fix: Make router ready in case of custom _app getInitialProps

packages/next/server/render.tsx

@@ -571,7 +571,11 @@ export async function renderToHTML(
   }
 
   // url will always be set
-  const routerIsReady = !!(getServerSideProps || hasPageGetInitialProps)
+  const routerIsReady = !!(
+    getServerSideProps ||
+    hasPageGetInitialProps ||
+    !defaultAppGetInitialProps
+  )
   const router = new ServerRouter(
     pathname,
     query,

packages/next/shared/lib/router/router.ts

@@ -627,6 +627,7 @@ export default class Router implements BaseRouter {
     this.isReady = !!(
       self.__NEXT_DATA__.gssp ||
       self.__NEXT_DATA__.gip ||
+      self.__NEXT_DATA__.appGip ||
       (!autoExportDynamic &&
         !self.location.search &&
         !process.env.__NEXT_HAS_REWRITES)

test/integration/router-is-ready-app-gip/pages/_app.js

@@ -0,0 +1,15 @@
+export default function TestApp({ Component, pageProps }) {
+  return <Component {...pageProps} />
+}
+
+TestApp.getInitialProps = async ({ Component, ctx }) => {
+  let pageProps
+
+  if (Component.getInitialProps) {
+    pageProps = await Component.getInitialProps(ctx)
+  }
+
+  return {
+    pageProps,
+  }
+}

test/integration/router-is-ready-app-gip/pages/appGip.js

@@ -0,0 +1,23 @@
+import { useRouter } from 'next/router'
+import { useLayoutEffect } from 'react'
+
+export default function Page(props) {
+  const router = useRouter()
+
+  if (typeof window !== 'undefined') {
+    // eslint-disable-next-line react-hooks/rules-of-hooks
+    useLayoutEffect(() => {
+      if (!window.isReadyValues) {
+        window.isReadyValues = []
+      }
+      window.isReadyValues.push(router.isReady)
+    }, [router])
+  }
+
+  return (
+    <>
+      <p id="appGip">appGip page</p>
+      <p id="props">{JSON.stringify(props)}</p>
+    </>
+  )
+}

test/integration/router-is-ready-app-gip/pages/invalid.js

@@ -0,0 +1,15 @@
+import { useRouter } from 'next/router'
+
+export default function Page(props) {
+  // eslint-disable-next-line
+  const router = useRouter()
+
+  // console.log(router.isReady)
+
+  return (
+    <>
+      <p id="invalid">invalid page</p>
+      <p id="props">{JSON.stringify(props)}</p>
+    </>
+  )
+}

test/integration/router-is-ready-app-gip/test/index.test.js

@@ -0,0 +1,58 @@
+/* eslint-env jest */
+
+import { join } from 'path'
+import webdriver from 'next-webdriver'
+import {
+  findPort,
+  launchApp,
+  killApp,
+  nextStart,
+  nextBuild,
+  File,
+} from 'next-test-utils'
+
+jest.setTimeout(1000 * 60 * 1)
+
+let app
+let appPort
+const appDir = join(__dirname, '../')
+const invalidPage = new File(join(appDir, 'pages/invalid.js'))
+
+function runTests(isDev) {
+  it('isReady should be true immediately for pages with getInitialProps in _app', async () => {
+    const browser = await webdriver(appPort, '/appGip')
+    expect(await browser.eval('window.isReadyValues')).toEqual([true])
+  })
+
+  it('isReady should be true immediately for pages with getInitialProps in _app, with query', async () => {
+    const browser = await webdriver(appPort, '/appGip?hello=world')
+    expect(await browser.eval('window.isReadyValues')).toEqual([true])
+  })
+}
+
+describe('router.isReady with appGip', () => {
+  describe('dev mode', () => {
+    beforeAll(async () => {
+      appPort = await findPort()
+      app = await launchApp(appDir, appPort)
+    })
+    afterAll(async () => {
+      await killApp(app)
+      invalidPage.restore()
+    })
+
+    runTests(true)
+  })
+
+  describe('production mode', () => {
+    beforeAll(async () => {
+      await nextBuild(appDir)
+
+      appPort = await findPort()
+      app = await nextStart(appDir, appPort)
+    })
+    afterAll(() => killApp(app))
+
+    runTests()
+  })
+})