Precise, consistent, and reliable code coverage (Jynn Nelson at RustWeek)

Precise, consistent, and reliable code coverage by Jynn Nelson. Most existing coverage tools are aimed at "good enough" measurements, where percentages are used as a rough estimate, and the change in percentage is used to determine whether a code change hurts or helps total coverage. For Ferrocene, a safety-certified Rust compiler, rough estimates aren't enough. In this talk I describe how we made coverage precise enough that we can test in CI the exact source code lines that are covered, applied this to Rust's core library, and used it to demonstrate to a safety assessor that a subset of core has 100% line coverage, allowing it to be used in safety-critical systems. About Jynn Nelson (they/she/it): I enjoy doing evil and deranged things to computers. I think a lot about how to make them more useful and fun, and how to decentralize programs away from large companies that reify power structures in their code. In my spare time, I play piano, visit dog parks, and go hiking in national parks. git: https://github.com/jyn514/ mastodon/fedi: https://tech.lgbt/@jyn website: https://jyn.dev/ This talk was given at RustWeek 2026 as part of the Compiler track on Tuesday 19 May. You can find a playlist of all talks in this track at    • RustWeek 2026 Compiler Track Day 1  , and a playlist of all RustWeek 2026 talks at    • RustWeek 2026 All Talks   For information about RustWeek 2027, go to https://2027.rustweek.org. We hope to see you there!