Stabilize `fN::BITS`#154065

Apersoma · 2026-03-19T01:30:45Z

Tracking issue: #151073
Closes: #151073

rustbot · 2026-03-19T01:30:51Z

rustbot has assigned @scottmcm.
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rustbot · 2026-03-19T20:04:56Z

compiler-builtins is developed in its own repository. If possible, consider making this change to rust-lang/compiler-builtins instead.

cc @tgross35

tgross35 · 2026-03-19T20:29:08Z

This has only been around since January but it seems pretty unobjectionable to have. However, this does conflict with a constant in use in the ecosystem (showed up in the implementation PR) so we need to take a look at crater.

@bors try

@rustbot label +I-libs-api-nominated

Stabilize `fN::BITS`

rust-bors · 2026-03-19T22:40:16Z

☀️ Try build successful (CI)
Build commit: 0abe69e (0abe69e6c16114311cc2700e972492e64d69c28f, parent: 1f7f8ea0721a3b1eb73e6c6d25cccb371434b320)

tgross35 · 2026-03-19T22:44:46Z

Doing a run with tests in case somebody has a different value for BITS for some reason.

@craterbot run mode=build-and-test

craterbot · 2026-03-19T22:45:19Z

👌 Experiment pr-154065 created and queued.
🤖 Automatically detected try build 0abe69e
🔍 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

Amanieu · 2026-03-24T15:54:14Z

FCP started in #151073

tgross35 · 2026-03-25T22:51:19Z

@Apersoma please squash the commits and give it a reasonable message, the first commit just says "cmplt" (we don't have squash merging on this repo).

craterbot · 2026-03-26T13:49:19Z

🚧 Experiment pr-154065 is now running

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

craterbot · 2026-03-28T17:47:59Z

🎉 Experiment pr-154065 is completed!
📊 297 regressed and 292 fixed (857798 total)
📊 132042 spurious results on the retry-regressed-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-154065/retry-regressed-list.txt ↩

tgross35 · 2026-03-28T18:11:30Z

@craterbot run mode=build-and-test p=1 crates=https://crater-reports.s3.amazonaws.com/pr-154065/retry-regressed-list.txt

craterbot · 2026-03-28T18:11:41Z

👌 Experiment pr-154065-1 created and queued.
🤖 Automatically detected try build 0abe69e
🔍 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

Apersoma · 2026-03-28T19:51:07Z

Crater isn't too bad, but there are a couple of crates that I think we could resolve reasonably easy:

[common_traits]: this one has a few depenents. It seems pretty actively developed so I opened f*::BITS will break if float_bits_const stabilizes zommiommy/common_traits#7

float_math: Doesn't seem to have any dependents and hasn't been published in a while. Author is @Lokathor, any chance you could publish a version that disambiguates?

Crates that depend on common_traits might run into some an issue too, we'll have to rerun the regressed list once a new version is published.

Let's give some time for fixes here.

@rustbot blocked @SnoozeThis wait 2 months

How do you filter for what's actually useful in crater?

tgross35 · 2026-03-28T20:19:46Z

Look for "regressed: dependencies" (some crate in the dep tree failed) and "regressed: root results" (the crate itself failed) in the summary. We retry the spurious results.

You can also go to the downloads tab to grab the results and do something like rg '::BITS' which can be a bit more clear.

Apersoma · 2026-03-28T20:37:20Z

This probably going to need a second crater run for errors causes by users of common_traits after the new version gets published, right?

tgross35 · 2026-03-28T22:18:20Z

This probably going to need a second crater run for errors causes by users of common_traits after the new version gets published, right?

I think so ^^ 🙂

Crates that depend on common_traits might run into some an issue too, we'll have to rerun the regressed list once a new version is published.

zommiommy · 2026-03-29T10:26:09Z

done, sorry!

tgross35 · 2026-03-29T17:41:33Z

Not a problem, there’s no way of knowing until this happens :) thank you for the quick action!

craterbot · 2026-03-30T01:10:48Z

🚧 Experiment pr-154065-1 is now running

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

craterbot · 2026-03-30T12:08:52Z

🎉 Experiment pr-154065-1 is completed!
📊 114 regressed and 120 fixed (132208 total)
📊 1656 spurious results on the retry-regressed-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-154065-1/retry-regressed-list.txt ↩

See rust-lang/rust#154065

SnoozeThis · 2026-05-28T19:27:25Z

Resolved.

@rustbot assign @tgross35.

rustbot · 2026-05-28T19:27:31Z

tgross35 is currently at their maximum review capacity.
They may take a while to respond.

tgross35 · 2026-05-28T21:18:53Z

@bors try

Stabilize `fN::BITS`

rust-bors · 2026-05-28T23:29:10Z

☀️ Try build successful (CI)
Build commit: 28f9593 (28f95933dc0727396c07b48d0a8cb5211b7fb472, parent: cced03bfd61a304243a34504618ecec86c17063f)

tgross35 · 2026-05-29T05:17:41Z

@craterbot run mode=build-and-test

craterbot · 2026-05-29T05:18:10Z

👌 Experiment pr-154065-2 created and queued.
🤖 Automatically detected try build 28f9593
🔍 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 · 2026-06-11T17:33:40Z

🚧 Experiment pr-154065-2 is now running

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

craterbot · 2026-06-14T14:56:46Z

🎉 Experiment pr-154065-2 is completed!
📊 459 regressed and 426 fixed (954864 total)
📊 5782 spurious results on the retry-regressed-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-154065-2/retry-regressed-list.txt ↩

cmplt

e203c4d

rustbot assigned scottmcm Mar 19, 2026

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 Mar 19, 2026

removed FIXMEs

2448f7d

rustbot added the A-compiler-builtins Area: compiler-builtins (https://github.com/rust-lang/compiler-builtins) label Mar 19, 2026

tgross35 assigned tgross35 and unassigned scottmcm Mar 19, 2026

rustbot added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Mar 19, 2026

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rust-bors Bot pushed a commit that referenced this pull request Mar 19, 2026

Auto merge of #154065 - Apersoma:stabilize-fN-bits, r=<try>

0abe69e

Stabilize `fN::BITS`

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 Mar 19, 2026

Amanieu removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Mar 24, 2026

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 Mar 28, 2026

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 Mar 28, 2026

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. S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Mar 30, 2026

jannic added a commit to jannic/rp-hal that referenced this pull request Apr 11, 2026

Fix future incompatibility warning regarding fN::BITS

2663295

See rust-lang/rust#154065

jannic mentioned this pull request Apr 11, 2026

Fix future incompatibility warning about fN::BITS rp-rs/rp-hal#992

Merged

jannic added a commit to rp-rs/rp-hal that referenced this pull request Apr 11, 2026

Fix future incompatibility warning regarding fN::BITS (#992)

74a382d

See rust-lang/rust#154065

rustbot assigned tgross35 and unassigned SnoozeThis May 28, 2026

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rust-bors Bot pushed a commit that referenced this pull request May 28, 2026

Auto merge of #154065 - Apersoma:stabilize-fN-bits, r=<try>

28f9593

Stabilize `fN::BITS`

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 May 29, 2026

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 Jun 14, 2026

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