fix: add require.main when using isolateModules

[flozender]

Summary

Aims to close #9470.

Modules required through jest.isolateModules() do not have a require.main property on them.

I have attached a mainModule variable to the runtime instance. It will be null at first, and the first module seen will be assigned to the mainModule variable. Required modules will get the mainModule attached to them as main.

Test plan

Emulate the scenario from the issue as a test.

[SimenB]

Thanks again, @flozender!

[jsg2021]

In 26.5.3 require.main is undefined in general for me... works fine in 26.4.2. I'm not using isolateModules.

[jsg2021]

I should clarify, in the test file require.main is populated, but in code that my tests require() in, there the require.main is undefined.

[Function: bound requireModuleOrMock] {
  extensions: [Object: null prototype] {},
  resolve: [Function: resolve] { paths: [Function (anonymous)] },
  cache: [Object: null prototype] {},
  main: undefined
}

[jsg2021]

Here is a code sandbox reproduction:
https://codesandbox.io/s/gifted-sara-x25fr

[flozender]

@jsg2021 I'm able to run it with no issues locally, I don't know what's happening on CodeSandbox. Have you tried running it locally?

[jsg2021]

I created it after local tests started failing.

[jsg2021]

Are there environment vars in your local env set that effect jest?

[flozender]

No, I don't think so.

[flozender]

@jsg2021 Looks like CodeSandbox doesn't work on v26.4.2 either: https://codesandbox.io/s/thirsty-rgb-pt0xf

[jsg2021]

I have had a really hard time pinning jest to any minor version... the jest library will pin, but it appears all its dependencies use ^ so they will all install the 26.5.3. To replicate, we would have to specify all jest's dependencies with a pin.

[jsg2021]

@flozender So, its still failing because all the jest dependencies of the jest package are at 26.5.3, not 26.4.2

[jsg2021]

Interesting. I downloaded the code from the sandbox and ran it, passed... so that made me compare configs, and I found the code fails if I add this to the package.json:

"jest": {
	"resetModules": true
}

[flozender]

Interesting, maybe you should open an issue for this!

[jsg2021]

My pre-existing tests still pass on 26.4.2 (I have a package-lock) but fail on 26.5.3. My jest config does not enable that flag.

[flozender]

Can confirm it fails on using "resetModules": true. I can take up the issue once you open it. Let me know!

[flozender]

@jsg2021 here's a sample repo you can add to the issue: https://github.com/flozender/jest-resetModules

[jsg2021]

Done! #10625

[SimenB]

@jsg2021 are you able to put together a repository showing your failure? Even if it's a work project you should be able to copy over the lockfile and just delete everything not jest from package.json then run npm or yarn and have the lockfile keep the jest packages while removing everything else. then just stick a simple test in there that shows the failure

[jsg2021]

Ah! thanks for the tip @SimenB! Here is a repo that exemplifies my passing state:
https://github.com/jsg2021/jest-require-main-issue

Side note: I figured out why it looked like I had resetModules: true... my test suite had a beforeEach calling jest.resetModules()...

Anyways... the test cases we were trying to make before were directly importing the module... I didn't think that mattered, so I didn't think anything of it, but I added a redirection layer and the tests started passing for that... they still fail for the direct case and probably shouldn't... so if you delete the lock and install latest, all tests fail.

[SimenB]

Thanks @jsg2021. Does that mean it was covered by #10625?

[jsg2021]

@SimenB I think so. That repo will reproduce my exact issue where it was passing with the lock file, but broken when updating. It also has the original attempt to reproduce the issue where we simply wrote a test that inspected require.main directly... which was always broken with resetModules:true/jest.resetModules(). However, my project had one module require in between the test and the code referencing require.main...and that was working until I updated. I believe the fix for #10625 will resolve it, but I do think the additional test cases should be added.

[SimenB]

Sounds good, thanks! @flozender wanna send a PR for the extra test cases? 😀

[flozender]

@SimenB @jsg2021 I went ahead and added tests for both the variations of resetModules in #10626 before we merged the PR! :)

[jsg2021]

@flozender I saw that, but the indirect case is missing for each variation.

[jsg2021]

The indirect case is where the test verifies that requireFromMain works indirectly... so it's not being directly imported by the test.

[flozender]

Oh, I see. I'll send in a PR shortly, thanks.

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