Emit a real framework for React-cxxstableapi under use_frameworks! (#57936)

packages/react-native/Package.swift

@@ -959,6 +959,10 @@ extension Target {
       (REMOVE_LEGACY_MODULE_INTEROP ? [.define("RCT_REMOVE_LEGACY_MODULE_INTEROP", to: "1")] : [])
       + (REMOVE_LEGACY_COMPONENT_INTEROP ? [.define("RCT_REMOVE_LEGACY_COMPONENT_INTEROP", to: "1")] : [])
 
+    // Every target built through this factory is React Native's own, so RN_BUILDING
+    // keeps the react/cxxstableapi guards inert for internal sources. cxxSettings are
+    // per-target and are not inherited by packages that depend on React, so this does
+    // not exempt consumers from the guards.
     let cxxSettings =
       [
         .unsafeFlags(["-std=c++20"]),
@@ -967,6 +971,7 @@ extension Target {
         .define("USE_HERMES", to: "1"),
         .define("RCT_REMOVE_LEGACY_ARCH", to: "1"),
         .define("HERMES_V1_ENABLED", to: "1"),
+        .define("RN_BUILDING", to: "1"),
       ] + legacyInteropDefines + defines + cxxCommonHeaderPaths
 
     return .target(

packages/react-native/ReactAndroid/src/main/jni/CMakeLists.txt

@@ -58,6 +58,14 @@ add_react_third_party_ndk_subdir(fast_float)
 add_react_third_party_ndk_subdir(fmt)
 add_react_third_party_ndk_subdir(folly)
 
+# Marks everything added below as React Native's own build, so the
+# react/cxxstableapi guards let internal sources keep including the
+# fine-grained headers they fence off from consumers. Deliberately declared
+# after the third-party subdirectories so it never reaches them, and this
+# project never compiles app or third-party module code (those build against
+# the prefab artifacts through ReactNative-application.cmake).
+add_compile_definitions(RN_BUILDING)
+
 # Common targets
 add_react_common_subdir(yoga)
 add_react_common_subdir(runtimeexecutor)

packages/react-native/ReactCommon/react/cxxstableapi/React-cxxstableapi.podspec

@@ -25,7 +25,7 @@ Pod::Spec.new do |s|
   s.author                 = "Meta Platforms, Inc. and its affiliates"
   s.platforms              = min_supported_versions
   s.source                 = source
-  s.source_files           = podspec_sources("*.h", "*.h")
+  s.source_files           = podspec_sources("*.{cpp,h}", "*.h")
   s.header_dir             = "react/cxxstableapi"
   s.pod_target_xcconfig    = { "CLANG_CXX_LANGUAGE_STANDARD" => rct_cxx_language_standard(),
                                "DEFINES_MODULE" => "YES" }

packages/react-native/ReactCommon/react/cxxstableapi/StableApiAnchor.cpp

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// Anchor translation unit for the `react/cxxstableapi` pod.
+//
+// The guards in this module are pure preprocessor headers, so the pod would
+// otherwise ship no compilable source. CocoaPods emits a PBXAggregateTarget for
+// a pod with no compilable sources, and an aggregate target produces no
+// `.framework` under `use_frameworks!` — dependents are then unable to resolve
+// the guard headers. Giving the pod a single source file forces CocoaPods to
+// emit a real framework target instead.
+//
+// This file intentionally declares nothing: `react/cxxstableapi` has no runtime
+// API, only preprocessor guards. Do not add code here.

private/react-native-fantom/tester/CMakeLists.txt

@@ -58,6 +58,7 @@ add_react_common_subdir(jsitooling)
 add_react_common_subdir(logger)
 add_react_common_subdir(oscompat)
 add_react_common_subdir(react/bridging)
+add_react_common_subdir(react/cxxstableapi)
 add_react_common_subdir(react/debug)
 add_react_common_subdir(react/featureflags)
 add_react_common_subdir(react/nativemodule/core)