Fix barrel optimizer conflicts with client entry module (vercel#56020)

The barrel optimization loader creates a virtual module to re-export
from the original file, which causes the situation that now there are 2
modules with the same resource but only one of them is the actual code.

When the code contains `"use client"`, the Flight plugin has to collect
its `buildInfo` and generate the manifest and client entry module.
However, we currently deduplicate module by resource in the traversal
logic to avoid unnecessary loops. To make it work together with the
virtual barrel module, we'll need to prefix the resource path to make it
different from the original module.

Closes vercel#54967.
Closes vercel#55609.
Closes vercel#55566.

Author: shuding

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

@@ -37,6 +37,7 @@ import {
   SERVER_DIRECTORY,
   COMPILER_NAMES,
   CompilerNameValues,
+  BARREL_OPTIMIZATION_PREFIX,
 } from '../shared/lib/constants'
 import { execOnce } from '../shared/lib/utils'
 import { NextConfigComplete } from '../server/config-shared'
@@ -1217,9 +1218,9 @@ export default async function getBaseWebpackConfig(
       return
     }
 
-    // __barrel_optimize__ is a special marker that tells Next.js to
+    // BARREL_OPTIMIZATION_PREFIX is a special marker that tells Next.js to
     // optimize the import by removing unused exports. This has to be compiled.
-    if (request.startsWith('__barrel_optimize__')) {
+    if (request.startsWith(BARREL_OPTIMIZATION_PREFIX)) {
       return
     }
 

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

@@ -17,6 +17,7 @@ import {
 import { WEBPACK_LAYERS } from '../../../lib/constants'
 import {
   APP_CLIENT_INTERNALS,
+  BARREL_OPTIMIZATION_PREFIX,
   COMPILER_NAMES,
   EDGE_RUNTIME_WEBPACK,
   SERVER_REFERENCE_MANIFEST,
@@ -510,9 +511,17 @@ export class FlightClientEntryPlugin {
         // We have to always use the resolved request here to make sure the
         // server and client are using the same module path (required by RSC), as
         // the server compiler and client compiler have different resolve configs.
-        const modRequest: string | undefined =
+        let modRequest: string | undefined =
           mod.resourceResolveData?.path + mod.resourceResolveData?.query
 
+        // For the barrel optimization, we need to use the match resource instead
+        // because there will be 2 modules for the same file (same resource path)
+        // but they're different modules and can't be deduped via `visitedModule`.
+        // The first module is a virtual re-export module created by the loader.
+        if (mod.matchResource?.startsWith(BARREL_OPTIMIZATION_PREFIX)) {
+          modRequest = mod.matchResource + ':' + modRequest
+        }
+
         if (!modRequest || visitedModule.has(modRequest)) return
         visitedModule.add(modRequest)
 
@@ -596,6 +605,14 @@ export class FlightClientEntryPlugin {
         modRequest = (mod as any)._identifier
       }
 
+      // For the barrel optimization, we need to use the match resource instead
+      // because there will be 2 modules for the same file (same resource path)
+      // but they're different modules and can't be deduped via `visitedModule`.
+      // The first module is a virtual re-export module created by the loader.
+      if (mod.matchResource?.startsWith(BARREL_OPTIMIZATION_PREFIX)) {
+        modRequest = mod.matchResource + ':' + modRequest
+      }
+
       if (!modRequest || visited.has(modRequest)) return
       visited.add(modRequest)
 

packages/next/src/shared/lib/constants.ts

@@ -61,6 +61,7 @@ export const CLIENT_PUBLIC_FILES_PATH = 'public'
 export const CLIENT_STATIC_FILES_PATH = 'static'
 export const STRING_LITERAL_DROP_BUNDLE = '__NEXT_DROP_CLIENT_FILE__'
 export const NEXT_BUILTIN_DOCUMENT = '__NEXT_BUILTIN_DOCUMENT__'
+export const BARREL_OPTIMIZATION_PREFIX = '__barrel_optimize__'
 
 // server/[entry]/page_client-reference-manifest.js
 export const CLIENT_REFERENCE_MANIFEST = 'client-reference-manifest'

test/development/basic/barrel-optimization.test.ts

@@ -126,4 +126,9 @@ describe('optimizePackageImports', () => {
     const html = await next.render('/visx')
     expect(html).toContain('<linearGradient')
   })
+
+  it('should not break "use client" directive in optimized packages', async () => {
+    const html = await next.render('/client')
+    expect(html).toContain('this is a client component')
+  })
 })

test/development/basic/barrel-optimization/app/client/page.js

@@ -0,0 +1,9 @@
+import { Client } from 'my-lib'
+
+export default function Page() {
+  return (
+    <h1>
+      <Client />
+    </h1>
+  )
+}

test/development/basic/barrel-optimization/node_modules_bak/my-lib/client.js

@@ -0,0 +1,5 @@
+'use client'
+
+export function Client() {
+  return 'this is a client component'
+}

test/development/basic/barrel-optimization/node_modules_bak/my-lib/index.js

@@ -1 +1,2 @@
 export * from './a'
+export * from './client'