fix error serving with older vite versions when config.css was not defined

[mruthh]

Summary

When attempting to serve a Vue app using Vite 4.3.5 with the tailwind/vite plugin, I received the following error:

[vite] Internal server error: Cannot read properties of undefined (reading 'devSourcemap')
  Plugin: @tailwindcss/vite:generate:serve

The issue was a missing ?. check. My vite.config file did not contain a css property and that crashed the plugin.

Test plan

• In pnpm-workspace.yaml, change the vite version to ^4.3.5.
• Run pnpm install
• In playgrounds/vite, run pnpm build && pnpm vite
• The example app should serve normally. Note that without the change from the PR, it fails to serve.

[coderabbitai]

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• packages/@tailwindcss-vite/src/index.ts

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Walkthrough

The tailwindcss Vite plugin was updated to add an additional null-safe access operator when checking the devSourcemap configuration property. The change modifies the source-map enablement flag passed to new Root() from config?.css.devSourcemap ?? false to config?.css?.devSourcemap ?? false. This adjustment introduces an optional chaining operator between css and devSourcemap to safely handle cases where the css property itself is undefined, preventing potential runtime errors during property access.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly and specifically describes the main change: fixing an error when serving with older Vite versions when config.css is undefined.
Description check	✅ Passed	The description is directly related to the changeset, providing context about the bug, the error encountered, and a clear test plan for verification.

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[RobinMalfait]

Hey! I appreciate the PR, but I would highly recommend to upgrade to a newer Vite version.

While we can merge this as is, if you are on the older Vite version the build won't even work due to type checking reasons.

The @tailwindcss/vite package supports Vite 5.2 and up, and note that even Vite 5 is officially unsupported by the Vite team now: https://vite.dev/releases#supported-versions

Additionally, if you ignore all the types, run the Vite playground, it will work ~ish. If you make a change, no new CSS will be generated, there is no HMR and a hard reload won't work either. In this case you will have to restart the server for the changes to take effect.

So while this is a small fix, it's not complete and doesn't add support for Vite 4. Since Vite 4 and 5 are not supported anymore, I don't think we should spend time supporting it either.

I appreciate the PR, but going to close it because of the above mentioned reasons. Thanks!