feat: Vercel adapter

[JuanM04]

Changes

Adds the Vercel adapter that works with Vercel's Files System API.

Testing

TBD

Docs

TBD

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Latest commit: bf2199e

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

This PR includes changesets to release 1 package

Name	Type
@astrojs/vercel	Patch

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[JuanM04]

.output folder works without any configuration in Vercel but ENABLE_FILE_SYSTEM_API=1. API Routes are still in progress.

I've created @juanm04/astro and @juanm04/astro-vercel for testing, and I'm doing pnpm add astro@npm:@juanm04/astro in the starter template

[JuanM04]

Perfect, I've made it work somehow. It turned out the Node.js helpers Vercel gives you (like res.query or res.send()) didn't work — the handler gets a plain Node HTTP Request. But it works!

[JuanM04]

I had a lot of trouble generating the pages statically and converting the endpoints to API Routes. So, I took a similar approach to what the Netlify adapter does. Nonetheless, I'm waiting to #2937 to get mergerd.

In the future I could do a PR that lets you generate statically all the pages for both Netlify and Vercel

[matthewp]

@JuanM04 Our SSR implementation is currently designed to be SSR-only, not a mixture of static + SSR. Something we might change in the future.