Preserve lazy ViewManager initialization in UIManager (#58097)

Summary:
- Preserve lazy ViewManager property descriptors when composing UIManager.
- Avoid eagerly invoking lazy ViewManager getters and unnecessary getConstantsForViewManager calls during Bridgeless initialization.
- Add regression coverage for lazy, own, enumerable and one-time getter behavior.
- Platform scope: This targets the Android Bridgeless lazy ViewManager path. iOS does not currently expose this lazy getter path, so no iOS runtime behavior or performance change is expected.

## Changelog:

[ANDROID] [FIXED] - Avoid unnecessary getConstantsForViewManager calls during UIManager initialization.

Pull Request resolved: #58097

Test Plan:
- `yarn flow-check`
- `yarn test packages/react-native/Libraries/ReactNative --runInBand`
- `yarn lint --quiet`
- `yarn format-check`
- Verified with Android RNTester offlineDebug that startup no longer triggers eager getConstantsForViewManager calls.

Reviewed By: cipolleschi

Differential Revision: D124967747

Pulled By: javache

fbshipit-source-id: 1a4daf139b555ed266d5a7d3a0b90ebb02cfe5be

Author: fairysword

packages/react-native/Libraries/ReactNative/UIManager.js

@@ -8,6 +8,7 @@
  * @format
  */
 
+import type {UnsafeObject} from '../Types/CodegenTypes';
 import type {UIManagerJSInterface} from '../Types/UIManagerJSInterface';
 
 import {getFabricUIManager} from './FabricUIManager';
@@ -23,9 +24,7 @@ const UIManagerImpl: UIManagerJSInterface =
     ? require('./BridgelessUIManager').default
     : require('./PaperUIManager').default;
 
-// $FlowFixMe[cannot-spread-interface]
-const UIManager: UIManagerJSInterface = {
-  ...UIManagerImpl,
+const UIManagerOverrides = {
   /**
    * Determines the location on screen, width, and height of the given view and
    * returns the values via an async callback. If successful, the callback will
@@ -129,7 +128,7 @@ const UIManager: UIManagerJSInterface = {
   measureLayout(
     reactTag: number,
     ancestorReactTag: number,
-    errorCallback,
+    errorCallback: (error: UnsafeObject) => void,
     callback: (
       left: number,
       top: number,
@@ -167,7 +166,7 @@ const UIManager: UIManagerJSInterface = {
 
   measureLayoutRelativeToParent(
     reactTag: number,
-    errorCallback,
+    errorCallback: (error: UnsafeObject) => void,
     callback: (
       left: number,
       top: number,
@@ -249,4 +248,19 @@ const UIManager: UIManagerJSInterface = {
   },
 };
 
+// Copy property descriptors instead of spreading UIManagerImpl. In Bridgeless
+// mode, UIManagerImpl may define enumerable lazy ViewManager getters. Spreading
+// the object would invoke every getter during module initialization.
+// $FlowFixMe[incompatible-type] Flow cannot infer properties from descriptors.
+const UIManager: UIManagerJSInterface = Object.create(
+  Object.getPrototypeOf(UIManagerImpl),
+  {
+    ...Object.getOwnPropertyDescriptors(
+      // $FlowFixMe[class-object-subtyping] UIManagerImpl is a runtime object.
+      UIManagerImpl,
+    ),
+    ...Object.getOwnPropertyDescriptors(UIManagerOverrides),
+  },
+);
+
 export default UIManager;

packages/react-native/Libraries/ReactNative/__tests__/UIManager-test.js

@@ -0,0 +1,74 @@
+/**
+ * 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.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+'use strict';
+
+jest.mock('../../Utilities/Platform', () => ({
+  OS: 'android',
+  select: spec => spec.android ?? spec.native ?? spec.default,
+}));
+jest.unmock('../UIManager');
+
+describe('UIManager', () => {
+  it('preserves lazy ViewManager getters when composing the Bridgeless implementation', () => {
+    const originalBridgelessValue = global.RN$Bridgeless;
+    const originalGetConstants = global.RN$LegacyInterop_UIManager_getConstants;
+    const originalGetConstantsForViewManager =
+      global.RN$LegacyInterop_UIManager_getConstantsForViewManager;
+    const originalGetDefaultEventTypes =
+      global.RN$LegacyInterop_UIManager_getDefaultEventTypes;
+    const viewManagerConfig = {Commands: {focus: 1}};
+    const getConstants = jest.fn(() => ({
+      LazyViewManagersEnabled: true,
+      ViewManagerNames: ['RCTTestView'],
+    }));
+    const getConstantsForViewManager = jest.fn(() => viewManagerConfig);
+
+    jest.resetModules();
+    try {
+      // $FlowExpectedError[cannot-write]
+      global.RN$Bridgeless = true;
+      // $FlowExpectedError[cannot-write]
+      global.RN$LegacyInterop_UIManager_getConstants = getConstants;
+      // $FlowExpectedError[cannot-write]
+      global.RN$LegacyInterop_UIManager_getConstantsForViewManager =
+        getConstantsForViewManager;
+      // $FlowExpectedError[cannot-write]
+      global.RN$LegacyInterop_UIManager_getDefaultEventTypes = jest.fn(
+        () => ({}),
+      );
+
+      const UIManager = require('../UIManager').default;
+
+      expect(getConstants).toHaveBeenCalledTimes(1);
+      expect(getConstantsForViewManager).not.toHaveBeenCalled();
+      expect(
+        Object.getOwnPropertyDescriptor(UIManager, 'RCTTestView'),
+      ).toBeDefined();
+      expect(Object.keys(UIManager)).toContain('RCTTestView');
+
+      expect(Reflect.get(UIManager, 'RCTTestView')).toBe(viewManagerConfig);
+      expect(Reflect.get(UIManager, 'RCTTestView')).toBe(viewManagerConfig);
+      expect(getConstantsForViewManager).toHaveBeenCalledTimes(1);
+    } finally {
+      // $FlowExpectedError[cannot-write]
+      global.RN$Bridgeless = originalBridgelessValue;
+      // $FlowExpectedError[cannot-write]
+      global.RN$LegacyInterop_UIManager_getConstants = originalGetConstants;
+      // $FlowExpectedError[cannot-write]
+      global.RN$LegacyInterop_UIManager_getConstantsForViewManager =
+        originalGetConstantsForViewManager;
+      // $FlowExpectedError[cannot-write]
+      global.RN$LegacyInterop_UIManager_getDefaultEventTypes =
+        originalGetDefaultEventTypes;
+      jest.resetModules();
+    }
+  });
+});