Improve typing of renderApplication

Summary:
General typing improvements to the `renderApplication` module:

- Refactors `renderApplication` to take a single options object instead
  of positional arguments, and removes the unused `fabric` and `_unused`
  parameters. The `fabric` parameter was already always treated as
  `true` internally, and the `_unused` slot was a reserved positional
  placeholder for a removed `scopedPerformanceLogger` argument.
- Migrates the file to `flow strict-local`.
- Types `RootComponent` and `WrapperComponent` using component syntax
  instead of `React.ComponentType`.
- Replaces `rootTag: any` with `number | RootTag`, normalizing via the
  existing `createRootTag` helper for `<AppContainer>` and `Number()`
  for `Renderer.renderElement`.
- Simplifies `ActivityType` (drops the unnecessary spread) and tightens
  null/boolean checks (`debugName != null`, `useOffscreen === true`).

Exports a new `RenderApplicationOptions<Props>` type and updates all
internal callers accordingly.

Changelog:
[Internal]

Reviewed By: javache

Differential Revision: D102325691

Author: rubennorte

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

@@ -83,21 +83,21 @@ export function registerComponent(
 ): string {
   runnables[appKey] = (appParameters, displayMode) => {
     const renderApplication = require('./renderApplication').default;
-    renderApplication(
-      componentProviderInstrumentationHook(
+    renderApplication({
+      RootComponent: componentProviderInstrumentationHook(
         componentProvider,
         DeprecatedPerformanceLoggerStub,
       ),
-      appParameters.initialProps,
-      appParameters.rootTag,
-      wrapperComponentProvider && wrapperComponentProvider(appParameters),
-      rootViewStyleProvider && rootViewStyleProvider(appParameters),
-      true, // fabric - deprecated, always true
-      undefined, // formerly scopedPerformanceLogger; reserved positional slot
-      appKey === 'LogBox', // is logbox
-      appKey,
+      initialProps: appParameters.initialProps,
+      rootTag: appParameters.rootTag,
+      WrapperComponent:
+        wrapperComponentProvider && wrapperComponentProvider(appParameters),
+      rootViewStyle:
+        rootViewStyleProvider && rootViewStyleProvider(appParameters),
+      isLogBox: appKey === 'LogBox',
+      debugName: appKey,
       displayMode,
-    );
+    });
   };
   if (section) {
     sections[appKey] = runnables[appKey];

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

@@ -8,6 +8,8 @@
  * @format
  */
 
+import type {RootTag} from './RootTag';
+
 import {
   onCaughtError,
   onRecoverableError,
@@ -21,11 +23,11 @@ export function renderElement({
   rootTag,
 }: {
   element: React.MixedElement,
-  rootTag: number,
+  rootTag: RootTag,
 }): void {
   ReactFabric.render(
     element,
-    rootTag,
+    Number(rootTag),
     /* callback */ null,
     /* useConcurrentRoot */ true,
     {

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

@@ -4,47 +4,49 @@
  * 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 type {ViewStyleProp} from '../StyleSheet/StyleSheet';
+import type {RootTag} from './RootTag';
 
 import AppContainer from './AppContainer';
 import DisplayMode, {type DisplayModeType} from './DisplayMode';
 import getCachedComponentWithDebugName from './getCachedComponentWithDebugName';
 import * as Renderer from './RendererProxy';
+import {createRootTag} from './RootTag';
 import invariant from 'invariant';
 import * as React from 'react';
 
 // require BackHandler so it sets the default handler that exits the app if no listeners respond
 import '../Utilities/BackHandler';
 
-type ActivityType = component(
-  ...{
-    mode: 'visible' | 'hidden',
-    children: React.Node,
-  }
-);
+type ActivityType = component(mode: 'visible' | 'hidden', children: React.Node);
 
-export default function renderApplication<Props extends Object>(
-  RootComponent: React.ComponentType<Props>,
+export type RenderApplicationOptions<Props extends {...}> = {
+  RootComponent: component(...Props),
   initialProps: Props,
-  rootTag: any,
-  WrapperComponent?: ?React.ComponentType<any>,
+  rootTag: number | RootTag,
+  WrapperComponent?: ?component(initialProps: Props, children: React.Node),
   rootViewStyle?: ?ViewStyleProp,
-  // Keep this parameter for backwards compatibility only. It is always treated as
-  // true internally.
-  fabric?: true | void,
-  // Reserved positional slot (formerly `scopedPerformanceLogger`). Preserved so
-  // existing callers that supply this argument continue to type-check; the
-  // value is ignored.
-  _unused?: void,
   isLogBox?: boolean,
   debugName?: string,
   displayMode?: ?DisplayModeType,
   useOffscreen?: boolean,
-) {
+};
+
+export default function renderApplication<Props extends {...}>({
+  RootComponent,
+  initialProps,
+  rootTag,
+  WrapperComponent,
+  rootViewStyle,
+  isLogBox,
+  debugName,
+  displayMode,
+  useOffscreen,
+}: RenderApplicationOptions<Props>) {
   invariant(rootTag, 'Expect to have a valid rootTag, instead got ', rootTag);
 
   let renderable: React.MixedElement = (
@@ -58,7 +60,7 @@ export default function renderApplication<Props extends Object>(
     </AppContainer>
   );
 
-  if (__DEV__ && debugName) {
+  if (__DEV__ && debugName != null) {
     const RootComponentWithMeaningfulName = getCachedComponentWithDebugName(
       `${debugName}(RootComponent)`,
     );
@@ -69,7 +71,7 @@ export default function renderApplication<Props extends Object>(
     );
   }
 
-  if (useOffscreen && displayMode != null) {
+  if (useOffscreen === true && displayMode != null) {
     // $FlowFixMe[incompatible-type]
     // $FlowFixMe[missing-export]
     // $FlowFixMe[prop-missing] `unstable_Activity` is not yet in the React types.
@@ -85,6 +87,6 @@ export default function renderApplication<Props extends Object>(
 
   Renderer.renderElement({
     element: renderable,
-    rootTag,
+    rootTag: createRootTag(rootTag),
   });
 }