Revert "perf: enable webpack build worker (#57346)" (#57854)

This reverts commit 907f37978e.

x-ref: https://github.com/vercel/next.js/pull/57346

errors/webpack-build-worker-opt-out.mdx

@@ -1,15 +0,0 @@
----
-title: Webpack Build Worker automatic opt-out
----
-
-## Webpack Build Worker Opt-out
-
-#### Why This Error Occurred
-
-The Next.js config contains custom webpack configuration, as a result, the webpack build worker optimization was disabled.
-
-The webpack build worker optimization helps alleviate memory stress during builds and reduce out-of-memory errors although some custom configurations may not be compatible.
-
-#### Possible Ways to Fix It
-
-You can force enable the option by setting `config.experimental.webpackBuildWorker: true` in the config.

packages/next/src/build/index.ts

@@ -1061,35 +1061,16 @@ export default async function build(
         })
 
         const [duration] = process.hrtime(turboNextBuildStart)
-        return { duration, buildTraceContext: undefined }
+        return { duration, buildTraceContext: null }
       }
       let buildTraceContext: undefined | BuildTraceContext
       let buildTracesPromise: Promise<any> | undefined = undefined
 
-      // if the option is set, we respect it, otherwise we check if the user
-      // has a custom webpack config and disable the build worker by default.
-      const useBuildWorker =
-        config.experimental.webpackBuildWorker || !config.webpack
-      nextBuildSpan.setAttribute(
-        'has-custom-webpack-config',
-        String(!!config.webpack)
-      )
-      nextBuildSpan.setAttribute('use-build-worker', String(useBuildWorker))
-
-      if (
-        config.webpack &&
-        config.experimental.webpackBuildWorker === undefined
-      ) {
-        Log.warn(
-          'Custom webpack configuration is detected. When using a custom webpack configuration, the Webpack build worker is disabled by default. To force enable it, set the "experimental.webpackBuildWorker" option to "true". Read more: https://nextjs.org/docs/messages/webpack-build-worker-opt-out'
-        )
-      }
-
       if (!isGenerate) {
-        if (isCompile && useBuildWorker) {
+        if (isCompile && config.experimental.webpackBuildWorker) {
           let durationInSeconds = 0
 
-          await webpackBuild(true, ['server']).then((res) => {
+          await webpackBuild(['server']).then((res) => {
             buildTraceContext = res.buildTraceContext
             durationInSeconds += res.duration
             const buildTraceWorker = new Worker(
@@ -1118,11 +1099,11 @@ export default async function build(
               })
           })
 
-          await webpackBuild(true, ['edge-server']).then((res) => {
+          await webpackBuild(['edge-server']).then((res) => {
             durationInSeconds += res.duration
           })
 
-          await webpackBuild(true, ['client']).then((res) => {
+          await webpackBuild(['client']).then((res) => {
             durationInSeconds += res.duration
           })
 
@@ -1138,7 +1119,7 @@ export default async function build(
         } else {
           const { duration: webpackBuildDuration, ...rest } = turboNextBuild
             ? await turbopackBuild()
-            : await webpackBuild(false)
+            : await webpackBuild()
 
           buildTraceContext = rest.buildTraceContext
 

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

@@ -134,16 +134,17 @@ async function webpackBuildWithWorker(
   return combinedResult
 }
 
-export function webpackBuild(
-  withWorker: boolean,
+export async function webpackBuild(
   compilerNames?: typeof ORDERED_COMPILER_NAMES
-): ReturnType<typeof webpackBuildWithWorker> {
-  if (withWorker) {
+) {
+  const config = NextBuildContext.config!
+
+  if (config.experimental.webpackBuildWorker) {
     debug('using separate compiler workers')
-    return webpackBuildWithWorker(compilerNames)
+    return await webpackBuildWithWorker(compilerNames)
   } else {
     debug('building all compilers in same process')
     const webpackBuildImpl = require('./impl').webpackBuildImpl
-    return webpackBuildImpl()
+    return await webpackBuildImpl()
   }
 }

packages/next/src/server/config-shared.ts

@@ -282,11 +282,7 @@ export interface ExperimentalConfig {
   typedRoutes?: boolean
 
   /**
-   * Run the Webpack build in a separate process to optimize memory usage during build.
-   * Valid values are:
-   * - `false`: Disable the Webpack build worker
-   * - `true`: Enable the Webpack build worker
-   * - `undefined`: Enable the Webpack build worker only if the webpack config is not customized
+   * This option is to enable running the Webpack build in a worker thread.
    */
   webpackBuildWorker?: boolean
 
@@ -780,7 +776,6 @@ export const defaultConfig: NextConfig = {
     typedRoutes: false,
     instrumentationHook: false,
     bundlePagesExternals: false,
-    webpackBuildWorker: undefined,
   },
 }
 

test/integration/next-image-legacy/svgo-webpack/test/index.test.ts

@@ -23,10 +23,7 @@ let devOutput
       () => {
         it('should not fail to build invalid usage of the Image component', async () => {
           const { stderr, code } = await nextBuild(appDir, [], { stderr: true })
-          const errors = stderr
-            .split('\n')
-            .filter((line: string) => line && !line.trim().startsWith('⚠'))
-          expect(errors).toEqual([])
+          expect(stderr).toBeFalsy()
           expect(code).toBe(0)
         })
       }

test/integration/next-image-new/svgo-webpack/test/index.test.ts

@@ -25,7 +25,7 @@ let devOutput
           const { stderr, code } = await nextBuild(appDir, [], { stderr: true })
           const errors = stderr
             .split('\n')
-            .filter((line: string) => line && !line.trim().startsWith('⚠'))
+            .filter((line) => line && !line.trim().startsWith('⚠️'))
           expect(errors).toEqual([])
           expect(code).toBe(0)
         })

test/integration/webpack-require-hook/test/index.test.js

@@ -22,10 +22,8 @@ const appDir = path.join(__dirname, '..')
           stdout: true,
           stderr: true,
         })
-        const errors = stderr
-          .split('\n')
-          .filter((line) => line && !line.trim().startsWith('⚠'))
-        expect(errors).toEqual([])
+        console.log(stderr)
+        expect(stderr.length).toStrictEqual(0)
         expect(stdout).toMatch(/Initialized config/)
       })
     })