[polyfill] Add warning for bad Map/Set polyfills

packages/react/src/BadMapPolyfill.js

@@ -17,7 +17,11 @@ if (__DEV__) {
     new Set([frozenObject]);
     /* eslint-enable no-new */
   } catch (e) {
-    // TODO: Consider warning about bad polyfills
+    // Warn about bad polyfills that don't support frozen objects
+    console['warn'](
+      'React detected a Map/Set polyfill that cannot handle frozen objects. ' +
+        'This might cause issues with React\'s internals.'
+    );
     hasBadMapPolyfill = true;
   }
 }

packages/react/src/__tests__/BadMapPolyfill-test.js

@@ -0,0 +1,71 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+describe('BadMapPolyfill', () => {
+  let consoleWarnSpy;
+
+  beforeEach(() => {
+    consoleWarnSpy = jest.spyOn(console, 'warn').mockImplementation(() => {});
+  });
+
+  afterEach(() => {
+    consoleWarnSpy.mockRestore();
+  });
+
+  // @gate __DEV__
+  it('should warn when a bad Map/Set polyfill is detected', () => {
+    // Mock a Map/Set that fails with frozen objects
+    const originalMap = global.Map;
+    const originalSet = global.Set;
+
+    global.Map = function BadMap() {
+      if (arguments.length > 0 && arguments[0]) {
+        const entries = arguments[0];
+        for (let i = 0; i < entries.length; i++) {
+          if (Object.isFrozen(entries[i][0])) {
+            throw new Error('Cannot handle frozen object');
+          }
+        }
+      }
+    };
+
+    global.Set = function BadSet() {
+      if (arguments.length > 0 && arguments[0]) {
+        const values = arguments[0];
+        for (let i = 0; i < values.length; i++) {
+          if (Object.isFrozen(values[i])) {
+            throw new Error('Cannot handle frozen object');
+          }
+        }
+      }
+    };
+
+    // Re-require the module to trigger the polyfill detection
+    jest.resetModules();
+    require('../BadMapPolyfill');
+
+    expect(consoleWarnSpy).toHaveBeenCalledWith(
+      'React detected a Map/Set polyfill that cannot handle frozen objects. ' +
+        'This might cause issues with React\'s internals.'
+    );
+
+    // Restore original Map/Set
+    global.Map = originalMap;
+    global.Set = originalSet;
+  });
+
+  // @gate __DEV__
+  it('should not warn when Map/Set polyfill works correctly', () => {
+    // Re-require the module to trigger the polyfill detection with good polyfill
+    jest.resetModules();
+    require('../BadMapPolyfill');
+
+    expect(consoleWarnSpy).not.toHaveBeenCalled();
+  });
+});