fix(standalone): support type: "module" (vercel#41268)

Fixes vercel#41258

When we detect `type: "module"` in `package.json`:

~1. generate `server.mjs`~ Not necessary when `type: "module"` is set.
2. use `import` instead of `require`
3. replace `__dirname` with [ESM compatible
alternative](https://blog.logrocket.com/alternatives-dirname-node-js-es-modules/)

In this PR, I also moved some tests (those using `output: "standalone"`)
to a new `test/production/standalone-mode` directory for easier
discoverability in the future.

Run the related test with `pnpm test
test/production/standalone-mode/type-module/index.test.ts`

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

packages/next/build/utils.ts

@@ -1558,6 +1558,12 @@ export async function copyTracedFiles(
   middlewareManifest: MiddlewareManifest
 ) {
   const outputPath = path.join(distDir, 'standalone')
+  let moduleType = false
+  try {
+    const packageJsonPath = path.join(distDir, '../package.json')
+    const packageJson = JSON.parse(await fs.readFile(packageJsonPath, 'utf8'))
+    moduleType = packageJson.type === 'module'
+  } catch {}
   const copiedFiles = new Set()
   await recursiveDelete(outputPath)
 
@@ -1635,12 +1641,21 @@ export async function copyTracedFiles(
   )
   await fs.writeFile(
     serverOutputPath,
-    `
-process.env.NODE_ENV = 'production'
-process.chdir(__dirname)
+    `${
+      moduleType
+        ? `import Server from 'next/dist/server/next-server.js'
+import http from 'http'
+import path from 'path'
+import { fileURLToPath } from 'url'
+const __dirname = fileURLToPath(new URL('.', import.meta.url))
+const NextServer = Server.default`
+        : `
 const NextServer = require('next/dist/server/next-server').default
 const http = require('http')
-const path = require('path')
+const path = require('path')`
+    }
+process.env.NODE_ENV = 'production'
+process.chdir(__dirname)
 
 // Make sure commands gracefully respect termination signals (e.g. from Docker)
 // Allow the graceful termination to be manually configurable
@@ -1680,9 +1695,12 @@ server.listen(currentPort, (err) => {
   })
   handler = nextServer.getRequestHandler()
 
-  console.log("Listening on port", currentPort)
-})
-    `
+  console.log(
+    'Listening on port',
+    currentPort,
+    'url: http://localhost:' + currentPort
+  )
+})`
   )
 }
 export function isReservedPage(page: string) {

test/production/pnpm-support/test/index.test.ts → test/production/pnpm-support/index.test.ts

@@ -23,9 +23,9 @@ describe('pnpm support', () => {
   it('should build with dependencies installed via pnpm', async () => {
     next = await createNext({
       files: {
-        pages: new FileRef(path.join(__dirname, '..', 'app/pages')),
+        pages: new FileRef(path.join(__dirname, 'app/pages')),
         'next.config.js': new FileRef(
-          path.join(__dirname, '..', 'app/next.config.js')
+          path.join(__dirname, 'app/next.config.js')
         ),
       },
       packageJson: {
@@ -48,12 +48,10 @@ describe('pnpm support', () => {
   it('should execute client-side JS on each page in output: "standalone"', async () => {
     next = await createNext({
       files: {
-        pages: new FileRef(path.join(__dirname, '..', 'app-multi-page/pages')),
-        '.npmrc': new FileRef(
-          path.join(__dirname, '..', 'app-multi-page/.npmrc')
-        ),
+        pages: new FileRef(path.join(__dirname, 'app-multi-page/pages')),
+        '.npmrc': new FileRef(path.join(__dirname, 'app-multi-page/.npmrc')),
         'next.config.js': new FileRef(
-          path.join(__dirname, '..', 'app-multi-page/next.config.js')
+          path.join(__dirname, 'app-multi-page/next.config.js')
         ),
       },
       packageJson: {

test/production/required-server-files-i18n.test.ts → test/production/standalone-mode/required-server-files/required-server-files-i18n.test.ts

@@ -41,11 +41,9 @@ describe('should set-up next', () => {
 
     next = await createNext({
       files: {
-        pages: new FileRef(join(__dirname, 'required-server-files/pages')),
-        lib: new FileRef(join(__dirname, 'required-server-files/lib')),
-        'data.txt': new FileRef(
-          join(__dirname, 'required-server-files/data.txt')
-        ),
+        pages: new FileRef(join(__dirname, 'pages')),
+        lib: new FileRef(join(__dirname, 'lib')),
+        'data.txt': new FileRef(join(__dirname, 'data.txt')),
       },
       packageJson: {
         scripts: {

test/production/required-server-files.test.ts → test/production/standalone-mode/required-server-files/required-server-files.test.ts

@@ -28,21 +28,13 @@ describe('should set-up next', () => {
 
     next = await createNext({
       files: {
-        pages: new FileRef(join(__dirname, 'required-server-files/pages')),
-        lib: new FileRef(join(__dirname, 'required-server-files/lib')),
-        'middleware.js': new FileRef(
-          join(__dirname, 'required-server-files/middleware.js')
-        ),
-        'data.txt': new FileRef(
-          join(__dirname, 'required-server-files/data.txt')
-        ),
-        '.env': new FileRef(join(__dirname, 'required-server-files/.env')),
-        '.env.local': new FileRef(
-          join(__dirname, 'required-server-files/.env.local')
-        ),
-        '.env.production': new FileRef(
-          join(__dirname, 'required-server-files/.env.production')
-        ),
+        pages: new FileRef(join(__dirname, 'pages')),
+        lib: new FileRef(join(__dirname, 'lib')),
+        'middleware.js': new FileRef(join(__dirname, 'middleware.js')),
+        'data.txt': new FileRef(join(__dirname, 'data.txt')),
+        '.env': new FileRef(join(__dirname, '.env')),
+        '.env.local': new FileRef(join(__dirname, '.env.local')),
+        '.env.production': new FileRef(join(__dirname, '.env.production')),
       },
       nextConfig: {
         eslint: {

test/production/standalone-mode/type-module/index.test.ts

@@ -0,0 +1,55 @@
+import { createNext } from 'e2e-utils'
+import { NextInstance } from 'test/lib/next-modes/base'
+import { join } from 'path'
+import fs from 'fs-extra'
+import {
+  fetchViaHTTP,
+  findPort,
+  initNextServerScript,
+  killApp,
+} from 'next-test-utils'
+
+describe('type-module', () => {
+  let next: NextInstance
+
+  beforeAll(async () => {
+    next = await createNext({
+      files: {
+        'pages/index.js': `
+          export default function Page() { 
+            return <p>hello world</p>
+          } 
+        `,
+        'next.config.mjs': `export default ${JSON.stringify({
+          output: 'standalone',
+        })}`,
+      },
+      packageJson: { type: 'module' },
+    })
+    await next.stop()
+  })
+
+  afterAll(() => next.destroy())
+
+  it('should work', async () => {
+    const standalonePath = join(next.testDir, '.next/standalone')
+    const staticSrc = join(next.testDir, '.next/static')
+
+    const staticDest = join(standalonePath, '.next/static')
+
+    await fs.move(staticSrc, staticDest)
+
+    const serverFile = join(standalonePath, 'server.js')
+    const appPort = await findPort()
+    const server = await initNextServerScript(
+      serverFile,
+      /Listening on/,
+      { ...process.env, PORT: appPort },
+      undefined,
+      { cwd: next.testDir }
+    )
+    const res = await fetchViaHTTP(appPort, '/')
+    expect(await res.text()).toContain('hello world')
+    await killApp(server)
+  })
+})