Why I use brand, but not zod's .brand

[akomm]

type UserKeyBrand = {readonly UserKey: unique symbol}
type UserKey = string & UserKeyBrand
const UserKey = z.string().min(8).transform(k => k as UserKey)

type ProjectKeyBrand = {readonly ProjectKey: unique symbol}
type ProjectKey = string & ProjectKeyBrand
const ProjectKey = z.string().min(8).transform(k => k as ProjectKey)

type User = z.infer<typeof User>
// type User = {
//   _key: UserKey
// }

const User = z.object({
  _key: UserKey
})

declare const uk: UserKey
const pk: ProjectKey = uk
// Type 'UserKey' is not assignable to type 'ProjectKey'.
//   Property 'ProjectKey' is missing in type 'String & UserKeyBrand' but required in type 'ProjectKeyBrand'.ts(2322)

Using .brand:

declare const UserKeyBrand: unique symbol
type UserKey = z.infer<typeof UserKey>
const UserKey = z.string().min(8).brand<typeof UserKeyBrand>()

declare const ProjectKeyBrand: unique symbol
type ProjectKey = z.infer<typeof ProjectKey>
const ProjectKey = z.string().min(8).brand<typeof ProjectKeyBrand>()

type User = z.infer<typeof User>
const User = z.object({
  _key: UserKey
})
// type User = {
//     _key: string & z.BRAND<typeof UserKeyBrand>;
// }

declare const uk: UserKey
const pk: ProjectKey = uk
// Type 'string & Zod.BRAND<typeof UserKeyBrand>' is not assignable to type 'string & Zod.BRAND<typeof ProjectKeyBrand>'.
//   Type 'string & BRAND<unique symbol>' is not assignable to type 'BRAND<unique symbol>'.
//     Types of property '[BRAND]' are incompatible.
//       Property '[ProjectKeyBrand]' is missing in type '{ [UserKeyBrand]: true; }' but required in type '{ [ProjectKeyBrand]: true; }'.ts(2322)

Now this is a simplified, distilled situation. Typically you have nested data where it gets really messy.

Also with type safety for the underlying type:

type UserKeyBrand = {readonly UserKey: unique symbol}
type UserKey = string & UserKeyBrand
const UserKey = brand(z.string().min(8))<UserKey>()

type ProjectKeyBrand = {readonly ProjectKey: unique symbol}
type ProjectKey = number & ProjectKeyBrand // notice the number, while we brand z.string
const ProjectKey = brand(z.string().min(8))<ProjectKey>() // error: Type 'ProjectKey' does not satisfy the constraint 'string'.ts(2344)

function brand<O, D extends z.ZodTypeDef, I>(t: z.ZodType<O, D, I>) {
  return <B extends O>() => t.transform(v => v as B)
}