Unexpected output type in ZodDefault

[hanakannzashi]

ZodDefault use util.noUndefined<T["_output"] as output, which actually means Exclude<T["_output"], undefined>. If output is converted to undefined, e.g.

const checker = z.number().optional().transform((n) => {
  console.log(n); // n is 0 which means `default` is reachable
  return undefined; // return `undefined`
}).default(0);

// data got `undefined` without panic but actually return type of `parse` is `number` instead of `number | undefined` due to usage of `default`
const data = checker.parse(undefined); 

I think this is a type issue caused by util.noUndefined, maybe it should be undefined extends T ? never : T instead of T extends undefined ? never : T

[sunnylost]

data's type is undefined.

If you place default() last, it generates a default value and uses it as input for the preceding schema (which is a transform()). If you place transform() last, it will take the result from the previous schema and apply the transformation. In both cases, transform() has the highest priority and takes control of the final output.

[hanakannzashi]

data's type is undefined.

If you place default() last, it generates a default value and uses it as input for the preceding schema (which is a transform()). If you place transform() last, it will take the result from the previous schema and apply the transformation. In both cases, transform() has the highest priority and takes control of the final output.

Yes, I know how it works, I means, return type of parse is incorrect, TypeScript tell me that is a number, but actually I got undefined

[sunnylost]

Actually, when I pasted this code, I ended up with a never type.

[hanakannzashi]

const checker = z.number().optional().transform((n) => {
  console.log(n); // n is 0 which means `default` is reachable
  return undefined; // return `undefined`
}).default(0);

// data got `undefined` without panic but actually return type of `parse` is `number` instead of `number | undefined` due to usage of `default`
const data = checker.parse(undefined); 

Sorry my mistake