Ah took me a while to understand the reason behind this.

It wasn’t “let’s build a faster Rust based Typescript compiler” at all. That was a nice side-effect.

They needed a Typescript compiler that can run on their WASM only sandbox. So the only existing option was to export tsc Go to WASM, but that comes with the full Go runtime.

And to avoid that cost, they experimented with a Rust compiler and turns out it’s even faster than the reference tsc/Go implementation.