From c47e2aec28006fcd71ee68262d751bce8d7cf5c9 Mon Sep 17 00:00:00 2001
From: JJ Kasper <jj@jjsweb.site>
Date: Wed, 24 Mar 2021 15:16:53 -0500
Subject: [PATCH] Update serial mode to be behind config

---
 packages/next/build/index.ts                  | 45 +++++++++++--------
 .../next/next-server/server/config-shared.ts  |  1 +
 2 files changed, 27 insertions(+), 19 deletions(-)

diff --git a/packages/next/build/index.ts b/packages/next/build/index.ts
index 19a3ca6485de5..e395bc44cfc1d 100644
--- a/packages/next/build/index.ts
+++ b/packages/next/build/index.ts
@@ -511,26 +511,33 @@ export default async function build(
     const webpackBuildStart = process.hrtime()
 
     let result: CompilerResult = { warnings: [], errors: [] }
-    // we run client and server compilation separately for memory and for
-    // serverless to be able to load manifests produced in previous build
-    await nextBuildSpan
-      .traceChild('run-webpack-compiler')
-      .traceAsyncFn(async () => {
-        const clientResult = await runCompiler(clientConfig)
-        // Fail build if clientResult contains errors
-        if (clientResult.errors.length > 0) {
-          result = {
-            warnings: [...clientResult.warnings],
-            errors: [...clientResult.errors],
-          }
-        } else {
-          const serverResult = await runCompiler(configs[1])
-          result = {
-            warnings: [...clientResult.warnings, ...serverResult.warnings],
-            errors: [...clientResult.errors, ...serverResult.errors],
+    // We run client and server compilation separately when configured for
+    // memory constraint and for serverless to be able to load manifests
+    // produced in the client build
+    if (isLikeServerless || config.expeirmental.serialWebpackBuild) {
+      await nextBuildSpan
+        .traceChild('run-webpack-compiler')
+        .traceAsyncFn(async () => {
+          const clientResult = await runCompiler(clientConfig)
+          // Fail build if clientResult contains errors
+          if (clientResult.errors.length > 0) {
+            result = {
+              warnings: [...clientResult.warnings],
+              errors: [...clientResult.errors],
+            }
+          } else {
+            const serverResult = await runCompiler(configs[1])
+            result = {
+              warnings: [...clientResult.warnings, ...serverResult.warnings],
+              errors: [...clientResult.errors, ...serverResult.errors],
+            }
           }
-        }
-      })
+        })
+    } else {
+      result = await nextBuildSpan
+        .traceChild('run-webpack-compiler')
+        .traceAsyncFn(() => runCompiler(configs))
+    }
 
     const webpackBuildEnd = process.hrtime(webpackBuildStart)
     if (buildSpinner) {
diff --git a/packages/next/next-server/server/config-shared.ts b/packages/next/next-server/server/config-shared.ts
index 196973e5709bb..a7776ce1d1b4b 100644
--- a/packages/next/next-server/server/config-shared.ts
+++ b/packages/next/next-server/server/config-shared.ts
@@ -80,6 +80,7 @@ export const defaultConfig: NextConfig = {
     scriptLoader: false,
     stats: false,
     externalDir: false,
+    serialWebpackBuild: false,
   },
   future: {
     strictPostcssConfiguration: false,