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)

ArkType

@arktype.io

27 Mar 2025

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

tsplay.devTS Playground - An online editor for exploring TypeScript and JavaScriptThe Playground lets you write TypeScript or JavaScript online in a safe and sharable way.

ArkType

@arktype.io

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☠️

27/3/25, 4:29 pm0 reposts9 likes

ArkType

@arktype.io

27 Mar 2025

@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 🙏

Jayden Carey

@jaydencarey.bsky.social

27 Mar 2025

Is this being tracked in a github issue?

Mateusz Burzyński

@andarist.bsky.social

30 Mar 2025

github.com/microsoft/Ty...

github.com[experiment] Cache mapper instantiations by Andarist · Pull Request #61505 · microsoft/TypeScript@ssalbdivad found out that a chain of somewhat trivial operations can easily end up with dreaded "Type instantiation is excessively deep and possibly infinite". Two different reproduction...

hmnd.dev

@hmnd.dev

27 Mar 2025

Would be very curious to learn how you go about investigating this and fixing it; maybe on here or in a blog post? I've been dealing with some mysterious excessively deep errors and it's usually rather difficult to narrow down the cause.