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.

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Updates from Rust Community


Project/Tooling Updates


Rust Walkthroughs


Crate of the Week

This week's crate is rustc_codegen_nvvm, a rustc codegen backend that targets NVIDIA's libnvvm CUDA library.

Thanks to troiganto 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

284 pull requests were merged in the last week

Rust Compiler Performance Triage

This week, there were a number of cases where the incr-unchanged variants of inflate went up or down by 5% to 6%; we believe these are instances of increased noise in benchmarks documented on rustc-perf#1105. I was tempted to remove these from the report, but its non-trivial to re-construct the report "as if" some benchmark were omitted.

Otherwise, there were some nice wins for performance. For example, PR #90996 more than halved the time to document builds of diesel by revising how we hash ObligationCauseData. If anyone is interested, it might be good to follow-up on the effects of PR #90352, "Simplify for loop desugar", where we have hypothesized that the increased compilation time is due to more LLVM optimizations being applied.

Triage done by @pnkfelix. Revision range: 934624fe..22c2d9dd

1 Regressions, 3 Improvements, 8 Mixed; 3 of them in rollups 34 comparisons made in total

Full report here

Approved RFCs

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

Final Comment Period

Every week the team announces the 'final comment period' for RFCs and key PRs which are reaching a decision. Express your opinions now.


  • No RFCs entered final comment period this week.

Tracking Issues & PRs

New RFCs

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Quote of the Week

On the topic of reframing UB, I was reminded of an article about the mechanics of oaths and vows in historical cultures.

When a programmer writes get_unchecked , we can imagine them wanting to promise the compiler that they uphold its preconditions. But since the compiler is normally not so trusting of unproven assertions, the programmer swears an oath that their argument is in bounds.

The compiler, seeing such a solemn commitment, treats the programmer's word as true and optimizes accordingly. The compiler is so thoroughly convinced that it never even entertains the possibility of doubting the programmer's oath.

But if the programmer has sworn falsely, then they might well suffer divine retribution in the form of nasal demons — or worse, subtly baffling program behaviour.

/u/scook0 on /r/rust

Thanks to G. Thorondorsen for the suggestion!

Please submit quotes and vote for next week!

This Week in Rust is edited by: nellshamrell, llogiq, cdmistman, ericseppanen, extrawurst, andrewpollack, U007D, kolharsam, joelmarcey, marriannegoldin.

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