Support new hydrate API in latest react 18 alpha release (#26664)

* fix: react 18 new hydration API

* support react 18

* compat latest react only, fix resolved version

* fix tests

* Some changes based on reactwg/react-18#5

* fix test

Co-authored-by: Tim Neutkens <timneutkens@me.com>
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

Author: 3 people

package.json

@@ -115,7 +115,9 @@
     "pretty-bytes": "5.3.0",
     "pretty-ms": "7.0.0",
     "react": "17.0.2",
+    "react-18": "npm:react@next",
     "react-dom": "17.0.2",
+    "react-dom-18": "npm:react-dom@next",
     "react-ssr-prepass": "1.0.8",
     "release": "6.3.0",
     "request-promise-core": "1.1.2",

packages/next/client/index.tsx

@@ -489,7 +489,8 @@ export function renderError(renderErrorProps: RenderErrorProps): Promise<any> {
 }
 
 let reactRoot: any = null
-let shouldHydrate: boolean = typeof ReactDOM.hydrate === 'function'
+// On initial render a hydrate should always happen
+let shouldHydrate: boolean = true
 
 function renderReactElement(
   domEl: HTMLElement,
@@ -503,12 +504,13 @@ function renderReactElement(
   const reactEl = fn(shouldHydrate ? markHydrateComplete : markRenderComplete)
   if (process.env.__NEXT_REACT_ROOT) {
     if (!reactRoot) {
-      reactRoot = (ReactDOM as any).createRoot(domEl, {
-        hydrate: shouldHydrate,
-      })
+      // Unlike with createRoot, you don't need a separate root.render() call here
+      reactRoot = (ReactDOM as any).hydrateRoot(domEl, reactEl)
+      // TODO: Remove shouldHydrate variable when React 18 is stable as it can depend on `reactRoot` existing
+      shouldHydrate = false
+    } else {
+      reactRoot.render(reactEl)
     }
-    reactRoot.render(reactEl)
-    shouldHydrate = false
   } else {
     // The check for `.hydrate` is there to support React alternatives like preact
     if (shouldHydrate) {

test/integration/build-output/test/index.test.js

@@ -129,7 +129,7 @@ describe('Build Output', () => {
           expect(parseFloat(err404Size)).toBeCloseTo(gz ? 3.17 : 8.51, 1)
           expect(err404Size.endsWith('kB')).toBe(true)
 
-          expect(parseFloat(err404FirstLoad)).toBeCloseTo(gz ? 66.9 : 205, 1)
+          expect(parseFloat(err404FirstLoad)).toBeCloseTo(gz ? 66.9 : 204, 1)
           expect(err404FirstLoad.endsWith('kB')).toBe(true)
 
           expect(parseFloat(sharedByAll)).toBeCloseTo(gz ? 63.7 : 196, 1)

test/integration/fallback-modules/test/index.test.js

@@ -49,7 +49,7 @@ describe('Build Output', () => {
       expect(indexSize.endsWith('kB')).toBe(true)
 
       expect(parseFloat(indexFirstLoad)).toBeLessThanOrEqual(
-        process.env.NEXT_PRIVATE_TEST_WEBPACK4_MODE ? 68 : 67.9
+        process.env.NEXT_PRIVATE_TEST_WEBPACK4_MODE ? 68.1 : 67.9
       )
       expect(parseFloat(indexFirstLoad)).toBeGreaterThanOrEqual(60)
       expect(indexFirstLoad.endsWith('kB')).toBe(true)

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

@@ -0,0 +1,14 @@
+module.exports = {
+  webpack(config) {
+    const { alias } = config.resolve
+    // FIXME: resolving react/jsx-runtime https://github.com/facebook/react/issues/20235
+    alias['react/jsx-dev-runtime'] = require.resolve('react/jsx-dev-runtime.js')
+    alias['react/jsx-runtime'] = require.resolve('react/jsx-runtime.js')
+
+    // Use react 18
+    alias['react'] = require.resolve('react-18')
+    alias['react-dom'] = require.resolve('react-dom-18')
+
+    return config
+  },
+}

test/integration/react-18/prerelease/node_modules/react-dom/index.js

@@ -1,5 +1,6 @@
 {
   "dependencies": {
+    "react": "*",
     "react-dom": "*"
   }
 }

test/integration/react-18/prerelease/node_modules/react-dom/package.json

@@ -1,3 +1,6 @@
 export default function Index() {
+  if (typeof window !== 'undefined') {
+    window.didHydrate = true
+  }
   return <p>Hello</p>
 }

test/integration/react-18/prerelease/package.json

@@ -1,7 +1,16 @@
 /* eslint-env jest */
 
-import { findPort, killApp, launchApp, runNextCommand } from 'next-test-utils'
 import { join } from 'path'
+import fs from 'fs-extra'
+import webdriver from 'next-webdriver'
+import {
+  findPort,
+  killApp,
+  launchApp,
+  runNextCommand,
+  nextBuild,
+  nextStart,
+} from 'next-test-utils'
 
 jest.setTimeout(1000 * 60 * 5)
 
@@ -67,4 +76,21 @@ describe('React 18 Support', () => {
       expect(output).toMatch(UNSUPPORTED_PRERELEASE)
     })
   })
+
+  describe('hydration', () => {
+    const appDir = join(__dirname, '../prerelease')
+    let app
+    let appPort
+    beforeAll(async () => {
+      await fs.remove(join(appDir, '.next'))
+      await nextBuild(appDir, [dirPrerelease])
+      appPort = await findPort()
+      app = await nextStart(appDir, appPort)
+    })
+    afterAll(async () => await killApp(app))
+    it('hydrates correctly for normal page', async () => {
+      const browser = await webdriver(appPort, '/')
+      expect(await browser.eval('window.didHydrate')).toBe(true)
+    })
+  })
 })