set the bunlder props from the next servers

Author: lukesandberg

packages/next/errors.json

@@ -847,5 +847,6 @@
   "846": "Route %s used \\`cookies()\\` inside a function cached with \\`unstable_cache()\\`. Accessing Dynamic data sources inside a cache scope is not supported. If you need this data inside a cached function use \\`cookies()\\` outside of the cached function and pass the required dynamic data in as an argument. See more info here: https://nextjs.org/docs/app/api-reference/functions/unstable_cache",
   "847": "Route %s with \\`dynamic = \"error\"\\` couldn't be rendered statically because it used \\`connection()\\`. See more info here: https://nextjs.org/docs/app/building-your-application/rendering/static-and-dynamic#dynamic-rendering",
   "848": "%sused %s. \\`searchParams\\` is a Promise and must be unwrapped with \\`await\\` or \\`React.use()\\` before accessing its properties. Learn more: https://nextjs.org/docs/messages/sync-dynamic-apis",
-  "849": "Route %s with \\`dynamic = \"error\"\\` couldn't be rendered statically because it used \\`cookies()\\`. See more info here: https://nextjs.org/docs/app/building-your-application/rendering/static-and-dynamic#dynamic-rendering"
+  "849": "Route %s with \\`dynamic = \"error\"\\` couldn't be rendered statically because it used \\`cookies()\\`. See more info here: https://nextjs.org/docs/app/building-your-application/rendering/static-and-dynamic#dynamic-rendering",
+  "850": "Pass either `webpack` or `turbopack`, not both."
 }

packages/next/src/server/lib/render-server.ts

@@ -90,6 +90,8 @@ async function initializeImpl(opts: {
   bundlerService: DevBundlerService | undefined
   startServerSpan: Span | undefined
   quiet?: boolean
+  turbopack?: boolean
+  webpack?: boolean
   onDevServerCleanup: ((listener: () => Promise<void>) => void) | undefined
 }): Promise<ServerInitResult> {
   const type = process.env.__NEXT_PRIVATE_RENDER_WORKER

packages/next/src/server/lib/router-server.ts

@@ -91,6 +91,8 @@ export async function initialize(opts: {
   experimentalHttpsServer?: boolean
   startServerSpan?: Span
   quiet?: boolean
+  turbopack?: boolean
+  webpack?: boolean
 }): Promise<ServerInitResult> {
   if (!process.env.NODE_ENV) {
     // @ts-ignore not readonly
@@ -699,6 +701,8 @@ export async function initialize(opts: {
     experimentalHttpsServer: !!opts.experimentalHttpsServer,
     bundlerService: devBundlerService,
     startServerSpan: opts.startServerSpan,
+    turbopack: opts.turbopack,
+    webpack: opts.webpack,
     quiet: opts.quiet,
     onDevServerCleanup: opts.onDevServerCleanup,
   }

packages/next/src/server/lib/start-server.ts

@@ -140,6 +140,8 @@ export async function getRequestHandlers({
   keepAliveTimeout,
   experimentalHttpsServer,
   quiet,
+  turbopack,
+  webpack,
 }: {
   dir: string
   port: number
@@ -151,6 +153,8 @@ export async function getRequestHandlers({
   keepAliveTimeout?: number
   experimentalHttpsServer?: boolean
   quiet?: boolean
+  turbopack?: boolean
+  webpack?: boolean
 }): ReturnType<typeof initialize> {
   return initialize({
     dir,
@@ -164,6 +168,8 @@ export async function getRequestHandlers({
     experimentalHttpsServer,
     startServerSpan,
     quiet,
+    turbopack,
+    webpack,
   })
 }
 
@@ -440,6 +446,9 @@ export async function startServer(
           minimalMode,
           keepAliveTimeout,
           experimentalHttpsServer: !!selfSignedCertificate,
+          // Explicitly pass the bundler flag down so it doesn't override the environment variable.
+          turbopack: process.env.TURBOPACK ? true : undefined,
+          webpack: process.env.TURBOPACK ? undefined : true,
         })
         requestHandler = initResult.requestHandler
         upgradeHandler = initResult.upgradeHandler

packages/next/src/server/next.ts

@@ -534,13 +534,21 @@ function createServer(
   options: NextServerOptions & {
     turbo?: boolean
     turbopack?: boolean
+    webpack?: boolean
   }
 ): NextWrapperServer {
   if (
     options &&
     (options.turbo || options.turbopack || process.env.IS_TURBOPACK_TEST)
   ) {
-    process.env.TURBOPACK = '1'
+    if (options.webpack) {
+      throw new Error('Pass either `webpack` or `turbopack`, not both.')
+    }
+    process.env.TURBOPACK ??= '1'
+  } else if (!options?.webpack) {
+    // If no options are set we default to turbopack
+    // If TURBOPACK was already set we preserve it.
+    process.env.TURBOPACK ??= 'auto'
   }
   // The package is used as a TypeScript plugin.
   if (