v7.2.4 breaks "Mixins" decorator usage

[Ky6uk]

After upgrading from v7.2.3 to v7.2.4 I'm getting a lot of different TypeScript compilation errors because of using Mixins decorator as generics. Something like

Type 'MixinName<Data>' does not satisfy the constraint 'VueClass<Vue>[]'.

I'm using mixins like that

@Component
export class MixinName<T> extends Vue {
  // ...
}

export default class Page extends Mixins<MixinName<Data>>(MixinName) {
  // ...
}

It looks like breaking changes has been introduced in v7.2.4, but I have no idea what wrong exactly. v7.2.3 works perfectly.

[Ky6uk]

Opened different issue kaorun343/vue-property-decorator#335

[wangziling]

Yes. I had encountered this issue.
If you Mixins as Mixins-ed Component.

class A extends Mixins(B) {
  get a () {
     // This will come up an issue that `b` is nonexistent in `A`
     return this.b;
  }
}

class B extends Mixins(C) {
    b!: number;
}

class C extend Vue {}

I think this may be an issue about the declarition type for Mixins method.
In previous version, Mixins used the declarition merging.

export declare function mixins<A, B>(CtorA: VueClass<A>, CtorB: VueClass<B>): VueClass<A & B>;

But now using the infer keyword.

export declare type MixedVueClass<Mixins extends VueClass<Vue>[]> = Mixins extends (infer T)[] ? VueClass<UnionToIntersection<ExtractInstance<T>>> : never;

export declare function mixins<T extends VueClass<Vue>[]>(...Ctors: T): MixedVueClass<T>;

I just recognized by my ts coding experiences, that here maybe a little problem when using infer in typescript. It is not very smart and accurate, sometimes it cannot infer a type with a deep and complex logic correctly...

[wangziling]

This will not encountered in 7.2.3 version.

[Ky6uk]

It looks the breaking change has been introduced in this PR #433 @ktsn