From f5528063eecf505e2d49a38b5f95ca256289daad Mon Sep 17 00:00:00 2001
From: Ricky Hanlon <rickhanlonii@gmail.com>
Date: Mon, 29 Jan 2024 17:09:51 -0500
Subject: [PATCH 1/3] Move modern strict to experimental

---
 .../src/__tests__/ReactStrictMode-test.js     | 32 +++++++++++++------
 packages/shared/ReactFeatureFlags.js          |  2 +-
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/packages/react/src/__tests__/ReactStrictMode-test.js b/packages/react/src/__tests__/ReactStrictMode-test.js
index 4ccc9a2687175..1834a7d0f30e6 100644
--- a/packages/react/src/__tests__/ReactStrictMode-test.js
+++ b/packages/react/src/__tests__/ReactStrictMode-test.js
@@ -116,15 +116,29 @@ describe('ReactStrictMode', () => {
       container,
     );
 
-    expect(log).toEqual([
-      'constructor',
-      'constructor',
-      'getDerivedStateFromProps',
-      'getDerivedStateFromProps',
-      'render',
-      'render',
-      'componentDidMount',
-    ]);
+    if (gate(flags => flags.useModernStrictMode)) {
+      expect(log).toEqual([
+        'constructor',
+        'constructor',
+        'getDerivedStateFromProps',
+        'getDerivedStateFromProps',
+        'render',
+        'render',
+        'componentDidMount',
+        'componentWillUnmount',
+        'componentDidMount',
+      ]);
+    } else {
+      expect(log).toEqual([
+        'constructor',
+        'constructor',
+        'getDerivedStateFromProps',
+        'getDerivedStateFromProps',
+        'render',
+        'render',
+        'componentDidMount',
+      ]);
+    }
 
     log = [];
     shouldComponentUpdate = true;
diff --git a/packages/shared/ReactFeatureFlags.js b/packages/shared/ReactFeatureFlags.js
index 67862a4f14288..3d8a7cf563bc8 100644
--- a/packages/shared/ReactFeatureFlags.js
+++ b/packages/shared/ReactFeatureFlags.js
@@ -147,7 +147,7 @@ export const disableJavaScriptURLs = false;
 // Modern <StrictMode /> behaviour aligns more with what components
 // components will encounter in production, especially when used With <Offscreen />.
 // TODO: clean up legacy <StrictMode /> once tests pass WWW.
-export const useModernStrictMode = false;
+export const useModernStrictMode = __NEXT_MAJOR__;
 
 // Not ready to break experimental yet.
 // Remove IE and MsApp specific workarounds for innerHTML

From a92a3acedbea4b8933d1cb26bfbd77f8226ed727 Mon Sep 17 00:00:00 2001
From: Ricky Hanlon <rickhanlonii@gmail.com>
Date: Fri, 9 Feb 2024 15:58:49 -0500
Subject: [PATCH 2/3] Turn off strict effects in legacy roots with
 useModernStrictMode

---
 packages/react-reconciler/src/ReactFiberWorkLoop.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.js b/packages/react-reconciler/src/ReactFiberWorkLoop.js
index 5fafd8de5c903..d045fa08496e1 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.js
@@ -3792,12 +3792,9 @@ function commitDoubleInvokeEffectsInDEV(
   hasPassiveEffects: boolean,
 ) {
   if (__DEV__) {
-    if (useModernStrictMode) {
+    if (useModernStrictMode && root.tag !== LegacyRoot) {
       let doubleInvokeEffects = true;
 
-      if (root.tag === LegacyRoot && !(root.current.mode & StrictLegacyMode)) {
-        doubleInvokeEffects = false;
-      }
       if (
         root.tag === ConcurrentRoot &&
         !(root.current.mode & (StrictLegacyMode | StrictEffectsMode))

From 4afefce3f6c5fe5eb6e965ae898f2cd5df39ee46 Mon Sep 17 00:00:00 2001
From: Ricky Hanlon <rickhanlonii@gmail.com>
Date: Fri, 9 Feb 2024 16:45:10 -0500
Subject: [PATCH 3/3] Legacy mode never double invokes effects

---
 .../src/__tests__/ReactStrictMode-test.js     | 32 ++++++-------------
 1 file changed, 9 insertions(+), 23 deletions(-)

diff --git a/packages/react/src/__tests__/ReactStrictMode-test.js b/packages/react/src/__tests__/ReactStrictMode-test.js
index 1834a7d0f30e6..4ccc9a2687175 100644
--- a/packages/react/src/__tests__/ReactStrictMode-test.js
+++ b/packages/react/src/__tests__/ReactStrictMode-test.js
@@ -116,29 +116,15 @@ describe('ReactStrictMode', () => {
       container,
     );
 
-    if (gate(flags => flags.useModernStrictMode)) {
-      expect(log).toEqual([
-        'constructor',
-        'constructor',
-        'getDerivedStateFromProps',
-        'getDerivedStateFromProps',
-        'render',
-        'render',
-        'componentDidMount',
-        'componentWillUnmount',
-        'componentDidMount',
-      ]);
-    } else {
-      expect(log).toEqual([
-        'constructor',
-        'constructor',
-        'getDerivedStateFromProps',
-        'getDerivedStateFromProps',
-        'render',
-        'render',
-        'componentDidMount',
-      ]);
-    }
+    expect(log).toEqual([
+      'constructor',
+      'constructor',
+      'getDerivedStateFromProps',
+      'getDerivedStateFromProps',
+      'render',
+      'render',
+      'componentDidMount',
+    ]);
 
     log = [];
     shouldComponentUpdate = true;