Add `Default` impls for `Pin`ned `Box`, `Rc`, `Arc` #143717

Jules-Bertholet · 2025-07-10T04:23:46Z

@rustbot label T-libs-api needs-fcp

Also needs a crater run, as the Box impls could theoretically be breaking due to #[fundamental] (though a cursory search suggests this is unlikely to cause issues).

rustbot · 2025-07-10T04:23:51Z

r? @tgross35

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tgross35 · 2025-07-10T05:43:48Z

@bors2 try

rust-bors · 2025-07-10T05:43:53Z

⌛ Trying commit 9060b6b with merge 5ef65a4…

To cancel the try build, run the command @bors2 try cancel.

Add `Default` impls for `Pin`ned `Box`, `Rc`, `Arc` Fixes #143688. `@rustbot` label T-libs-api needs-fcp Also needs a crater run, as the `Box` impls could theoretically be breaking due to `#[fundamental]` (though a [cursory search](https://github.com/search?q=%2Fimpl%28%3C.*%3E%29%3F+Default+for+Pin%3C%2F+path%3A*.rs&type=code) suggests this is unlikely to cause issues).

rust-bors · 2025-07-10T08:00:22Z

☀️ Try build successful (CI)
Build commit: 5ef65a4 (5ef65a4ed75279dc1b7a26cedc27293a9f4ca8db, parent: 32cd9114712a24010b0583624dc52ac302194128)

tgross35 · 2025-07-10T08:06:01Z

@craterbot check

craterbot · 2025-07-10T08:06:29Z

👌 Experiment pr-143717 created and queued.
🤖 Automatically detected try build 5ef65a4
🔍 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

craterbot · 2025-07-11T02:45:35Z

🚧 Experiment pr-143717 is now running

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

craterbot · 2025-07-12T08:28:59Z

🎉 Experiment pr-143717 is completed!
📊 7 regressed and 5 fixed (662328 total)
📰 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

Jules-Bertholet · 2025-07-12T13:36:07Z

All spurious failures. “prepare-fail (112811)” seems not-great though. Looks like a lot of “no space left on device” errors? If an issue with crater is preventing a large proportion of the crates from being properly tested…

Skgland · 2025-07-12T16:54:02Z

All spurious failures. “prepare-fail (112811)” seems not-great though. Looks like a lot of “no space left on device” errors? If an issue with crater is preventing a large proportion of the crates from being properly tested…

Note that the prepare-fail category is a relatively recent change, they used to be categorized as error. Also prepare-fail results are included in the retry-regressed-list.txt

Amanieu · 2025-07-15T15:45:33Z

@rfcbot merge

rfcbot · 2025-07-15T15:45:36Z

Team member @Amanieu has proposed to merge this. The next step is review by the rest of the tagged team members:

Concerns:

~~Box<T>: Default~~ resolved by Add Default impls for Pinned Box, Rc, Arc #143717 (comment)

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

dtolnay · 2025-07-15T15:52:00Z

Consider generalizing the Pin<Box<>> impl like this:

  impl<T> Default for Pin<Box<T>>
  where
-     T: Default,
+     T: ?Sized,
+     Box<T>: Default,

This would apply to types like Pin<Box<serde_json::value::RawValue>>, where RawValue does not implement Default but Box<RawValue> does.

@rfcbot concern Box<T>: Default

Jules-Bertholet · 2025-07-15T21:45:08Z

@dtolnay I’ve done as you asked.

dtolnay · 2025-07-15T22:18:42Z

@rfcbot resolve Box<T>: Default

tgross35 · 2025-07-29T03:32:35Z

For after fcp,
r? @dtolnay

rfcbot · 2025-08-05T13:04:13Z

🔔 This is now entering its final comment period, as per the review above. 🔔

rfcbot · 2025-08-15T13:04:22Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

dtolnay

Thanks!

dtolnay · 2025-08-15T15:09:54Z

@bors r+

bors · 2025-08-15T15:09:57Z

📌 Commit 87dd469 has been approved by dtolnay

It is now in the queue for this repository.

Rollup of 11 pull requests Successful merges: - #143717 (Add `Default` impls for `Pin`ned `Box`, `Rc`, `Arc`) - #144054 (Stabilize as_array_of_cells) - #144907 (fix: Reject async assoc fns of const traits/impls in ast_passes) - #144922 (Implement `#[derive(From)]`) - #144963 (Stabilize `core::iter::chain`) - #145436 (fix(tests/rmake/wasm-unexpected-features): change features from `WASM1` to `MVP`) - #145453 (Remove duplicated tracing span in bootstrap) - #145454 (Fix tracing debug representation of steps without arguments in bootstrap) - #145455 (Do not copy files in `copy_src_dirs` in dry run) - #145462 (Stabilize `const_exposed_provenance` feature) - #145466 (Enable new `[range-diff]` feature in triagebot) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143717 - Jules-Bertholet:pin-default, r=dtolnay Add `Default` impls for `Pin`ned `Box`, `Rc`, `Arc` Fixes #143688. `@rustbot` label T-libs-api needs-fcp Also needs a crater run, as the `Box` impls could theoretically be breaking due to `#[fundamental]` (though a [cursory search](https://github.com/search?q=%2Fimpl%28%3C.*%3E%29%3F+Default+for+Pin%3C%2F+path%3A*.rs&type=code) suggests this is unlikely to cause issues).

jhpratt · 2025-08-16T05:16:21Z

still in queue; merged in #145475

@bors r-

rustbot assigned tgross35 Jul 10, 2025

tgross35 added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Jul 10, 2025

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 10, 2025

craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Jul 12, 2025

Amanieu removed T-libs Relevant to the library team, which will review and decide on the PR/issue. I-libs-api-nominated Nominated for discussion during a libs-api team meeting. labels Jul 15, 2025

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Jul 15, 2025

Amanieu removed the needs-fcp This change is insta-stable, or significant enough to need a team FCP to proceed. label Jul 15, 2025

dtolnay added needs-crater This change needs a crater run to check for possible breakage in the ecosystem. and removed needs-crater This change needs a crater run to check for possible breakage in the ecosystem. labels Jul 15, 2025

Add Default impls for Pinned Box, Rc, Arc

87dd469

Jules-Bertholet force-pushed the pin-default branch from 9060b6b to 87dd469 Compare July 15, 2025 21:43

rustbot assigned dtolnay and unassigned tgross35 Jul 29, 2025

rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Aug 5, 2025

rustbot mentioned this pull request Aug 15, 2025

Tracking issue for release notes of #143717: Add Default impls for Pinned Box, Rc, Arc #145442

Open

dtolnay approved these changes Aug 15, 2025

View reviewed changes

bors 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 Aug 15, 2025

jhpratt mentioned this pull request Aug 15, 2025

Rollup of 11 pull requests #145475

Merged

bors merged commit 41e40f3 into rust-lang:master Aug 16, 2025
11 checks passed

rustbot added this to the 1.91.0 milestone Aug 16, 2025

bors 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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 16, 2025

Jules-Bertholet deleted the pin-default branch August 16, 2025 06:10

Add Default impls for Pinned Box, Rc, Arc #143717

Add Default impls for Pinned Box, Rc, Arc #143717

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Add `Default` impls for `Pin`ned `Box`, `Rc`, `Arc` #143717

Add `Default` impls for `Pin`ned `Box`, `Rc`, `Arc` #143717

Jules-Bertholet commented Jul 10, 2025 •

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Skgland commented Jul 12, 2025 •

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rfcbot commented Jul 15, 2025 •

edited by m-ou-se

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dtolnay commented Jul 15, 2025 •

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