lodash - change weakmap declaration to work with TS 2.2

[budiadiono]

In TS 2.2 WeakMap interface for ES6 has been changed from WeakMap<K, V> to WeakMap<K extends object, V>. This changes makes @types/lodash not working with new ES6 introduced in TS2.2.

To keep the backward compatibility with ES5, I think it is safe to rename the WeakMap declaration.

I know TS 2.2 is still in RC version now, but many people using it, including me :). So if you think this is too early and also bad idea then feel free to close this PR without merging it.

If this get merged then it's should close #14324.

This pull request is clean version of pull request #14502

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[dt-bot]

lodash/index.d.ts

to authors (@bczengel @chrootsu @stepancar). Could you review this PR?
👍 or 👎?

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• pass the Travis CI test?

[TonyPythoneer]

@budiadiono I appreciate your idea but it's too early. It's because TypeScript hasn't released stable 2.2 version yet.
I hope this proposal can be an issue and make up a TODO list. It doesn't make you work in vain.

[corbinu]

Can this be merged now that 2.2 is stable?

[Dirrk]

Builds breaking waiting for this change, 2.2 is now live

[chrootsu]

👍

[sshquack]

Thanks for the fix @budiadiono

Just to echo what others have already mentioned here, this problem is causing issues with the TypeScript 2.2 release

microsoft/TypeScript#14256

[mhegazy]

this change disables the guard. WeakMapLike does not even have the declarations of WeakMap, so it is not usable.

I would say just remove WeakMap declaration altogether, and make this function return boolean.

[JProgrammer]

@mhegazy would #14787 be a better solution?

[mhegazy]

I do not think so. this change seems good to me, but we just need to remove the weakMap reference altogether.

[budiadiono]

@mhegazy thanks for the review. I'll update it now.

[ghost]

A better fix would be to have isWeakMap(value: any): value is WeakMap<any, any>;.
It doesn't make sense to have type parameters because generics are erased, and isWeakMap<{ x: number }, boolean>(foo) would still return true even if foo is a WeakMap<{ y: string }, Date>.
(It also doesn't make sense to have an optional parameter, because no one would ever call isWeakMap() with no parameters.)

Then the test must be changed to use e.g. WeakMap<{ x: number }, number> because of the type constraint on WeakMaps.

[mhegazy]

A better fix would be to have isWeakMap(value: any): value is WeakMap<any, any>;.

@andy-ms, the issue is not the user-defined type guard, the issue is the declaration of WeakMap. WeakMap is not defined in lib.d.ts (only lib.es2015.collections.d.ts or one of its dependents); so lodash had a forward declaration of it. TS 2.2 changed the declaration to include T extends object on the key, now lodash needs to do the same, but object is a TS 2.2 feature. so you see it is a catch-22.

Ultimiatlly #14787 is the correct fix, but this unblocks ppl at the moment.