From a58ba301ebcd1d6d16041e2ba18f727c6df4b6fc Mon Sep 17 00:00:00 2001
From: Tim Neutkens <tim@timneutkens.nl>
Date: Thu, 27 Oct 2022 16:00:40 -0700
Subject: [PATCH] Enable strict mode by default for app dir

---
 packages/next/build/webpack-config.ts | 12 +++++++++++-
 packages/next/client/app-index.tsx    |  2 +-
 packages/next/server/config-shared.ts |  4 ++--
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/packages/next/build/webpack-config.ts b/packages/next/build/webpack-config.ts
index a51abb5acbac..9a95f3f2c694 100644
--- a/packages/next/build/webpack-config.ts
+++ b/packages/next/build/webpack-config.ts
@@ -244,7 +244,17 @@ export function getDefineEnv({
     'process.env.__NEXT_BUILD_INDICATOR_POSITION': JSON.stringify(
       config.devIndicators.buildActivityPosition
     ),
-    'process.env.__NEXT_STRICT_MODE': JSON.stringify(config.reactStrictMode),
+    'process.env.__NEXT_STRICT_MODE': JSON.stringify(
+      config.reactStrictMode === null ? false : config.reactStrictMode
+    ),
+    'process.env.__NEXT_STRICT_MODE_APP': JSON.stringify(
+      // When next.config.js does not have reactStrictMode enabling appDir will enable it.
+      config.reactStrictMode === null
+        ? config.experimental.appDir
+          ? true
+          : false
+        : config.reactStrictMode
+    ),
     'process.env.__NEXT_REACT_ROOT': JSON.stringify(hasReactRoot),
     'process.env.__NEXT_OPTIMIZE_FONTS': JSON.stringify(
       !dev && config.optimizeFonts
diff --git a/packages/next/client/app-index.tsx b/packages/next/client/app-index.tsx
index 3fe2df062935..cc9c73882806 100644
--- a/packages/next/client/app-index.tsx
+++ b/packages/next/client/app-index.tsx
@@ -149,7 +149,7 @@ function ServerRoot({ cacheKey }: { cacheKey: string }): JSX.Element {
   return root
 }
 
-const StrictModeIfEnabled = process.env.__NEXT_STRICT_MODE
+const StrictModeIfEnabled = process.env.__NEXT_STRICT_MODE_APP
   ? React.StrictMode
   : React.Fragment
 
diff --git a/packages/next/server/config-shared.ts b/packages/next/server/config-shared.ts
index 8b46186c766d..957ab2b69119 100644
--- a/packages/next/server/config-shared.ts
+++ b/packages/next/server/config-shared.ts
@@ -391,7 +391,7 @@ export interface NextConfig extends Record<string, any> {
    *
    * @see [React Strict Mode](https://nextjs.org/docs/api-reference/next.config.js/react-strict-mode)
    */
-  reactStrictMode?: boolean
+  reactStrictMode?: boolean | null
 
   /**
    * Add public (in browser) runtime configuration to your app
@@ -545,7 +545,7 @@ export const defaultConfig: NextConfig = {
   excludeDefaultMomentLocales: true,
   serverRuntimeConfig: {},
   publicRuntimeConfig: {},
-  reactStrictMode: false,
+  reactStrictMode: null,
   httpAgentOptions: {
     keepAlive: true,
   },