The Ladybird independent web browser project has embarked on transitioning its codebase from C++ to Rust, starting with the JavaScript engine, LibJS. This strategic shift comes after a decision to abandon Swift due to its inadequate interoperability with C++ and limited platform support. The choice of Rust was driven by its mature ecosystem and robust memory safety features.
Lead developer Andreas Kling spearheaded this transition using AI tools, Claude Code and Codex, to expedite the translation process. Over a span of two weeks, approximately 25,000 lines of C++ were converted to Rust—a task that would have otherwise taken months. Notably, the translated code produces byte-for-byte identical output with the original C++ pipeline and passed extensive testing without any regressions.
Despite this successful shift, the team has no plans to eliminate C++. Both Rust and C++ will coexist in Ladybird’s development. The port to Rust will proceed as a gradual and ongoing effort, with C++ development remaining active. By using a human-directed approach, Kling ensured architectural decisions were meticulously managed, blending AI capabilities with expert oversight to maintain codebase integrity.

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The Ladybird browser project is migrating its codebase from C++ to Rust, beginning with the JavaScript engine LibJS. Lead developer Andreas Kling used AI coding tools—Claude Code and Codex—to accelerate the translation, converting ~25,000 lines of C++ to Rust in two weeks, a process that would otherwise have taken months. The translated code produces byte-for-byte identical output and passed all regression tests. Rust was chosen over Swift due to better C++ interoperability and a more mature ecosystem. C++ and Rust will coexist going forward, with the migration proceeding gradually under human-directed architectural oversight.

Ladybird Browser Transitions to Rust with AI Assistance

I was wondering how idiomatic the code would be but they mentioned that they were aiming for compatibility first so that answers my question.
In college they taught us c++ and I hated the process so much that I wouldn’t code again for over a decade. There was probably a bunch of reasons I had such a poor experience (teaching vs learning style, etc) but moving from c++ to rust does put a smile on my face. Hell, if they are able to add Go as well, I might switch browsers…
lol, I was going to test drive the browser regardless

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[…] transition using AI tools […] Over a span of two weeks, approximately 25,000 lines of C++ were converted to Rust […]
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Yup. So, Ladybird’s off the list of valiable browser alternatives. At that speed it’s clear the review process for the AI-generated code was minimal, if any.