Allow setting typeName in custom types

[defrex]

I'm using a custom type for Decimal.js fields like so

const decimal = z.custom<Decimal>(Decimal.isDecimal)

This is nice and simple, which is great!

However, when building a UI based on an arbitrary zod-typed input, I use _def.typeName to determine the expected output type for the sake of formatting, etc. Currently custom fields are labeled as ZodEffects, which isn't particularly helpful.

Something like this would be great

const decimal = z.custom<Decimal>(Decimal.isDecimal, { typeName: 'ZodDecimal' })

Alternatively, a custom metadata solution as described in #273 would also enable me to solve the problem.

[rotu]

Maybe it would be better to use a Map (or WeakMap) to keep track of this.

const customTypeName = new Map()

const decimal = z.custom<Decimal>(Decimal.isDecimal)
customTypeName.set(decimal._def, "Decimal")

function getExtendedTypeName(someZodType){
  return customTypeName.get(someZodType._def) ?? someZodType._def.typeName;
}

[baloodevil]

I have the same need; I'm showing UI controls based on the typeName. But when I changed a property from a ZodDate to a z.custom... the typeName becomes ZodAny so I don't know to show a date picker in the UI.

[defrex]

Maybe it would be better to use a Map (or WeakMap) to keep track of this.

It definitely feels worse to me to require an extra data structure taped to the side of Zod in order to track what type a field is, since Zod is supposed to be the source of truth for the schema.

I sortof understand the stance on custom metadata, but tracking type information feels like something Zod should support, IMO.

[colinhacks]

Currently z.custom is actually just syntactic sugar over z.any().refine(). If you're relying on typeName or other internals, it's better to define a subclass of ZodType.