Support Babel 8 in plugins and presets

[nicolo-ribaudo]

Summary

The only remaining blocker for the Babel 8 stable release is to make sure that it works for major Babel consumers. This PR is the first step towards making Jest ready for it. It updates babel-plugin-jest-hoist, babel-preset-jest and babel-jest to support running with Babel 8 in addition to supporting Babel 7.

Test plan

Tests updated to run both with Babel 7 and Babel 8.

Unfortunately, while the Babel plugins/presets maintained in this repo work reasonably well with Babel 8, Babel 8 itself cannot be loaded inside Jest-run tests, because it's written in ESM. Or maybe it's possible, but not the way that Jest is configured in this repo.

As a workaround, I'm loading the Babel 8 ESM packages using Node.js' native require, rather than Jest's sandboxed version.

Most of the diff in tests is indentation changes. I suggest disabling whitespace diff when reviewing.

(fyi @JLHwung @liuxingbaoyu)

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commit: 92a3c81

[nicolo-ribaudo]

Ok I give up. @cpojer / @SimenB do you know how to solve that "› 12 obsolete snapshots found" error in Node.js 18, which I assume is due to those tests being skipped in Node.js 18?

[cpojer]

I assume we'll release this as a major, and we'll drop Node 18 next so don't worry about those.

[nicolo-ribaudo]

Oh I was planning to go with this PR first just allowing users to use Babel 8, and then a separate one (major) upgrading the whole repo to it. I'll do the whole upgrade immediately then.

[cpojer]

@nicolo-ribaudo sorry I was away for a month. Just to confirm, with this PR Babel 7 or 8 can be used with Jest, and this is not a breaking change, is that correct?

[nicolo-ribaudo]

Correct! I can also open a PR with the breaking change next week of you prefer.

[cpojer]

Got it! We can discuss the breaking changes in the other PR then and figure out what's the right time to merge that.

I see some test failures related to this change on CI: "TypeError: Cannot read properties of null (reading 'transformSync')".

[nicolo-ribaudo]

@cpojer I'm struggling a bit with the CI failure. Babel 8 does not support Node.js 18, so I'm using describe.skip for its tests in Node.js 18. However, this means that the tests are skipped, so the snapshots are unused, and so CI is failing due to unused snapshots.

[nicolo-ribaudo]

Ok maybe I found a (ugly) workaround.

[SimenB]

@nicolo-ribaudo sorry, I've ignored all OSS for a long time 😅

We have a onNodeVersion (ish spelling) helper for skipping tests on certain node versions

[SimenB]

jest/packages/test-utils/src/ConditionalTest.ts

Lines 33 to 36 in 15e3e7c

	export function onNodeVersions(
	versionRange: string,
	testBody: () => void,
	): void {

This 🙂

[nicolo-ribaudo]

Thanks, updated! Unfortunately I think I still need the workaround for the babel-plugin-jest-hoist tests, because snapshots in .skipped tests don't work (Jest wants me to remove the snapshot, as it's unused).

[SimenB]

Hmm, that helper should fix that as it'll mark the snapshots as skipped rathe than unused 🤔

[cpojer]

Ok, just checking in here to help move this over the line.

Is this understanding correct:

• Babel 8 only works with Node 20+
• Jest 30 still supports Node 18
• I'm happy to drop Node 18 for Jest 31

If we merge this PR, Jest 30 with Babel 7 will still keep working in Node 18, right?

I can figure out the test skipping for Node 18, but I still see tests fail on all versions of Node, so let's fix that and then I'll take over.

[nicolo-ribaudo]

Yes, right!

Sorry I've had limited time for this, I'll get CI green today :)

[nicolo-ribaudo]

Jest really dislikes conditionally skipping tests that contain snapshots (also when using onNodeVersion, because internally it's just a describe.skip). I'm going to re-add the two separate files for Node.js 18 and Node.js 20+ so that it doesn't load the unused snapshot for 18.

[nicolo-ribaudo]

Ping? :)

[cpojer]

Oh apologies, I thought it was still in progress last time I checked. I'll get to it by Monday.

[cpojer]

Thank you for doing this 🙇‍♂️

[cpojer]

@nicolo-ribaudo this was released in Jest 30.2.0.

[nicolo-ribaudo]

Thank you! I'll now open a PR switching all of Jest packages to Babel 8.

It will be a breaking change, and also feel free to wait until Babel 8 is stable to release it, but I need to make sure that everything works before the stable release :)

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