Overview
Ladybird browser project successfully migrated their JavaScript engine from C++ to Rust using AI coding agents in a carefully managed process. The human-directed AI assistance reduced development time from months to weeks while maintaining perfect code compatibility.
Key Points
- AI-assisted port of 25,000 lines of JavaScript engine code from C++ to Rust - months of manual work compressed into just two weeks
- Human-directed approach where developers steered AI agents through hundreds of small prompts - proves AI can handle critical system code when properly supervised
- Achieved byte-for-byte identical output between old and new implementations with zero regressions - comprehensive test coverage made large-scale AI porting safe and verifiable
- Extensive conformance testing suite (test262) was crucial enabler - existing test suites unlock AI-assisted migration of complex codebases