Move @jest/types to dev dependencies

[fedyk]

Summary

The @jest/types has @types/node as dependency. As a result, after installing the recent version of pretty-format, TypeScript thinks that my web app is nodejs. The main problem is the timers. In nodejs they return Timeout object. In browser it returns a number:

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[SimenB]

It needs to be a dependency otherwise TypeScript compilation will fail.

I don't know how to best deal with globals in differing environments. This is an issue for TS to figure out I believe.

microsoft/TypeScript#33111
microsoft/TypeScript#37775

@orta is this something the TS team is looking into/have a good workaround for? The two issues I found didn't have much traffic

[orta]

We've come up with a bunch of ideas, and keep dismissed them as infeasible at scale (either through complexity, or putting too much onus on individuals o line things up perfectly which won't happen).

https://gist.github.com/RyanCavanaugh/702ebd1ca2fc060e58e634b4e30c1c1c is the latest idea which hasn't been disproven yet - that said, I wouldn't bet on it landing anytime soon.

For the long term, I'd recommend something like this PR, more importantly I'd look into weakening the external 'user-facing' Jest types to remove any explicit node references if possible. The same conflict would exist inside electron, or react native apps too for example.

[SimenB]

Thanks for the link @orta, that looks really promising! Having the references only affect the file it's in is how I thought it worked until I started getting issues with it 😅

Not sure how we can make our own types less exact though - main issue is where we expose e.g. fs.Stat, or we depend on some library which does it. That said, we already verify that the only allowed references is node^*, so we could trivially disallow it in our own types (although migration would not be trivial).

*) https://github.com/facebook/jest/blob/ca47512c77e6a325bca734a35a4ad15a45dee8aa/scripts/buildTs.js#L78-L104

[SimenB]

Would just using optional peer dep work? I assume TS will just explode due to a /// reference to node even though the file is not directly imported

[Nemikolh]

@SimenB I think it might work if the user's tsconfig has skipLibCheck set to true?

But if it doesn't then I think you are right, TS won't like it.

[jameswilddev]

Hmm. Is it not possible to just move @types/node to a devDependency? I figured that was what you were supposed to do. I'm having conflicts between Jest and another package.

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