const `select_unpredictable`#145939

clarfonthey · 2025-08-27T15:57:15Z

Tracking issue: #145938

rustbot · 2025-08-27T15:57:20Z

rustbot has assigned @tgross35.
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

library/core/src/hint.rs

clarfonthey · 2025-08-28T20:34:26Z

@rustbot blocked

bors · 2025-08-31T16:16:29Z

☔ The latest upstream changes (presumably #146052) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2025-10-15T00:24:02Z

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

clarfonthey · 2025-10-15T00:36:28Z

@rustbot ready

Should be good, but will fix if CI shows up with any weird issues. Now that ptr::drop_in_place works in const context, we can just mark this method and its corresponding intrinsic as const. I also updated the existing test to test both at runtime and const-time, so that we verify that the drop behaviour is consistent across both.

library/coretests/tests/hint.rs

oli-obk · 2025-10-16T15:49:24Z

library/coretests/tests/hint.rs

+    impl const Drop for X {
        fn drop(&mut self) {
-            self.0.set(true);
+            // FIXME(const-hack): Once const cells work, we could remove unsafe code here.


Somewhat surprised we haven't done this yet. If it doesn't require anything weird, maybe just do that first?

I know that cells are allowed in constants now that mutable references stabilised but I had just assumed this was due to some other blocker since get is allowed but set is not.

But I guess, if that's not the case, I can go through and mark all the methods const in a separate PR.

You can use replace already. set needs a T: [const] Destruct bound which we probably just didn't support when it was constified.

That makes a lot of sense. I guess that also goes along with this comment I made in the const_destruct issue asking why Copy doesn't imply const Destruct, since presumably we'd be able to avoid the bounds here.

Ha, more to add to the list of interesting things we didn't consider beforehand https://hackmd.io/ZnyR91NhQDO6aJ6EceMrQw

Makes total sense to me. Maybe leave two FIXMEs wrt cell add and removing the bound again?

r=me with that plus moving to using replace

Oh, never mind, since Cell::set no longer requires T: Copy, it would be a true [const] Destruct bound here.

I'm already in the middle of drafting up a PR for the cell methods, so, I'll just cc you on that one and fix this to use set here.

clarfonthey · 2025-10-16T19:14:24Z

r? @oli-obk

@rustbot blocked #147788

rustbot · 2025-10-16T19:14:28Z

oli-obk is not on the review rotation at the moment.
They may take a while to respond.

rustbot · 2025-10-27T01:39:59Z

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.

clarfonthey · 2025-10-27T03:10:29Z

@rustbot ready

Had forgotten about this, but it is no longer blocked since the Cell PR got merged.

oli-obk · 2025-10-27T07:04:58Z

@bors r+ rollup

bors · 2025-10-27T07:05:01Z

📌 Commit 6f649e4 has been approved by oli-obk

It is now in the queue for this repository.

Rollup of 4 pull requests Successful merges: - #145939 (const `select_unpredictable`) - #147478 (More intuitive error when using self to instantiate tuple struct with private field) - #147866 (Add built-in `const` impls for `Clone` and `Copy`) - #148153 (Fix duplicate 'the the' typos in comments) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #145939 - clarfonthey:const-select-unpredictable, r=oli-obk const `select_unpredictable` Tracking issue: #145938

rustbot assigned tgross35 Aug 27, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Aug 27, 2025

clarfonthey changed the title ~~const `select_unpredictable~~ const select_unpredictable Aug 27, 2025

clarfonthey mentioned this pull request Aug 27, 2025

Tracking Issue for const hint::select_unpredictable #145938

Open

3 tasks

This comment has been minimized.

Sign in to view

bjorn3 reviewed Aug 27, 2025

View reviewed changes

library/core/src/hint.rs Outdated Show resolved Hide resolved

rustbot added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 28, 2025

clarfonthey mentioned this pull request Sep 1, 2025

unstably constify ptr::drop_in_place #145725

Closed

clarfonthey force-pushed the const-select-unpredictable branch from c07fc68 to c6f7eab Compare October 15, 2025 00:23

This comment has been minimized.

Sign in to view

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Oct 15, 2025

clarfonthey force-pushed the const-select-unpredictable branch from c6f7eab to 003a538 Compare October 15, 2025 00:37

clarfonthey commented Oct 15, 2025

View reviewed changes

library/coretests/tests/hint.rs Outdated Show resolved Hide resolved

clarfonthey force-pushed the const-select-unpredictable branch from 003a538 to 7a17d4a Compare October 16, 2025 05:30

oli-obk reviewed Oct 16, 2025

View reviewed changes

clarfonthey force-pushed the const-select-unpredictable branch from 7a17d4a to 7a0824c Compare October 16, 2025 19:14

rustbot assigned oli-obk Oct 16, 2025

rustbot unassigned tgross35 Oct 16, 2025

rustbot added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 16, 2025

This comment has been minimized.

Sign in to view

const select_unpredictable

6f649e4

clarfonthey force-pushed the const-select-unpredictable branch from 7a0824c to 6f649e4 Compare October 27, 2025 01:39

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Oct 27, 2025

oli-obk approved these changes Oct 27, 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 Oct 27, 2025

Zalathar mentioned this pull request Oct 27, 2025

Rollup of 4 pull requests #148167

Merged

bors merged commit 537a778 into rust-lang:master Oct 27, 2025
11 checks passed

rustbot added this to the 1.93.0 milestone Oct 27, 2025

rust-timer added a commit that referenced this pull request Oct 27, 2025

Unrolled build for #145939

1940cfd

Rollup merge of #145939 - clarfonthey:const-select-unpredictable, r=oli-obk const `select_unpredictable` Tracking issue: #145938

Uh oh!

Conversation

clarfonthey commented Aug 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Aug 27, 2025

Uh oh!

This comment has been minimized.

Uh oh!

clarfonthey commented Aug 28, 2025

Uh oh!

bors commented Aug 31, 2025

Uh oh!

rustbot commented Oct 15, 2025

Uh oh!

This comment has been minimized.

clarfonthey commented Oct 15, 2025

Uh oh!

Uh oh!

oli-obk Oct 16, 2025

Choose a reason for hiding this comment

Uh oh!

clarfonthey Oct 16, 2025

Choose a reason for hiding this comment

Uh oh!

oli-obk Oct 16, 2025

Choose a reason for hiding this comment

Uh oh!

clarfonthey Oct 16, 2025

Choose a reason for hiding this comment

Uh oh!

oli-obk Oct 16, 2025

Choose a reason for hiding this comment

Uh oh!

clarfonthey Oct 16, 2025

Choose a reason for hiding this comment

Uh oh!

clarfonthey Oct 16, 2025

Choose a reason for hiding this comment

Uh oh!

clarfonthey commented Oct 16, 2025

Uh oh!

rustbot commented Oct 16, 2025

Uh oh!

This comment has been minimized.

rustbot commented Oct 27, 2025

Uh oh!

clarfonthey commented Oct 27, 2025

Uh oh!

oli-obk commented Oct 27, 2025

Uh oh!

bors commented Oct 27, 2025

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

7 participants

clarfonthey commented Aug 27, 2025 •

edited

Loading