Type Guards and CallBack Parameters are any, if worked, could successfully defined a callback type and respective guard

**TypeScript Version:** typescript@3.2.0-dev.20181003 Two bugs in one, if both of these issues work, I would be able to properly defined a callback type function call signature overloads and a type guard to go with it. <!-- Search terms you tried before logging this (so others can find this issue more easily) --> CallBack, Type Guards with extends fails, CallBack with overloads signatures types become any type, instead of union of their respective params. ## Issues 1. Callback types params with methods overloading are always any type, should be respective union of each parameters types. 2. Type Guards for more complex type guards doesn't work. ## Summary If all of this were to work, I would be able to correct write a typescript type for a callback with its associated type guard. ### 1. CallbackTypes are not correctly computed, which expected to be a union of the respective overloads params. ```.ts // function call signatures. interface CallBack<T> { () : void (error : Error) : void (error : undefined, result : T) : void (error : null, result : T) : void } function takeCallBack(callback: CallBack<number>) { callback(); callback(null, {A:77}); callback(new Error('')); } //Fails to determine which function signature was used to call, because it could have been any of the //formats. The final format is an any type. It would be nice to be able to write a type guard //[ts] 'result' is declared but its value is never read. //[ts] Argument of type '(error: any, result: any) => void' is not assignable to parameter of type 'CallBack<number>' takeCallBack((error, result) => { }); ``` Expected, however, this is not enough information us to write a proper type guards and we have also lost information about the results, which is the most important. we need to be able to distinguish between T and T | undefined. ```.ts takeCallBack((error : Error | undefined | null, result : T | undefined) => { }); ``` ## CallBack type formulation The only was to be…