Implement async dependency resolution

[SimenB]

Similar to #9504, but for dependency resolution. Like there, this wouldn't be used by Jest just yet, but could (and would, if support is implemented) be used by the ESM support. This logic is implemented in jest-resolve.

I wonder if it makes sense to reintroduce resolve as a dependency since this already has an async code path. That is callback based, but just promisifying that should work fine. But the increased complexity of mjs, cjs etc makes me want to depend on a dedicated module rather than have that complexity live in Jest itself - Jest should just manipulate resolution based on moduleNameMapper etc and possibly cache some stuff on our side.

resolve was actually removed in #4315, via #2925. Some of #2925 reasoning was that resolve was somewhat unmaintained and that we didn't need the async parts of it - neither of which are true anymore.

Added in #9520

import.meta.resolve has landed on node master (nodejs/node#31032, albeit currently behind a flag), so we'll need to implement this regardless of whether we'd want to use it ourselves or not

[moljac024]

Any chance of seeing this one in 27? This would unblock vitejs/vite#1955 and allow first-class integration of Jest into Vite.

I am willing to help bring this to life but I would need some guidance as I'm not really familiar with jest and it's internals

[SimenB]

PRs are very much welcome! 👍

Similar to how we did async transform (#9889), you can start by adding support to jest-resolve, the module that does the reoslution in Jest. That means adding async APIs to https://github.com/facebook/jest/blob/26cb29a42cc9b967f29d70d8c70169993965cf01/packages/jest-resolve/src/index.ts#L51 and https://github.com/facebook/jest/blob/26cb29a42cc9b967f29d70d8c70169993965cf01/packages/jest-resolve/src/defaultResolver.ts#L34-L37

Note that resolve does not have a promise API which is what we want in jest-resolve, but using its callback API should be fine (there is browserify/resolve#210, but not much movement) as long as teh API exposed by jest-resolve is promise based.

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Once jest-resolve supports it we can add support to Jest by modifying jest-runtime. Feel free to look into it of course, but I suspect that will fall to me as the code there is quite complex. But of course if you're up for it I'd love for you to pick that up as well 👍

[rememberlenny]

I would like to help here, but am not quite sure where to start. @SimenB Is there a reference and just a matter of implementing this to a new context?

[lloydjatkinson]

Is there any roadmap on implementing this? I believe it’s having quite a significant knock on effect with build tools that wish to use Jest but cannot, Vite being one example.

[IanVS]

@lloydjatkinson I need to rebase #11540, but it sounds like Simen is ready to give it a review once I do, and then get it into Jest 28.

[SimenB]

Yep, I'll make sure it's in 28 before releasing it to give a nice major target version for downstream 🙂

[SimenB]

https://github.com/facebook/jest/releases/tag/v28.0.0-alpha.4

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