Typescript: Type 'null' is not assignable to type 'PropValidator<any>'

[KaelWD]

Version

2.5.16

Reproduction link

Vue.component('union-prop', {
  props: {
    anything: null,
    primitive: [String, Number],
    object: [Cat, User],
    regex: RegExp,
    mixed: [RegExp, Array],
    union: [User, Number] as {new(): User | Number}[] // requires annotation
  },
  data() {
    this.anything;
    this.primitive;
    this.object;
    this.union;
    this.regex.compile;
    this.mixed;
    return {
      fixedSize: this.union,
    }
  }
});

Steps to reproduce

Paste it into options-test.ts and run yarn test:types

What is expected?

No errors, type should be any

What is actually happening?

Type 'null' is not assignable to type 'PropValidator'

It works with strictNullChecks disabled, but the type is {} instead of any

[posva]

Why would you even put null as a type or to say a prop can be anything (which can be done with a custom validator that always returns true)?

[KaelWD]

From https://vuejs.org/v2/guide/components-props.html#Prop-Validation

// Basic type check (null matches any type)

I've also seen it mentioned by you guys in quite a few issues on here too, and it seems to work just fine in regular JS.

[HerringtonDarkholme]

This is impossible to do in current typing schema. You have to cast it manually.

anything: (null as any) as PropValidator<any>

We might change this in future version. We can exploit TS2.8's conditional type to model prop type. However, this might be a breaking change.

[HerringtonDarkholme]

I personally prefer to rewrite typing schema with Vue 3.0. As said above, typing null as validator is impossible for current type files.
So let's patiently wait for Vue 3.0.

[KaelWD]

Why would this be a breaking change? Vue 2.5 required a specific version of typescript and wasn't considered breaking. I'd be happy to help implement this for 2.6.