How I modified the streaming server to build with client conditions and "redirect" server imports.

buildForStreamingServer.ts

import fs from 'node:fs'
import path from 'node:path'

import { build as viteBuild } from 'vite'
import { cjsInterop } from 'vite-plugin-cjs-interop'

import { getPaths } from '@redwoodjs/project-config'

export async function buildForStreamingServer({
  verbose = false,
  clientEntryFiles,
  serverEntryFiles,
}: {
  verbose?: boolean
  clientEntryFiles: Record<string, string>
  serverEntryFiles: Record<string, string>
}) {
  console.log('Starting streaming server build...\n')

  const rwPaths = getPaths()

  const rscBuildManifest: Record<string, any> = JSON.parse(
    fs.readFileSync(
      path.join(rwPaths.web.distRsc, 'server-build-manifest.json'),
      'utf-8',
    ),
  )

  const serverEntriesPaths = Object.values(serverEntryFiles)

  if (!rwPaths.web.viteConfig) {
    throw new Error('Vite config not found')
  }

  await viteBuild({
    configFile: rwPaths.web.viteConfig,
    plugins: [
      cjsInterop({
        dependencies: ['@redwoodjs/**'],
      }),
      {
        name: 'rw-resolve-redirect',
        enforce: 'pre',
        async resolveId(source, importer, _options) {
          // Not sure how this is possible but TS says so
          if (!importer) {
            return null
          }

          // @TODO: ignore node_modules, this seems like a lot of processing otherwise

          // Step 1: create path for lookup
          const absPath = path.join(path.parse(importer).dir, source)

          // Only do it for files with "use server" in src, ignore node_modules
          // @MARK @TODO Temporary!!!!
          const absPathWithHackedExtension = absPath + '.ts'
          if (
            !serverEntriesPaths.includes(absPathWithHackedExtension) ||
            absPath.includes('node_modules')
          ) {
            return null
          }

          const relToSrc = path.relative(
            rwPaths.web.src,
            absPathWithHackedExtension,
          )

          // Step 2: lookup in the manifest
          // const manifest = await getManifest()
          const fileId = rscBuildManifest[relToSrc].file

          // Step 3, return fileId and external: true
          return {
            id: path.join('../../rsc', fileId),
            external: true,
          }
        },
      },
    ],
    build: {
      rollupOptions: {
        input: {
          ...clientEntryFiles,
          entries: rwPaths.web.entries as string,
        },
      },
      outDir: rwPaths.web.distServer,
      ssr: true,
      emptyOutDir: true,
    },
    ssr: {
      noExternal: /^(?!node:)/,
      // Can't inline prisma client
      external: ['@prisma/client'],
    },
    envFile: false,
    logLevel: verbose ? 'info' : 'warn',
  })
}

What this is effectively achieving:

• Build SSR with "node conditions": i.e. not react-server
• Import redirection using the plugin: if you encounter a server entry (NOT a server component) change the import to what it is from the rsc build. In the RSA fixture, if you enounter "./actions" (it'll be in the serverEntries) - you need to redirect the import to the built rsc assets
• when you build with client conditions (and noExternal things) - the final output will not contain "use client". In this example, check if HomePage has an import to "use-client" - it shouldn't.

We then need to launch the server with:

╰─ NODE_OPTIONS="--conditions=react-server" yarn rw serve