Remove esm loader

packages/next/src/bin/next.ts

@@ -5,14 +5,7 @@ import arg from 'next/dist/compiled/arg/index.js'
 import { NON_STANDARD_NODE_ENV } from '../lib/constants'
 import { commands } from '../lib/commands'
 import { commandArgs } from '../lib/command-args'
-import loadConfig from '../server/config'
-import {
-  PHASE_PRODUCTION_SERVER,
-  PHASE_DEVELOPMENT_SERVER,
-} from '../shared/lib/constants'
-import { getProjectDir } from '../lib/get-project-dir'
 import { getValidatedArgs } from '../lib/get-validated-args'
-import { findPagesDir } from '../lib/find-pages-dir'
 
 const defaultCommand = 'dev'
 const args = arg(
@@ -126,48 +119,6 @@ async function main() {
   const currentArgsSpec = commandArgs[command]()
   const validatedArgs = getValidatedArgs(currentArgsSpec, forwardedArgs)
 
-  if (
-    (command === 'start' || command === 'dev') &&
-    !process.env.NEXT_PRIVATE_WORKER
-  ) {
-    const dir = getProjectDir(
-      process.env.NEXT_PRIVATE_DEV_DIR || validatedArgs._[0]
-    )
-    process.env.NEXT_PRIVATE_DIR = dir
-    const origEnv = Object.assign({}, process.env)
-
-    // TODO: set config to env variable to be re-used so we don't reload
-    // un-necessarily
-    const config = await loadConfig(
-      command === 'dev' ? PHASE_DEVELOPMENT_SERVER : PHASE_PRODUCTION_SERVER,
-      dir,
-      {
-        silent: false,
-      }
-    )
-    let dirsResult: ReturnType<typeof findPagesDir> | undefined = undefined
-
-    try {
-      dirsResult = findPagesDir(dir)
-    } catch (_) {
-      // handle this error further down
-    }
-
-    if (dirsResult?.appDir || process.env.NODE_ENV === 'development') {
-      process.env = origEnv
-    }
-
-    if (dirsResult?.appDir) {
-      // we need to reset env if we are going to create
-      // the worker process with the esm loader so that the
-      // initial env state is correct
-      process.env.__NEXT_PRIVATE_PREBUNDLED_REACT = config.experimental
-        .serverActions
-        ? 'experimental'
-        : 'next'
-    }
-  }
-
   for (const dependency of ['react', 'react-dom']) {
     try {
       // When 'npm link' is used it checks the clone location. Not the project.

packages/next/src/build/index.ts

@@ -147,10 +147,9 @@ import { startTypeChecking } from './type-check'
 import { generateInterceptionRoutesRewrites } from '../lib/generate-interception-routes-rewrites'
 
 import { buildDataRoute } from '../server/lib/router-utils/build-data-route'
-import { defaultOverrides } from '../server/import-overrides'
+import { defaultOverrides } from '../server/require-hook'
 import { initialize as initializeIncrementalCache } from '../server/lib/incremental-cache-server'
 import { nodeFs } from '../server/lib/node-fs-methods'
-import { getEsmLoaderPath } from '../server/lib/get-esm-loader-path'
 
 export type SsgRoute = {
   initialRevalidateSeconds: number | false
@@ -1251,11 +1250,6 @@ export default async function build(
           },
           numWorkers,
           forkOptions: {
-            execArgv: [
-              '--experimental-loader',
-              getEsmLoaderPath(),
-              '--no-warnings',
-            ],
             env: {
               ...process.env,
               __NEXT_INCREMENTAL_CACHE_IPC_PORT: incrementalCacheIpcPort + '',
@@ -2135,8 +2129,7 @@ export default async function build(
                 ? [
                     require.resolve('next/dist/server/lib/start-server'),
                     require.resolve('next/dist/server/next'),
-                    require.resolve('next/dist/esm/server/esm-loader.mjs'),
-                    require.resolve('next/dist/server/import-overrides'),
+                    require.resolve('next/dist/server/require-hook'),
                   ]
                 : []),
               require.resolve('next/dist/server/next-server'),

packages/next/src/build/webpack-config.ts

@@ -69,7 +69,7 @@ import { NextFontManifestPlugin } from './webpack/plugins/next-font-manifest-plu
 import { getSupportedBrowsers } from './utils'
 import { MemoryWithGcCachePlugin } from './webpack/plugins/memory-with-gc-cache-plugin'
 import { getBabelConfigFile } from './get-babel-config-file'
-import { defaultOverrides } from '../server/import-overrides'
+import { defaultOverrides } from '../server/require-hook'
 
 type ExcludesFalse = <T>(x: T | false) => x is T
 type ClientEntries = {

packages/next/src/cli/next-dev.ts

@@ -17,23 +17,28 @@ import { fileExists, FileType } from '../lib/file-exists'
 import { getNpxCommand } from '../lib/helpers/get-npx-command'
 import { createSelfSignedCertificate } from '../lib/mkcert'
 import uploadTrace from '../trace/upload-trace'
-import { startServer } from '../server/lib/start-server'
-import { loadEnvConfig } from '@next/env'
+import { initialEnv, loadEnvConfig } from '@next/env'
 import { trace } from '../trace'
+import { validateTurboNextConfig } from '../lib/turbopack-warning'
+import { fork } from 'child_process'
+import { RESTART_EXIT_CODE } from '../server/lib/setup-server-worker'
 import {
   getReservedPortExplanation,
   isPortIsReserved,
 } from '../lib/helpers/get-reserved-port'
-import { validateTurboNextConfig } from '../lib/turbopack-warning'
 
 let dir: string
+let child: undefined | ReturnType<typeof fork>
 let config: NextConfigComplete
 let isTurboSession = false
 let traceUploadUrl: string
 let sessionStopHandled = false
 let sessionStarted = Date.now()
 
-const handleSessionStop = async () => {
+const handleSessionStop = async (signal: string | null) => {
+  if (child) {
+    child.kill((signal as any) || 0)
+  }
   if (sessionStopHandled) return
   sessionStopHandled = true
 
@@ -96,8 +101,8 @@ const handleSessionStop = async () => {
   process.exit(0)
 }
 
-process.on('SIGINT', handleSessionStop)
-process.on('SIGTERM', handleSessionStop)
+process.on('SIGINT', () => handleSessionStop('SIGINT'))
+process.on('SIGTERM', () => handleSessionStop('SIGTERM'))
 
 const nextDev: CliCommand = async (args) => {
   if (args['--help']) {
@@ -193,6 +198,14 @@ const nextDev: CliCommand = async (args) => {
     },
   })
 
+  process.env.__NEXT_PRIVATE_PREBUNDLED_REACT = config.experimental
+    .serverActions
+    ? 'experimental'
+    : 'next'
+
+  // we need to reset env if we are going to create
+  // the worker process with the esm loader so that the
+  // initial env state is correct
   let envInfo: string[] = []
   if (loadedEnvFiles.length > 0) {
     envInfo = loadedEnvFiles.map((f) => f.path)
@@ -231,6 +244,42 @@ const nextDev: CliCommand = async (args) => {
   setGlobal('phase', PHASE_DEVELOPMENT_SERVER)
   setGlobal('distDir', distDir)
 
+  const startServerPath = require.resolve('../server/lib/start-server')
+  async function startServer(options: StartServerOptions) {
+    return new Promise<void>((resolve) => {
+      let resolved = false
+
+      child = fork(startServerPath, {
+        stdio: 'inherit',
+        env: {
+          ...((initialEnv || process.env) as typeof process.env),
+          NEXT_PRIVATE_WORKER: '1',
+        },
+      })
+
+      child.on('message', (msg: any) => {
+        if (msg && typeof msg === 'object') {
+          if (msg.nextWorkerReady) {
+            child?.send({ nextWorkerOptions: options })
+          } else if (msg.nextServerReady && !resolved) {
+            resolved = true
+            resolve()
+          }
+        }
+      })
+
+      child.on('exit', async (code, signal) => {
+        if (sessionStopHandled || signal) {
+          return
+        }
+        if (code === RESTART_EXIT_CODE) {
+          return startServer(options)
+        }
+        await handleSessionStop(signal)
+      })
+    })
+  }
+
   const runDevServer = async (reboot: boolean) => {
     try {
       if (!!args['--experimental-https']) {

packages/next/src/server/config-utils.ts

@@ -10,7 +10,7 @@ export function loadWebpackHook() {
 
   // hook the Node.js require so that webpack requires are
   // routed to the bundled and now initialized webpack version
-  require('../server/import-overrides').addHookAliases(
+  require('../server/require-hook').addHookAliases(
     [
       ['webpack', 'next/dist/compiled/webpack/webpack-lib'],
       ['webpack/package', 'next/dist/compiled/webpack/package'],

packages/next/src/server/config.ts

@@ -865,7 +865,7 @@ export default async function loadConfig(
 
       if (shouldExit) {
         for (const message of messages) {
-          curLog.error(message)
+          console.error(message)
         }
         await flushAndExit(1)
       } else {

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

@@ -84,7 +84,8 @@ export async function initialize(opts: {
 
   const config = await loadConfig(
     opts.dev ? PHASE_DEVELOPMENT_SERVER : PHASE_PRODUCTION_SERVER,
-    opts.dir
+    opts.dir,
+    { silent: false }
   )
 
   let compress: ReturnType<typeof setupCompression> | undefined

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

@@ -358,3 +358,13 @@ export async function startServer({
     })
   }
 }
+
+if (process.env.NEXT_PRIVATE_WORKER && process.send) {
+  process.addListener('message', async (msg: any) => {
+    if (msg && typeof msg && msg.nextWorkerOptions && process.send) {
+      await startServer(msg.nextWorkerOptions)
+      process.send({ nextServerReady: true })
+    }
+  })
+  process.send({ nextWorkerReady: true })
+}