From fb2a3d3a018ad51d4a5ca6c95f44d530c88c2876 Mon Sep 17 00:00:00 2001
From: Pedro Fontoura <me@pedrofontoura.io>
Date: Tue, 25 Feb 2025 12:50:32 -0300
Subject: [PATCH 1/2] Add TraceUpdateRepro to DevTools test harness

---
 .../src/app/TraceUpdateRepro/index.js         | 46 +++++++++++++++++++
 .../react-devtools-shell/src/app/index.js     |  2 +
 2 files changed, 48 insertions(+)
 create mode 100644 packages/react-devtools-shell/src/app/TraceUpdateRepro/index.js

diff --git a/packages/react-devtools-shell/src/app/TraceUpdateRepro/index.js b/packages/react-devtools-shell/src/app/TraceUpdateRepro/index.js
new file mode 100644
index 0000000000000..1232a154e0419
--- /dev/null
+++ b/packages/react-devtools-shell/src/app/TraceUpdateRepro/index.js
@@ -0,0 +1,46 @@
+import * as React from 'react';
+import {useEffect, useRef, useState} from 'react';
+
+function ShouldReRender() {
+  // Used just to trigger the re-render
+  const [, setCount] = useState(0);
+
+  const renders = useRef(0);
+  renders.current += 1;
+
+  useEffect(() => {
+    const interval = setInterval(() => {
+      setCount(value => value + 1);
+    }, 500);
+    return () => clearInterval(interval);
+  }, [setCount]);
+
+  return <p>Should re-render count: {renders.current}x</p>;
+}
+
+function ShouldNotReRender() {
+  const renders = useRef(0);
+  renders.current += 1;
+  return <p>Should not re-render count: {renders.current}x</p>;
+}
+
+export default function TraceUpdateRepro() {
+  return (
+    <>
+      <ShouldReRender />
+
+      {/* This one isn't highlighted... */}
+      <ShouldNotReRender />
+
+      {/* These ones are highlighted. I wonder if there is some sort of tree depth check?*/}
+      <div>
+        <ShouldNotReRender />
+      </div>
+      <div>
+        <div>
+          <ShouldNotReRender />
+        </div>
+      </div>
+    </>
+  );
+}
diff --git a/packages/react-devtools-shell/src/app/index.js b/packages/react-devtools-shell/src/app/index.js
index 11f13bec47b22..2e03334c152da 100644
--- a/packages/react-devtools-shell/src/app/index.js
+++ b/packages/react-devtools-shell/src/app/index.js
@@ -19,6 +19,7 @@ import Toggle from './Toggle';
 import ErrorBoundaries from './ErrorBoundaries';
 import PartiallyStrictApp from './PartiallyStrictApp';
 import SuspenseTree from './SuspenseTree';
+import TraceUpdateRepro from './TraceUpdateRepro';
 import {ignoreErrors, ignoreLogs, ignoreWarnings} from './console';
 
 import './styles.css';
@@ -112,6 +113,7 @@ function mountTestApp() {
   mountApp(SuspenseTree);
   mountApp(DeeplyNestedComponents);
   mountApp(Iframe);
+  mountApp(TraceUpdateRepro);
 
   if (shouldRenderLegacy) {
     mountLegacyApp(PartiallyStrictApp);

From 5e65a61af2b21157acb9e40bc78325e053c6c7c3 Mon Sep 17 00:00:00 2001
From: Pedro Fontoura <me@pedrofontoura.io>
Date: Tue, 25 Feb 2025 14:22:31 -0300
Subject: [PATCH 2/2] Don't fallback to descendants when tracing updates

---
 .../src/backend/fiber/renderer.js                    | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/packages/react-devtools-shared/src/backend/fiber/renderer.js b/packages/react-devtools-shared/src/backend/fiber/renderer.js
index ef8bac0099a2b..5c9df9baaf71e 100644
--- a/packages/react-devtools-shared/src/backend/fiber/renderer.js
+++ b/packages/react-devtools-shared/src/backend/fiber/renderer.js
@@ -3419,18 +3419,6 @@ export function attach(
             // I.e. we just restore them by undoing what we did above.
             fiberInstance.firstChild = remainingReconcilingChildren;
             remainingReconcilingChildren = null;
-
-            if (traceUpdatesEnabled) {
-              // If we're tracing updates and we've bailed out before reaching a host node,
-              // we should fall back to recursively marking the nearest host descendants for highlight.
-              if (traceNearestHostComponentUpdate) {
-                const hostInstances =
-                  findAllCurrentHostInstances(fiberInstance);
-                hostInstances.forEach(hostInstance => {
-                  traceUpdatesForNodes.add(hostInstance);
-                });
-              }
-            }
           } else {
             // If this fiber is filtered there might be changes to this set elsewhere so we have
             // to visit each child to place it back in the set. We let the child bail out instead.