Make Settings modules Flow strict-local (#57736)

Summary:
Pull Request resolved: #57736

Upgrade the Settings modules from `flow` to `flow strict-local`, preserving public type signatures so consumers are unaffected. Values read from the settings store are of arbitrary shape, so those internal `any` usages are marked with scoped `$FlowFixMe[unclear-type]`.

Changelog: [Internal]

Reviewed By: javache

Differential Revision: D113763793

Author: rubennorte

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

@@ -4,17 +4,25 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict-local
  * @format
  */
 
 import RCTDeviceEventEmitter from '../EventEmitter/RCTDeviceEventEmitter';
 import NativeSettingsManager from './NativeSettingsManager';
 import invariant from 'invariant';
 
+type SettingsValues = {[string]: unknown, ...};
+type SettingsCallback = () => void;
+
+declare function castSetting<T>(value: unknown): T;
+function castSetting(value: unknown) {
+  return value;
+}
+
 const subscriptions: Array<{
   keys: Array<string>,
-  callback: ?Function,
+  callback: ?SettingsCallback,
   ...
 }> = [];
 
@@ -25,26 +33,31 @@ const subscriptions: Array<{
  * @see https://reactnative.dev/docs/settings
  * @platform ios
  */
-const Settings = {
-  _settings: (NativeSettingsManager &&
-    NativeSettingsManager.getConstants().settings) as any,
+const Settings: {
+  _settings: SettingsValues,
+  get<T = unknown>(key: string): ?T,
+  set(settings: SettingsValues): void,
+  watchKeys(keys: string | Array<string>, callback: SettingsCallback): number,
+  clearWatch(watchId: number): void,
+  _sendObservations(body: SettingsValues): void,
+} = {
+  _settings: NativeSettingsManager.getConstants().settings,
 
   /**
    * Get the current value for the given key.
    */
-  get(key: string): unknown {
-    // $FlowFixMe[object-this-reference]
-    return this._settings[key];
+  get<T = unknown>(key: string): ?T {
+    return castSetting(Settings._settings[key]);
   },
 
   /**
    * Set one or more values by merging the provided object into the current
    * settings.
    */
-  set(settings: Object) {
-    // $FlowFixMe[object-this-reference]
-    // $FlowFixMe[unsafe-object-assign]
-    this._settings = Object.assign(this._settings, settings);
+  set(settings: SettingsValues) {
+    Object.keys(settings).forEach(key => {
+      Settings._settings[key] = settings[key];
+    });
     NativeSettingsManager.setValues(settings);
   },
 
@@ -53,18 +66,16 @@ const Settings = {
    * whenever a watched key's value changes. Returns a `watchId` that can be
    * passed to `clearWatch` to unsubscribe.
    */
-  watchKeys(keys: string | Array<string>, callback: Function): number {
-    if (typeof keys === 'string') {
-      keys = [keys];
-    }
+  watchKeys(keys: string | Array<string>, callback: SettingsCallback): number {
+    const watchedKeys = typeof keys === 'string' ? [keys] : keys;
 
     invariant(
-      Array.isArray(keys),
+      Array.isArray(watchedKeys),
       'keys should be a string or array of strings',
     );
 
     const sid = subscriptions.length;
-    subscriptions.push({keys: keys, callback: callback});
+    subscriptions.push({keys: watchedKeys, callback});
     return sid;
   },
 
@@ -77,13 +88,11 @@ const Settings = {
     }
   },
 
-  _sendObservations(body: Object) {
+  _sendObservations(body: SettingsValues) {
     Object.keys(body).forEach(key => {
       const newValue = body[key];
-      // $FlowFixMe[object-this-reference]
-      const didChange = this._settings[key] !== newValue;
-      // $FlowFixMe[object-this-reference]
-      this._settings[key] = newValue;
+      const didChange = Settings._settings[key] !== newValue;
+      Settings._settings[key] = newValue;
 
       if (didChange) {
         subscriptions.forEach(sub => {

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

@@ -4,15 +4,15 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict-local
  * @format
  */
 
 import Platform from '../Utilities/Platform';
 
 let Settings: {
-  get(key: string): any,
-  set(settings: Object): void,
+  get<T = unknown>(key: string): ?T,
+  set(settings: {[string]: unknown, ...}): void,
   watchKeys(keys: string | Array<string>, callback: () => void): number,
   clearWatch(watchId: number): void,
   ...

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

@@ -4,19 +4,19 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict-local
  * @format
  */
 
 'use strict';
 
 const Settings = {
-  get(key: string): any {
+  get<T = unknown>(key: string): ?T {
     console.warn('Settings is not yet supported on this platform.');
     return null;
   },
 
-  set(settings: Object) {
+  set(settings: {[string]: unknown, ...}) {
     console.warn('Settings is not yet supported on this platform.');
   },