[Flight] Standardize ClientReferenceMetadata tuple type

Previously, `ClientReferenceMetadata` was declared as an opaque type in
the Flight server config (`ReactFlightServerConfigBundlerCustom.js`),
with each bundler defining its own tuple shape. Webpack, Turbopack, and
Unbundled used `[id, chunks, name, async?]` while Parcel used `[id,
name, bundles, importMap?]`, placing the chunks array at different
indices. This made it impossible for `ReactFlightServer.js` to access
the chunks array without bundler-specific accessor functions.

This change standardizes all bundlers on a common shape where `id` is at
index 0, `name` is at index 1, and `chunks` is at index 2. A bundler-
specific extra like the async flag or Parcel's `importMap` can go at
index 3. The `ClientReferenceMetadata` type is changed from an opaque
type to a concrete union type, so `ReactFlightServer.js` can now
directly access `metadata[2]` to get the chunks array with proper Flow
typing.

This only affects the internal wire format tuple, not the
`ClientManifest` that frameworks pass into Flight. The manifest entry
shape (`{id, chunks, name, async?}`) remains unchanged.

The motivation is to enable deduplicating individual chunk URLs across
client references in the RSC stream. With a known, non-opaque type,
`emitImportChunk` can extract, deduplicate, and replace chunk entries
without needing bundler-specific callback functions or accessor methods.

Author: unstubbable

packages/react-noop-renderer/src/ReactNoopFlightClient.js

@@ -37,10 +37,14 @@ const {createResponse, createStreamState, processBinaryChunk, getRoot, close} =
     readFinalStringChunk(decoder: TextDecoder, buffer: Uint8Array): string {
       return decoder.decode(buffer);
     },
-    resolveClientReference(bundlerConfig: null, idx: string) {
-      return idx;
+    resolveClientReference(bundlerConfig: null, metadata: [string, string]) {
+      return metadata[0];
     },
-    prepareDestinationForModule(moduleLoading: null, metadata: string) {},
+    prepareDestinationForModule(
+      moduleLoading: null,
+      nonce: ?string,
+      metadata: [string, string],
+    ) {},
     preloadModule(idx: string) {},
     requireModule(idx: string) {
       return readModule(idx);

packages/react-noop-renderer/src/ReactNoopFlightServer.js

@@ -63,7 +63,7 @@ const ReactNoopFlightServer = ReactFlightServer({
     config: void,
     reference: {$$typeof: symbol, value: any},
   ) {
-    return saveModule(reference.value);
+    return [saveModule(reference.value), '*'];
   },
 });
 

packages/react-server-dom-parcel/src/shared/ReactFlightImportMetadata.js

@@ -15,7 +15,7 @@ export type ImportMetadata = [
   id: string,
   name: string,
   bundles: Array<string>,
-  importMap?: {[string]: string},
+  importMap?: {[string]: string} | void,
   /* eslint-enable */
 ];
 

packages/react-server-dom-turbopack/src/client/ReactFlightClientConfigBundlerTurbopack.js

@@ -95,12 +95,12 @@ export function resolveClientReference<T>(
     if (isAsyncImport(metadata)) {
       return [
         resolvedModuleData.id,
-        resolvedModuleData.chunks,
         name,
+        resolvedModuleData.chunks,
         1 /* async */,
       ];
     } else {
-      return [resolvedModuleData.id, resolvedModuleData.chunks, name];
+      return [resolvedModuleData.id, name, resolvedModuleData.chunks];
     }
   }
   return metadata;
@@ -142,12 +142,12 @@ export function resolveServerReference<T>(
     // manifest.
     return [
       resolvedModuleData.id,
-      resolvedModuleData.chunks,
       name,
+      resolvedModuleData.chunks,
       1 /* async */,
     ];
   }
-  return [resolvedModuleData.id, resolvedModuleData.chunks, name];
+  return [resolvedModuleData.id, name, resolvedModuleData.chunks];
 }
 
 function requireAsyncModule(id: string): null | Thenable<any> {

packages/react-server-dom-turbopack/src/server/ReactFlightServerConfigTurbopackBundler.js

@@ -80,9 +80,9 @@ export function resolveClientReferenceMetadata<T>(
     );
   }
   if (resolvedModuleData.async === true || clientReference.$$async === true) {
-    return [resolvedModuleData.id, resolvedModuleData.chunks, name, 1];
+    return [resolvedModuleData.id, name, resolvedModuleData.chunks, 1];
   } else {
-    return [resolvedModuleData.id, resolvedModuleData.chunks, name];
+    return [resolvedModuleData.id, name, resolvedModuleData.chunks];
   }
 }
 

packages/react-server-dom-turbopack/src/shared/ReactFlightImportMetadata.js

@@ -20,15 +20,15 @@ export type ImportManifestEntry = {
 export type ImportMetadata =
   | [
       /* id */ string,
-      /* chunk filenames */ Array<string>,
       /* name */ string,
+      /* chunk filenames */ Array<string>,
       /* async */ 1,
     ]
-  | [/* id */ string, /* chunk filenames */ Array<string>, /* name */ string];
+  | [/* id */ string, /* name */ string, /* chunk filenames */ Array<string>];
 
 export const ID = 0;
-export const CHUNKS = 1;
-export const NAME = 2;
+export const NAME = 1;
+export const CHUNKS = 2;
 // export const ASYNC = 3;
 
 // This logic is correct because currently only include the 4th tuple member

packages/react-server-dom-unbundled/src/server/ReactFlightServerConfigUnbundledBundler.js

@@ -80,9 +80,9 @@ export function resolveClientReferenceMetadata<T>(
     );
   }
   if (resolvedModuleData.async === true || clientReference.$$async === true) {
-    return [resolvedModuleData.id, resolvedModuleData.chunks, name, 1];
+    return [resolvedModuleData.id, name, resolvedModuleData.chunks, 1];
   } else {
-    return [resolvedModuleData.id, resolvedModuleData.chunks, name];
+    return [resolvedModuleData.id, name, resolvedModuleData.chunks];
   }
 }
 

packages/react-server-dom-unbundled/src/shared/ReactFlightImportMetadata.js

@@ -16,23 +16,23 @@ export type ImportManifestEntry = {
 };
 
 // This is the parsed shape of the wire format which is why it is
-// condensed to only the essentialy information
+// condensed to only the essentially information
 export type ImportMetadata =
   | [
       /* id */ string,
-      /* chunks id/filename pairs, double indexed */ Array<string>,
       /* name */ string,
+      /* chunks id/filename pairs, double indexed */ Array<string>,
       /* async */ 1,
     ]
   | [
       /* id */ string,
-      /* chunks id/filename pairs, double indexed */ Array<string>,
       /* name */ string,
+      /* chunks id/filename pairs, double indexed */ Array<string>,
     ];
 
 export const ID = 0;
-export const CHUNKS = 1;
-export const NAME = 2;
+export const NAME = 1;
+export const CHUNKS = 2;
 // export const ASYNC = 3;
 
 // This logic is correct because currently only include the 4th tuple member

packages/react-server-dom-webpack/src/client/ReactFlightClientConfigBundlerWebpack.js

@@ -102,12 +102,12 @@ export function resolveClientReference<T>(
     if (isAsyncImport(metadata)) {
       return [
         resolvedModuleData.id,
-        resolvedModuleData.chunks,
         name,
+        resolvedModuleData.chunks,
         1 /* async */,
       ];
     } else {
-      return [resolvedModuleData.id, resolvedModuleData.chunks, name];
+      return [resolvedModuleData.id, name, resolvedModuleData.chunks];
     }
   }
   return metadata;
@@ -149,12 +149,12 @@ export function resolveServerReference<T>(
     // manifest.
     return [
       resolvedModuleData.id,
-      resolvedModuleData.chunks,
       name,
+      resolvedModuleData.chunks,
       1 /* async */,
     ];
   }
-  return [resolvedModuleData.id, resolvedModuleData.chunks, name];
+  return [resolvedModuleData.id, name, resolvedModuleData.chunks];
 }
 
 // The chunk cache contains all the chunks we've preloaded so far.

packages/react-server-dom-webpack/src/server/ReactFlightServerConfigWebpackBundler.js

@@ -80,9 +80,9 @@ export function resolveClientReferenceMetadata<T>(
     );
   }
   if (resolvedModuleData.async === true || clientReference.$$async === true) {
-    return [resolvedModuleData.id, resolvedModuleData.chunks, name, 1];
+    return [resolvedModuleData.id, name, resolvedModuleData.chunks, 1];
   } else {
-    return [resolvedModuleData.id, resolvedModuleData.chunks, name];
+    return [resolvedModuleData.id, name, resolvedModuleData.chunks];
   }
 }