Support Functions in non-Pages environments

[GregBrimble]

Adds support for building a Worker from a folder of functions which isn't tied to the Pages platform.

This lets developers use the same file-based routing system an simplified syntax when developing their own Workers!

---

For example, I can create a folder of functions:

// functions/hello.ts

export const onRequest = () => {
  return new Response("Hello, world!")
}

And run npx wrangler pages functions build --fallback-service='' --script-path=worker.js.

This will generate a Worker worker.js which will respond with "Hello, world!" for requests coming to /hello.

The --fallback-service determines the handling of requests which either don't match, or hit the end of their next chain. In Pages world, we fallback to env.ASSETS.fetch which serves a project's static assets.

In this case, when I pass --fallback-service='', I'm signally that I don't want to fallback to any service, and instead, I fallback to the global fetch function. So if this Worker was deployed on my zone, when I make a request to anything other than /hello, I'd hit my origin.

If I wanted to fallback to another service or Durable Object, I could specify --fallback-service MY_SERVICE.

Middleware, nested/routes, [segmented routes] are all supported with this.

[changeset-bot]

🦋 Changeset detected

Latest commit: 618292c

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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wrangler	Patch

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[threepointone]

Are you planning on exposing this for regular developers, or is this just for internal usage?

[threepointone]

maybe it's a good time to make a build of this file too. I'd like to keep packages out of dependencies, and would rather deliver bundled files. In a followup PR is fine, but before GA.

[GregBrimble]

Regular developers, yeah. There's a few other things I want to do before its ready for prime-time, but the hope is that some people chose to write Workers with this file-based routing.

[threepointone]

That package lock thing is a little worrisome, but maybe it's fine now. I'll test myself tomorrow. Feel free to land.

[GregBrimble]

Regenerated it properly in the latest commit. The changes now are just due to updated packages because we're not pinning versions.