Compile out RCTGetModuleClasses/RCTRegisterModule when both legacy interops are removed (#57670)

Summary:

Changelog: [iOS][Changed] - Compile out `RCTGetModuleClasses`/`RCTRegisterModule` and skip static module registration when both `RCT_REMOVE_LEGACY_MODULE_INTEROP` and `RCT_REMOVE_LEGACY_COMPONENT_INTEROP` are defined


`RCTGetModuleClasses()` and the `RCTModuleClasses` registry it reads (populated by
`RCTRegisterModule`) exist solely to support the two legacy interop layers. Every reader
of the registry is already gated behind either `RCT_REMOVE_LEGACY_MODULE_INTEROP` (TurboModule
⇄ legacy NativeModule interop) or `RCT_REMOVE_LEGACY_COMPONENT_INTEROP` (Fabric ⇄ legacy
ViewManager interop). When an app defines **both** macros, the registry has no readers and the
function, its backing statics, and `RCTRegisterModule` are dead code.

This diff compiles them out in that configuration:

- `React/Base/RCTBridge.mm`: guard `RCTModuleClasses`/`RCTModuleClassesSyncQueue`,
  `RCTGetModuleClasses()`, `getCoreModuleClasses()`, and `RCTRegisterModule()` behind
  `#if !defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) || !defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)`.
  The old-arch warning helpers (`getModulesLoadedWithOldArch` et al.) stay compiled in — they have
  an external caller in `RCTInstance.mm` — and simply observe an empty list once the registry's only
  writer is gone.
- `React/Base/RCTBridge+Private.h`: guard the matching `RCT_EXTERN` declarations.
- `React/Base/RCTBridgeModule.h`: add a "both-removed" variant of `RCT_EXPORT_MODULE` /
  `RCT_EXPORT_MODULE_NO_LOAD` that emits only `+moduleName` and omits the `RCTRegisterModule` call,
  so native modules still link when the symbol is gone.
- `RCTLegacyUIManagerConstantsProvider.{h,mm}`: wrap the file body in
  `#ifndef RCT_REMOVE_LEGACY_COMPONENT_INTEROP`, matching the sibling `LegacyViewManagerInterop*`
  files. It was the one caller of `RCTGetModuleClasses` whose file body was not already guarded.
- `fbobjc/Libraries/FBReactModuleRegistration/FBReactModuleRegistration.mm`: the FIT/new-arch path
  (`RCT_REMOVE_LEGACY_ARCH`) hand-calls `RCTRegisterModule`. On `cove-ios`, which sets all three
  macros, that symbol is now compiled out, so the call is additionally gated to only run when
  `RCTRegisterModule` still exists. The registry has no readers in that config, so this is a no-op.

The default build (neither/one macro set) is behavior-unchanged: all guarded code is still compiled in.

Differential Revision: D113555374

Author: christophpurrer

packages/react-native/React/Base/RCTBridge+Private.h

@@ -11,8 +11,10 @@
 @class RCTModuleData;
 @protocol RCTJavaScriptExecutor;
 
+#if !defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) || !defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)
 RCT_EXTERN NSArray<Class> *RCTGetModuleClasses(void);
 RCT_EXTERN void RCTRegisterModule(Class);
+#endif // !defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) || !defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)
 
 @interface RCTBridge ()
 

packages/react-native/React/Base/RCTBridge.mm

@@ -31,6 +31,7 @@
 #import "RCTReloadCommand.h"
 #import "RCTUtils.h"
 
+#if !defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) || !defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)
 static NSMutableArray<Class> *RCTModuleClasses;
 static dispatch_queue_t RCTModuleClassesSyncQueue;
 NSArray<Class> *RCTGetModuleClasses(void)
@@ -115,6 +116,7 @@
 
   return coreModuleClasses;
 }
+#endif // !defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) || !defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)
 
 static NSMutableArray<NSString *> *modulesLoadedWithOldArch;
 void addModuleLoadedWithOldArch(NSString * /*moduleName*/);
@@ -133,6 +135,7 @@ void addModuleLoadedWithOldArch(NSString *moduleName)
   return modulesLoadedWithOldArch;
 }
 
+#if !defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) || !defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)
 /**
  * Register the given class as a bridge module. All modules must be registered
  * prior to the first bridge initialization.
@@ -161,6 +164,7 @@ void RCTRegisterModule(Class moduleClass)
     [RCTModuleClasses addObject:moduleClass];
   });
 }
+#endif // !defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) || !defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)
 
 /**
  * This function returns the module name for a given class.

packages/react-native/React/Base/RCTBridgeModule.h

@@ -69,6 +69,18 @@ RCT_EXTERN_C_END
  * will be used as the JS module name. If omitted, the JS module name will
  * match the Objective-C class name.
  */
+#if defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) && defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)
+
+// With both legacy interop layers removed, RCTRegisterModule is compiled out, so
+// static module registration is a no-op: only the JS module name is emitted.
+#define RCT_EXPORT_MODULE(js_name) \
+  +(NSString *)moduleName          \
+  {                                \
+    return @ #js_name;             \
+  }
+
+#else
+
 #ifndef RCT_DISABLE_STATIC_MODULE_REGISTRATION
 #define RCT_EXPORT_MODULE(js_name)          \
   RCT_EXTERN void RCTRegisterModule(Class); \
@@ -108,6 +120,8 @@ RCT_EXTERN_C_END
     RCTRegisterModule([objc_name class]);                                           \
   }
 
+#endif // defined(RCT_REMOVE_LEGACY_MODULE_INTEROP) && defined(RCT_REMOVE_LEGACY_COMPONENT_INTEROP)
+
 // Implemented by RCT_EXPORT_MODULE
 + (NSString *)moduleName;
 

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTLegacyUIManagerConstantsProvider.h

@@ -7,6 +7,8 @@
 
 #pragma once
 
+#ifndef RCT_REMOVE_LEGACY_COMPONENT_INTEROP
+
 #include <jsi/jsi.h>
 
 namespace facebook::react {
@@ -17,3 +19,5 @@ namespace facebook::react {
  */
 void installLegacyUIManagerConstantsProviderBinding(jsi::Runtime &runtime);
 } // namespace facebook::react
+
+#endif // RCT_REMOVE_LEGACY_COMPONENT_INTEROP

packages/react-native/ReactCommon/react/runtime/platform/ios/ReactCommon/RCTLegacyUIManagerConstantsProvider.mm

@@ -7,6 +7,8 @@
 
 #include "RCTLegacyUIManagerConstantsProvider.h"
 
+#ifndef RCT_REMOVE_LEGACY_COMPONENT_INTEROP
+
 #import <React/RCTBridge+Private.h>
 #import <React/RCTComponentData.h>
 #import <React/RCTUIManager.h>
@@ -41,3 +43,5 @@ void installLegacyUIManagerConstantsProviderBinding(jsi::Runtime &runtime)
   LegacyUIManagerConstantsProviderBinding::install(runtime, "getConstants", getConstants);
 }
 } // namespace facebook::react
+
+#endif // RCT_REMOVE_LEGACY_COMPONENT_INTEROP