Mapped type with enum keys produces {}

[tyrielv]

TypeScript Version: 2.9.0-dev2.0180402

Search Terms: mapped generic type array

Code

enum Fruits {
    Mango = 0,
    Banana = 1
}

interface IFruitMetadata<T> {
    [Fruits.Mango]: T;
    [Fruits.Banana]: T;
}

const onSale1: IFruitMetadata<boolean>[] = [{
    [Fruits.Banana]: 22,
    [Fruits.Mango]: 32,
}];

const onSale2: Partial<IFruitMetadata<boolean>>[] = [{
    [Fruits.Banana]: 22,
}];

Expected behavior:
Both assignments have compile errors (number not assignable to boolean) (This is the behavior on 2.7.2)
Actual behavior:
Only the unmapped type assignment has a compile error.
Playground Link

Related Issues:

[ghost]

The problem is that Partial<IFruitMetadata<boolean>> is {}. Simplified example:

const enum E { A }
interface I { [E.A]: number; }

type T = { [K in keyof I]: boolean }; // Fails

type Bools<T> = { [K in keyof T]: boolean };
type B = Bools<I>; // No error, returns {}

[mhegazy]

Duplicate of #13042.

[mhegazy]

keyof I should be never really. but that is a different bug.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.