Add failing end-to-end test for an action that returns client components

This playwright test is using the Flight Fixture to demonstrate the
Flight Reply equivalent of the scenario that was fixed in facebook#30528 for the
Flight Client.

It's basically an advanced case of what was outlined in facebook#28564,
returning a client component from a server action that is used in
`useActionState`. In addition, the client component uses another element
twice, which leads to the element's props being deduped. Resolving those
references needs to be handled specifically, both in the Flight Client
(done in facebook#30528), as well as in the temporary references of the Flight
Reply Client (and possibly Flight Reply Server?).

The test should probably be converted into a unit test, e.g. in
`packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMBrowser-test.js`
or
`packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMReply-test.js`.

fixtures/flight/__tests__/__e2e__/action.test.js

@@ -0,0 +1,35 @@
+// @ts-check
+
+import {test, expect} from '@playwright/test';
+
+test('action returning client component with deduped references', async ({
+  page,
+}) => {
+  const pageErrors = [];
+
+  page.on('pageerror', error => {
+    pageErrors.push(error.stack);
+  });
+
+  await page.goto('/');
+
+  const button = await page.getByRole('button', {
+    name: 'Return element from action',
+  });
+
+  await button.click();
+
+  await expect(
+    page.getByTestId('temporary-references-action-result')
+  ).toHaveText('Hello');
+
+  // Click the button one more time to send the previous result (i.e. the
+  // returned element) back to the server.
+  await button.click();
+
+  await expect(pageErrors).toEqual([]);
+
+  await expect(
+    page.getByTestId('temporary-references-action-result')
+  ).toHaveText('HelloHello');
+});

fixtures/flight/server/region.js

@@ -50,7 +50,7 @@ const {readFile} = require('fs').promises;
 
 const React = require('react');
 
-async function renderApp(res, returnValue, formState) {
+async function renderApp(res, returnValue, formState, temporaryReferences) {
   const {renderToPipeableStream} = await import(
     'react-server-dom-webpack/server'
   );
@@ -101,7 +101,9 @@ async function renderApp(res, returnValue, formState) {
   );
   // For client-invoked server actions we refresh the tree and return a return value.
   const payload = {root, returnValue, formState};
-  const {pipe} = renderToPipeableStream(payload, moduleMap);
+  const {pipe} = renderToPipeableStream(payload, moduleMap, {
+    temporaryReferences,
+  });
   pipe(res);
 }
 
@@ -110,8 +112,13 @@ app.get('/', async function (req, res) {
 });
 
 app.post('/', bodyParser.text(), async function (req, res) {
-  const {decodeReply, decodeReplyFromBusboy, decodeAction, decodeFormState} =
-    await import('react-server-dom-webpack/server');
+  const {
+    decodeReply,
+    decodeReplyFromBusboy,
+    decodeAction,
+    decodeFormState,
+    createTemporaryReferenceSet,
+  } = await import('react-server-dom-webpack/server');
   const serverReference = req.get('rsc-action');
   if (serverReference) {
     // This is the client-side case
@@ -124,15 +131,17 @@ app.post('/', bodyParser.text(), async function (req, res) {
       throw new Error('Invalid action');
     }
 
+    const temporaryReferences = createTemporaryReferenceSet();
+
     let args;
     if (req.is('multipart/form-data')) {
       // Use busboy to streamingly parse the reply from form-data.
       const bb = busboy({headers: req.headers});
-      const reply = decodeReplyFromBusboy(bb);
+      const reply = decodeReplyFromBusboy(bb, {}, {temporaryReferences});
       req.pipe(bb);
       args = await reply;
     } else {
-      args = await decodeReply(req.body);
+      args = await decodeReply(req.body, {}, {temporaryReferences});
     }
     const result = action.apply(null, args);
     try {
@@ -142,7 +151,7 @@ app.post('/', bodyParser.text(), async function (req, res) {
       // We handle the error on the client
     }
     // Refresh the client and return the value
-    renderApp(res, result, null);
+    renderApp(res, result, null, temporaryReferences);
   } else {
     // This is the progressive enhancement case
     const UndiciRequest = require('undici').Request;

fixtures/flight/src/App.js

@@ -12,10 +12,11 @@ import Button from './Button.js';
 import Form from './Form.js';
 import {Dynamic} from './Dynamic.js';
 import {Client} from './Client.js';
+import {TemporaryReferences} from './TemporaryReferences.js';
 
 import {Note} from './cjs/Note.js';
 
-import {like, greet, increment} from './actions.js';
+import {like, greet, increment, returnElement} from './actions.js';
 
 import {getServerState} from './ServerState.js';
 
@@ -61,6 +62,7 @@ export default async function App() {
           </div>
           <Client />
           <Note />
+          <TemporaryReferences action={returnElement} />
         </Container>
       </body>
     </html>

fixtures/flight/src/Deduped.js

@@ -0,0 +1,8 @@
+'use client';
+
+import * as React from 'react';
+
+export default function Deduped({children, thing}) {
+  console.log({thing});
+  return <div>{children}</div>;
+}

fixtures/flight/src/TemporaryReferences.js

@@ -0,0 +1,14 @@
+'use client';
+
+import * as React from 'react';
+
+export function TemporaryReferences({action}) {
+  const [result, formAction] = React.useActionState(action, null);
+
+  return (
+    <form action={formAction}>
+      <button>Return element from action</button>
+      <div data-testid="temporary-references-action-result">{result}</div>
+    </form>
+  );
+}

fixtures/flight/src/actions.js

@@ -1,6 +1,8 @@
 'use server';
 
+import * as React from 'react';
 import {setServerState} from './ServerState.js';
+import Deduped from './Deduped.js';
 
 export async function like() {
   setServerState('Liked!');
@@ -22,3 +24,14 @@ export async function greet(formData) {
 export async function increment(n) {
   return n + 1;
 }
+
+export async function returnElement(prevElement) {
+  const text = <div>Hello</div>;
+
+  return (
+    <Deduped thing={text}>
+      {prevElement}
+      {text}
+    </Deduped>
+  );
+}

fixtures/flight/src/index.js

@@ -1,22 +1,31 @@
 import * as React from 'react';
 import {use, Suspense, useState, startTransition} from 'react';
 import ReactDOM from 'react-dom/client';
-import {createFromFetch, encodeReply} from 'react-server-dom-webpack/client';
+import {
+  createFromFetch,
+  createTemporaryReferenceSet,
+  encodeReply,
+} from 'react-server-dom-webpack/client';
 
 // TODO: This should be a dependency of the App but we haven't implemented CSS in Node yet.
 import './style.css';
 
 let updateRoot;
+const temporaryReferences = createTemporaryReferenceSet();
+
 async function callServer(id, args) {
   const response = fetch('/', {
     method: 'POST',
     headers: {
       Accept: 'text/x-component',
       'rsc-action': id,
     },
-    body: await encodeReply(args),
+    body: await encodeReply(args, {temporaryReferences}),
+  });
+  const {returnValue, root} = await createFromFetch(response, {
+    callServer,
+    temporaryReferences,
   });
-  const {returnValue, root} = await createFromFetch(response, {callServer});
   // Refresh the tree with the new RSC payload.
   startTransition(() => {
     updateRoot(root);
@@ -39,6 +48,7 @@ async function hydrateApp() {
     }),
     {
       callServer,
+      temporaryReferences,
       findSourceMapURL(fileName) {
         return (
           document.location.origin +