From 654dc2094f690210ead1657843152cd3cae7e773 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rub=C3=A9n=20Norte?= <rubennorte@meta.com>
Date: Mon, 21 Sep 2026 06:37:25 -0700
Subject: [PATCH] Test ResizeObserver structured clone errors (#58592)

Summary:
Pull Request resolved: https://github.com/react/react-native/pull/58592

Add structured-clone coverage for `ResizeObserver`, `ResizeObserverEntry`, and `ResizeObserverSize` using real observer entries.

Changelog: [Internal]

Reviewed By: andrewdacenko

Differential Revision: D120691617
---
 .../__tests__/structuredClone-itest.js        | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/packages/react-native/src/private/webapis/structuredClone/__tests__/structuredClone-itest.js b/packages/react-native/src/private/webapis/structuredClone/__tests__/structuredClone-itest.js
index 23e8473fd4d..0bede29eb06 100644
--- a/packages/react-native/src/private/webapis/structuredClone/__tests__/structuredClone-itest.js
+++ b/packages/react-native/src/private/webapis/structuredClone/__tests__/structuredClone-itest.js
@@ -6,6 +6,7 @@
  *
  * @fantom_flags enableIntersectionObserverByDefault:true
  * @fantom_flags enableMutationObserverByDefault:true
+ * @fantom_flags enableResizeObserverByDefault:true
  * @flow strict-local
  * @format
  */
@@ -39,6 +40,26 @@ function expectDataCloneError(fn: () => unknown) {
   throw new Error('Expected function to throw DataCloneError, but it did not');
 }
 
+function createResizeObserverEntryForTest(): ResizeObserverEntry {
+  const ref = createRef<HostInstance>();
+  const root = Fantom.createRoot();
+  Fantom.runTask(() => {
+    root.render(<View style={{height: 10, width: 10}} ref={ref} />);
+  });
+
+  const target = ensureInstance(ref.current, HTMLElement);
+  const entries: Array<unknown> = [];
+  Fantom.runTask(() => {
+    const observer = new ResizeObserver((newEntries, self) => {
+      entries.push(...newEntries);
+      self.disconnect();
+    });
+    observer.observe(target);
+  });
+
+  return ensureInstance(entries[0], ResizeObserverEntry);
+}
+
 describe('structuredClone', () => {
   it('clones primitive types', () => {
     expect(structuredClone(undefined)).toBe(undefined);
@@ -435,6 +456,28 @@ describe('structuredClone', () => {
 
         expectDataCloneError(() => structuredClone(records[0]));
       });
+
+      it('does NOT clone ResizeObserver', () => {
+        expectDataCloneError(() =>
+          structuredClone(new ResizeObserver(() => {})),
+        );
+      });
+
+      it('does NOT clone ResizeObserverEntry', () => {
+        expectDataCloneError(() =>
+          structuredClone(createResizeObserverEntryForTest()),
+        );
+      });
+
+      it('does NOT clone ResizeObserverSize', () => {
+        const entry = createResizeObserverEntryForTest();
+        const size = ensureInstance(
+          entry.contentBoxSize[0],
+          ResizeObserverSize,
+        );
+
+        expectDataCloneError(() => structuredClone(size));
+      });
     });
   });
 });