# Sprint 53 - Feature Flag Implementation Summary

## Overview

As part of Sprint 53, we successfully implemented a feature flag system for the polyglot AST framework. This enhancement allows for more modular and customizable language support in the PMAT codebase, reducing binary size and compilation time for users who only need specific language support.

## Implementation Details

### 1. Feature Flag Definition

We added the following feature flags to `server/Cargo.toml`:

```toml
# Polyglot AST meta-feature for cross-language analysis
polyglot-ast = []

# Language-specific features
polyglot-java = ["polyglot-ast"]
polyglot-kotlin = ["polyglot-ast"]
polyglot-scala = ["polyglot-ast"]
polyglot-typescript = ["polyglot-ast"]
polyglot-javascript = ["polyglot-ast"]
polyglot-csharp = ["polyglot-ast"]
polyglot-ruby = ["polyglot-ast"]
```

These feature flags enable conditional compilation of language-specific components:

1. The `polyglot-ast` meta-feature enables the core cross-language analysis framework
2. Language-specific features depend on the meta-feature and enable support for specific languages

### 2. LanguageMapper Updates

We enhanced the LanguageMapper trait with additional functionality to support feature flags:

```rust
pub trait LanguageMapper: Send + Sync {
    // Existing methods...
    
    /// Clone this mapper as a trait object
    fn clone_box(&self) -> Box<dyn LanguageMapper>;
    
    /// Create a test node for unit testing
    fn create_test_node(&self, kind: NodeKind, name: &str) -> UnifiedNode {
        UnifiedNode::new(kind, name, self.language())
    }
}
```

These changes enabled:
- Better trait object handling through `clone_box`
- Simplified testing through `create_test_node`
- Consistent behavior across all language mappers

### 3. Language Mapper Factory

We updated the language mapper factory to use conditional compilation based on feature flags:

```rust
pub fn create(language: Language) -> Result<Arc<dyn LanguageMapper>> {
    match language {
        #[cfg(feature = "polyglot-java")]
        Language::Java => Ok(Arc::new(JavaMapper::new())),
        
        #[cfg(feature = "polyglot-kotlin")]
        Language::Kotlin => Ok(Arc::new(KotlinMapper::new())),
        
        // Other language-specific mappers...
        
        _ => {
            // Default to StubMapper for unsupported languages
            Ok(Arc::new(StubMapper::new(language)))
        }
    }
}
```

This implementation ensures that:
1. Only enabled languages are included in the build
2. Unsupported languages fallback to StubMapper
3. The code remains modular and maintainable

### 4. StubMapper Implementation

We created a StubMapper implementation to handle unsupported languages:

```rust
#[derive(Clone)]
pub struct StubMapper {
    language: Language,
}

impl StubMapper {
    pub fn new(language: Language) -> Self {
        Self { language }
    }
}

impl LanguageMapper for StubMapper {
    // Implementation of LanguageMapper trait methods
    
    fn clone_box(&self) -> Box<dyn LanguageMapper> {
        Box::new(self.clone())
    }
    
    // Other methods...
}
```

The StubMapper provides basic functionality for unsupported languages, ensuring graceful degradation rather than runtime failures.

### 5. Language Module Creation

We created missing language modules to support TypeScript and JavaScript:

1. `server/src/services/languages/typescript.rs`
2. `server/src/services/languages/javascript.rs`

These modules include the necessary visitor classes and feature-gated implementation.

### 6. Documentation

We created comprehensive documentation for the feature flag system:

1. `/docs/polyglot-ast-feature-flags.md`: Detailed documentation on feature flag usage
2. `/docs/cross-language-analysis.md`: Overview of cross-language analysis capabilities
3. `/docs/language-support.md`: Comprehensive language support documentation

We also updated the README.md to include information about the feature flags and cross-language analysis capabilities.

## Benefits

The implementation of feature flags for the polyglot AST framework provides several benefits:

1. **Reduced Binary Size**: Users can build PMAT with only the languages they need
2. **Faster Compilation**: Skip compilation of unnecessary language parsers
3. **Customizable Deployment**: Create specialized builds for specific use cases
4. **Testing Flexibility**: Test specific language combinations in isolation
5. **Clear Dependency Structure**: The meta-feature creates a clear dependency hierarchy

## Next Steps

Based on the implementation, the following next steps are recommended:

1. **Update Individual Language Mappers**: Enhance Java, Kotlin, and Scala language mappers to fully support the NodeKind alignment
2. **Comprehensive Testing**: Create integration tests for cross-language analysis with various language combinations
3. **Documentation Enhancements**: Add examples of customizing builds with specific language support

## Conclusion

The feature flag implementation for the polyglot AST framework is a significant enhancement to PMAT's flexibility and modularity. By allowing users to select specific language support, we've made the system more efficient and customizable while maintaining the powerful cross-language analysis capabilities.