Code duplication in refinements

[eventualbuddha]

I've been using zod for parsing JSON objects in my project, and I'm trying to replace some custom validation with a zod refinement. However, I've found I'm unable to provide the error messages I want in zod v1. I noticed that v3 added the ability to customize the error message by passing a function instead of a static message. That's good! However, in my case having the "check" and "message" be two different things would mean duplicating the validation. Here's what I'm doing now, for reference.

Here's a simple example below. Note that I have to call findDuplicateIds multiple times:

const Person = z.object({
  id: z.string(),
})

const People = z.array(Person).refine(
  (people) => !findDuplicateIds(people).next().done,
  (people) => ({
    message: `person IDs must be unique, but found duplicates: ${[...findDuplicateIds(people)].join(', ')}`
  })
)

function* findDuplicateIds<T extends { id: unknown }>(
  identifiables: Iterable<T>
): Generator<T['id']> {
  const knownIds = new Set<T['id']>()

  for (const { id } of identifiables) {
    if (knownIds.has(id)) {
      yield id
    } else {
      knownIds.add(id)
    }
  }
}

Ideally I'd be able to combine the two, returning errors if there are any and returning nothing if it's valid:

const People = z.array(Person).refine(
  (people) => {
    const duplicateIds = [...findDuplicateIds(people)]
    if (duplicateIds.length) {
      return {
        message: `person IDs must be unique, but found duplicates: ${duplicateIds.join(', ')}`
      }
    }
  }
)

[colinhacks]

You can do this! It's called superRefine and it's not yet documented (but its what .refine() uses under the hood). Here's how to do what you're looking for:

const People = z.array(Person).superRefine((people, ctx) => {
    const duplicateIds = [...findDuplicateIds(people)];
    if (duplicateIds.length) {
      ctx.addIssue({
        code: ZodIssueCode.custom,
        message: `person IDs must be unique, but found duplicates: ${duplicateIds.join(
          ", "
        )}`,
      });
    }
  });

Instead of returning { message: string } you just call ctx.addIssue multiple times (which lets you create multiple issues in a single superRefine call). Haven't documented this yet because it's a bit complex and it's only useful to power-users. So congrats on being a power user!

[eventualbuddha]

Great, thanks!