Addon-docs: Fix MDX compilation with @vitejs/plugin-react-swc and plugins

[JReinhold]

Closes #24857

What I did

Moved the MDX Vite plugin to the start of the plugins-array instead of the end.

The MDX plugin must run before any React plugins to work. In 99 % of the cases it is because we have enforce: 'pre' defined in the plugin. However when:

1. Using @vitejs/plugin-react-swc
2. And have defined plugins for that Vite plugin with eg. react({ plugins: [] })

Our MDX plugin is runned after @vitejs/plugin-react-swc, causing build (but now dev) to crash.

This is because we get into this case in @vitejs/plugin-react-swc, where they also add enforce: 'pre', causing it to run before our MDX plugin. The fix is to add it to the beginning of the array instead of the end. Also see this condition in @vitejs/plugin-react-swc where they explicitly check for this case, except with the official MDX Vite plugin and not ours of course.

I can't come up with any downsides to this fix, as this shouldn't really change anything for most users AFAIK. I've tested it in basic situations with React+Vite without issues.

Side-note: I wonder if in the future we could just use the MDX Vite plugin directly instead of creating our own (extremely thin) wrapper around the low-level MDX compiler. 🤔 I can imagine it solving the problem better, ie. supporting source maps.

Checklist for Contributors

Testing

I think the only way to truly test this would be to have a sandbox with this scenario, but that's definitely not worth it.

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

1. Create a new Vite project with npm create vite
2. Choose "React" and "TypeScript + SWC"
3. Init Storybook in the project
4. Edit vite.config.ts, change the line plugins: [react()], to plugins: [react({ plugins: [] })],
5. Build the Storybook
6. See it fail with the latest version
7. Install this canary of Storybook
8. Build again
9. See it succeeds
10. Serve with npx http-serve storybook-static -c-1h
11. See that the "Configure..." MDX page works

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This pull request has been released as version 0.0.0-pr-26837-sha-6fdb569c. Try it out in a new sandbox by running npx storybook@0.0.0-pr-26837-sha-6fdb569c sandbox or in an existing project with npx storybook@0.0.0-pr-26837-sha-6fdb569c upgrade.

More information

Published version	0.0.0-pr-26[8](https://github.com/storybookjs/storybook/actions/runs/8680911801/job/23802522844#step:10:8)37-sha-6fdb56[9](https://github.com/storybookjs/storybook/actions/runs/8680911801/job/23802522844#step:10:9)c
Triggered by	@JReinhold
Repository	storybookjs/storybook
Branch	jeppe/24857-bug-mdx-compilation-breaks-when-using-vitejsplugin-react-swc-and-extending-its-plugins
Commit	6fdb569c
Datetime	Sun Apr 14 19:39:24 UTC 2024 (1713123564)
Workflow run	[8680911801](https://github.com/storybookjs/storybook/actions/runs/8680911801)

To request a new release of this pull request, mention the @storybookjs/core team.

core team members can create a new canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=26837

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[valentinpalkovic]

Code-wise LGTM!

[storybook-bot]

Failed to publish canary version of this pull request, triggered by @JReinhold. See the failed workflow run at: https://github.com/storybookjs/storybook/actions/runs/8943682626