Hello and welcome to another issue of This Week in Rust! Rust is a programming language empowering everyone to build reliable and efficient software. This is a weekly summary of its progress and community. Want something mentioned? Tweet us at @ThisWeekInRust or send us a pull request. Want to get involved? We love contributions.

This Week in Rust is openly developed on GitHub. If you find any errors in this week's issue, please submit a PR.

This week's crate is bstr, a fast and featureful byte-string library.

Thanks to 8573 for the suggestion!

Please submit your suggestions and votes for next week!

Call for Participation

Always wanted to contribute to open-source projects but didn't know where to start? Every week we highlight some tasks from the Rust community for you to pick and get started!

Some of these tasks may also have mentors available, visit the task page for more information.

If you are a Rust project owner and are looking for contributors, please submit tasks here.

Updates from the Rust Project

324 pull requests were merged in the last week

Rust Compiler Performance Triage

From the viewpoint of metrics gathering, this was an absolutely terrible week, because the vast majority of this week's report is dominated by noise. Several benchmarks (html5ever, cranelift-codegen, and keccak) have all been exhibiting bimodal behavior where their compile-times would regress and improve randomly from run to run. Looking past that, we had one small win from adding an inline directive.

Triage done by @pnkfelix. Revision range: e7cdd4c0..17cbdfd0

Summary:

(instructions:u)	mean	range	count
Regressions ❌ (primary)	1.1%	[0.2%, 6.2%]	26
Regressions ❌ (secondary)	1.9%	[0.1%, 5.6%]	34
Improvements ✅ (primary)	-1.8%	[-29.4%, -0.2%]	42
Improvements ✅ (secondary)	-1.3%	[-5.3%, -0.2%]	50
All ❌✅ (primary)	-0.7%	[-29.4%, 6.2%]	68

11 Regressions, 11 Improvements, 13 Mixed; 11 of them in rollups 71 artifact comparisons made in total

Full report here

Call for Testing

An important step for RFC implementation is for people to experiment with the implementation and give feedback, especially before stabilization. The following RFCs would benefit from user testing before moving forward:

No RFCs issued a call for testing this week.

If you are a feature implementer and would like your RFC to appear on the above list, add the new call-for-testing label to your RFC along with a comment providing testing instructions and/or guidance on which aspect(s) of the feature need testing.

Approved RFCs

Changes to Rust follow the Rust RFC (request for comments) process. These are the RFCs that were approved for implementation this week:

De-RFC: Remove type ascription

[disposition: close] Loosen shadowing check inside macro contexts (attempt 2).
[disposition: merge] Tracking issue for std::hint::black_box
[disposition: merge] Commit to safety rules for dyn trait upcasting
[disposition: merge] Tracking Issue for constifying some {BTreeMap,Set} functions
[disposition: merge] Tracking Issue for Option::unzip()
[disposition: merge] Tracking issue for map_first_last: first/last methods on BTreeSet and BTreeMap
[disposition: merge] Make Sized coinductive, again
[disposition: merge] Neither require nor imply lifetime bounds on opaque type for well formedness
[disposition: merge] Make typeck aware of uninhabited types
[disposition: merge] Stabilize let else
[disposition: merge] Fix #[derive(Default)] on a generic #[default] enum adding unnecessary Default bounds

New and Updated RFCs

No New or Updated RFCs were created this week.

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