fix(css): enhance error message for missing preprocessor dependency

[EastSun5566]

Hi Vite team

Thanks for the great tool!

Description

I recently encountered an error while migrating my build tool to Vite. I had forgotten to install the preprocessor dependency. However, I really appreciate the helpful and clear TypeScript diagnostic messages that include instructions on how to fix the issue. I think these messages greatly improve DX, so I decided to add them to it.

What do you think? Thank you for your help!

Additional context

enhance error messages for missing preprocessor dependency by giving instructions like npm i -D sass etc.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[EastSun5566]

I hope that the pkgFromUserAgent function can be reused in the same way as import { pkgFromUserAgent } from '@vite/create-vite' or import { pkgFromUserAgent } from '@vite/shared', but currently, it is not exposed in that way.

[bluwy]

I think it's ok to duplicate it for now. It would be nice to move this into utils.ts though, and have a separate function that returns package manager specific commands.

e.g. with yarn and pnpm, we want yarn add and pnpm add instead. That way we can do something like ${installCommand} -D ${lang} instead.

[EastSun5566]

Oh right... I completely forgot that yarn does not support the i/install command. However, pnpm does support pnpm i <package_name> as an alias for pnpm add <package_name>. Nonetheless, pnpm add is the more officially supported method.

I will refactor it to utils.ts and make it more verbose. Thank you for your suggestion!

[EastSun5566]

Hi @bluwy

Sorry for the long delay. As previously discussed, I have extracted getPackageManagerCommand to the utils. Could you please take a look at it?

Thank you 🙏

[bluwy]

Looks great, thanks!