Inconsistent type inference for optional

[anatoly-tenenev]

Code to reproduce:

import * as v from 'valibot';

const S1 = v.pipe(
  v.optional(v.number()),
  v.transform(() => 'success')
);

type T1 = v.InferOutput<typeof S1>;

// expected type error when assign undefined
const test1: T1 = undefined;

const S2 = v.object({
  s1: S1,
});

type T2 = v.InferOutput<typeof S2>;

// inconsistent ability to assign undefined
const test2: T2['s1'] = undefined;

https://valibot.dev/playground/?code=JYWwDg9gTgLgBAKjgQwM5wG5wGZQiOAcg2QBtgAjCGQgbgCh6BjCAO1XgGUBGOAXkwA6MMDABTABT04QiGBjA2ZCRkGsAriApioEgJR6ANNKEwoydtmggJ+-gD4iqdUyZjUqQnvp6G9GACe4nAAKrwCqgCSrNg6APLqMGCJADyB4hDYcDz2fgD0eXBiAB7iTDBiACZw6WJFUHhQzGwcNe4w3ABcoeFw6qyVYtjArFV+LOxcAEz8shQAVmLlEgDeJqhd2dzGAL6+jLWhMxGC0bFQCUmptZnZU7mMBXAjE6jAHGKs8MgUwOSBNQgKA8wAA5qw+gMhiMqs1Jm0OFNuiEpgBtQgbQgAXVm-UGw1GlQYQA

[anatoly-tenenev]

This code fixes the problem

v.optional(v.number(), () => undefined)

https://valibot.dev/playground/?code=JYWwDg9gTgLgBAKjgQwM5wG5wGZQiOAcg2QBtgAjCGQgbgCh6BjCAO1XgGUBGOAXkwA6MMDABTABT04QiGBjA2ZCRkGsAriApioEgJQAaOPv4A+OOtYATMdmCsxVw9KEwoydtmggJJvucJUdSYmMVRUQj16PQZ6GABPcTgAFV4BVQBJVmwdAHl1GDACgB4E8QhsOB5TWIB6WrgxAA9xJhhHODKxRqg8KGY2Dk6wmG4ALhS0i2tbe0dYlnYuACZ+WQoAKzE2iQBvF1Rxqu4DegBfGMYulNX0wSycqHzCkq6KquWaxnq4e0XUYAcMSseDICjAcgJToQFDhYAAc1Y0xsdgcVgGS2GHGWE2SywA2oFuIQALprSwouZWBhAA

[fabian-hiller]

Hey! 👋 This is expected. The reason is that there's a difference between a missing object entry and an undefined one. optional allows missing object entries, in which case the pipe is not executed. However, you can control this behaviour by using a different schema. You are probably looking for undefinedable, which only allows undefined object entries. We have a guide on optionals, but we should probably document this behaviour more clearly.

This code fixes the problem

Yes, adding a default value solves the problem because, if an entry is missing, our object schemas fall back to the provided default value and execute the provided pipe.

[lianghx-319]

Using v.undefinedable still suffer this issue. Is typescript version requirement more latest?
I am using the latest v4 of typescript.

[fabian-hiller]

Can you share a playground link with us? Valibot requires TypeScript v5.