From eefdfc46d67ea57d9c248e2c799cced2f1390c49 Mon Sep 17 00:00:00 2001
From: Gerald Monaco <gbmonaco@google.com>
Date: Wed, 9 Oct 2019 20:50:37 +0000
Subject: [PATCH 1/3] Add StrictMode toggle

---
 packages/next/build/webpack-config.ts      |  1 +
 packages/next/client/index.js              | 14 +++++++++++---
 packages/next/next-server/server/config.ts |  1 +
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/packages/next/build/webpack-config.ts b/packages/next/build/webpack-config.ts
index bf049ee6eac1b..fa618466df2f3 100644
--- a/packages/next/build/webpack-config.ts
+++ b/packages/next/build/webpack-config.ts
@@ -736,6 +736,7 @@ export default async function getBaseWebpackConfig(
         'process.env.__NEXT_PRERENDER_INDICATOR': JSON.stringify(
           config.devIndicators.autoPrerender
         ),
+        'process.env.__NEXT_STRICT_MODE': JSON.stringify(config.strictMode),
         ...(isServer
           ? {
               // Fix bad-actors in the npm ecosystem (e.g. `node-formidable`)
diff --git a/packages/next/client/index.js b/packages/next/client/index.js
index 2eed1010881e8..02118913c1c4e 100644
--- a/packages/next/client/index.js
+++ b/packages/next/client/index.js
@@ -372,11 +372,19 @@ async function doRender ({ App, Component, props, err }) {
     appProps
   })
 
-  // We catch runtime errors using componentDidCatch which will trigger renderError
-  renderReactElement(
+  const elem = (
     <AppContainer>
       <App {...appProps} />
-    </AppContainer>,
+    </AppContainer>
+  )
+
+  // We catch runtime errors using componentDidCatch which will trigger renderError
+  renderReactElement(
+    process.env.__NEXT_STRICT_MODE ? (
+      <React.StrictMode>{elem}</React.StrictMode>
+    ) : (
+      elem
+    ),
     appElement
   )
 
diff --git a/packages/next/next-server/server/config.ts b/packages/next/next-server/server/config.ts
index 60f3ac43758eb..8e81b56a0a58d 100644
--- a/packages/next/next-server/server/config.ts
+++ b/packages/next/next-server/server/config.ts
@@ -53,6 +53,7 @@ const defaultConfig: { [key: string]: any } = {
   },
   serverRuntimeConfig: {},
   publicRuntimeConfig: {},
+  strictMode: true,
 }
 
 const experimentalWarning = execOnce(() => {

From 5f27e0de35044a4a8d5248111112c936d3a4daf1 Mon Sep 17 00:00:00 2001
From: Tim Neutkens <timneutkens@me.com>
Date: Sat, 26 Oct 2019 00:07:05 +0200
Subject: [PATCH 2/3] Rename option to reactStrictMode

---
 packages/next/build/webpack-config.ts      | 4 +++-
 packages/next/next-server/server/config.ts | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/packages/next/build/webpack-config.ts b/packages/next/build/webpack-config.ts
index fa618466df2f3..fd6ec5cd00d00 100644
--- a/packages/next/build/webpack-config.ts
+++ b/packages/next/build/webpack-config.ts
@@ -736,7 +736,9 @@ export default async function getBaseWebpackConfig(
         'process.env.__NEXT_PRERENDER_INDICATOR': JSON.stringify(
           config.devIndicators.autoPrerender
         ),
-        'process.env.__NEXT_STRICT_MODE': JSON.stringify(config.strictMode),
+        'process.env.__NEXT_STRICT_MODE': JSON.stringify(
+          config.reactStrictMode
+        ),
         ...(isServer
           ? {
               // Fix bad-actors in the npm ecosystem (e.g. `node-formidable`)
diff --git a/packages/next/next-server/server/config.ts b/packages/next/next-server/server/config.ts
index 8e81b56a0a58d..23021ed427502 100644
--- a/packages/next/next-server/server/config.ts
+++ b/packages/next/next-server/server/config.ts
@@ -53,7 +53,7 @@ const defaultConfig: { [key: string]: any } = {
   },
   serverRuntimeConfig: {},
   publicRuntimeConfig: {},
-  strictMode: true,
+  reactStrictMode: true,
 }
 
 const experimentalWarning = execOnce(() => {

From 3ad10e806dbcbee8878c0a7a0c8c38bcbb1f2d19 Mon Sep 17 00:00:00 2001
From: Tim Neutkens <timneutkens@me.com>
Date: Sat, 26 Oct 2019 00:17:32 +0200
Subject: [PATCH 3/3] Default to false initially

---
 packages/next/next-server/server/config.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/next/next-server/server/config.ts b/packages/next/next-server/server/config.ts
index 23021ed427502..712eca701718a 100644
--- a/packages/next/next-server/server/config.ts
+++ b/packages/next/next-server/server/config.ts
@@ -53,7 +53,7 @@ const defaultConfig: { [key: string]: any } = {
   },
   serverRuntimeConfig: {},
   publicRuntimeConfig: {},
-  reactStrictMode: true,
+  reactStrictMode: false,
 }
 
 const experimentalWarning = execOnce(() => {