SemVer in the Rust ecosystem: breakage, tooling, and edge cases

• Tooling

In theory, semantic versioning (SemVer) is simple: breaking changes require major versions. SemVer rules do not change over time. Crates always adhere to SemVer. Careful coding is enough to avoid accidental breaking changes. None of those statements are true! In practice, SemVer is complex and accidental breakage is common: 1 in 6 of the top 1000 Rust crates has violated semantic versioning at least once, frustrating both users and maintainers alike. If you write Rust but don't have the time for a PhD in SemVer, this talk is for you. We'll take a practical look at SemVer in Rust: what it buys us, how Rust's features lead to strange SemVer edge cases, and how we can prevent accidental breakage using a SemVer linter called cargo-semver-checks.