Prevent ESM client component modules from getting DCE'd in the RSC layer

.vscode/launch.json

@@ -8,7 +8,7 @@
       "id": "appDirname",
       "type": "promptString",
       "description": "Enter an app dirname from examples or test/e2e",
-      "default": "examples/hello-world"
+      "default": "test/e2e/app-dir/use-cache"
     },
     {
       "id": "nextCommand",
@@ -47,6 +47,7 @@
         "webpack://(?:_N_E)?/(?:../)*src/(.*)": "${workspaceFolder}/packages/next/src/$1",
         "webpack://next/./dist/src/*": "${workspaceFolder}/packages/next/src/*",
         "webpack://next/./dist/compiled/*": "${workspaceFolder}/packages/next/src/compiled/*",
+        "webpack:///(?:../)*packages/next/dist/compiled/(.*)": "${workspaceFolder}/packages/next/src/compiled/$1",
         "webpack://next/./src/*": "${workspaceFolder}/packages/next/src/*",
         "webpack-internal:///\\(rsc\\)/(?:../)*packages/next/dist/(.*)": "${workspaceFolder}/packages/next/src/$1",
         "turbopack://[project]/*": "${workspaceFolder}/*"

packages/next/src/build/webpack-config.ts

@@ -88,7 +88,6 @@ import {
   getBabelLoader,
   getReactCompilerLoader,
 } from './get-babel-loader-config'
-import type { NextFlightLoaderOptions } from './webpack/loaders/next-flight-loader'
 import {
   NEXT_PROJECT_ROOT,
   NEXT_PROJECT_ROOT_DIST_CLIENT,
@@ -519,13 +518,6 @@ export default async function getBaseWebpackConfig(
     babel: useSWCLoader ? swcDefaultLoader : babelLoader!,
   }
 
-  const nextFlightLoader = {
-    loader: 'next-flight-loader',
-    options: {
-      isEdgeServer,
-    } satisfies NextFlightLoaderOptions,
-  }
-
   const appServerLayerLoaders = hasAppDir
     ? [
         // When using Babel, we will have to add the SWC loader
@@ -539,7 +531,7 @@ export default async function getBaseWebpackConfig(
     : []
 
   const instrumentLayerLoaders = [
-    nextFlightLoader,
+    'next-flight-loader',
     // When using Babel, we will have to add the SWC loader
     // as an additional pass to handle RSC correctly.
     // This will cause some performance overhead but
@@ -549,7 +541,7 @@ export default async function getBaseWebpackConfig(
   ].filter(Boolean)
 
   const middlewareLayerLoaders = [
-    nextFlightLoader,
+    'next-flight-loader',
     // When using Babel, we will have to use SWC to do the optimization
     // for middleware to tree shake the unused default optimized imports like "next/server".
     // This will cause some performance overhead but
@@ -1366,7 +1358,7 @@ export default async function getBaseWebpackConfig(
                     isEdgeServer,
                   }),
                 },
-                use: nextFlightLoader,
+                use: 'next-flight-loader',
               },
             ]
           : []),

packages/next/src/build/webpack/loaders/next-flight-loader/index.ts

@@ -2,8 +2,6 @@ import type { webpack } from 'next/dist/compiled/webpack/webpack'
 import { RSC_MOD_REF_PROXY_ALIAS } from '../../../../lib/constants'
 import {
   BARREL_OPTIMIZATION_PREFIX,
-  DEFAULT_RUNTIME_WEBPACK,
-  EDGE_RUNTIME_WEBPACK,
   RSC_MODULE_TYPES,
 } from '../../../../shared/lib/constants'
 import { warnOnce } from '../../../../shared/lib/utils/warn-once'
@@ -14,11 +12,6 @@ import type {
   javascript,
   LoaderContext,
 } from 'next/dist/compiled/webpack/webpack'
-import picomatch from 'next/dist/compiled/picomatch'
-
-export interface NextFlightLoaderOptions {
-  isEdgeServer: boolean
-}
 
 type SourceType = javascript.JavascriptParser['sourceType'] | 'commonjs'
 
@@ -27,10 +20,6 @@ const noopHeadPath = require.resolve('next/dist/client/components/noop-head')
 const MODULE_PROXY_PATH =
   'next/dist/build/webpack/loaders/next-flight-loader/module-proxy'
 
-const isSharedRuntime = picomatch('**/next/dist/**/*.shared-runtime.js', {
-  dot: true, // required for .pnpm paths
-})
-
 export function getAssumedSourceType(
   mod: webpack.Module,
   sourceType: SourceType
@@ -66,7 +55,7 @@ export function getAssumedSourceType(
 }
 
 export default function transformSource(
-  this: LoaderContext<NextFlightLoaderOptions>,
+  this: LoaderContext<undefined>,
   source: string,
   sourceMap: any
 ) {
@@ -75,8 +64,6 @@ export default function transformSource(
     throw new Error('Expected source to have been transformed to a string.')
   }
 
-  const options = this.getOptions()
-  const { isEdgeServer } = options
   const module = this._module!
 
   // Assign the RSC meta information to buildInfo.
@@ -124,18 +111,6 @@ export default function transformSource(
         return
       }
 
-      if (!isSharedRuntime(resourceKey)) {
-        // Prevent module concatenation, and prevent export names from being
-        // mangled, in production builds, so that exports of client reference
-        // modules can be resolved by React using the metadata from the client
-        // manifest.
-        this._compilation!.moduleGraph.getExportsInfo(
-          module
-        ).setUsedInUnknownWay(
-          isEdgeServer ? EDGE_RUNTIME_WEBPACK : DEFAULT_RUNTIME_WEBPACK
-        )
-      }
-
       let esmSource = `\
 import { registerClientReference } from "react-server-dom-webpack/server.edge";
 `

packages/next/src/build/webpack/plugins/flight-client-entry-plugin.ts

@@ -286,7 +286,7 @@ export class FlightClientEntryPlugin {
     > = []
     const createdSSRDependenciesForEntry: Record<
       string,
-      ReturnType<typeof this.injectClientEntryAndSSRModules>[2][]
+      ReturnType<typeof this.injectClientEntryAndSSRModules>[3][]
     > = {}
 
     const addActionEntryList: Array<ReturnType<typeof this.injectActionEntry>> =
@@ -400,7 +400,7 @@ export class FlightClientEntryPlugin {
           createdSSRDependenciesForEntry[clientEntryToInject.entryName] = []
         }
         createdSSRDependenciesForEntry[clientEntryToInject.entryName].push(
-          injected[2]
+          injected[3]
         )
 
         addClientEntryAndSSRModulesList.push(injected)
@@ -457,12 +457,14 @@ export class FlightClientEntryPlugin {
       invalidator.invalidate([COMPILER_NAMES.client])
     }
 
-    // Client compiler is invalidated before awaiting the compilation of the SSR client component entries
-    // so that the client compiler is running in parallel to the server compiler.
+    // Client compiler is invalidated before awaiting the compilation of the SSR
+    // and RSC client component entries so that the client compiler is running
+    // in parallel to the server compiler.
     await Promise.all(
-      addClientEntryAndSSRModulesList.map(
-        (addClientEntryAndSSRModules) => addClientEntryAndSSRModules[1]
-      )
+      addClientEntryAndSSRModulesList.flatMap((addClientEntryAndSSRModules) => [
+        addClientEntryAndSSRModules[1],
+        addClientEntryAndSSRModules[2],
+      ])
     )
 
     // Wait for action entries to be added.
@@ -744,7 +746,8 @@ export class FlightClientEntryPlugin {
     absolutePagePath?: string
   }): [
     shouldInvalidate: boolean,
-    addEntryPromise: Promise<void>,
+    addSSREntryPromise: Promise<void>,
+    addRSCEntryPromise: Promise<void>,
     ssrDep: ReturnType<typeof webpack.EntryPlugin.createDependency>,
   ] {
     let shouldInvalidate = false
@@ -773,7 +776,7 @@ export class FlightClientEntryPlugin {
       server: false,
     })}!`
 
-    const clientSSRLoader = `next-flight-client-entry-loader?${stringify({
+    const clientServerLoader = `next-flight-client-entry-loader?${stringify({
       modules: modules.map((x) => JSON.stringify(x)),
       server: true,
     })}!`
@@ -816,33 +819,30 @@ export class FlightClientEntryPlugin {
       pluginState.injectedClientEntries[bundlePath] = clientBrowserLoader
     }
 
-    // Inject the entry to the server compiler (__ssr__).
-    const clientComponentEntryDep = webpack.EntryPlugin.createDependency(
-      clientSSRLoader,
-      {
-        name: bundlePath,
-      }
+    const clientComponentSSREntryDep = webpack.EntryPlugin.createDependency(
+      clientServerLoader,
+      { name: bundlePath }
+    )
+
+    const clientComponentRSCEntryDep = webpack.EntryPlugin.createDependency(
+      clientServerLoader,
+      { name: bundlePath }
     )
 
     return [
       shouldInvalidate,
-      // Add the dependency to the server compiler.
-      // This promise is awaited later using `Promise.all` in order to parallelize adding the entries.
-      // It ensures we can parallelize the SSR and Client compiler entries.
-      this.addEntry(
-        compilation,
-        // Reuse compilation context.
-        compiler.context,
-        clientComponentEntryDep,
-        {
-          // By using the same entry name
-          name: entryName,
-          // Layer should be client for the SSR modules
-          // This ensures the client components are bundled on client layer
-          layer: WEBPACK_LAYERS.serverSideRendering,
-        }
-      ),
-      clientComponentEntryDep,
+      // Add the entries to the server compiler for the SSR and RSC layers. The
+      // promises are awaited later using `Promise.all` in order to parallelize
+      // adding the entries.
+      this.addEntry(compilation, compiler.context, clientComponentSSREntryDep, {
+        name: entryName,
+        layer: WEBPACK_LAYERS.serverSideRendering,
+      }),
+      this.addEntry(compilation, compiler.context, clientComponentRSCEntryDep, {
+        name: entryName,
+        layer: WEBPACK_LAYERS.reactServerComponents,
+      }),
+      clientComponentSSREntryDep,
     ]
   }