chore: replace @types/jest with a new private @jest/test-globals package

[mrazauskas]

Summary

What if @types/jest would be replaced with a new private package @jest/test-globals? Here is how I came to this:

1. There is a need to have some .d.ts file with type declarations of Jest globals. For example, it could live in root of the repo. In the .d.ts it is unavoidable to have something like import('@jest/globals')['beforeAll'] which would reference a package like @jest/globals which might be not yet build. TypeScript will see these broken references and will not be happy.
2. A better idea would be to keep this .d.ts file in some package and to use project references. This way TypeScript would build the referenced projects first. The problem is solved.
3. The private @jest/type-utils looked like a good candidate to be that package. I was adding "./globals": {"types": "./build/globals.d.ts"} to package.json, but TypeScript was still not happy to see "types": ["@jest/test-utils/globals"] in tsconfig.josn. Also everything looked clumsy.
4. A new private @jest/test-globals package only for type declaration of Jest global APIs looked like a cleaner solution. (Indeed it is somewhat similar to feat(jest): allow enabling Jest global types through "types": ["jest"] in tsconfig.json #12856.)

It might sound unnecessary to have one more private package, but I think it is worth a discussion.

First the new package has very clear task – to provide type declarations of Jest's global test APIs for tests of Jest repo. Task is clear and simple as well as the usage of the package: "types": ["@jest/test-globals"]. (Also replacing of @types/jest package with another package is sort of logic.)

One more detail to keep in mind. DefinitelyTyped/DefinitelyTyped#62037 is not a solution for Jest repo, because in that case @types/jest will include import('@jest/globals'), i.e. it will again reference packages which are not yet build. So having a private package which is replacing @types/jest makes even more sense.

One detail is left to think about:

• examples are still using @types/jest. Since there is no future for @types/jest in this repo, I will that to use imports from @jest/globals

Test plan

Green CI.

[SimenB]

It might sound unnecessary to have one more private package, but I think it is worth a discussion.

I don't mind more private packages 🙂

One more detail to keep in mind. DefinitelyTyped/DefinitelyTyped#62037 is not a solution for Jest repo, because in that case @types/jest will include import('@jest/globals'), i.e. it will again reference packages which are not yet build. So having a private package which is replacing @types/jest makes even more sense.

That make sense, but the contents of the files should probably be identical.

[SimenB]

Super exciting stuff! I'll take a look tomorrow - currently on my way to a concert 🙂

[mrazauskas]

Yes, I think this is the best idea so far. Have a nice evening (;

[SimenB]

this is super exciting!

(came back from concert full of adrenaline, so... 😅 )

[SimenB]

really? how? it's running in node env, so shouldn't need or use any DOM APIs

[mrazauskas]

This is odd one. Window type does not work without "dom":

https://github.com/facebook/jest/blob/aae0d3ac3498ece4673ec29277dc040234f9f643/packages/jest-fake-timers/src/__tests__/legacyFakeTimers.test.ts#L464-L467

And it is used to type requestAnimationFrame:

https://github.com/facebook/jest/blob/aae0d3ac3498ece4673ec29277dc040234f9f643/packages/jest-fake-timers/src/__tests__/legacyFakeTimers.test.ts#L494

I added reference to silence a lot of type errors, but will come back to this.

[SimenB]

ah, for rAF it makes sense 👍

[SimenB]

object seems weakly typed, but that's not for this PR to figure out 😀

[SimenB]

conflicts 😅

[SimenB]

super awesome! 👍

[mrazauskas]

Nice! Now it would be good to run type checks for test files. I was trying out already. This will be fun ;D

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