Rust

Rust Project Rules

Agent Automation Commands

CRITICAL: Execute these commands after EVERY implementation (see AGENT_AUTOMATION module for full workflow).

# Complete quality check sequence:
cargo fmt --all -- --check           # Format check
cargo clippy --workspace --all-targets --all-features -- -D warnings  # Lint
cargo test --workspace --all-features  # All tests (100% pass)
cargo build --release                # Build verification
cargo llvm-cov --all                 # Coverage (95%+ required)

# Security audit:
cargo audit                          # Vulnerability scan
cargo outdated                       # Check outdated deps

Rust Edition and Toolchain

CRITICAL: Always use Rust Edition 2024 with nightly toolchain.

• Edition: 2024
• Toolchain: nightly 1.85+
• Update: Run rustup update nightly regularly

Formatting

• Use rustfmt with nightly toolchain
• Configuration in rustfmt.toml or .rustfmt.toml
• Always format before committing: cargo +nightly fmt --all
• CI must check formatting: cargo +nightly fmt --all -- --check

Linting

• Use clippy with -D warnings (warnings as errors)
• Fix all clippy warnings before committing
• Acceptable exceptions must be documented with #[allow(clippy::...)] and justification
• CI must enforce clippy: cargo clippy --workspace -- -D warnings

Testing

• Location: Tests in /tests directory for integration tests
• Unit Tests: In same file as implementation with #[cfg(test)]
• Coverage: Must meet project threshold (default 95%)
• Tools: Use cargo-nextest for faster test execution
• Async: Use tokio::test for async tests with Tokio runtime

Example test structure:

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_feature() {
        // Test implementation
    }

    #[tokio::test]
    async fn test_async_feature() {
        // Async test implementation
    }
}

Test Categories: S2S and Slow Tests

CRITICAL: Tests must be categorized based on execution time and dependencies.

Test Time Limits

• Fast Tests: Must complete in ≤ 10-20 seconds
• Slow Tests: Any test taking > 10-20 seconds must be marked as slow
• S2S Tests: Tests requiring active server/database must be isolated and run on-demand

S2S (Server-to-Server) Tests

Tests that require active servers, databases, or external services must be isolated using Cargo features.

Implementation:

1. Create s2s feature in Cargo.toml:

[features]
default = []
s2s = []  # Enable server-to-server tests

2. Mark S2S tests with feature flag:

#[cfg(test)]
mod tests {
    use super::*;

    // Regular fast test (always runs)
    #[test]
    fn test_local_computation() {
        // Fast test, no external dependencies
    }

    // S2S test (only runs with --features s2s)
    #[cfg(feature = "s2s")]
    #[tokio::test]
    async fn test_database_connection() {
        // Requires active database server
        let db = connect_to_database().await?;
        // ... test implementation
    }

    #[cfg(feature = "s2s")]
    #[tokio::test]
    async fn test_api_integration() {
        // Requires active API server
        let client = create_api_client().await?;
        // ... test implementation
    }
}

3. Run tests:

# Regular tests (excludes S2S)
cargo test

# Include S2S tests (requires active servers)
cargo test --features s2s

# CI/CD: Run S2S tests only when servers are available
cargo test --features s2s --test-args '--test-threads=1'

Slow Tests

Tests that take > 10-20 seconds must be marked and run separately.

Implementation:

1. Create slow feature in Cargo.toml:

[features]
default = []
slow = []  # Enable slow tests

2. Mark slow tests:

#[cfg(test)]
mod tests {
    use super::*;

    // Fast test (always runs)
    #[test]
    fn test_quick_operation() {
        // Completes in < 1 second
    }

    // Slow test (only runs with --features slow)
    #[cfg(feature = "slow")]
    #[test]
    fn test_heavy_computation() {
        // Takes 30+ seconds
        // Heavy processing, large dataset, etc.
    }

    #[cfg(feature = "slow")]
    #[tokio::test]
    async fn test_large_file_processing() {
        // Processes large files, takes > 20 seconds
    }
}

3. Run tests:

# Regular tests (excludes slow)
cargo test

# Include slow tests
cargo test --features slow

# Run both S2S and slow tests
cargo test --features s2s,slow

Best Practices

• ✅ Always run fast tests in CI/CD by default
• ✅ Isolate S2S tests - never run them in standard test suite
• ✅ Mark slow tests - prevent CI/CD timeouts
• ✅ Document requirements - specify which servers/services are needed for S2S tests
• ✅ Use timeouts - Set appropriate timeouts for S2S tests: tokio::time::timeout(Duration::from_secs(30), test_fn).await?
• ❌ Never mix fast and slow/S2S tests in same test run
• ❌ Never require external services for standard test suite
• ❌ Never exceed 10-20 seconds for regular tests

Async Programming

CRITICAL: Follow Tokio best practices for async code.

• Runtime: Use Tokio for async runtime
• Blocking: Never block in async context - use spawn_blocking for CPU-intensive tasks
• Channels: Use tokio::sync::mpsc or tokio::sync::broadcast for async communication
• Timeouts: Always set timeouts for network operations: tokio::time::timeout

Example:

use tokio::time::{timeout, Duration};

async fn fetch_data() -> Result<Data, Error> {
    timeout(Duration::from_secs(30), async {
        // Network operation
    }).await?
}

Dependency Management

CRITICAL: Always verify latest versions before adding dependencies.

Before Adding Any Dependency

1. Check Context7 for latest version:

   • Use MCP Context7 tool if available
   • Search for the crate documentation
   • Verify the latest stable version
   • Review breaking changes and migration guides

2. Example Workflow:

   Adding tokio → Check crates.io and docs.rs
   Adding serde → Verify latest version with security updates
   Adding axum → Check for breaking changes in latest version
   

3. Document Version Choice:

   • Note why specific version chosen in Cargo.toml comments
   • Document any compatibility constraints
   • Update CHANGELOG.md with new dependencies

Dependency Guidelines

• ✅ Use latest stable versions
• ✅ Check for security advisories: cargo audit
• ✅ Prefer well-maintained crates (active development, good documentation)
• ✅ Minimize dependency count
• ✅ Use workspace dependencies for monorepos
• ❌ Don't use outdated versions without justification
• ❌ Don't add dependencies without checking latest version

Codespell Configuration

CRITICAL: Use codespell to catch typos in code and documentation.

Install: pip install 'codespell[toml]'

Configuration in pyproject.toml:

[tool.codespell]
skip = "*.lock,*.json,target,node_modules,.git"
ignore-words-list = "crate,ser,deser"

Or run with flags:

codespell \
  --skip="*.lock,*.json,target,node_modules,.git" \
  --ignore-words-list="crate,ser,deser"

Error Handling

• Use Result<T, E> for recoverable errors
• Use thiserror for custom error types
• Use anyhow for application-level error handling
• Document error conditions in function docs
• Never use unwrap() or expect() in production code without justification

Example:

use thiserror::Error;

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

pub fn process_data(input: &str) -> Result<Data, MyError> {
    // Implementation
}

Documentation

• Public APIs: Must have doc comments (///)
• Examples: Include examples in doc comments
• Modules: Document module purpose with //!
• Unsafe: Always document safety requirements for unsafe code
• Run doctests: cargo test --doc

Example:

/// Processes the input data and returns a result.
///
/// # Arguments
///
/// * `input` - The input string to process
///
/// # Examples
///
/// ```
/// use mylib::process;
/// let result = process("hello");
/// assert_eq!(result, "HELLO");
/// ```
///
/// # Errors
///
/// Returns `MyError::InvalidInput` if input is empty.
pub fn process(input: &str) -> Result<String, MyError> {
    // Implementation
}

Project Structure

project/
├── Cargo.toml          # Package manifest
├── Cargo.lock          # Dependency lock file (commit this)
├── README.md           # Project overview (allowed in root)
├── CHANGELOG.md        # Version history (allowed in root)
├── AGENTS.md          # AI assistant rules (allowed in root)
├── LICENSE            # Project license (allowed in root)
├── CONTRIBUTING.md    # Contribution guidelines (allowed in root)
├── CODE_OF_CONDUCT.md # Code of conduct (allowed in root)
├── SECURITY.md        # Security policy (allowed in root)
├── src/
│   ├── lib.rs          # Library root (for libraries)
│   ├── main.rs         # Binary root (for applications)
│   └── ...
├── tests/              # Integration tests
├── examples/           # Example code
├── benches/            # Benchmarks
└── docs/               # Project documentation

CI/CD Requirements

Must include GitHub Actions workflows for:

1. Testing (rust-test.yml):

   • Test on ubuntu-latest, windows-latest, macos-latest
   • Use cargo-nextest for fast test execution
   • Upload test results

2. Linting (rust-lint.yml):

   • Format check: cargo +nightly fmt --all -- --check
   • Clippy: cargo clippy --workspace -- -D warnings
   • All targets: cargo clippy --workspace --all-targets -- -D warnings

3. Codespell (codespell.yml):

   • Check for typos in code and documentation
   • Fail on errors

Crate Publication

Publishing to crates.io

Prerequisites:

1. Create account at https://crates.io
2. Generate API token: cargo login
3. Add CARGO_TOKEN to GitHub repository secrets

Cargo.toml Configuration:

[package]
name = "your-crate-name"
version = "1.0.0"
edition = "2024"
authors = ["Your Name <your.email@example.com>"]
license = "MIT OR Apache-2.0"
description = "A short description of your crate"
documentation = "https://docs.rs/your-crate-name"
homepage = "https://github.com/your-org/your-crate-name"
repository = "https://github.com/your-org/your-crate-name"
readme = "README.md"
keywords = ["your", "keywords", "here"]
categories = ["category"]
exclude = [
    ".github/",
    "tests/",
    "benches/",
    "examples/",
    "*.sh",
]

[package.metadata.docs.rs]
all-features = true
rustdoc-args = ["--cfg", "docsrs"]

Publishing Workflow:

1. Update version in Cargo.toml
2. Update CHANGELOG.md
3. Run quality checks:

   cargo fmt --all
   cargo clippy --workspace --all-targets -- -D warnings
   cargo test --all-features
   cargo doc --no-deps --all-features
   

4. Create git tag: git tag v1.0.0 && git push --tags
5. GitHub Actions automatically publishes to crates.io
6. Or manual publish: cargo publish

Publishing Checklist:

• ✅ All tests passing (cargo test --all-features)
• ✅ No clippy warnings (cargo clippy -- -D warnings)
• ✅ Code formatted (cargo fmt --all -- --check)
• ✅ Documentation builds (cargo doc --no-deps)
• ✅ Version updated in Cargo.toml
• ✅ CHANGELOG.md updated
• ✅ README.md up to date
• ✅ LICENSE file present
• ✅ Package size < 10MB (check with cargo package --list)
• ✅ Verify with cargo publish --dry-run

Semantic Versioning:

Follow SemVer strictly:

• MAJOR: Breaking API changes
• MINOR: New features (backwards compatible)
• PATCH: Bug fixes (backwards compatible)

Documentation:

• Use /// for public API documentation
• Include examples in doc comments
• Use #![deny(missing_docs)] for libraries
• Test documentation examples with cargo test --doc

/// Processes the input data and returns a result.
///
/// # Arguments
///
/// * `input` - The input string to process
///
/// # Examples
///
/// ```
/// use your_crate::process;
///
/// let result = process("hello");
/// assert_eq!(result, "HELLO");
/// ```
///
/// # Errors
///
/// Returns an error if the input is empty.
pub fn process(input: &str) -> Result<String, Error> {
    // Implementation
}

Source: hivellm/rulebook — distributed by TomeVault.