[Flight Parcel] Implement prepareDestinationForModule (#31799)

Followup to #31725

This implements `prepareDestinationForModule` in the Parcel Flight
client. On the Parcel side, the `<Resources>` component now only inserts
`<link>` elements for stylesheets (along with a bootstrap script when
needed), and React is responsible for inserting scripts. This ensures
that components that are conditionally dynamic imported during render
are also preloaded.

CSS must be added to the RSC tree using `<Resources>` to avoid FOUC.
This must be manually rendered in both the top-level page, and in any
component that is dynamic imported. It would be nice if there was a way
for React to automatically insert CSS as well, but unfortunately
`prepareDestinationForModule` only knows about client components and not
CSS for server components. Perhaps there could be a way we could
annotate components at code splitting boundaries with the resources they
need? More thoughts in this thread:
#31725 (comment)

fixtures/flight-parcel/package.json

@@ -18,7 +18,7 @@
   "scripts": {
     "predev": "cp -r ../../build/oss-experimental/* ./node_modules/",
     "prebuild": "cp -r ../../build/oss-experimental/* ./node_modules/",
-    "dev": "concurrently \"npm run dev:watch\" \"npm run dev:start\"",
+    "dev": "concurrently \"npm run dev:watch\" \"sleep 2 && npm run dev:start\"",
     "dev:watch": "NODE_ENV=development parcel watch",
     "dev:start": "NODE_ENV=development node dist/server.js",
     "build": "parcel build",
@@ -28,16 +28,16 @@
     "packageExports": true
   },
   "dependencies": {
-    "@parcel/config-default": "2.0.0-dev.1789",
-    "@parcel/runtime-rsc": "2.13.3-dev.3412",
+    "@parcel/config-default": "2.0.0-dev.1795",
+    "@parcel/runtime-rsc": "2.13.3-dev.3418",
     "@types/parcel-env": "^0.0.6",
     "@types/express": "*",
     "@types/node": "^22.10.1",
     "@types/react": "^19",
     "@types/react-dom": "^19",
     "concurrently": "^7.3.0",
     "express": "^4.18.2",
-    "parcel": "2.0.0-dev.1787",
+    "parcel": "2.0.0-dev.1793",
     "process": "^0.11.10",
     "react": "experimental",
     "react-dom": "experimental",

fixtures/flight-parcel/src/server.tsx

@@ -15,8 +15,8 @@ import {injectRSCPayload} from 'rsc-html-stream/server';
 
 // Client dependencies, used for SSR.
 // These must run in the same environment as client components (e.g. same instance of React).
-import {createFromReadableStream} from 'react-server-dom-parcel/client' with {env: 'react-client'};
-import {renderToReadableStream as renderHTMLToReadableStream} from 'react-dom/server' with {env: 'react-client'};
+import {createFromReadableStream} from 'react-server-dom-parcel/client.edge' with {env: 'react-client'};
+import {renderToReadableStream as renderHTMLToReadableStream} from 'react-dom/server.edge' with {env: 'react-client'};
 import ReactClient, {ReactElement} from 'react' with {env: 'react-client'};
 
 // Page components. These must have "use server-entry" so they are treated as code splitting entry points.
@@ -66,8 +66,9 @@ async function render(
 
     // Use client react to render the RSC payload to HTML.
     let [s1, s2] = stream.tee();
-    let data = createFromReadableStream<ReactElement>(s1);
+    let data: Promise<ReactElement>;
     function Content() {
+      data ??= createFromReadableStream<ReactElement>(s1);
       return ReactClient.use(data);
     }
 

fixtures/flight-parcel/types.d.ts

@@ -2,13 +2,16 @@
 
 declare module 'react-server-dom-parcel/client' {
   export function createFromFetch<T>(res: Promise<Response>): Promise<T>;
-  export function createFromReadableStream<T>(stream: ReadableStream): Promise<T>;
   export function encodeReply(value: any): Promise<string | URLSearchParams | FormData>;
 
   type CallServerCallback = <T>(id: string, args: any[]) => Promise<T>;
   export function setServerCallback(cb: CallServerCallback): void;
 }
 
+declare module 'react-server-dom-parcel/client.edge' {
+  export function createFromReadableStream<T>(stream: ReadableStream): Promise<T>;
+}
+
 declare module 'react-server-dom-parcel/server.edge' {
   export function renderToReadableStream(value: any): ReadableStream;
   export function loadServerAction(id: string): Promise<(...args: any[]) => any>;
@@ -17,5 +20,10 @@ declare module 'react-server-dom-parcel/server.edge' {
 }
 
 declare module '@parcel/runtime-rsc' {
+  import {JSX} from 'react';
   export function Resources(): JSX.Element;
 }
+
+declare module 'react-dom/server.edge' {
+  export * from 'react-dom/server';
+}

packages/react-client/src/forks/ReactFlightClientConfig.dom-browser-parcel.js

@@ -13,5 +13,6 @@ export const rendererPackageName = 'react-server-dom-parcel';
 export * from 'react-client/src/ReactFlightClientStreamConfigWeb';
 export * from 'react-client/src/ReactClientConsoleConfigBrowser';
 export * from 'react-server-dom-parcel/src/client/ReactFlightClientConfigBundlerParcel';
+export * from 'react-server-dom-parcel/src/client/ReactFlightClientConfigTargetParcelBrowser';
 export * from 'react-dom-bindings/src/shared/ReactFlightClientConfigDOM';
 export const usedWithSSR = false;

packages/react-client/src/forks/ReactFlightClientConfig.dom-edge-parcel.js

@@ -13,5 +13,6 @@ export const rendererPackageName = 'react-server-dom-parcel';
 export * from 'react-client/src/ReactFlightClientStreamConfigWeb';
 export * from 'react-client/src/ReactClientConsoleConfigServer';
 export * from 'react-server-dom-parcel/src/client/ReactFlightClientConfigBundlerParcel';
+export * from 'react-server-dom-parcel/src/client/ReactFlightClientConfigTargetParcelServer';
 export * from 'react-dom-bindings/src/shared/ReactFlightClientConfigDOM';
 export const usedWithSSR = true;

packages/react-client/src/forks/ReactFlightClientConfig.dom-node-parcel.js

@@ -13,5 +13,6 @@ export const rendererPackageName = 'react-server-dom-parcel';
 export * from 'react-client/src/ReactFlightClientStreamConfigNode';
 export * from 'react-client/src/ReactClientConsoleConfigServer';
 export * from 'react-server-dom-parcel/src/client/ReactFlightClientConfigBundlerParcel';
+export * from 'react-server-dom-parcel/src/client/ReactFlightClientConfigTargetParcelServer';
 export * from 'react-dom-bindings/src/shared/ReactFlightClientConfigDOM';
 export const usedWithSSR = true;

packages/react-server-dom-parcel/src/client/ReactFlightClientConfigBundlerParcel.js

@@ -12,6 +12,7 @@ import type {Thenable} from 'shared/ReactTypes';
 import type {ImportMetadata} from '../shared/ReactFlightImportMetadata';
 
 import {ID, NAME, BUNDLES} from '../shared/ReactFlightImportMetadata';
+import {prepareDestinationWithChunks} from 'react-client/src/ReactFlightClientConfig';
 
 export type ServerManifest = {
   [string]: Array<string>,
@@ -24,33 +25,22 @@ export type ServerReferenceId = string;
 export opaque type ClientReferenceMetadata = ImportMetadata;
 
 // eslint-disable-next-line no-unused-vars
-export opaque type ClientReference<T> = {
-  // Module id.
-  id: string,
-  // Export name.
-  name: string,
-  // List of bundle URLs, relative to the distDir.
-  bundles: Array<string>,
-};
+export opaque type ClientReference<T> = ImportMetadata;
 
 export function prepareDestinationForModule(
   moduleLoading: ModuleLoading,
   nonce: ?string,
   metadata: ClientReferenceMetadata,
 ) {
-  return;
+  prepareDestinationWithChunks(moduleLoading, metadata[BUNDLES], nonce);
 }
 
 export function resolveClientReference<T>(
   bundlerConfig: null,
   metadata: ClientReferenceMetadata,
 ): ClientReference<T> {
   // Reference is already resolved during the build.
-  return {
-    id: metadata[ID],
-    name: metadata[NAME],
-    bundles: metadata[BUNDLES],
-  };
+  return metadata;
 }
 
 export function resolveServerReference<T>(
@@ -64,20 +54,19 @@ export function resolveServerReference<T>(
   if (!bundles) {
     throw new Error('Invalid server action: ' + ref);
   }
-  return {
-    id,
-    name,
-    bundles,
-  };
+  return [id, name, bundles];
 }
 
 export function preloadModule<T>(
   metadata: ClientReference<T>,
 ): null | Thenable<any> {
-  return Promise.all(metadata.bundles.map(url => parcelRequire.load(url)));
+  if (metadata[BUNDLES].length === 0) {
+    return null;
+  }
+  return Promise.all(metadata[BUNDLES].map(url => parcelRequire.load(url)));
 }
 
 export function requireModule<T>(metadata: ClientReference<T>): T {
-  const moduleExports = parcelRequire(metadata.id);
-  return moduleExports[metadata.name];
+  const moduleExports = parcelRequire(metadata[ID]);
+  return moduleExports[metadata[NAME]];
 }

packages/react-server-dom-parcel/src/client/ReactFlightClientConfigTargetParcelBrowser.js

@@ -0,0 +1,18 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import type {ModuleLoading} from './ReactFlightClientConfigBundlerParcel';
+
+export function prepareDestinationWithChunks(
+  moduleLoading: ModuleLoading,
+  bundles: Array<string>,
+  nonce: ?string,
+) {
+  // In the browser we don't need to prepare our destination since the browser is the Destination
+}

packages/react-server-dom-parcel/src/client/ReactFlightClientConfigTargetParcelServer.js

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import type {ModuleLoading} from './ReactFlightClientConfigBundlerParcel';
+import {preinitModuleForSSR} from 'react-client/src/ReactFlightClientConfig';
+
+export function prepareDestinationWithChunks(
+  moduleLoading: ModuleLoading,
+  bundles: Array<string>,
+  nonce: ?string,
+) {
+  for (let i = 0; i < bundles.length; i++) {
+    preinitModuleForSSR(parcelRequire.meta.publicUrl + bundles[i], nonce);
+  }
+}

scripts/flow/environment.js

@@ -106,6 +106,9 @@ declare const __turbopack_require__: ((id: string) => any) & {
 declare var parcelRequire: {
   (id: string): any,
   load: (url: string) => Promise<mixed>,
+  meta: {
+    publicUrl: string,
+  },
 };
 
 declare module 'fs/promises' {