Rust Best Practices

Rust Best Practices

Apply these guidelines when writing or reviewing Rust code. Based on Apollo GraphQL's Rust Best Practices Handbook.

Best Practices Reference

Before reviewing, familiarize yourself with Apollo's Rust best practices. Read ALL relevant chapters in the same turn in parallel. Reference these files when providing feedback:

• Chapter 1 - Coding Styles and Idioms: Borrowing vs cloning, Copy trait, Option/Result handling, iterators, comments, when to extract a function (duplication vs. wrong abstraction)
• Chapter 2 - Clippy and Linting: Clippy configuration, important lints, workspace lint setup
• Chapter 3 - Performance Mindset: Profiling, avoiding redundant clones, stack vs heap, zero-cost abstractions
• Chapter 4 - Error Handling: Result vs panic, thiserror vs anyhow, error hierarchies
• Chapter 5 - Automated Testing: Test naming, one assertion per test, snapshot testing
• Chapter 6 - Generics and Dispatch: Static vs dynamic dispatch, trait objects
• Chapter 7 - Type State Pattern: Compile-time state safety, when to use it
• Chapter 8 - Comments vs Documentation: When to comment, doc comments, rustdoc
• Chapter 9 - Understanding Pointers: Thread safety, Send/Sync, pointer types

Quick Reference

Borrowing & Ownership

• Prefer &T over .clone() unless ownership transfer is required
• Use &str over String, &[T] over Vec<T> in function parameters
• Small Copy types (≤24 bytes) can be passed by value
• Use Cow<'_, T> when ownership is ambiguous

Error Handling

• Return Result<T, E> for fallible operations; avoid panic! in production
• Never use unwrap()/expect() outside tests
• Use thiserror for library errors, anyhow for binaries only
• Prefer ? operator over match chains for error propagation

Performance

• Always benchmark with --release flag
• Run cargo clippy -- -D clippy::perf for performance hints
• Avoid cloning in loops; use .iter() instead of .into_iter() for Copy types
• Prefer iterators over manual loops; avoid intermediate .collect() calls

Linting

Run regularly: cargo clippy --all-targets --all-features --locked -- -D warnings