Opt-into worker mode when appDir is enabled

packages/next/src/server/lib/start-server.ts

@@ -1,10 +1,14 @@
 import http from 'http'
+import { resolve } from 'path'
 import { isIPv6 } from 'net'
 import * as Log from '../../build/output/log'
 import { getNodeOptionsWithoutInspect } from './utils'
 import type { IncomingMessage, ServerResponse } from 'http'
 import type { ChildProcess } from 'child_process'
 import { normalizeRepeatedSlashes } from '../../shared/lib/utils'
+import { PHASE_DEVELOPMENT_SERVER } from '../../shared/lib/constants'
+import { PHASE_PRODUCTION_SERVER } from '../../shared/lib/constants'
+import loadConfig from '../config'
 
 export interface StartServerOptions {
   dir: string
@@ -162,8 +166,19 @@ export async function startServer({
     server.listen(port, hostname)
   })
 
+  const config = await loadConfig(
+    isDev ? PHASE_DEVELOPMENT_SERVER : PHASE_PRODUCTION_SERVER,
+    resolve(dir || '.'),
+    undefined,
+    undefined,
+    false
+  )
+
+  // Always use workers when `appDir` is enabled.
+  const shouldUseWorkers = useWorkers || config.experimental.appDir
+
   try {
-    if (useWorkers) {
+    if (shouldUseWorkers) {
       const httpProxy =
         require('next/dist/compiled/http-proxy') as typeof import('next/dist/compiled/http-proxy')
 
@@ -295,6 +310,7 @@ export async function startServer({
         httpServer: server,
         customServer: false,
         port: addr && typeof addr === 'object' ? addr.port : port,
+        preloadedConfig: config,
       })
       // handle in process
       requestHandler = app.getRequestHandler()

packages/next/src/server/next.ts

@@ -1,6 +1,8 @@
 import type { Options as DevServerOptions } from './dev/next-dev-server'
 import type { NodeRequestHandler } from './next-server'
 import type { UrlWithParsedQuery } from 'url'
+import type { NextConfigComplete } from './config-shared'
+
 import './node-polyfill-fetch'
 import { default as Server } from './next-server'
 import * as log from '../build/output/log'
@@ -29,7 +31,9 @@ const getServerImpl = async () => {
   return ServerImpl
 }
 
-export type NextServerOptions = Partial<DevServerOptions>
+export type NextServerOptions = Partial<DevServerOptions> & {
+  preloadedConfig?: NextConfigComplete
+}
 
 export interface RequestHandler {
   (
@@ -144,12 +148,15 @@ export class NextServer {
   }
 
   private async loadConfig() {
-    return loadConfig(
-      this.options.dev ? PHASE_DEVELOPMENT_SERVER : PHASE_PRODUCTION_SERVER,
-      resolve(this.options.dir || '.'),
-      this.options.conf,
-      undefined,
-      !!this.options._renderWorker
+    return (
+      this.options.preloadedConfig ||
+      loadConfig(
+        this.options.dev ? PHASE_DEVELOPMENT_SERVER : PHASE_PRODUCTION_SERVER,
+        resolve(this.options.dir || '.'),
+        this.options.conf,
+        undefined,
+        !!this.options._renderWorker
+      )
     )
   }