Rust Development Best Practices

This skill outlines the industry standards and best practices for developing software in Rust.

1. Project Layout (The Cargo Standard)

Follow the standard Cargo project layout strictly:

• •src/main.rs: Entry point for binary crates.
• •src/lib.rs: Entry point for library crates (and the library part of binaries).
• •src/bin/: Additional binaries.
• •tests/: Integration tests (treats your crate as an external dependency).
• •benches/: Benchmarks (using criterion usually).
• •examples/: Example usage code.

Guidelines

• •Split main.rs and lib.rs: Even for binaries, put most logic in lib.rs. main.rs should only parse args and call into lib.rs. This makes logic testable.
• •Workspaces: For multi-crate projects, use a Cargo Workspace in the root Cargo.toml.

2. Idiomatic Rust

• •Clippy is Law: Always run cargo clippy. Fix all warnings. It catches non-idiomatic code.
• •Result Handling:
  • •Never use .unwrap() or .expect() in production/library code (recoverable errors).
  • •Use ? operator for error propagation.
  • •Use .expect("...") only in tests or prototypes to document why it shouldn't fail.
• •Iterators: Prefer iterator chains (.map(), .filter(), .collect()) over raw for loops for transformation logic. It's often faster and more readable.
• •Type Safety: Use the type system!
  • •Newtypes: struct UserId(String) instead of passing raw strings.
  • •Enums: Make invalid states unrepresentable.

3. Error Handling

• •Libraries: Define a custom Error enum using thiserror.
  rust

  #[derive(thiserror::Error, Debug)]
  pub enum MyError {
      #[error("IO error: {0}")]
      Io(#[from] std::io::Error),
      #[error("Invalid input: {0}")]
      InvalidInput(String),
  }
  

• •Binaries/Apps: Use anyhow::Result for flexible error bubbling in applications.
  rust

  fn main() -> anyhow::Result<()> { ... }
  

4. Async Rust (Tokio)

• •Runtime: Use #[tokio::main] for the entry point.
• •Blocking: NEVER call blocking functions (file IO, heavy computation, std::thread::sleep) inside an async function. It blocks the executor thread.
  • •Use tokio::fs instead of std::fs.
  • •Use tokio::task::spawn_blocking for CPU-heavy or blocking synchronous APIs.
• •Concurrency:
  • •tokio::spawn: Spawns a background task (fire and forget or await handle).
  • •tokio::join!: Wait for multiple futures concurrently.
  • •tokio::select!: Race multiple futures (cancellation safety is key here).
• •Channels: Use tokio::sync::mpsc for message passing between tasks.

5. Testing

• •Unit Tests: Put them in the same file as the code, in a mod tests block.
  rust

  #[cfg(test)]
  mod tests {
      use super::*;
      #[test]
      fn it_works() { ... }
  }
  

• •Integration Tests: Put them in tests/*.rs. These test your public API.
• •Property Testing: Consider proptest for complex logic to automatically find edge cases.

6. Formatting & Documentation

• •Formatting: Always run cargo fmt. No arguments.
• •Docs:
  • •Triple slash /// for public item documentation.
  • •Module level docs //! at the top of files.
  • •Run cargo doc --open to preview.

7. Common Dependencies

• •Serialization: serde, serde_json
• •Async: tokio, futures
• •Error: thiserror (lib), anyhow (bin)
• •Logging: tracing, tracing-subscriber (do not use log crate directly anymore, tracing is the standard for async apps).
• •CLI: clap