Drop experimental.reactRoot in favor of auto detection

packages/next/bin/next.ts

@@ -1,8 +1,8 @@
 #!/usr/bin/env node
 import * as log from '../build/output/log'
 import arg from 'next/dist/compiled/arg/index.js'
-import React from 'react'
 import { NON_STANDARD_NODE_ENV } from '../lib/constants'
+import { shouldUseReactRoot } from '../server/utils'
 ;['react', 'react-dom'].forEach((dependency) => {
   try {
     // When 'npm link' is used it checks the clone location. Not the project.
@@ -107,7 +107,6 @@ if (process.env.NODE_ENV) {
 ;(process.env as any).NODE_ENV = process.env.NODE_ENV || defaultEnv
 ;(process.env as any).NEXT_RUNTIME = 'nodejs'
 
-const shouldUseReactRoot = parseInt(React.version) >= 18
 if (shouldUseReactRoot) {
   ;(process.env as any).__NEXT_REACT_ROOT = 'true'
 }

packages/next/build/entries.ts

@@ -247,7 +247,6 @@ export function getServerlessEntry(opts: {
     page: opts.page,
     poweredByHeader: opts.config.poweredByHeader ? 'true' : '',
     previewProps: JSON.stringify(opts.previewMode),
-    reactRoot: !!opts.config.experimental.reactRoot ? 'true' : '',
     runtimeConfig:
       Object.keys(opts.config.publicRuntimeConfig).length > 0 ||
       Object.keys(opts.config.serverRuntimeConfig).length > 0

packages/next/build/webpack-config.ts

@@ -364,26 +364,17 @@ export default async function getBaseWebpackConfig(
     rewrites.afterFiles.length > 0 ||
     rewrites.fallback.length > 0
 
-  // Make sure `reactRoot` is enabled when React 18 or experimental is detected.
-  if (hasReactRoot) {
-    config.experimental.reactRoot = true
-  }
-
-  // Only inform during one of the builds
-  if (isClient && config.experimental.reactRoot && !hasReactRoot) {
-    // It's fine to only mention React 18 here as we don't recommend people to try experimental.
-    Log.warn('You have to use React 18 to use `experimental.reactRoot`.')
-  }
-
-  if (isClient && config.experimental.runtime && !hasReactRoot) {
-    throw new Error(
-      '`experimental.runtime` requires `experimental.reactRoot` to be enabled along with React 18.'
-    )
-  }
-  if (config.experimental.serverComponents && !hasReactRoot) {
-    throw new Error(
-      '`experimental.serverComponents` requires React 18 to be installed.'
-    )
+  if (isClient && !hasReactRoot) {
+    if (config.experimental.runtime) {
+      throw new Error(
+        '`experimental.runtime` requires React 18 to be installed.'
+      )
+    }
+    if (config.experimental.serverComponents) {
+      throw new Error(
+        '`experimental.serverComponents` requires React 18 to be installed.'
+      )
+    }
   }
 
   const hasConcurrentFeatures = hasReactRoot
@@ -1830,7 +1821,6 @@ export default async function getBaseWebpackConfig(
     reactProductionProfiling,
     webpack: !!config.webpack,
     hasRewrites,
-    reactRoot: config.experimental.reactRoot,
     runtime: config.experimental.runtime,
     swcMinify: config.swcMinify,
     swcLoader: useSWCLoader,

packages/next/build/webpack/loaders/next-middleware-ssr-loader/render.ts

@@ -55,7 +55,6 @@ export function getRender({
       page,
       extendRenderOpts: {
         buildId,
-        reactRoot: true,
         runtime: 'edge',
         supportsDynamicHTML: true,
         disableOptimizedLoading: true,

packages/next/build/webpack/loaders/next-serverless-loader/index.ts

@@ -31,7 +31,6 @@ export type ServerlessLoaderQuery = {
   previewProps: string
   loadedEnvFiles: string
   i18n: string
-  reactRoot: string
 }
 
 const nextServerlessLoader: webpack.loader.Loader = function () {
@@ -53,7 +52,6 @@ const nextServerlessLoader: webpack.loader.Loader = function () {
     previewProps,
     loadedEnvFiles,
     i18n,
-    reactRoot,
   }: ServerlessLoaderQuery =
     typeof this.query === 'string' ? parse(this.query.slice(1)) : this.query
 
@@ -187,7 +185,6 @@ const nextServerlessLoader: webpack.loader.Loader = function () {
         canonicalBase: "${canonicalBase}",
         generateEtags: ${generateEtags || 'false'},
         poweredByHeader: ${poweredByHeader || 'false'},
-        reactRoot: ${reactRoot || 'false'},
 
         runtimeConfig,
         buildManifest,

packages/next/export/index.ts

@@ -388,7 +388,6 @@ export default async function exportApp(
       optimizeCss: nextConfig.experimental.optimizeCss,
       nextScriptWorkers: nextConfig.experimental.nextScriptWorkers,
       optimizeFonts: nextConfig.optimizeFonts,
-      reactRoot: nextConfig.experimental.reactRoot || false,
       largePageDataBytes: nextConfig.experimental.largePageDataBytes,
     }
 

packages/next/server/app-render.tsx

@@ -32,7 +32,6 @@ export type RenderOptsPartial = {
   supportsDynamicHTML?: boolean
   runtime?: 'nodejs' | 'edge'
   serverComponents?: boolean
-  reactRoot: boolean
 }
 
 export type RenderOpts = LoadComponentsReturnType & RenderOptsPartial

packages/next/server/base-server.ts

@@ -177,7 +177,6 @@ export default abstract class Server<ServerOptions extends Options = Options> {
     serverComponentManifest?: any
     renderServerComponentData?: boolean
     serverComponentProps?: any
-    reactRoot: boolean
     largePageDataBytes?: number
   }
   protected serverOptions: ServerOptions
@@ -328,7 +327,6 @@ export default abstract class Server<ServerOptions extends Options = Options> {
       crossOrigin: this.nextConfig.crossOrigin
         ? this.nextConfig.crossOrigin
         : undefined,
-      reactRoot: this.nextConfig.experimental.reactRoot === true,
       largePageDataBytes: this.nextConfig.experimental.largePageDataBytes,
     }
 
@@ -1292,7 +1290,7 @@ export default abstract class Server<ServerOptions extends Options = Options> {
         typeof components.Document?.getInitialProps !== 'function' ||
         // When concurrent features is enabled, the built-in `Document`
         // component also supports dynamic HTML.
-        (this.renderOpts.reactRoot &&
+        (!!process.env.__NEXT_REACT_ROOT &&
           NEXT_BUILTIN_DOCUMENT in components.Document)
 
       // Disable dynamic HTML in cases that we know it won't be generated,

packages/next/server/config-shared.ts

@@ -107,7 +107,6 @@ export interface ExperimentalConfig {
     validator?: string
     skipValidation?: boolean
   }
-  reactRoot?: boolean
   disableOptimizedLoading?: boolean
   gzipSize?: boolean
   craCompat?: boolean
@@ -511,7 +510,6 @@ export const defaultConfig: NextConfig = {
     nextScriptWorkers: false,
     scrollRestoration: false,
     externalDir: false,
-    reactRoot: Number(process.env.NEXT_PRIVATE_REACT_ROOT) > 0,
     disableOptimizedLoading: false,
     gzipSize: true,
     swcFileReading: true,

packages/next/server/config.ts

@@ -74,19 +74,6 @@ function assignDefaults(userConfig: { [key: string]: any }) {
     delete userConfig.exportTrailingSlash
   }
 
-  if (typeof userConfig.experimental?.reactMode !== 'undefined') {
-    console.warn(
-      chalk.yellow.bold('Warning: ') +
-        `The experimental "reactMode" option has been replaced with "reactRoot". Please update your ${configFileName}.`
-    )
-    if (typeof userConfig.experimental?.reactRoot === 'undefined') {
-      userConfig.experimental.reactRoot = ['concurrent', 'blocking'].includes(
-        userConfig.experimental.reactMode
-      )
-    }
-    delete userConfig.experimental.reactMode
-  }
-
   const config = Object.keys(userConfig).reduce<{ [key: string]: any }>(
     (currentConfig, key) => {
       const value = userConfig[key]
@@ -233,13 +220,6 @@ function assignDefaults(userConfig: { [key: string]: any }) {
     }
   }
 
-  const hasReactRoot = process.env.__NEXT_REACT_ROOT
-  if (hasReactRoot) {
-    // users might not have the `experimental` key in their config
-    result.experimental = result.experimental || {}
-    result.experimental.reactRoot = true
-  }
-
   if (result?.images) {
     const images: ImageConfig = result.images
 

packages/next/server/next-server.ts

@@ -25,7 +25,6 @@ import type {
 import fs from 'fs'
 import { join, relative, resolve, sep } from 'path'
 import { IncomingMessage, ServerResponse } from 'http'
-import React from 'react'
 import { addRequestMeta, getRequestMeta } from './request-meta'
 
 import {
@@ -88,8 +87,8 @@ import {
 } from './body-streams'
 import { checkIsManualRevalidate } from './api-utils'
 import { isDynamicRoute } from '../shared/lib/router/utils'
+import { shouldUseReactRoot } from './utils'
 
-const shouldUseReactRoot = parseInt(React.version) >= 18
 if (shouldUseReactRoot) {
   ;(process.env as any).__NEXT_REACT_ROOT = 'true'
 }

packages/next/server/next.ts

@@ -3,7 +3,6 @@ import type { NodeRequestHandler } from './next-server'
 import type { UrlWithParsedQuery } from 'url'
 
 import './node-polyfill-fetch'
-import React from 'react'
 import { default as Server } from './next-server'
 import * as log from '../build/output/log'
 import loadConfig from './config'
@@ -13,6 +12,7 @@ import { PHASE_DEVELOPMENT_SERVER } from '../shared/lib/constants'
 import { PHASE_PRODUCTION_SERVER } from '../shared/lib/constants'
 import { IncomingMessage, ServerResponse } from 'http'
 import { NextUrlWithParsedQuery } from './request-meta'
+import { shouldUseReactRoot } from './utils'
 
 let ServerImpl: typeof Server
 
@@ -183,7 +183,6 @@ function createServer(options: NextServerOptions): NextServer {
     )
   }
 
-  const shouldUseReactRoot = parseInt(React.version) >= 18
   if (shouldUseReactRoot) {
     ;(process.env as any).__NEXT_REACT_ROOT = 'true'
   }

packages/next/server/render.tsx

@@ -83,16 +83,15 @@ import stripAnsi from 'next/dist/compiled/strip-ansi'
 import { urlQueryToSearchParams } from '../shared/lib/router/utils/querystring'
 import { postProcessHTML } from './post-process'
 import { htmlEscapeJsonString } from './htmlescape'
-import { stripInternalQueries } from './utils'
+import { shouldUseReactRoot, stripInternalQueries } from './utils'
 
 let tryGetPreviewData: typeof import('./api-utils/node').tryGetPreviewData
 let warn: typeof import('../build/output/log').warn
 
 const DOCTYPE = '<!DOCTYPE html>'
-const ReactDOMServer =
-  parseInt(React.version) >= 18
-    ? require('react-dom/server.browser')
-    : require('react-dom/server')
+const ReactDOMServer = shouldUseReactRoot
+  ? require('react-dom/server.browser')
+  : require('react-dom/server')
 
 if (process.env.NEXT_RUNTIME !== 'edge') {
   require('./node-polyfill-web-streams')
@@ -244,7 +243,6 @@ export type RenderOptsPartial = {
   customServer?: boolean
   crossOrigin?: string
   images: ImageConfigComplete
-  reactRoot: boolean
   largePageDataBytes?: number
 }
 

packages/next/server/utils.ts

@@ -1,4 +1,5 @@
 import type { NextParsedUrlQuery } from './request-meta'
+import React from 'react'
 import { BLOCKED_PAGES } from '../shared/lib/constants'
 
 export function isBlockedPage(pathname: string): boolean {
@@ -42,3 +43,6 @@ export function stripInternalQueries(query: NextParsedUrlQuery) {
 
   return query
 }
+
+// When react version is >= 18 opt-in using reactRoot
+export const shouldUseReactRoot = parseInt(React.version) >= 18

test/e2e/app-dir/app-rendering/next.config.js

@@ -2,7 +2,6 @@ module.exports = {
   experimental: {
     appDir: true,
     runtime: 'nodejs',
-    reactRoot: true,
     serverComponents: true,
   },
 }

test/e2e/app-dir/app/next.config.js

@@ -2,7 +2,6 @@ module.exports = {
   experimental: {
     appDir: true,
     runtime: 'nodejs',
-    reactRoot: true,
     serverComponents: true,
   },
 }

test/integration/react-18-invalid-config/index.test.js

@@ -48,15 +48,15 @@ function writeNextConfig(config, reactVersion = 17) {
 }
 
 describe('Invalid react 18 webpack config', () => {
-  it('should enable `experimental.reactRoot` when `experimental.runtime` is enabled', async () => {
+  it('should install react 18 when `experimental.runtime` is enabled', async () => {
     writeNextConfig({
       runtime: 'edge',
     })
     const { stderr } = await nextBuild(appDir, [], { stderr: true, nodeArgs })
     nextConfig.restore()
 
     expect(stderr).toContain(
-      '`experimental.runtime` requires `experimental.reactRoot` to be enabled along with React 18.'
+      '`experimental.runtime` requires React 18 to be installed.'
     )
   })
 })
@@ -68,20 +68,13 @@ describe('React 17 with React 18 config', () => {
       join(reactDomPackagePah, 'package.json'),
       JSON.stringify({ name: 'react-dom', version: '17.0.0' })
     )
-    writeNextConfig({ reactRoot: true })
+    writeNextConfig({})
   })
   afterAll(async () => {
     await fs.remove(reactDomPackagePah)
     nextConfig.restore()
   })
 
-  it('should warn user when not using react 18 and `experimental.reactRoot` is enabled', async () => {
-    const { stderr } = await nextBuild(appDir, [], { stderr: true, nodeArgs })
-    expect(stderr).toContain(
-      'You have to use React 18 to use `experimental.reactRoot`.'
-    )
-  })
-
   it('suspense is not allowed in blocking rendering mode', async () => {
     const { stderr, code } = await nextBuild(appDir, [], {
       stderr: true,

test/integration/react-18-invalid-config/next.config.js

@@ -1 +1 @@
-module.exports = { experimental: { reactRoot: true } }
+module.exports = {}

test/integration/react-18/app/next.config.js

@@ -1,7 +1,6 @@
 module.exports = {
   // reactStrictMode: true,
   experimental: {
-    reactRoot: true,
     // runtime: 'edge',
   },
   images: {

test/integration/react-streaming-and-server-components/unsupported-native-module/next.config.js

@@ -1,6 +1,5 @@
 module.exports = {
   experimental: {
-    reactRoot: true,
     serverComponents: true,
   },
 }

test/unit/parse-page-runtime.test.ts

@@ -5,7 +5,7 @@ const fixtureDir = join(__dirname, 'fixtures')
 
 function createNextConfig(runtime?: 'edge' | 'nodejs') {
   return {
-    experimental: { reactRoot: true, runtime },
+    experimental: { runtime },
   }
 }