Development Guidelines

Overview

This skill provides procedural guidance for applying core software engineering principles to the ai-cli-syncer Rust project. Apply SOLID design patterns, Test-Driven Development (TDD), and simplicity principles (DRY, KISS, YAGNI) to maintain high code quality and maintainability.

When to Use This Skill

This skill should be invoked when:

• Planning new features - Designing modules following SOLID principles before implementation
• Writing code - Applying SRP, DIP, and other patterns to maintain clean architecture
• Implementing tests - Following TDD cycle (Red-Green-Refactor) for all functionality
• Code review - Verifying adherence to development principles and best practices
• Refactoring - Identifying and eliminating principle violations (bloated classes, tight coupling, repeated code)
• Resolving design questions - Determining proper abstraction levels and module responsibilities

Core Development Principles

SOLID Principles

Apply these five design principles to Rust code:

1. Single Responsibility (SRP) - Each module/struct has one clear purpose

   • Separate file I/O operations from business logic
   • Keep repository structs focused on data operations only
   • Isolate validation logic into dedicated validator modules
   • Example: Split ConfigManager into ConfigReader and ConfigValidator
   • Benefits: Easier testing, clearer code purpose, simpler maintenance

2. Open/Closed (OCP) - Design for extension through traits, not modification

   • Define trait abstractions for contracts
   • Extend functionality by implementing new types
   • Example: Create SyncStrategy trait, then implement FileSyncStrategy, McpSyncStrategy
   • Benefits: Reduces bugs in existing code, safer to add features

3. Liskov Substitution (LSP) - Trait implementations must be substitutable

   • Ensure all implementations honor trait contracts
   • Don't throw unexpected errors in trait methods
   • Example: All ConfigLoader implementations must handle missing files consistently
   • Benefits: Predictable behavior, safer inheritance hierarchies

4. Interface Segregation (ISP) - Create focused traits, not monolithic ones

   • Split large traits into smaller, specific traits
   • Structs implement only the traits they need
   • Example: Split FileHandler into FileReader, FileWriter, FileValidator
   • Benefits: More flexible code, easier to implement and test

5. Dependency Inversion (DIP) - Depend on trait abstractions, inject implementations

   • High-level modules depend on trait abstractions
   • Use dependency injection for concrete implementations
   • Example: SyncEngine depends on trait ConfigLoader, not JsonConfigLoader
   • Benefits: Easier testing with mocks, flexible architecture, decoupled code

TDD (Test-Driven Development)

Follow the Red-Green-Refactor cycle for all feature development:

1. Red - Write a failing test for the desired functionality

   • Test should compile but fail assertion
   • Verify test actually fails before proceeding

2. Green - Implement minimum code to make the test pass

   • Focus on making it work, not making it perfect
   • Don't add functionality beyond what the test requires

3. Refactor - Improve code while keeping tests green

   • Apply SOLID principles to clean up implementation
   • Remove duplication, improve names, simplify logic
   • Run tests after each refactor to ensure behavior preserved

Test Structure:

• Place unit tests in mod tests within each module
• Place integration tests in tests/ directory at project root
• Follow Arrange-Act-Assert (AAA) pattern
• Use descriptive test names: test_config_loader_returns_error_for_missing_file

Benefits: Catches bugs early, provides living documentation, makes refactoring safer, builds confidence when making changes

Simplicity Principles

• DRY (Don't Repeat Yourself) - Extract repeated patterns into reusable functions or modules

  • Create utility modules for common operations
  • Use Rust traits to share functionality across types
  • Avoid copy-pasting code blocks
  • Benefits: Less code to maintain, fewer bugs, better testing

• KISS (Keep It Simple) - Favor simple solutions over complex ones

  • Use standard library features before adding external crates
  • Write self-explanatory code with clear naming
  • Break complex functions into smaller, focused ones
  • Benefits: Easier to understand, faster to debug, lower cognitive load

• YAGNI (You Aren't Gonna Need It) - Implement only what's needed now

  • Don't create abstractions until multiple implementations exist
  • Avoid premature optimization
  • Don't build features for hypothetical future requirements
  • Benefits: Faster delivery, less code to maintain, lower complexity, easier to change

Development Workflow

1. Understand the Requirement

Before coding, clarify:

• What specific problem needs solving?
• What are the acceptance criteria?
• What's the simplest solution that could work?

2. Plan the Design

Apply SOLID principles to planning:

• Which module should own this responsibility? (SRP)
• Is a trait abstraction needed? (DIP, OCP)
• Should existing traits be split? (ISP)
• Can implementations be substituted? (LSP)

3. Write the Test First (Red)

Follow TDD:

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

    #[test]
    fn test_feature_behavior() {
        // Arrange: Set up test data
        let input = "test data";

        // Act: Call the function (this doesn't exist yet!)
        let result = my_function(input);

        // Assert: Verify expected behavior
        assert_eq!(result, expected_value);
    }
}

Run cargo test - it should fail with "function not found".

4. Implement Minimal Solution (Green)

Write the simplest code to pass the test:

pub fn my_function(input: &str) -> ReturnType {
    // Minimum implementation to pass test
    expected_value
}

Run cargo test - it should now pass.

5. Refactor

Now improve the code while keeping tests green:

• Apply SOLID principles
• Remove duplication (DRY)
• Simplify complex logic (KISS)
• Add error handling with anyhow::Context
• Improve variable and function names

Run cargo test after each change to ensure behavior preserved.

6. Verify Principles

Before committing, check:

• ✓ SRP: Does each module/struct have one clear responsibility?
• ✓ Tests: Do all tests pass? Is behavior tested?
• ✓ Simplicity: Is this the simplest solution? Any unnecessary complexity?
• ✓ DRY: Any duplicated code that should be extracted?
• ✓ Documentation: Are public APIs documented with /// comments?

Code Review Checklist

When reviewing code, verify:

SOLID Compliance

• Single Responsibility - Each module/struct has one purpose
• Open/Closed - Extensions use traits, not modifications
• Liskov Substitution - Implementations properly substitute traits
• Interface Segregation - Traits are focused, not bloated
• Dependency Inversion - Depends on traits, not concrete types

Test Coverage

• Tests exist for new functionality
• Tests follow AAA pattern (Arrange-Act-Assert)
• Test names describe behavior being tested
• Tests are independent and isolated
• TDD cycle was followed (Red-Green-Refactor)

Simplicity

• DRY - No repeated code blocks
• KISS - Solution is as simple as possible
• YAGNI - No unnecessary abstractions or features

Code Quality

• Error handling uses anyhow::Context
• Public APIs have /// doc comments
• Variable and function names are clear and descriptive
• No compiler warnings or clippy violations

Common Refactoring Patterns

Violation: Bloated Struct (SRP)

Before:

struct ConfigManager {
    // Too many responsibilities!
}

impl ConfigManager {
    fn read_file() -> Result<String> { ... }
    fn parse_json() -> Result<Config> { ... }
    fn validate() -> Result<()> { ... }
    fn sync_to_agents() -> Result<()> { ... }
}

After (Apply SRP):

struct ConfigReader;
impl ConfigReader {
    fn read(&self, path: &Path) -> Result<String> { ... }
}

struct ConfigParser;
impl ConfigParser {
    fn parse(&self, content: &str) -> Result<Config> { ... }
}

struct ConfigValidator;
impl ConfigValidator {
    fn validate(&self, config: &Config) -> Result<()> { ... }
}

struct ConfigSyncer;
impl ConfigSyncer {
    fn sync(&self, config: &Config) -> Result<()> { ... }
}

Violation: Tight Coupling (DIP)

Before:

struct SyncEngine {
    loader: JsonConfigLoader, // Concrete type!
}

After (Apply DIP):

trait ConfigLoader {
    fn load(&self, path: &Path) -> Result<Config>;
}

struct SyncEngine<L: ConfigLoader> {
    loader: L, // Depends on abstraction
}

Violation: Repeated Code (DRY)

Before:

fn sync_cursor() -> Result<()> {
    let path = home_dir().join(".cursor/config");
    let content = fs::read_to_string(&path)?;
    // ... sync logic
}

fn sync_windsurf() -> Result<()> {
    let path = home_dir().join(".windsurf/config");
    let content = fs::read_to_string(&path)?;
    // ... same sync logic
}

After (Apply DRY):

fn sync_agent(agent_name: &str) -> Result<()> {
    let path = home_dir().join(format!(".{}/config", agent_name));
    let content = fs::read_to_string(&path)?;
    // ... reusable sync logic
}

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Remember: Good code is simple, clear, and purposeful.