Removed BRAND from ZodBrand Input definition

[Xetera]

A type's brand should only be accessible in its output aka z.infer or z.output but it's also carried over to its input. This makes it difficult to create a typesafe parse function as the code doesn't compile

For example:

const Age = z.number().min(18).brand<"Age">()

type AgeInput = z.input<typeof Age>

an input for Age.parse(x) aka AgeInput should just be number but it's number & BRAND<"Age"> which doesn't make sense

Working typescript playground example

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[colinhacks]

Great call. Thanks!

[KATT]

I want the opposite behavior of this 😢

[KATT]

opened #3380 where we could have both 🙃

[colinhacks]

The inferred input type is supposed to be the set of inputs that will pass validation. So actually, this inferred input type for this schema:

z.number().brand<"USD">();

should be

number | (number & BRAND<"USD">)

Zod should definitely allow a "pre-branded" value, but it also "brands" any plain number values that are passed in. I can't tell if this pleases everyone or no one...but I do think it's the most correct behavior.

[KATT]

I'll add some context on what I'm doing.

I'm building a query string builder for filtering data where one of the parts is a date range

A date range is serializable to the URL and transformable into a real date range.

Some examples of input values:

• this_week
• past_week
• 2023-04-01,2024-04-30

for the last one, I want to brand it as string & X, otherwise all of them will be string in the union, which is annoying later on when building the UI since the data is too loose

in my case I don't care about the brand on the output at all (but it doesn't hurt it either)

Code

https://tsplay.dev/wgo4lw

import { Temporal } from '@js-temporal/polyfill';
import { z } from 'zod';

type DateRange = [Temporal.PlainDate, Temporal.PlainDate];
function getWeekDateRange(date: Temporal.PlainDate): DateRange {
  const start = date.subtract({ days: date.dayOfWeek });

  const end = start.add({ days: 6 });

  return [start, end];
}

export const anyDateRange = z.literal('any').transform(() => null);

export const thisWeekDateRange = z
  .literal('this_week')
  .transform((): DateRange => {
    const now = Temporal.Now.plainDate('iso8601');

    return getWeekDateRange(now);
  });

export const customDateRange = z
  .string()
  .regex(/^\d{4}-\d{2}-\d{2},\d{4}-\d{2}-\d{2}$/)
  .transform((value): DateRange => {
    const parts = value.split(',') as [string, string];
    const start = Temporal.PlainDate.from(parts[0]);
    const end = Temporal.PlainDate.from(parts[1]);

    return [start, end];
  })
  .brand('custom_date_range');

export const filters = z.object({
  dateRange: z
    .union([
      //
      anyDateRange,
      thisWeekDateRange,
      customDateRange, // <- try commenting out this line
    ])
    .default('any'),
});

type Input = z.input<typeof filters>;
type Output = z.output<typeof filters>;

type DateRangeInput = Input['dateRange'];
//     ^?

[colinhacks]

Even if the brand was applied to the input type, it still seems pretty un-ergonomic for the end user to cast a string to the branded type. How do you see this working?

type customDateRange = z.output<typeof customDateRange>;
const value = "2021-01-01,2021-01-02" as unknown as customDateRange;

Here's something that seems to work better:

const dateRangeParser = z
  .string()
  .regex(/^\d{4}-\d{2}-\d{2},\d{4}-\d{2}-\d{2}$/)
  .transform((value): DateRange => {
    const parts = value.split(',') as [string, string];
    const start = Temporal.PlainDate.from(parts[0]);
    const end = Temporal.PlainDate.from(parts[1]);

    return [start, end];
  })
  .brand('custom_date_range');

const customDataRange = z
  .custom<`${number}-${number}-${number},${number}-${number}-${number}`>()
  .pipe(dateRangeParser);

type customDataRange = z.input<typeof customDataRange2>; 
// `${number}-${number}-${number},${number}-${number}-${number}`

[KATT]

That's awesome. Thanks ♥