fix(Settings): defer Platform lookup to fix circular dependency startup crash (#56967)

packages/react-native/Libraries/Settings/Settings.js

@@ -8,20 +8,45 @@
  * @format
  */
 
-import Platform from '../Utilities/Platform';
-
-let Settings: {
+type SettingsStatic = {
   get(key: string): any,
   set(settings: Object): void,
   watchKeys(keys: string | Array<string>, callback: () => void): number,
   clearWatch(watchId: number): void,
   ...
 };
 
-if (Platform.OS === 'ios') {
-  Settings = require('./Settings').default;
-} else {
-  Settings = require('./SettingsFallback').default;
+let SettingsImpl: ?SettingsStatic = null;
+
+function getSettings(): SettingsStatic {
+  if (SettingsImpl != null) {
+    return SettingsImpl;
+  }
+  const Platform = require('../Utilities/Platform').default;
+  if (Platform.OS === 'ios') {
+    SettingsImpl = require('./Settings').default;
+  } else {
+    SettingsImpl = require('./SettingsFallback').default;
+  }
+  return (SettingsImpl: SettingsStatic);
 }
 
+const Settings: SettingsStatic = {
+  get(key: string): any {
+    return getSettings().get(key);
+  },
+
+  set(settings: Object): void {
+    getSettings().set(settings);
+  },
+
+  watchKeys(keys: string | Array<string>, callback: () => void): number {
+    return getSettings().watchKeys(keys, callback);
+  },
+
+  clearWatch(watchId: number): void {
+    getSettings().clearWatch(watchId);
+  },
+};
+
 export default Settings;

packages/react-native/Libraries/Settings/__tests__/Settings-test.js

@@ -0,0 +1,101 @@
+/**
+ * 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';
+
+describe('Settings', () => {
+  beforeEach(() => {
+    jest.resetModules();
+  });
+
+  it('should not throw due to circular dependency during Platform initialization', () => {
+    // Intercept NativePlatformConstantsIOS (which Platform.ios requires during
+    // load) to simulate another module requiring Settings during Platform's
+    // initialization phase.
+    jest.mock('../../Utilities/NativePlatformConstantsIOS', () => {
+      // Accessing Settings while Platform is loading
+      require('../Settings.js');
+      return {
+        getConstants() {
+          return {
+            interfaceIdiom: 'phone',
+            isTesting: true,
+            osVersion: '16.0',
+            systemName: 'iOS',
+          };
+        },
+      };
+    });
+
+    expect(() => {
+      require('../../Utilities/Platform');
+    }).not.toThrow();
+  });
+
+  it('defers accessing Platform until a method is first invoked', () => {
+    let platformAccessCount = 0;
+    jest.doMock('../../Utilities/Platform', () => ({
+      __esModule: true,
+      get default() {
+        platformAccessCount++;
+        return {OS: 'android'};
+      },
+    }));
+
+    const Settings = require('../Settings.js').default;
+    expect(platformAccessCount).toBe(0);
+
+    const warnSpy = jest.spyOn(console, 'warn').mockImplementation(() => {});
+    Settings.get('any');
+    expect(platformAccessCount).toBeGreaterThan(0);
+    warnSpy.mockRestore();
+  });
+
+  it('delegates get/set/watchKeys/clearWatch to the iOS implementation', () => {
+    const setValues = jest.fn();
+    jest.doMock('../../Utilities/Platform', () => ({
+      __esModule: true,
+      default: {OS: 'ios'},
+    }));
+    jest.doMock('../NativeSettingsManager', () => ({
+      __esModule: true,
+      default: {
+        getConstants: () => ({settings: {existing: 'initial'}}),
+        setValues,
+      },
+    }));
+
+    const Settings = require('../Settings.js').default;
+
+    expect(Settings.get('existing')).toBe('initial');
+    Settings.set({added: 'value'});
+    expect(Settings.get('added')).toBe('value');
+    expect(setValues).toHaveBeenCalledWith({added: 'value'});
+
+    const watchId = Settings.watchKeys('key', () => {});
+    expect(typeof watchId).toBe('number');
+    expect(() => Settings.clearWatch(watchId)).not.toThrow();
+  });
+
+  it('uses the fallback implementation on non-iOS platforms', () => {
+    jest.doMock('../../Utilities/Platform', () => ({
+      __esModule: true,
+      default: {OS: 'android'},
+    }));
+
+    const warnSpy = jest.spyOn(console, 'warn').mockImplementation(() => {});
+    const Settings = require('../Settings.js').default;
+
+    expect(Settings.get('foo')).toBeNull();
+    expect(Settings.watchKeys('foo', () => {})).toBe(-1);
+    expect(warnSpy).toHaveBeenCalled();
+    warnSpy.mockRestore();
+  });
+});