Wait for entry to resolve in production build (#7104)

* Wait for entry to resolve in production build

* Return promise

packages/next/build/webpack-config.ts

@@ -20,7 +20,7 @@ import { importAutoDllPlugin } from './webpack/plugins/dll-import'
 import { WebpackEntrypoints } from './entries'
 type ExcludesFalse = <T>(x: T | false) => x is T
 
-export default function getBaseWebpackConfig (dir: string, {dev = false, debug = false, isServer = false, buildId, config, target = 'server', entrypoints, selectivePageBuilding = false, selectivePageBuildingCacheIdentifier = ''}: {dev?: boolean, debug?: boolean, isServer?: boolean, buildId: string, config: any, target?: string, entrypoints: WebpackEntrypoints, selectivePageBuilding?: boolean, selectivePageBuildingCacheIdentifier?: string}): webpack.Configuration {
+export default async function getBaseWebpackConfig (dir: string, {dev = false, debug = false, isServer = false, buildId, config, target = 'server', entrypoints, selectivePageBuilding = false, selectivePageBuildingCacheIdentifier = ''}: {dev?: boolean, debug?: boolean, isServer?: boolean, buildId: string, config: any, target?: string, entrypoints: WebpackEntrypoints, selectivePageBuilding?: boolean, selectivePageBuildingCacheIdentifier?: string}): Promise<webpack.Configuration> {
   const distDir = path.join(dir, config.distDir)
   const defaultLoaders = {
     babel: {
@@ -375,5 +375,10 @@ export default function getBaseWebpackConfig (dir: string, {dev = false, debug =
     }
   }
 
+  if(!dev) {
+    // @ts-ignore entry is always a function
+    webpackConfig.entry = await webpackConfig.entry()
+  }
+
   return webpackConfig
 }

packages/next/server/hot-reloader.js

@@ -175,10 +175,10 @@ export default class HotReloader {
     let additionalClientEntrypoints = {}
     additionalClientEntrypoints[CLIENT_STATIC_FILES_RUNTIME_AMP] = `.${sep}` + relativePath(this.dir, join(NEXT_PROJECT_ROOT_DIST_CLIENT, 'amp-dev'))
 
-    return [
+    return Promise.all([
       getBaseWebpackConfig(this.dir, { dev: true, isServer: false, config: this.config, buildId: this.buildId, entrypoints: { ...entrypoints.client, ...additionalClientEntrypoints } }),
       getBaseWebpackConfig(this.dir, { dev: true, isServer: true, config: this.config, buildId: this.buildId, entrypoints: entrypoints.server })
-    ]
+    ])
   }
 
   async start () {