Make fabric parameter always true in renderApplication

Summary:
Changelog: [Internal]

Remove the fabric parameter from renderApplication and AppContainer. The parameter
is kept in renderApplication for backwards compatibility but is always treated as
true internally. The legacy Paper renderer path is no longer used.

Differential Revision: D101353116

Author: rubennorte

packages/react-native/Libraries/ReactNative/AppContainer-dev.js

@@ -100,7 +100,6 @@ const ReactDevToolsOverlayDeferred = ({
 
 const AppContainer = ({
   children,
-  fabric,
   initialProps,
   internal_excludeInspector = false,
   internal_excludeLogBox = false,
@@ -165,7 +164,7 @@ const AppContainer = ({
 
   if (WrapperComponent != null) {
     innerView = (
-      <WrapperComponent initialProps={initialProps} fabric={fabric === true}>
+      <WrapperComponent initialProps={initialProps}>
         {innerView}
       </WrapperComponent>
     );

packages/react-native/Libraries/ReactNative/AppContainer-prod.js

@@ -17,7 +17,6 @@ import * as React from 'react';
 
 const AppContainer = ({
   children,
-  fabric,
   initialProps,
   rootTag,
   WrapperComponent,
@@ -27,7 +26,7 @@ const AppContainer = ({
 
   if (WrapperComponent != null) {
     innerView = (
-      <WrapperComponent initialProps={initialProps} fabric={fabric === true}>
+      <WrapperComponent initialProps={initialProps}>
         {innerView}
       </WrapperComponent>
     );

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

@@ -15,7 +15,6 @@ import * as React from 'react';
 
 export type Props = Readonly<{
   children?: React.Node,
-  fabric?: boolean,
   rootTag: number | RootTag,
   initialProps?: {...},
   WrapperComponent?: ?React.ComponentType<any>,

packages/react-native/Libraries/ReactNative/AppRegistry.flow.js

@@ -31,7 +31,6 @@ export type AppConfig = {
 export type AppParameters = {
   initialProps: Readonly<{[string]: unknown, ...}>,
   rootTag: RootTag,
-  fabric?: boolean,
 };
 export type Runnable = (
   appParameters: AppParameters,

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

@@ -94,7 +94,7 @@ export function registerComponent(
       appParameters.rootTag,
       wrapperComponentProvider && wrapperComponentProvider(appParameters),
       rootViewStyleProvider && rootViewStyleProvider(appParameters),
-      appParameters.fabric,
+      true, // fabric - deprecated, always true
       scopedPerformanceLogger,
       appKey === 'LogBox', // is logbox
       appKey,

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

@@ -13,7 +13,6 @@ import type {IPerformanceLogger} from '../Utilities/createPerformanceLogger';
 
 import GlobalPerformanceLogger from '../Utilities/GlobalPerformanceLogger';
 import PerformanceLoggerContext from '../Utilities/PerformanceLoggerContext';
-import warnOnce from '../Utilities/warnOnce';
 import AppContainer from './AppContainer';
 import DisplayMode, {type DisplayModeType} from './DisplayMode';
 import getCachedComponentWithDebugName from './getCachedComponentWithDebugName';
@@ -37,7 +36,9 @@ export default function renderApplication<Props extends Object>(
   rootTag: any,
   WrapperComponent?: ?React.ComponentType<any>,
   rootViewStyle?: ?ViewStyleProp,
-  fabric?: boolean,
+  // Keep this parameter for backwards compatibility only. It is always treated as
+  // true internally.
+  fabric?: true | void,
   scopedPerformanceLogger?: IPerformanceLogger,
   isLogBox?: boolean,
   debugName?: string,
@@ -52,7 +53,6 @@ export default function renderApplication<Props extends Object>(
     <PerformanceLoggerContext.Provider value={performanceLogger}>
       <AppContainer
         rootTag={rootTag}
-        fabric={fabric}
         WrapperComponent={WrapperComponent}
         rootViewStyle={rootViewStyle}
         initialProps={initialProps ?? Object.freeze({})}
@@ -87,32 +87,18 @@ export default function renderApplication<Props extends Object>(
     );
   }
 
-  // We want to have concurrentRoot always enabled when you're on Fabric.
-  const useConcurrentRoot = Boolean(fabric);
-
   performanceLogger.startTimespan('renderApplication_React_render');
-  performanceLogger.setExtra(
-    'usedReactConcurrentRoot',
-    useConcurrentRoot ? '1' : '0',
-  );
-  performanceLogger.setExtra('usedReactFabric', fabric ? '1' : '0');
+  performanceLogger.setExtra('usedReactConcurrentRoot', '1');
+  performanceLogger.setExtra('usedReactFabric', '1');
   performanceLogger.setExtra(
     'usedReactProfiler',
     Renderer.isProfilingRenderer(),
   );
   Renderer.renderElement({
     element: renderable,
     rootTag,
-    useFabric: Boolean(fabric),
-    useConcurrentRoot,
+    useFabric: true,
+    useConcurrentRoot: true,
   });
-
-  const newArchitecture = !!fabric;
-  if (!newArchitecture) {
-    warnOnce(
-      '[OSS][OldArchDeprecatedWarning]',
-      'The app is running using the Legacy Architecture. The Legacy Architecture is deprecated and will be removed in a future version of React Native. Please consider migrating to the New Architecture. For more information, please see https://reactnative.dev/blog/2024/10/23/the-new-architecture-is-here',
-    );
-  }
   performanceLogger.stopTimespan('renderApplication_React_render');
 }