - #151944 (Convert to inline diagnostics in `rustc_attr_parsing`) - #152019 (`NativeLib` cleanups) - #152029 (disable socket tests in Miri) - #152041 (Convert to inline diagnostics in `rustc_query_system`) - #152050 (Try to fix `rustdoc-gui/globals.goml` flakyness) Failed merges: - #152046 (Use glob imports for attribute parsers)

Rollup merge of #149263 - frank-king:feature/unpin-check, r=BoxyUwU Forbid manual `Unpin` impls for structurally pinned types Part of [`pin_ergonomics`](#130494). It forbids to `impl Unpin for T` where `T` is an ADT marked with `#[pin_v2]`.

JonathanBrouwer · 2026-02-04T07:21:05Z

@rust-timer build 95dcb3b

rust-timer · 2026-02-04T09:20:55Z

Finished benchmarking commit (95dcb3b): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@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)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -2.5%, secondary -0.6%)

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)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-0.6%	[-0.6%, -0.6%]	1
All ❌✅ (primary)	-2.5%	[-2.5%, -2.5%]	1

Cycles

Results (primary 1.8%, secondary -2.2%)

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

	mean	range	count
Regressions ❌ (primary)	1.8%	[1.8%, 1.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.2%, -2.2%]	1
All ❌✅ (primary)	1.8%	[1.8%, 1.8%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 471.991s -> 473.254s (0.27%)
Artifact size: 397.70 MiB -> 397.69 MiB (-0.00%)

rustbot assigned madsmtm Nov 24, 2025

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 Nov 24, 2025

rustbot added the T-types Relevant to the types team, which will review and decide on the PR/issue. label Dec 4, 2025

rustbot assigned jackh726 and unassigned madsmtm Dec 4, 2025

frank-king force-pushed the feature/unpin-check branch from f0b30c4 to 522ff7b Compare December 15, 2025 02:19

This comment has been minimized.

Sign in to view

frank-king mentioned this pull request Dec 18, 2025

Continue Experimentation with Pin Ergonomics rust-lang/rust-project-goals#389

Open

4 tasks

rustbot assigned BoxyUwU and unassigned jackh726 Jan 7, 2026

BoxyUwU reviewed Jan 7, 2026

View reviewed changes

compiler/rustc_hir_analysis/src/coherence/mod.rs Outdated Show resolved Hide resolved

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 Jan 19, 2026

frank-king force-pushed the feature/unpin-check branch from 522ff7b to 4def78a Compare January 30, 2026 06:15

frank-king force-pushed the feature/unpin-check branch from 4def78a to 636e7b2 Compare January 30, 2026 07:10

This comment has been minimized.

Sign in to view

Forbid manual Unpin impls for structurally pinned types

e12acb9

frank-king force-pushed the feature/unpin-check branch from 636e7b2 to e12acb9 Compare January 30, 2026 12:25

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 Jan 31, 2026

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 Feb 3, 2026

JonathanBrouwer mentioned this pull request Feb 3, 2026

Rollup of 7 pull requests #152048

Closed

JonathanBrouwer mentioned this pull request Feb 3, 2026

Rollup of 9 pull requests #152052

Closed

JonathanBrouwer mentioned this pull request Feb 3, 2026

Rollup of 13 pull requests #152055

Closed

JonathanBrouwer mentioned this pull request Feb 3, 2026

Rollup of 13 pull requests #152058

Closed

JonathanBrouwer mentioned this pull request Feb 3, 2026

Rollup of 12 pull requests #152063

Merged

rust-bors bot merged commit b3b66b2 into rust-lang:main Feb 3, 2026
11 checks passed

rustbot added this to the 1.95.0 milestone Feb 3, 2026

This comment has been minimized.

Sign in to view

Uh oh!

Conversation

frank-king commented Nov 24, 2025

Uh oh!

rustbot commented Nov 24, 2025

Uh oh!

madsmtm commented Dec 4, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

bors commented Dec 14, 2025

Uh oh!

This comment has been minimized.

BoxyUwU commented Jan 7, 2026

Uh oh!

Uh oh!

BoxyUwU commented Jan 7, 2026

Uh oh!

frank-king commented Jan 7, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

BoxyUwU commented Jan 7, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

BoxyUwU commented Jan 19, 2026

Uh oh!

rustbot commented Jan 19, 2026

Uh oh!

rustbot commented Jan 30, 2026

Uh oh!

This comment has been minimized.

frank-king commented Jan 31, 2026

Uh oh!

BoxyUwU commented Feb 3, 2026

Uh oh!

rust-bors bot commented Feb 3, 2026

Uh oh!

Uh oh!

JonathanBrouwer commented Feb 4, 2026

Uh oh!

This comment has been minimized.

rust-timer commented Feb 4, 2026

Overall result: ❌ regressions - no action needed

Instruction count

Max RSS (memory usage)

Cycles

Binary size

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

9 participants

madsmtm commented Dec 4, 2025 •

edited

Loading

frank-king commented Jan 7, 2026 •

edited

Loading

BoxyUwU commented Jan 7, 2026 •

edited

Loading