I am getting this error when I deploy my simple Next.js app to Vercel (and only on deploy, locally it never has this error):

Type error: Type instantiation is excessively deep and possibly infinite.

When I run pnpm build locally it builds fine, but on Vercel it is failing I’d say 70% of the time (sometimes it does successfully deploy).

How can I better debug this, perhaps locally, or just on Vercel? How can I narrow down what the culprit might be?

I tried adding this prop to my tsconfig.json but it didn’t seem to do anything:

{
  "compilerOptions": {
    "maxNodeModuleJsDepth": 1000
    ...
  }
}

The only thing I can think of in my app where I manually used recursion in TypeScript is here:

type RecursivelyReplaceNullWithUndefined<T> = T extends null
  ? undefined
  : T extends Date
  ? T
  : {
      [K in keyof T]: T[K] extends (infer U)[]
        ? RecursivelyReplaceNullWithUndefined<U>[]
        : RecursivelyReplaceNullWithUndefined<T[K]>
    }

Used in this function:

import isArray from 'lodash/isArray'
import isObject from 'lodash/isObject'

export function removeNulls<T>(
  obj: T,
): RecursivelyReplaceNullWithUndefined<T> {
  const res = {} as any

  for (const name in obj) {
    let value = obj[name] as any

    if (isArray(value)) {
      value = value.map(removeNulls)
    } else if (isObject(value)) {
      value = removeNulls(value)
    } else if (value == null) {
      value = undefined
    }

    res[name] = value
  }

  return res
}

Which is used to cleanup database query nulls:

export async function findScript({ key }: { key: string }) {
  const script = await db
    .selectFrom('script')
    .selectAll()
    .where('slug', '=', key)
    .executeTakeFirstOrThrow()

  return removeNulls({
    id: script.id,
    slug: script.slug,
    name: script.name,
    category: script.category,
    is_rtl: script.is_rtl,
    is_vertical: script.is_vertical,
    iso_15924: script.iso_15924,
    iso_15924_numeric: script.iso_15924_numeric,
  })
}

And that is used in the Next.js route.ts file.