Rust & Blockchain Development Guidelines

This skill provides comprehensive Rust development best practices with emphasis on blockchain development patterns. It auto-activates when working on Rust files or discussing Rust/blockchain topics.

Quick Reference Checklist

When writing Rust code, always:

1. ✅ Use inline string interpolation: format!("{name}") not format!("{}", name)
2. ✅ Consolidate imports at file top: All use statements in single group
3. ✅ Use checked arithmetic: value.checked_add() not value + amount
4. ✅ Avoid .unwrap(): Use .expect() with clear reasoning or Result<T, E>
5. ✅ Document all pub items: Add doc-comments for public APIs
6. ✅ Add // SAFETY: comments: Required for all unsafe blocks
7. ✅ Run before commit: cargo +nightly fmt --all and cargo clippy
8. ✅ Prefer obvious over clever: Write idiomatic, maintainable Rust
9. ✅ Keep dependencies sorted: Alphabetize [dependencies] in Cargo.toml
10. ✅ Meaningful commits: Self-contained, logical commit history

When This Skill Activates

This skill automatically activates when:

• Working on files matching **/*.rs or **/Cargo.toml
• Discussing Rust topics (cargo, clippy, rustfmt, traits, async)
• Implementing blockchain features (consensus, transactions, state machines)
• Fixing Rust compilation errors (borrow checker, lifetimes, traits)
• Adding dependencies or managing workspace structure

Navigation Guide

For detailed guidance on specific topics, see:

Topic	Resource File
Code Style & Formatting	reference.md - String formatting, imports, unsafe, arithmetic
Working Examples	examples.md - Correct patterns with explanations
Common Mistakes	anti-patterns.md - What to avoid and why
Validation Scripts	scripts/ - Automated checking tools

Critical Anti-Patterns (❌ NEVER)

String Formatting:

// ❌ NEVER use positional arguments
println!("Hello {}", name);
format!("Value: {}", value);

// ✅ ALWAYS use inline interpolation
println!("Hello {name}");
format!("Value: {value}");

Import Organization:

// ❌ NEVER split imports
use std::path::Path;

fn my_function() {
    use std::fs::File;  // NEVER import within functions
}

// ✅ ALWAYS consolidate at top
use std::path::Path;
use std::fs::File;

fn my_function() { }

Arithmetic Operations:

// ❌ NEVER use unchecked arithmetic for values
let result = value + amount;  // Can panic or overflow

// ✅ ALWAYS use checked arithmetic
let result = value.checked_add(amount)
    .ok_or(Error::Overflow)?;

Error Handling:

// ❌ AVOID unwrap without justification
let value = some_option.unwrap();

// ✅ PREFER expect with reasoning or Result
let value = some_option.expect("Config::default always sets field");
// OR better:
fn load() -> Result<Config, Error> {
    let value = some_option.ok_or(Error::MissingField)?;
    Ok(Config { value })
}

Unsafe Code:

// ❌ NEVER use unsafe without SAFETY comments
unsafe { *ptr.add(index) = value }

// ✅ ALWAYS document invariants
// SAFETY: This pointer is guaranteed to be valid because the buffer is allocated
// with sufficient capacity and the index is bounds-checked above.
unsafe { *ptr.add(index) = value }

Comments:

// ❌ NEVER write comments that merely echo the code
// Increment counter by 1
counter += 1;

// Set the value to true
is_valid = true;

// ✅ ONLY write comments that explain WHY or provide context
// Reset counter after consensus round completes
counter = 0;

// Mark as valid once signature verification passes
is_valid = verify_signature(msg, sig);

Blockchain-Specific Patterns

When working on blockchain code:

• Consensus logic: Ensure determinism, handle all edge cases
• State transitions: Validate all inputs, prevent invalid states
• Cryptography: Use audited libraries, document security assumptions
• Economic models: Consider attack incentives, verify game theory
• Performance: Benchmark critical paths, optimize database queries

Validation Tools

Use the provided scripts in scripts/:

• check-fmt.sh - Verify code formatting
• check-clippy.sh - Run clippy lints
• validate-deps.sh - Check Cargo.toml dependency ordering

Pre-Commit Checklist

Before committing Rust code:

# Format code
cargo +nightly fmt --all

# Check for warnings
cargo clippy -- -D warnings

# Run tests
cargo test --workspace

# Verify builds
cargo build --workspace --all-features

Both formatting and clippy must complete with zero warnings or changes.

Additional Resources

For comprehensive details, progressive disclosure resources are available:

• reference.md: Deep dive into formatting rules, import organization, unsafe code guidelines, checked arithmetic patterns, error handling best practices
• examples.md: Working code samples demonstrating correct patterns
• anti-patterns.md: Common mistakes with explanations and fixes

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This skill follows Anthropic's best practices for progressive disclosure. The main SKILL.md provides quick reference while detailed resources load on-demand to optimize context usage.