Fixes #8317 map(...)

[AbdelrahmanHafez]

Will be testing other array methods soon, and fix any broken ones.

@vkarpov15 I am curious, what are the exact changes that introduced this bug?

[vkarpov15]

Thanks @AbdelrahmanHafez . I think this was always a bug, map() and slice() create a new instance of Mongoose's custom document array class. It's just that in #8265 we started relying on arrayParentSymbol when doing operations like push() and splice() to ensure that populated() stays in sync.

I've thought about it some more and I think the way to go is to just add a check in _updateParentPopulated() that does an early return if parent == null. If you do docArr.map(), you get back a new array that shouldn't be tied to the Mongoose document. So I'd remove the custom map() implementation in favor of just skipping _updateParentPopulated() if the array doesn't have a parent.

[AbdelrahmanHafez]

Thank you @Fonger

@vkarpov15
To understand correctly, what you're saying is map() and push() always had this bug? Because if that's the case, I've been using the combination and the test only started to fail lately.

You're right though, it makes more sense to return a good old JS array on mapping. Changes coming your way.

[AbdelrahmanHafez]

Got some failing tests on Node 4 and 5, will check them soon.

[vkarpov15]

Thanks! This should also fix #8312