Indexed access type with generics

[uittorio]

I've found a couple of issues related to indexed access type

NOTE: in definitely typed test results this may be references as
Cannot read property 'declarations' of undefined

Class[T]

Example 1

interface WithKeyGeneric<R> {
  test<U extends keyof R>(): WithGeneric<R[U]>
}

class WithGeneric<T> {
  public a: T;
}

const type = createMock<WithKeyGeneric();

This will fail to get R[U] for 2 reasons;

• the generic is not provided
• the type parameter used to find a type R is using currently PropertySignatureCache that is meant to be used to store properties name. (I'm not sure if can always work). Example 2 give more explanation about this

Example 2

class Normal {
  public a: number;
  public b: string;
}

interface Test<T extends keyof Normal> {
  prop: Normal[T]
}

const type = createMock<Test<'a'>>();
const type2 = createMock<Test<'b'>>();

type should have a prop with number 0 /// it works
type2 should have a prop with string '' // it doesn't work

The reason is failing is because we are not storing the generic correctly from Test<'a'> or Test<'b'> and we are not getting the correct property T because of the same reason of Example 1