Fix switch shadow node compilation for cross-platform SPM builds

Package.swift's #if os(macOS) runs on the host (always macOS), not
the target platform. This meant iOS builds got macOS switch excludes,
causing AppKit import errors.

Instead of conditionally excluding files in Package.swift, add
#if TARGET_OS_OSX guards directly in the .mm files. Both files are
now included in all builds but compile to empty on the wrong platform.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Saadnajmi

packages/react-native/Package.swift

@@ -385,11 +385,9 @@ let reactCore = RNTarget(
 #if os(macOS)
 let reactFabricViewPlatformSources = ["components/view/platform/macos"]
 let reactFabricViewPlatformExcludes = ["components/view/platform/cxx"]
-let reactFabricComponentsSwitchExcludes = ["components/switch/iosswitch/react/renderer/components/switch/IOSSwitchShadowNode.mm"]
 #else
 let reactFabricViewPlatformExcludes = ["components/view/platform/macos"]
 let reactFabricViewPlatformSources = ["components/view/platform/cxx"]
-let reactFabricComponentsSwitchExcludes = ["components/switch/iosswitch/react/renderer/components/switch/MacOSSwitchShadowNode.mm"]
 #endif
 // macOS]
 let reactFabric = RNTarget(
@@ -448,7 +446,8 @@ let reactFabricComponents = RNTarget(
     "components/view/platform/android",
     "components/view/platform/windows",
     "components/view/platform/macos",
-    // "components/switch/iosswitch/.../MacOSSwitchShadowNode.mm" or "IOSSwitchShadowNode.mm" — [macOS] see reactFabricComponentsSwitchExcludes
+    // [macOS] Both IOSSwitchShadowNode.mm and MacOSSwitchShadowNode.mm are included;
+    // they use #if TARGET_OS_OSX guards internally so only the correct one compiles.
     "components/textinput/platform/android",
     "components/text/platform/android",
     "components/textinput/platform/macos",
@@ -459,7 +458,7 @@ let reactFabricComponents = RNTarget(
     "textlayoutmanager/platform/windows",
     "textlayoutmanager/platform/macos",
     "conponents/rncore", // this was the old folder where RN Core Components were generated. If you ran codegen in the past, you might have some files in it that might make the build fail.
-  ] + reactFabricComponentsSwitchExcludes, // [macOS]
+  ],
   dependencies: [.reactNativeDependencies, .reactCore, .reactJsiExecutor, .reactTurboModuleCore, .jsi, .logger, .reactDebug, .reactFeatureFlags, .reactUtils, .reactRuntimeScheduler, .reactCxxReact, .yoga, .reactRendererDebug, .reactGraphics, .reactFabric, .reactTurboModuleBridging],
   sources: ["components/inputaccessory", "components/modal", "components/safeareaview", "components/text", "components/text/platform/cxx", "components/textinput", "components/textinput/platform/ios/", "components/unimplementedview", "components/virtualview", "textlayoutmanager", "textlayoutmanager/platform/ios", "components/switch/iosswitch"]
 )

packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/IOSSwitchShadowNode.mm

@@ -5,6 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <TargetConditionals.h> // [macOS]
+#if !TARGET_OS_OSX // [macOS]
+
 #import <React/RCTUtils.h>
 #import <UIKit/UIKit.h>
 #include "AppleSwitchShadowNode.h"
@@ -26,3 +29,5 @@
 }
 
 } // namespace facebook::react
+
+#endif // !TARGET_OS_OSX [macOS]

packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/MacOSSwitchShadowNode.mm

@@ -5,6 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <TargetConditionals.h> // [macOS]
+#if TARGET_OS_OSX // [macOS]
+
 #import <AppKit/AppKit.h>
 #include "AppleSwitchShadowNode.h"
 
@@ -30,3 +33,5 @@
 }
 
 } // namespace facebook::react
+
+#endif // TARGET_OS_OSX [macOS]