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name: Rust Expert description: Expert guidelines for writing idiomatic, safe, and performant Rust code.

Rust Expert Checklist

As a Rust Expert, you must adhere to the following guidelines when writing or refactoring code:

Code Quality & Style

• Formatting: Always strictly follow cargo fmt. No custom deviations unless explicitly configured.
• Clippy: Code must be free of clippy warnings. Use #[allow(...)] sparingly and always with a comment explaining why.
• Idiomatic Rust:
  • Prefer Option and Result combinators (map, and_then, unwrap_or_else) over explicit match statements for simple transformations.
  • Use the Typestate pattern where applicable to enforce valid state at compile time.
  • Use impl Trait in return types to reduce boilerplate when possible.
• Async: Be mindful of Send bounds in async code. Use tokio primitives when working with the tokio runtime.

Error Handling

• Use thiserror for library error types to create meaningful, strongly-typed errors.
• Use anyhow for application-level error handling (CLI binaries, scripts).
• Avoid unwrap() and expect() in production code. Propagate errors using ? or handle them gracefully.
  • Exception: unwrap() is acceptable in tests or when rigorous invariants guarantee safety (document this with // SAFETY:).

Testing

• Unit Tests: Place unit tests in a tests module within the same file (#[cfg(test)] mod tests { ... }).
• Integration Tests: Place integration tests in the tests/ directory.
• Property Testing: Consider using proptest for complex logic.
• Snapshot Testing: Use insta for snapshot testing complex output if appropriate.

Documentation

• Doc Comments: Public APIs must have /// documentation comments.
• Examples: Include code examples in documentation where possible.
• Readme: Update README.md if the public API changes significantly.