Rust Best Practices Agent Skill

Rust Best Practices Assistant

Core Principles

• Prefer safe Rust; use unsafe only when absolutely necessary and well-documented
• Leverage the type system to prevent bugs at compile time
• Use Result<T, E> for error handling, avoid panic! in library code
• Make illegal states unrepresentable through proper type design

Code Style

• Format all code with rustfmt
• Follow all clippy suggestions (run with cargo clippy -- -W clippy::pedantic)
• Use snake_case for variables and functions
• Use CamelCase for types and traits
• Use SCREAMING_SNAKE_CASE for constants

Memory & Ownership

• Prefer borrowing (&T, &mut T) over ownership when possible
• Use Cow<str> for strings that might be borrowed or owned
• Avoid unnecessary .clone() - consider borrowing or restructuring
• Use Arc<T> for shared ownership across threads, Rc<T> for single-threaded

Error Handling

• Use thiserror for defining library error types
• Use anyhow for application-level error handling
• Provide meaningful, actionable error messages
• Use ? operator for error propagation

Performance

• Avoid unnecessary heap allocations
• Prefer iterators over manual loops (zero-cost abstraction)
• Use &str instead of String for function parameters when possible
• Consider using SmallVec for small, stack-allocated vectors

Async Rust

• Use tokio as the async runtime for most applications
• Prefer async fn over manual Future implementations
• Avoid blocking operations in async contexts
• Use tokio::spawn for concurrent tasks

Testing

• Write unit tests in the same file using #[cfg(test)] module
• Use #[should_panic] for testing panic behavior
• Use proptest or quickcheck for property-based testing
• Aim for meaningful test coverage, not just line coverage

Common Patterns

• Use the builder pattern for complex object construction
• Use From and Into traits for type conversions
• Implement Default when a sensible default exists
• Use Option<T> instead of sentinel values

What to Avoid

• Avoid unwrap() in production code; use expect() with context or proper error handling
• Avoid String when &str suffices
• Avoid manual memory management when safe abstractions exist
• Avoid unsafe without thorough documentation and testing