Typecast for generic hashes not works as expected

[erickskrauch]

TypeScript Version: 3.2.2

Search Terms:

• object generic

Code

type Scope = {
    $scan: () => void;
}

type HashItemAsFunction<S> = <S extends Scope>(element: HTMLElement, scope: S) => void;

type HashItemAsObject<S extends Scope> = {
    link?: HashItemAsFunction<S>;
};

type HashItem<S extends Scope> = HashItemAsFunction<S> | HashItemAsObject<S>;

interface HashDefinitionValues<S extends Scope> {
    [Identifier: string]: HashItem<S>;
}

type HashDefinition<S extends Scope = Scope> = {
    [key: string]: HashDefinitionValues<S>;
}

class Test {
    static hash: HashDefinition;
}

// Module code

type ModuleScope = Scope & {
    myKey: string;
}

(Test.hash as HashDefinition<ModuleScope>).subType1.child = {
    link: (element, scope) => {
        scope.myKey = '123';
        scope.$scan();
    },
};

(Test.hash.subType1 as HashDefinitionValues<ModuleScope>).child = {
    link: (element, scope) => {
        scope.myKey = '123';
        scope.$scan();
    },
};

(Test.hash.subType1.child as HashItem<ModuleScope>) = {
    link: (element, scope) => {
        scope.myKey = '123';
        scope.$scan();
    },
};

Expected behavior:

One of type casts should provide ModuleScope type to the scope variable, but it only provides base Scope in any case.

Actual behavior:

src/test.ts:33:15 - error TS2339: Property 'myKey' does not exist on type 'S'.

33         scope.myKey = '123';
                 ~~~~~

src/test.ts:40:15 - error TS2339: Property 'myKey' does not exist on type 'S'.

40         scope.myKey = '123';
                 ~~~~~

src/test.ts:47:15 - error TS2339: Property 'myKey' does not exist on type 'S'.

47         scope.myKey = '123';
                 ~~~~~

Playground Link:
https://goo.gl/4kQHBW

Related Issues:
Didn't find any.