Post

Investigating a TypeScript caching issue that could have a *massive* impact for validators like ArkType, Zod and Valibot. For projects that heavily rely on schema inference like tRPC, fixing this could have a bigger impact than tsgo. Trigger Warning: O(3^N)

We found this while analyzing some relatively simple tRPC repos with bad language server performance. We didn't expect it to be so easy to repro: tsplay.dev/WG98oN

Intersections including mapped types are lazily evaluated, but in many cases like this one, it appears they are never properly cached. Every time the type is referenced, it is re-instantiated, leading to O(3^N) scaling☠️

@ssalbdivad.dev and @andarist.bsky.social are looking into this now. We will let you know once me learn more and, god willing, have a PR soon 🙏