Create a union from readonly array

[cjcartier]

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Question

I used to have a decent function for this in V0. But with V1 I get a TS error that slows down my entire project. Simply I want to do something like:

const array = ['a', 'b', 'c'] as const;

const fragment = q.fragment<any>().project({
   prop: constructUnionFromArray(array),
});

type FragmentResult = InferFragmentType<typeof fragment>;
{
   prop: 'a' | 'b' | 'c';
}

I was using this heavily as sometimes I might have pretty long lists of literals that would be cumbersome to update (like icon IDs, colors, etc). So I added a the function below in order to generate the lists and it was working great:

import { z } from 'zod';

import { q } from 'lib/client';

export const isValidZodLiteralUnion = <T extends z.ZodLiteral<unknown>>(literals: T[]): literals is [T, T, ...T[]] =>
  literals.length >= 2;

export const constructZodLiteralUnionType = <T extends z.ZodLiteral<unknown>>(literals: T[]) => {
  const uniqueLiterals = [...new Set(literals)];

  if (!isValidZodLiteralUnion(uniqueLiterals)) {
    throw new Error(
      'Literals passed do not meet the criteria for constructing a union schema, the minimum length is 2',
    );
  }

  return q.union(uniqueLiterals);
};

export const constructLiteralArray = <T extends string>(literals: T[]): z.ZodLiteral<T>[] =>
  literals.map(literal => z.literal(literal));

export const constructUnionFromArray = <T extends string>(literals: T[]) =>
  constructZodLiteralUnionType(constructLiteralArray(literals));

NOTE: There are updates below so that it works with the new V1.

Not the issue is with return q.union(uniqueLiterals). I get the error Type instantiation is excessively deep and possibly infinite. And that slows the project to a crawl. I have been trying to update this to get it to work again but figured I would shoot you all a message to see if you have a solution that you prefer.

Thank you!

[cjcartier]

Maybe creating a way to use Zod's enum instead of union might work?

const array = ['primary', 'secondary', 'tertiary', 'quaternary', 'quinary', 'senary', 'septenary', 'octonary', 'nonary'] as const;

const zEnum = z.enum(array);
// const zEnum: z.ZodEnum<["primary", "secondary", "tertiary", "quaternary", "quinary", "senary", "septenary", "octonary", "nonary"]>
type ZEnum = z.infer<typeof zEnum>;
// "primary" | "secondary" | "tertiary" | "quaternary" | "quinary" | "senary" | "septenary" | "octonary" | "nonary"

const zUnion = z.union(array);
// Argument of type 'readonly ["primary", "secondary", "tertiary", "quaternary", "quinary", "senary", "septenary", "octonary", "nonary"]' is not assignable to parameter of type 'readonly [ZodTypeAny, ZodTypeAny, ...ZodTypeAny[]]'.

[cjcartier]

I still think it would be great to get something working for that above case. But I was able to use .as() in order to get the typing that I wanted.

[scottrippey]

One thing worth noting, is that q.union === z.union, it's just a copy for convenience.

Can you get this example to work with just Zod? Like, when you do const abc = constructZodLiteralUnionType(['a','b','c',...]), does it give you this error?

Or does the error only occur when you do .project({ prop: abc })?