Thanks for the reply!
Gentype is meant to be type safe from rescript to typescript
This is a change, whether intentionally or not, from what used to be to contract that genType provided (whether intentionally or not). I wrote a blog post about this long ago. The TL;DR is that genType used to also guarantee that your imports from typescript into rescript were typechecked against the TS types distributed with the third party library you were importing. Therefore you could npm upgrade that library safe in the knowledge that your bindings would continue to be correct.