Handle bad CSS better

[matthewp]

Changes

• Currently the compiler expects preprocessStyle to return valid CSS. However if there is an error preprocessing it might now.
• This makes it so that preprocessStyle can return an error. The compiler uses that to know the CSS is bad.
• The styleError is returned in the transform result and the caller can use that error to do whatever it needs.
• Part of Astro hangs on invalid scss astro#4615, still need core update to completely fix.

Testing

Test added

Docs

N/A

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🦋 Changeset detected

Latest commit: c953187

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@astrojs/compiler	Minor

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[natemoo-re]

LGTM! Not sure what would happen with one-to-many styles, but if you're not worried about that, this is a good enough solution for now.

[matthewp]

That's a good point! Current in the Vite plugin we only handle the case where there's one style error. Let me see if I can improve on that here.

[matthewp]

Ok, I made it return an error of style errors instead.