Fix pageProps is missing when route changes (#38178)

## Bug

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


Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>

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

@@ -1857,8 +1857,9 @@ export default class Router implements BaseRouter {
         ).catch(() => {})
       }
 
+      let flightInfo
       if (routeInfo.__N_RSC) {
-        props.pageProps = Object.assign(props.pageProps, {
+        flightInfo = {
           __flight__: useStreamedFlightData
             ? (
                 await this._getData(() =>
@@ -1877,9 +1878,10 @@ export default class Router implements BaseRouter {
                 )
               ).data
             : props.__flight__,
-        })
+        }
       }
 
+      props.pageProps = Object.assign({}, props.pageProps, flightInfo)
       routeInfo.props = props
       routeInfo.route = route
       routeInfo.query = query

test/e2e/middleware-general/app/pages/_app.js

@@ -0,0 +1,8 @@
+export default function App({ Component, pageProps }) {
+  if (!pageProps || typeof pageProps !== 'object') {
+    throw new Error(
+      `Invariant: received invalid pageProps in _app, received ${pageProps}`
+    )
+  }
+  return <Component {...pageProps} />
+}

test/e2e/middleware-redirects/app/next.config.js

@@ -3,4 +3,13 @@ module.exports = {
     locales: ['en', 'fr', 'nl', 'es'],
     defaultLocale: 'en',
   },
+  redirects() {
+    return [
+      {
+        source: '/to-new',
+        destination: '/dynamic/new',
+        permanent: false,
+      },
+    ]
+  },
 }

test/e2e/middleware-redirects/app/pages/_app.js

@@ -0,0 +1,8 @@
+export default function App({ Component, pageProps }) {
+  if (!pageProps || typeof pageProps !== 'object') {
+    throw new Error(
+      `Invariant: received invalid pageProps in _app, received ${pageProps}`
+    )
+  }
+  return <Component {...pageProps} />
+}

test/e2e/middleware-redirects/app/pages/dynamic/[slug].js

@@ -0,0 +1,13 @@
+export default function Account() {
+  return (
+    <p id="dynamic" className="title">
+      Welcome to a /dynamic/[slug]
+    </p>
+  )
+}
+
+export function getServerSideProps() {
+  return {
+    props: {},
+  }
+}

test/e2e/middleware-redirects/test/index.test.ts

@@ -26,6 +26,14 @@ describe('Middleware Redirect', () => {
   testsWithLocale('/fr')
 
   function tests() {
+    it('should redirect correctly with redirect in next.config.js', async () => {
+      const browser = await webdriver(next.url, '/')
+      await browser.eval('window.beforeNav = 1')
+      await browser.eval('window.next.router.push("/to-new")')
+      await browser.waitForElementByCss('#dynamic')
+      expect(await browser.eval('window.beforeNav')).toBe(1)
+    })
+
     it('does not include the locale in redirects by default', async () => {
       const res = await fetchViaHTTP(next.url, `/old-home`, undefined, {
         redirect: 'manual',

test/e2e/middleware-rewrites/app/pages/_app.js

@@ -0,0 +1,8 @@
+export default function App({ Component, pageProps }) {
+  if (!pageProps || typeof pageProps !== 'object') {
+    throw new Error(
+      `Invariant: received invalid pageProps in _app, received ${pageProps}`
+    )
+  }
+  return <Component {...pageProps} />
+}

test/integration/dynamic-routing/pages/_app.js

@@ -0,0 +1,8 @@
+export default function App({ Component, pageProps }) {
+  if (!pageProps || typeof pageProps !== 'object') {
+    throw new Error(
+      `Invariant: received invalid pageProps in _app, received ${pageProps}`
+    )
+  }
+  return <Component {...pageProps} />
+}