From 944b9303f7699a8e96f1a8395710649824193ac4 Mon Sep 17 00:00:00 2001
From: Noah Lemen <noah.lemen@gmail.com>
Date: Fri, 12 Apr 2024 12:36:19 -0400
Subject: [PATCH] add tests capturing effects behavior for legacy and modern
 strict mode during fast refresh

---
 .../src/__tests__/ReactFresh-test.js          | 125 +++++++++++++++++-
 1 file changed, 124 insertions(+), 1 deletion(-)

diff --git a/packages/react-refresh/src/__tests__/ReactFresh-test.js b/packages/react-refresh/src/__tests__/ReactFresh-test.js
index 13ded584199e4..1e77a3033da39 100644
--- a/packages/react-refresh/src/__tests__/ReactFresh-test.js
+++ b/packages/react-refresh/src/__tests__/ReactFresh-test.js
@@ -51,7 +51,7 @@ describe('ReactFresh', () => {
     }
   });
 
-  afterEach(() => {
+  afterEach(async () => {
     if (__DEV__) {
       delete global.__REACT_DEVTOOLS_GLOBAL_HOOK__;
       document.body.removeChild(container);
@@ -3813,6 +3813,129 @@ describe('ReactFresh', () => {
     }
   });
 
+  it('double invokes effects in StrictMode when remounting', async () => {
+    if (__DEV__) {
+      await render(() => {
+        function App() {
+          React.useEffect(() => {
+            Scheduler.log('useEffect mount');
+            return () => Scheduler.log('useEffect unmount');
+          });
+
+          React.useLayoutEffect(() => {
+            Scheduler.log('useLayoutEffect mount');
+            return () => Scheduler.log('useLayoutEffect unmount');
+          });
+
+          return null;
+        }
+        $RefreshReg$(App, 'App');
+        $RefreshSig$(App, '1');
+        return () => (
+          <React.StrictMode>
+            <App />
+          </React.StrictMode>
+        );
+      });
+
+      if (gate(flags => flags.useModernStrictMode)) {
+        // this seems contrary to observed behavior in practice - unclear why effects are not double-invoked here
+        // effects should be double invoked here in modern strict mode
+        assertLog(['useLayoutEffect mount', 'useEffect mount']);
+      } else {
+        // in legacy strict mode, effects are double invoked on initial render
+        assertLog([
+          'useLayoutEffect mount',
+          'useEffect mount',
+          'useLayoutEffect unmount',
+          'useEffect unmount',
+          'useLayoutEffect mount',
+          'useEffect mount',
+        ]);
+      }
+
+      // Refresh without changing signature
+      await patch(() => {
+        function App() {
+          React.useEffect(() => {
+            Scheduler.log('useEffect mount');
+            return () => Scheduler.log('useEffect unmount');
+          });
+
+          React.useLayoutEffect(() => {
+            Scheduler.log('useLayoutEffect mount');
+            return () => Scheduler.log('useLayoutEffect unmount');
+          });
+
+          return null;
+        }
+        $RefreshReg$(App, 'App');
+        $RefreshSig$(App, '1');
+        return App;
+      });
+
+      // no difference between modern and legacy strict mode here -- we unmount and remount effects
+      if (gate(flags => flags.useModernStrictMode)) {
+        assertLog([
+          'useLayoutEffect unmount',
+          'useLayoutEffect mount',
+          'useEffect unmount',
+          'useEffect mount',
+        ]);
+      } else {
+        assertLog([
+          'useLayoutEffect unmount',
+          'useLayoutEffect mount',
+          'useEffect unmount',
+          'useEffect mount',
+        ]);
+      }
+
+      // Refresh with change to signature
+      await patch(() => {
+        function App() {
+          React.useEffect(() => {
+            Scheduler.log('useEffect mount');
+            return () => Scheduler.log('useEffect unmount');
+          });
+
+          React.useLayoutEffect(() => {
+            Scheduler.log('useLayoutEffect mount');
+            return () => Scheduler.log('useLayoutEffect unmount');
+          });
+
+          return null;
+        }
+        $RefreshReg$(App, 'App');
+        $RefreshSig$(App, '2');
+        return App;
+      });
+
+      if (gate(flags => flags.useModernStrictMode)) {
+        // in modern strict mode, we unmount and remount like above, but do not double-invoke effects
+        // we probably should be double invoking effects?
+        assertLog([
+          'useLayoutEffect unmount',
+          'useLayoutEffect mount',
+          'useEffect unmount',
+          'useEffect mount',
+        ]);
+      } else {
+        // in legacy strict mode, we unmount, remount, and then unmount and remount once more for double-invocation
+        assertLog([
+          'useLayoutEffect unmount',
+          'useLayoutEffect mount',
+          'useEffect unmount',
+          'useEffect mount',
+          'useLayoutEffect unmount',
+          'useEffect unmount',
+          'useLayoutEffect mount',
+          'useEffect mount',
+        ]);
+      }
+    }
+  });
+
   function initFauxDevToolsHook() {
     const onCommitFiberRoot = jest.fn();
     const onCommitFiberUnmount = jest.fn();