This is really impressive work, which can benefit other large JS tools.

I realise this is sort of a dead horse, but rewriting the Typescript checker in Rust would not be an impossible task for a team as well-resourced as Microsoft’s.

I know, because I rewrote a different 100KLOC typechecker myself in Rust (making a few small adjustments for a slightly different target language). It took me about a year.

It would speed up the TypeScript typechecker at least 3-5x, which would save a lot of programmer time (and also datacenter energy consumption).

There’s one obvious downside — it raises the bar for outside contributions — but given the expertise necessary to contribute usefully to a static analysis tool in the first place, and to contribute to TypeScript in particular, I’m not sure it’s a big additional impediment.