Make PinCoerceUnsized require Deref by theemathas · Pull Request #149218 · rust-lang/rust

theemathas · 2025-11-22T16:12:21Z

Also, delete impls on non-Deref types.

Pin doesn't do anything useful for non-Deref types, so PinCoerceUnsized on such types makes no sense.

This is a breaking change, since stable code can observe the deleted PinCoerceUnsized impls by uselessly coercing between such types inside a Pin.

There is still some strange behavior, such as Pin<&mut i32> being able to coerce to Pin<&dyn Send>, but not being able to coerce to Pin<&i32>. However, I don't think it's possible to fix this.

Fixes #145081

rustbot · 2025-11-22T16:12:25Z

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jdonszelmann · 2025-11-23T09:23:44Z

@bors try

Make PinCoerceUnsized require Deref

rust-bors · 2025-11-23T11:41:03Z

☀️ Try build successful (CI)
Build commit: 94e8487 (94e848735e78b58442e0b82e9c60f8f430840389, parent: e0e204f3e97ad5f79524b9c259dc38df606ed82c)

saethlin · 2025-11-24T01:11:42Z

@craterbot check

craterbot · 2025-11-24T01:12:13Z

👌 Experiment pr-149218 created and queued.
🤖 Automatically detected try build 94e8487
🔍 You can check out the queue and this experiment's details.

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craterbot · 2025-12-01T01:31:06Z

🚧 Experiment pr-149218 is now running

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Darksonn · 2025-12-01T13:12:49Z

I added these impls because otherwise the introduction of PinCoerceUnsized would have been a breaking change. I'm in favor of removing them.

library/core/src/pin.rs

craterbot · 2025-12-02T19:18:06Z

🎉 Experiment pr-149218 is completed!
📊 6 regressed and 5 fixed (743358 total)
📊 1966 spurious results on the retry-regessed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-149218/retry-regressed-list.txt ↩

workingjubilee · 2025-12-03T08:21:12Z

@craterbot check crates=https://crater-reports.s3.amazonaws.com/pr-149218/retry-regressed-list.txt

craterbot · 2025-12-03T08:21:21Z

👌 Experiment pr-149218-1 created and queued.
🤖 Automatically detected try build 94e8487
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

rust-bors · 2026-03-24T11:03:52Z

📌 Commit 969c3df has been approved by oli-obk

It is now in the queue for this repository.

…li-obk Make PinCoerceUnsized require Deref Also, delete impls on non-Deref types. Pin doesn't do anything useful for non-Deref types, so PinCoerceUnsized on such types makes no sense. This is a breaking change, since stable code can observe the deleted `PinCoerceUnsized` impls by uselessly coercing between such types inside a `Pin`. There is still some strange behavior, such as `Pin<&mut i32>` being able to coerce to `Pin<&dyn Send>`, but not being able to coerce to `Pin<&i32>`. However, I don't think it's possible to fix this. Fixes rust-lang#145081

…uwer Rollup of 7 pull requests Successful merges: - #149218 (Make PinCoerceUnsized require Deref) - #154094 (add neon load/store assembly test) - #154142 (Delegation: eliminate usage of AST from generics creation) - #154276 (allow `incomplete_features` in more tests) - #154284 (doc: linker-plugin-based LTO: update list of good combinations) - #154286 (Cherry-pick 1.94.1 release notes) - #154303 (Remove more `BuiltinLintDiag` variants - part 2)

rust-bors · 2026-03-24T15:09:50Z

⌛ Testing commit 969c3df with merge 31fcd54...

Workflow: https://github.com/rust-lang/rust/actions/runs/23496789264

Make PinCoerceUnsized require Deref Also, delete impls on non-Deref types. Pin doesn't do anything useful for non-Deref types, so PinCoerceUnsized on such types makes no sense. This is a breaking change, since stable code can observe the deleted `PinCoerceUnsized` impls by uselessly coercing between such types inside a `Pin`. There is still some strange behavior, such as `Pin<&mut i32>` being able to coerce to `Pin<&dyn Send>`, but not being able to coerce to `Pin<&i32>`. However, I don't think it's possible to fix this. Fixes #145081

JonathanBrouwer · 2026-03-24T15:22:12Z

@bors r-
#154312 (comment)

rust-bors · 2026-03-24T15:22:22Z

This pull request was unapproved.

This PR was contained in a rollup (#154312), which was unapproved.

Auto build was cancelled due to unapproval. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/23496789264

Also, delete impls on non-Deref types. Pin doesn't do anything useful for non-Deref types, so PinCoerceUnsized on such types makes no sense. This is a breaking change, since stable code can observe the deleted `PinCoerceUnsized` impls by uselessly coercing between such types inside a `Pin`. There is still some strange behavior, such as `Pin<&mut i32>` being able to coerce to `Pin<&dyn Send>`, but not being able to coerce to `Pin<&i32>`. However, I don't think it's possible to fix this. Fixes rust-lang#145081

rustbot · 2026-03-25T04:42:26Z

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.

theemathas · 2026-03-25T04:44:56Z

The UserRef type in the SGX code seemingly is meant to be used as &UserRef<T> and &mut UserRef<T>. It's never meant to be used as a by-value UserRef<T>. Therefore, the PinCoerceUnsized impl for it doesn't make much sense, as users aren't meant to be making a Pin<UserRef<T>>. Therefore, I've removed the impl.

@rustbot ready

oli-obk · 2026-03-25T11:17:35Z

@bors r+

rust-bors · 2026-03-25T11:17:38Z

📌 Commit f55c8cc has been approved by oli-obk

It is now in the queue for this repository.

rustbot assigned tgross35 Nov 22, 2025

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theemathas force-pushed the pin-coerce-unsized branch 2 times, most recently from f921d32 to f4fa919 Compare November 23, 2025 03:35

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Auto merge of #149218 - theemathas:pin-coerce-unsized, r=<try>

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Make PinCoerceUnsized require Deref

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Darksonn reviewed Dec 1, 2025

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Rollup of 6 pull requests #154306

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Rollup of 7 pull requests #154312

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theemathas added 2 commits March 25, 2026 11:40

Rewrite safety comment for PinCoerceUnsized

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