Yuki Okushi - Rust contributor - Work at Huawei - Working on diagnostics and some docs (Rustnomicon, rustc-dev-guide, ...) - Maintaining some crates (libc, actix-*, ...) - A member of prioritization WG
Rust’s release channels - Rust has three release channels - Stable - Beta - Nightly - Usually, people use Stable, or Nightly (for unstable and/or latest changes) - So, when is Beta used?
What are the different types of regressions? - Correctness changes (ICE, miscompilation, ...) - Performance changes (binary size, memory usage, ...) - Rustdoc-related - ...
Regression types - regression-from-stable-to-nightly: exists only on nightly - regression-from-stable-to-beta: exists on beta - regression-from-stable-to-stable: exists on stable😱 - We should definitely prevent this!
How to find? 1. Run `cargo check/build/test` and some tools (Clippy, Rustdoc) to a number of crates available on crates.io and GitHub 2. Compare the results with the latest Stable (or the current master branch if it’s PR)
Example case: #82565 - Found one crate’s build failed - Confirmed it was fixed on newer version - The team confirmed that the change was safe → The PR has been merged with less pain
Performance monitoring - perf.rust-lang.org - Run benchmarks on all the merged PRs - Triage them every week - Run benchmarks on perf-sensitive PRs before merging
Regression triage - We’ve been doing our best but we cannot reduce the number of regressions to 0. - What should we do if we find them? → This is where the Prioritization WG comes in!
What’s the prioritization working group? - Prioritize the regressions reported on GitHub issue tracker - Monitor critical ones not to slip out - Nominate some of them to t-compiler meetings if necessary - ...so that we do not ship regressions to stable mistakenly More details about WG can be found here
Priority levels - Critical - A release blocker, must be resolved/discussed until next release (e.g. unsound issue) - High - Not a blocker but should be resolved/triaged ASAP (e.g. working -> broken regression) - Medium - Low
How to contribute it? Prioritization WG welcomes everyone! - How to participate? Can I actually contribute? - Anyone can join the Zulip stream and say “Hi”! - See this blog post for more details
Other ways: “Cleanup Crew” - Prepare Minimal Complete and Verifiable Example (MCVE) - Bisect a commit or nightly that introduced a regression - Find related/duplicate issues if exists More details can be found here
Other ways: Use Rust - Everyone could find a regression by using Rust. - Report it to the issue tracker if you find it and have some time Early reporting allows contributors more (earlier) time to work on a fix 🚢
How to create a great bug report? - Fill out the issue template as possible - Try the latest Nightly if you’re on Stable or an old Nightly - MCVE would be helpful! - There’s a useful blog post by Felix S Klock II - Backtrace would also be helpful
Conclusion - Rust has several ways to prevent regressions - Crater, performance monitoring, prioritization WG - The discussion is open - Everyone can read a log and leave a comment - Prioritizing is one of good ways to get your feet wet at contributing
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