Narrow type from array passed to mixed().oneOf()

[karlhorky]

Closes #1230

Broken: https://codesandbox.io/s/blissful-field-xw9kjn?file=/src/index.ts
Working: https://codesandbox.io/s/funny-fire-s1nh9v?file=/src/index.ts

[karlhorky]

@jquense friendly bump, what do you think of the approach of this PR?

[karlhorky]

@jquense closed #1230 just a couple of days ago: #1230 (comment)

So it's possible this has been implemented in 1.0.0-beta.5 or 1.0.0-beta.7

[jquense]

Mixed still doesn't narrow, but string does. I'm not convinced that mixed should narrow, it may make the type too restrictive. Still need to think about it a bit

[karlhorky]

but string does

Is this new in 1.0.0-beta.5 or 1.0.0-beta.7? What does this look like in practice?

---

I'm not convinced that mixed should narrow

To me, it seems like usage of mixed().oneOf() should narrow in all cases. Especially if checking schemas against TS types.

For example, in what case would a user want something different than 'abc' | 'def' as the type of the following?

const mixed = yup.mixed().oneOf(['abc', 'def'] as const);

[karlhorky]

Regardless of whether it should narrow, mixed().oneOf() at least not return any as it currently does, see this sandbox for a demonstration of the broken behavior:

import { mixed } from "yup";

type IsAny<T> = unknown extends T ? (T extends {} ? T : never) : never;

type NotAny<T> = T extends IsAny<T> ? never : T;
function notAny<T>(x: NotAny<T>) {}

// Without using .oneOf() retains the type of MixedSchema<null, AnyObject, undefined, ''>
const schemaWorking = mixed<null>().defined();
notAny(schemaWorking); // ✅ This type is not `any`

// Using .oneOf() sets the type to `any`
const schemaBroken = mixed<null>().oneOf([null]).defined();
notAny(schemaBroken); // 💥 Type is `any`

[jquense]

Is this new in 1.0.0-beta.5 or 1.0.0-beta.7? What does this look like in practice?

not new, its been in in most of the v1 releases

Regardless of whether it should narrow, mixed().oneOf() at least not return any as it currently does,

that is definately true, will fix

[slashwhatever]

Update on this?

[karlhorky]

@jquense would you reconsider this PR?

Would be great to be able to represent this properly:

interface FormidableFile {
  hashAlgorithm: false | "sha1" | "md5" | "sha256";
}

const formidableFileSchema: ObjectSchema<FormidableFile> = object({ // 💥 Currently errors, see below
  hashAlgorithm: mixed()
    .oneOf([false, 'sha1', 'md5', 'sha256'] as const)
    .required(),
})

Currently this returns the following (confusing) error:

Type 'ObjectSchema<{ hashAlgorithm: AnyPresentValue; }, AnyObject, { hashAlgorithm: undefined; }, "">' is not assignable to type 'ObjectSchema<FormidableFile, AnyObject, any, "">'.
  The types of 'default(...).fields.hashAlgorithm' are incompatible between these types.
    Type 'Reference<unknown> | ISchema<AnyPresentValue, AnyObject, any, any>' is not assignable to type 'Reference<unknown> | ISchema<false | "sha1" | "md5" | "sha256", AnyObject, any, any>'.
      Type 'ISchema<AnyPresentValue, AnyObject, any, any>' is not assignable to type 'Reference<unknown> | ISchema<false | "sha1" | "md5" | "sha256", AnyObject, any, any>'.
        Type 'ISchema<AnyPresentValue, AnyObject, any, any>' is not assignable to type 'ISchema<false | "sha1" | "md5" | "sha256", AnyObject, any, any>'.
          Type 'AnyPresentValue' is not assignable to type 'false | "sha1" | "md5" | "sha256"'.

With the changes in this PR, the types match.