[DevTools] Use alternate as previous Fiber when reconciling root

eps1lon · eps1lon · commit af062816b1e7 · 2025-09-16T15:00:31.000+02:00
diff --git a/packages/react-devtools-shared/src/backend/fiber/renderer.js b/packages/react-devtools-shared/src/backend/fiber/renderer.js
@@ -5398,7 +5398,7 @@ export function attach(
       rootToFiberInstanceMap.set(root, rootInstance);
       idToDevToolsInstanceMap.set(rootInstance.id, rootInstance);
     } else {
-      prevFiber = rootInstance.data;
+      prevFiber = rootInstance.data.alternate;
     }
     currentRoot = rootInstance;
 

Original file line number	Diff line number	Diff line change
`@@ -5398,7 +5398,7 @@ export function attach(`
`5398`	`5398`	`rootToFiberInstanceMap.set(root, rootInstance);`
`5399`	`5399`	`idToDevToolsInstanceMap.set(rootInstance.id, rootInstance);`
`5400`	`5400`	`} else {`
`5401`		`- prevFiber = rootInstance.data;`
	`5401`	`+ prevFiber = rootInstance.data.alternate;`
`5402`	`5402`	`}`
`5403`	`5403`	`currentRoot = rootInstance;`
`5404`	`5404`