Allow decorators to change input value

[CodySchaaf]

Right now while using decorators the javascript seems to work, but the types are too strict.

As you can see here the following does not compile:

declare var _: any;
export function Throttle(milli: number) {
    interface Throttled extends Function {
            now: Function
    }
    return function<T extends Throttled>(target: Object, propertyKey: string, descriptor: TypedPropertyDescriptor<Function>): TypedPropertyDescriptor<T> {
            let originalMethod = descriptor.value;
            // NOTE: Do not use arrow syntax here. Use a function expression in
            // order to use the correct value of `this` in this method
            descriptor.value = <any>_.throttle(function() {
                originalMethod.apply(this, arguments);
            }, milli);
            (<Throttled>descriptor.value).now = <any>function() {
                originalMethod.apply(this, arguments);
            };
            return <TypedPropertyDescriptor<T>>descriptor;
        }
}



    class Ctrl {

        constructor(scope: any) { 
            scope.$watch("foo", this.throttledByClassWatch);
            this.throttledByClassWatch.now() //unrecommended now call
        }
        @Throttle(100000)
        private throttledByClassWatch() {
        }
    }

I might have the types a little wrong but I have tried many other permutations. It seems to be because the expected type is declare type MethodDecorator = <T>(target: Object, propertyKey: string | symbol, descriptor: TypedPropertyDescriptor<T>) => TypedPropertyDescriptor<T> | void; and so the input T must match the output T.

Ideally the now could also inherit the generic type T so it could be type checked.

[mhegazy]

looks like a duplicate of #4881. you might find my comment in #5627 (comment) helpful as a work around ins some cases, though would not work in your sample.