The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Rust Projects Workflow

Tool Grid

Task	Tool	Command
Lint	Clippy	cargo clippy
Format	rustfmt	cargo fmt
Type check	built-in	cargo check
Build	cargo	cargo build
Test	cargo	cargo test
Security	cargo-audit	cargo audit
Coverage	cargo-tarpaulin	cargo tarpaulin
Docs	rustdoc	cargo doc

Workflow Commands

Development Cycle

# Check before commit
cargo fmt --check && cargo clippy -- -D warnings && cargo test

# Full validation
cargo fmt && cargo clippy --fix --allow-dirty && cargo test && cargo doc --no-deps

Release Builds

cargo build --release
cargo test --release

---

Trait Requirements

Public Types

All public types MUST implement:

• Debug - Required for error messages and debugging
• Clone - Required unless the type explicitly manages unique resources

Public types SHOULD implement:

• PartialEq - When equality comparison is meaningful
• Eq - When PartialEq is reflexive (most cases)
• Hash - When the type may be used as a key
• Default - When a sensible default exists

Common Derive Patterns

// Minimal public struct
#[derive(Debug, Clone)]
pub struct Config { /* ... */ }

// Value type (data container)
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct UserId(String);

// With default
#[derive(Debug, Clone, Default, PartialEq)]
pub struct Settings { /* ... */ }

// Serializable types
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct ApiResponse { /* ... */ }

Display Trait

Types representing user-facing values SHOULD implement Display:

use std::fmt;

impl fmt::Display for UserId {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.0)
    }
}

---

Cargo.lock Rules

Binaries and Applications

• MUST commit Cargo.lock to version control
• Ensures reproducible builds across environments
• Add to .gitignore exceptions if using a global ignore

Libraries

• MAY ignore Cargo.lock (add to .gitignore)
• Downstream consumers use their own lockfile
• RECOMMENDED to commit for CI reproducibility, but not required

Workspaces

• MUST commit the root Cargo.lock
• All workspace members share the same lockfile

---

Error Handling

Libraries: Use thiserror

use thiserror::Error;

#[derive(Debug, Error)]
pub enum LibraryError {
    #[error("invalid configuration: {0}")]
    InvalidConfig(String),

    #[error("resource not found: {resource}")]
    NotFound { resource: String },

    #[error(transparent)]
    Io(#[from] std::io::Error),
}

Applications: Use anyhow

use anyhow::{Context, Result};

fn main() -> Result<()> {
    let config = load_config()
        .context("failed to load configuration")?;

    run_app(config)?;
    Ok(())
}

Error Handling Rules

• MUST NOT use .unwrap() in library code (except tests)
• MUST NOT use .expect() without a meaningful message
• SHOULD use ? operator for propagation
• SHOULD add context with .context() or .with_context()
• MAY use .unwrap() in main() for unrecoverable errors

Result Type Aliases

Libraries SHOULD define a Result alias:

pub type Result<T> = std::result::Result<T, LibraryError>;

---

Memory Safety

Ownership Rules

• Each value has exactly one owner
• When the owner goes out of scope, the value is dropped
• Ownership can be transferred (moved) or borrowed

Borrowing Rules

• Multiple immutable borrows (&T) allowed simultaneously
• Only one mutable borrow (&mut T) at a time
• Cannot mix mutable and immutable borrows

Lifetime Annotations

// Explicit lifetime when returning borrowed data
fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() { x } else { y }
}

// Struct containing references
struct Parser<'a> {
    input: &'a str,
}

Common Patterns

// Clone to avoid borrow issues (acceptable for small types)
let owned = borrowed.to_string();

// Use Cow for flexible ownership
use std::borrow::Cow;
fn process(input: Cow<'_, str>) -> String { /* ... */ }

// Arc/Rc for shared ownership
use std::sync::Arc;
let shared = Arc::new(data);

Memory Safety Rules

• MUST NOT use raw pointers outside unsafe blocks
• SHOULD prefer &[T] over raw pointers for slices
• SHOULD use Box<T> for heap allocation
• SHOULD use Arc<T> or Rc<T> for shared ownership

---

Module Organization

File Structure

src/
├── lib.rs          # Library root (pub mod declarations)
├── main.rs         # Binary entry point (optional)
├── config.rs       # Single-file module
├── handlers/       # Multi-file module
│   ├── mod.rs      # Module root (pub mod + re-exports)
│   ├── auth.rs     # Submodule
│   └── api.rs      # Submodule
└── utils/
    ├── mod.rs
    └── helpers.rs

mod.rs Patterns

// src/handlers/mod.rs
mod auth;
mod api;

// Re-export public items
pub use auth::AuthHandler;
pub use api::{ApiClient, ApiError};

// Keep private implementation details
use auth::internal_helper;

Visibility Rules

• MUST use pub only for intentional public API
• SHOULD use pub(crate) for crate-internal items
• SHOULD use pub(super) for parent-module access
• MAY use pub(in path) for fine-grained control

Prelude Pattern (Optional)

// src/prelude.rs
pub use crate::config::Config;
pub use crate::error::{Error, Result};
pub use crate::traits::*;

---

Testing

Unit Tests

Unit tests MUST be in the same file as the code being tested:

// src/calculator.rs
pub fn add(a: i32, b: i32) -> i32 {
    a + b
}

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

    #[test]
    fn test_add_positive() {
        assert_eq!(add(2, 3), 5);
    }

    #[test]
    fn test_add_negative() {
        assert_eq!(add(-1, -1), -2);
    }
}

Integration Tests

Integration tests MUST be in the tests/ directory:

tests/
├── common/
│   └── mod.rs      # Shared test utilities
├── api_tests.rs    # Integration test file
└── cli_tests.rs    # Another test file

Test Patterns

// Use test fixtures
#[test]
fn test_with_fixture() {
    let fixture = TestFixture::new();
    // test code
}

// Test error conditions
#[test]
fn test_invalid_input() {
    let result = parse("");
    assert!(result.is_err());
}

// Use should_panic for expected panics
#[test]
#[should_panic(expected = "index out of bounds")]
fn test_panic_condition() {
    let v = vec![1, 2, 3];
    let _ = v[10];
}

Test Configuration

// Run expensive tests only with --ignored
#[test]
#[ignore]
fn expensive_test() { /* ... */ }

// Async tests (with tokio)
#[tokio::test]
async fn async_test() { /* ... */ }

Testing Rules

• MUST have unit tests for public functions
• SHOULD have integration tests for public API
• SHOULD use #[ignore] for slow tests
• MUST NOT have tests that depend on execution order

---

Documentation

Item Documentation (///)

/// Calculates the factorial of a number.
///
/// # Arguments
///
/// * `n` - The number to calculate factorial for
///
/// # Returns
///
/// The factorial of `n`, or `None` if overflow occurs.
///
/// # Examples
///
/// ```
/// use mylib::factorial;
/// assert_eq!(factorial(5), Some(120));
/// ```
///
/// # Panics
///
/// This function does not panic.
pub fn factorial(n: u64) -> Option<u64> {
    // implementation
}

Module Documentation (//!)

//! # Authentication Module
//!
//! This module provides authentication and authorization
//! functionality for the application.
//!
//! ## Features
//!
//! - JWT token validation
//! - Role-based access control
//! - Session management

mod jwt;
mod roles;

Documentation Rules

• MUST document all public items
• MUST include # Examples for non-trivial functions
• SHOULD include # Panics if the function can panic
• SHOULD include # Errors for functions returning Result
• SHOULD include # Safety for unsafe functions
• MAY use #[doc(hidden)] for public-but-internal items

Doc Tests

Examples in documentation are compiled and run as tests:

/// ```
/// # use mylib::Config;  // Hidden setup line
/// let config = Config::default();
/// assert!(config.is_valid());
/// ```

---

Unsafe Code

Minimization Rules

• MUST minimize use of unsafe blocks
• MUST encapsulate unsafe in safe abstractions
• MUST NOT use unsafe for convenience/performance without justification

Documentation Requirements

/// Reads a value from the given pointer.
///
/// # Safety
///
/// The caller MUST ensure:
/// - `ptr` is valid and properly aligned
/// - `ptr` points to initialized memory
/// - No other references to this memory exist
pub unsafe fn read_ptr<T>(ptr: *const T) -> T {
    // SAFETY: Caller guarantees pointer validity per function contract
    unsafe { std::ptr::read(ptr) }
}

Safe Abstractions

pub struct SafeBuffer {
    ptr: *mut u8,
    len: usize,
}

impl SafeBuffer {
    pub fn new(size: usize) -> Self {
        let ptr = unsafe {
            // SAFETY: size > 0 checked, layout is valid
            std::alloc::alloc(std::alloc::Layout::array::<u8>(size).unwrap())
        };
        Self { ptr, len: size }
    }

    // Safe public API
    pub fn get(&self, index: usize) -> Option<u8> {
        if index < self.len {
            // SAFETY: bounds checked above
            Some(unsafe { *self.ptr.add(index) })
        } else {
            None
        }
    }
}

Unsafe Code Rules

• MUST add // SAFETY: comment before every unsafe block
• MUST document safety requirements in function docs
• SHOULD use #[deny(unsafe_op_in_unsafe_fn)]
• SHOULD audit unsafe code regularly

---

Common Patterns

Builder Pattern

#[derive(Debug, Clone, Default)]
pub struct RequestBuilder {
    url: String,
    headers: Vec<(String, String)>,
    timeout: Option<u64>,
}

impl RequestBuilder {
    pub fn new(url: impl Into<String>) -> Self {
        Self { url: url.into(), ..Default::default() }
    }

    pub fn header(mut self, key: &str, value: &str) -> Self {
        self.headers.push((key.to_string(), value.to_string()));
        self
    }

    pub fn timeout(mut self, seconds: u64) -> Self {
        self.timeout = Some(seconds);
        self
    }

    pub fn build(self) -> Request {
        Request { /* ... */ }
    }
}

Newtype Pattern

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct Email(String);

impl Email {
    pub fn new(value: &str) -> Result<Self, ValidationError> {
        if value.contains('@') {
            Ok(Self(value.to_string()))
        } else {
            Err(ValidationError::InvalidEmail)
        }
    }

    pub fn as_str(&self) -> &str {
        &self.0
    }
}

Type State Pattern

pub struct Connection<State> {
    inner: TcpStream,
    _state: std::marker::PhantomData<State>,
}

pub struct Disconnected;
pub struct Connected;

impl Connection<Disconnected> {
    pub fn connect(addr: &str) -> Result<Connection<Connected>, Error> {
        let stream = TcpStream::connect(addr)?;
        Ok(Connection { inner: stream, _state: std::marker::PhantomData })
    }
}

impl Connection<Connected> {
    pub fn send(&mut self, data: &[u8]) -> Result<(), Error> { /* ... */ }
}

---

Clippy Configuration

Recommended Lints

Add to Cargo.toml or clippy.toml:

# Cargo.toml
[lints.clippy]
pedantic = "warn"
nursery = "warn"
unwrap_used = "deny"
expect_used = "warn"

Allowing Specific Lints

#[allow(clippy::too_many_arguments)]
fn complex_function(/* many args */) { /* ... */ }

CI Configuration

cargo clippy -- -D warnings -D clippy::unwrap_used