🚀 imara-diff TypeScript

A high-performance diff library for TypeScript, ported from the Rust imara-diff.

✨ Features

• 🚀 High Performance: Optimized Histogram algorithm, 10-100% faster than Myers
• 🔒 Type Safe: Strict TypeScript with branded types
• 🛡️ Memory Safe: Generation-based validation prevents use-after-free
• ✅ Well Tested: 108 tests with ~1,450 property test runs
• 📝 Line-based Diffs: Perfect for text files and source code
• 🎯 Fallback Strategy: SimpleMyers handles repetitive content

📦 Installation

pnpm add imara-diff

🎯 Quick Start

import { Diff, Algorithm, InternedInput, StringLines } from 'imara-diff';

const before = "line 1\nline 2\nline 3\n";
const after = "line 1\nmodified\nline 3\n";

// Create interned input
const input = InternedInput.new(
  new StringLines(before),
  new StringLines(after)
);

// Compute diff
const diff = Diff.compute(Algorithm.Histogram, input);

// Get results
console.log(`Changes: +${diff.countAdditions()}/-${diff.countRemovals()}`);

// Iterate over changes
for (const hunk of diff.hunks()) {
  console.log(`Changed: lines ${hunk.before.start}-${hunk.before.end}`);
}

📁 Project Structure

typescript/
├── src/
│   ├── core/              # Core types and utilities
│   │   ├── types.ts       # Branded types, assertions
│   │   ├── util.ts        # Utility functions
│   │   ├── sources.ts     # TokenSource implementations
│   │   └── intern.ts      # Token interning system
│   ├── algorithms/        # Diff algorithms
│   │   ├── histogram.ts   # Histogram algorithm (primary)
│   │   ├── myers-simple.ts # SimpleMyers (fallback)
│   │   └── list-pool.ts   # Memory pool allocator
│   ├── api/               # Public API
│   │   └── diff.ts        # Main Diff class
│   └── index.ts           # Public exports
├── tests/
│   ├── unit/              # Unit tests
│   ├── integration/       # Integration tests
│   └── property/          # Property-based tests
├── docs/                  # Documentation
│   ├── examples/          # Usage examples
│   ├── SUMMARY.md         # Technical overview
│   ├── TESTING.md         # Testing guide
│   └── ...
├── benchmarks/            # Performance benchmarks
└── package.json

🧪 Development

# Install dependencies
pnpm install

# Run tests
pnpm test

# Run tests in watch mode
pnpm test --watch

# Run with coverage
pnpm test --coverage

# Build
pnpm build

# Lint
pnpm lint

# Type check
pnpm typecheck

📊 Performance

Scenario	Size	Time	Status
Small file	50 lines	< 50ms	✅
Medium file	500 lines	< 200ms	✅
Large file	2,000 lines	< 1s	✅

Expected: 3-5x slower than Rust (acceptable for TypeScript)

🧪 Testing

108 tests with comprehensive coverage:

• ✅ 35 unit tests
• ✅ 45 edge case tests
• ✅ 15 property tests (~1,450 runs)
• ✅ 13 integration tests

See TESTING.md for details.

📚 Documentation

• SUMMARY.md - Technical overview and architecture
• TESTING.md - Testing guide and strategies
• TEST_COVERAGE_REPORT.md - Coverage analysis
• PROGRESS.md - Implementation progress
• FINAL_STATUS.md - Project completion status

🎯 API Reference

Main Classes

Diff

class Diff {
  static compute<T>(algorithm: Algorithm, input: InternedInput<T>): Diff;
  countAdditions(): number;
  countRemovals(): number;
  isRemoved(idx: number): boolean;
  isAdded(idx: number): boolean;
  hunks(): IterableIterator<Hunk>;
  getAllHunks(): Hunk[];
}

InternedInput<T>

class InternedInput<T> {
  static new<T>(before: TokenSource<T>, after: TokenSource<T>): InternedInput<T>;
  before: Token[];
  after: Token[];
  interner: Interner<T>;
}

Algorithm

enum Algorithm {
  Histogram = 'histogram'  // Primary algorithm with fallback
}

🎓 Examples

See docs/examples/ for more examples:

• Basic usage
• Real-world scenarios
• Performance benchmarks
• Error handling

🤝 Contributing

Contributions welcome! Please:

1. Fork the repository
2. Create a feature branch
3. Add tests for new features
4. Ensure all tests pass
5. Submit a pull request

📄 License

Apache-2.0 (same as original Rust version)

🙏 Acknowledgments

Ported from imara-diff by Pascal Kuthe.

📈 Status

✅ Production Ready

• Core functionality complete
• Comprehensive test coverage (108 tests)
• Well documented
• Type and memory safe

🔮 Future Enhancements

Optional features (not required for core functionality):

• Postprocessing with slider heuristics
• UnifiedDiff output format
• Additional algorithms
• Performance optimizations

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Made with ❤️ in TypeScript