Cannot extend from type which constructs intersection of type parameter with a default

[DanielRosenwasser]

interface VueCtor {
    new <D = object>(d: D): Vue & D;
}

interface Vue {
}

declare var Vue: VueCtor;


class A extends Vue {
    //          ~~~
    // Error: Base constructor return type 'Vue & D' is not a class or interface type.
}

I thought this might have to do with the constraint, but adding an explicit D extends object = object doesn't work either.

Is it possible that D isn't correctly getting instantiated with its default type argument when extending from Vue?

[DanielRosenwasser]

For the record, class A extends Vue<object> works.

[sandersn]

Looks like D doesn't get substituted and then doesn't get instantiated.

[DanielRosenwasser]

Yup, @mhegazy and I are talking about why this is difficult to solve in a general context offline.

Hilariously this works:

interface VueCtor {
    new <D = object>(d: D): Vue & D;
}

interface Vue {
}

declare var Vue: VueCtor;

//                 vv ---wat?
class A extends Vue<> {
}

[rbuckton]

Regarding #16211 (comment), apparently we do not have a grammar check for ExpressionWithTypeArguments to enforce that a type argument list is non-empty.