using `union` as key of `record` adds `undefined` to the value type

[bug-brain]

import * as v from 'valibot';

const record = v.record(v.union([v.string()]), v.string());

const t: v.Output<typeof record> = { a: undefined }
//    ^ { [x: string]: string | undefined; }
//                              ^ should not be here
const result = v.safeParse(record, t);
console.log(result); // errors correctly

[Fabian Hiller]

This is the intended behavior when string is not used directly as the key schema. In your case, I recommend removing union and using only string. This should solve your problem. union can be used with literal to describe certain record keys, but record does not force you to specify them and therefore we mark it as optional in this case. Feel free to contact me if you have any further questions.

[Fabian Hiller]

But please leave this issue open. I agree that it would be better to specify it as undefined only when literal is used inside of union. I will see if I can improve the types.

[bug-brain]

How would I model the type Record<"a" | "b", number>? I would have expected v.record(v.union([v.literal("a"), v.literal("b")]), v.number()) but that makes the keys optional and adds undefined as you mentioned. The function required only works on ObjectSchema.

[Fabian Hiller]

I would use object and not record:

import * as v from 'valibot';

const Schema = v.object({ a: v.number(), b: v.number() });

But maybe you are right and our current typing and implementation is wrong and we should only mark it as optional when optional is used for the value of the record.

[Fabian Hiller]

@bug-brain I investigated this issue further. It is true that the behavior of Valibot is different from TypeScript and it would be nice to unify it. But there is a tradeoff. To support this behavior, record has to "understand" the schemas used and apply additional logic to ensure that every required entry is defined. This would increase the raw bundle size of the record function from 408 bytes to about 460 bytes (13%). Furthermore, this change would require us to limit the record key schema to string and picklist, as it would require much more code to handle other more "unpredictable" schemas such as union. That's probably also why Zod implemented it this way.

[Fabian Hiller]

Since many Zod users are also complaining about this problem in #2623, I will investigate this further to find an appropriate solution.

[Fabian Hiller]

I think I fixed it! Will test and investigate my code tomorrow. Thanks for bringing this up!

[Fabian Hiller]

Even if I found a solution, I am not sure if we should go this way as a library focused on bundle size. Supporting this behavior increases the bundle size of record, while the same behavior can already be achieved with object. Maybe we should limit the key argument of record to just string (or stick to the current behaviour with undefined) and provide a util function to convert a list of keys into the entries argument of object.

// `record` does only allow `string` as first argument
const Schema1 = v.record(v.string(), v.number());

// For explicit keys, `object` with `entriesFrom` is used instead
const Schema2 = v.object(v.entriesFrom(['foo', 'bar'], v.number()));

// Or without the util function
const Schema2 = v.object({ foo: v.number(), bar: v.number() });

[Milan Jaritz]

@fabian-hiller may I ask how much record would increase in bundle size?

[Milan Jaritz]

I am using a graphql-codegen-typescript-validation-schema to generate zod enums like this:

export const PosTypeEnumSchema = z.enum(['external', 'online', 'standard', 'telephone']);

That way I don't need to define all of my enum schemas manually.

Now I need a record with these enums as a key type and I don't want to re-define these keys by hand but instead use the generated z.enum. (the alternatives you showed unfortunately don't solve that issue)

[Fabian Hiller]

The next version of Valibot will allow you to write the following code to solve your problem. Feel free to give me feedback on this in the long run.

import * as v from 'valibot';

const ListSchema = v.picklist(['external', 'online', 'standard', 'telephone']);

const ObjectSchema = v.object(v.entriesFromList(ListSchema.options, v.number()));

[Fabian Hiller]

I am not a maintainer of Zod, so I cannot speak for it. I recommend asking the Zod team directly.

[Milan Jaritz]

Thank you, I'll do that :)

[Fabian Hiller]

The next version of Valibot will allow you to write the following code to solve your problem

This is now implemented and available.