Unable to specify return type of class extends T implements IFooable

TypeScript Version: 2.2.1 / nightly (2.2.0-dev.201xxxxx)

Code

// A *self-contained* demonstration of the problem follows...
export type Constructor<T> = new (...args: any[]) => T;
export interface IFooable { FooProp: string; }
export function FooableMixin<T extends Constructor<{}>>(Base: T) {
    return class extends Base implements IFooable {
        FooProp: string;
        constructor(...args: any[]) {
            super(...args);
        }
    }
}
export class BaseBar { BarProp: string = "baz"; }
export class FooableBar extends FooableMixin ( BaseBar ) {}
let foobar = new FooableBar();
foobar.FooProp = foobar.BarProp; 
/* This is ok since FooableBar extends an Anonymous class inheriting from BaseBar and implementing IFooable */

If I turn on "declaration: true" in tsconfig.json this constuct breaks since the Anonymous class counts as private and not exported type (error TS4060) which is kind of natural since it is Anonymous.

What we need is a way to describe Classes as return types.

Expected behavior:

A d.ts file with a type declaration for the Mixin function Fooable that defines a Anonymous Class return type in the style of:

declare function Fooable(T extends Constructor<{}>): (class extends T implements IFooable);

Actual behavior:

TS4060 error when compiling with the "declaration" flag.
If casting the Anonymous Class return value to or T, the interface is lost.

Start with the self-contained FooableMixin example in the issue and compile it with declaration enabled. Investigate declaration emit for the anonymous class returned by FooableMixin; done means the generated .d.ts describes the class extending T and implementing IFooable without TS4060 or losing the interface.