Extend Jsonify type to handle Tagged types

[marcuspoehls]

I’m using Tagged types in combination with Jsonify-ed types. It seems that tagged types aren’t unwrapped when creating their JSON type.

Am I missing something or is that an option for improvement?

Here’s the sample code that I’m using:

import type { Tagged, Jsonify } from 'type-fest'

export type UserId = Tagged<number, 'UserId'>

class User extends BaseModel {
  declare id: UserId
}

// then I’m extracting the DTO and DTO-JSON types

export interface UserDto {
  id: User['id']
}

export type UserDtoJson = Jsonify<UserDto>
// type UserDtoJson = {
//     id: UserId; ⚠️ still the tagged type, not the actual type
// }

I was hoping the UserDtoJson type would have the following shape:

type UserDtoJson = {
    id: number;
}

Using Unwrapped for the DTO type resolve the expected, unwrapped type from the tagged type:

import type { UnwrapTagged, Jsonify } from 'type-fest'

export interface UserDto {
  id: UnwrapTagged<User['id']>
}

export type UserDtoJson = Jsonify<UserDto>
// type UserDtoJson = {
//     id: number; ✅ the expected result
// }

Is extending the Jsonify type an option to resolve tagged types and unwrap them automatically?

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