breaking: replace builder.generateManifest with builder.generateServer and builder.getManifest

[ottomated]

alternative to #16827

Removes SSRManifest as a public api. Previously, adapters were using it directly; now they have a more limited api that mirrors $app/manifest. This ends up simplifying the code that adapters have to generate, because they only have to worry about a single server module vs server + manifest. It also removes the need for manifest._.foo in the internal code, which is nice.

Technically, SSRManifest is still used by some adapters (search server.manifest to find the uses). I don't know if we want to go all the way here and replace those with, i.e. rolldown defines?

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Preview: https://svelte-dev-git-preview-kit-16843-svelte.vercel.app/

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Additional Suggestion:

Netlify edge.js entry still uses the old new Server(manifest) API, so Server is undefined and the MANIFEST import is unresolved, breaking the edge function build.

[Rich-Harris]

Nice! This feels way better than what we have now. A few places where I think we could potentially go further:

• would it make sense to have an API like builder.generateServer(dest, { routes }) that writes the file to dest (instead of returning a string) and figures out the relative path itself? i.e. instead of this...

  writeFileSync(
    `${tmp}/server.js`,
    builder.generateServer({
      relativePath: path.posix.relative(tmp, builder.getServerDirectory())
    })
  );

  ...this:

  builder.generateServer(`${tmp}/server.js`);

  It would also mean getting rid of the export option; the Netlify that adapter that currently uses it would just import the generated module:

  /**
  -* @param {string} server
   * @returns {string}
   */
  -function generate_serverless_function_module(server) {
  +function generate_serverless_function_module() {
    return `\
  import { init } from '../serverless.js';
  -${server}
  +import { server } from '../server.js';
  
  export default init(server);
  `;
  }

  (Might need a serverDirectory option alongside routes that points to the dir in builder.writeServer(dir), in the cases where that happens which IIUC is only Netlify. It would default to builder.getServerDirectory().)

• Ideally I don't think we'd expose server.manifest at all, otherwise there's still an awkward public API that we will struggle to evolve. The adapters that need that stuff can use define (or equivalent) along with the config and manifest data that's available to builder:

  -const app_path = `/${server.manifest.app_path}`;
  +const app_path = APP_PATH;

  APP_PATH would basically be JSON.stringify(`${builder.config.paths.base}/${builder.config.appDir}`).

• We're already computing the manifest data inside buildApp, should we just pass it directly as builder.manifest rather than builder.getManifest()?

• If we did all that we'd presumably also need a builder.mimeTypes object or similar, since that's not exposed anywhere else and is needed by adapter-node

For the sake of the diff it might be easier to keep stuff under manifest._ for now, and tidy that up in a follow-up PR.

[ottomated]

would it make sense to have an API like builder.generateServer(dest, { routes })

Makes sense, maybe builder.writeServerModule is better in that case?

It would also mean getting rid of the export option; the Netlify that adapter that currently uses it would just import the generated module

I don't think we can do that; that function is used to generate a bunch of serverless functions in a magic netlify folder, each with a unique set of routes. They would each need to write a server-functionname.js file to a separate folder I think, which just seems more complicated.

Ideally I don't think we'd expose server.manifest at all, otherwise there's still an awkward public API that we will struggle to evolve. The adapters that need that stuff can use define (or equivalent) along with the config and manifest data that's available to builder:

I somehow missed that config is passed to the builder, that should make it possible. Maybe also deprecate builder.getAppPath() in favor of builder.config.paths.base + builder.config.appDir?

(side note, it would make my life a lot easier on the cloudflare stuff if we could somehow pass the svelte config to the adapter function before adapt is called so it can be used in vite plugins)

We're already computing the manifest data inside buildApp, should we just pass it directly as builder.manifest rather than builder.getManifest()?

Makes sense to me. I'll do a second pass on all of this