[jitl]

It's hard to come up with a compiler that produces a sound checker for arbitrarily complex union/intersection types. Perhaps there could be a restriction on reflection to "simple enough" types, but that's always going to be a weirdly moving target based on heuristics. There's already cases where Typescript tries to generate ~40MB+ .d.ts files which are just re-stating the types themselves. So it's easy to imagine a validator compiler emitting 100MB+ of code to check more wild and crazy types.

[pas]

Size, computation and other budgets seem like useful knobs to expose to developers. And anything that's locally decidable (so can be run on multiple cores easily).