Cover react/featureflags with Stable API guards (#58083)

Summary:

Classifies `react/featureflags:featureflags` as a public target under the C++ stable API three-tier visibility model and introduces the module umbrella `React/FeatureFlags.h` as its public entry point.

This module's headers are generated, so the `UmbrellaGuard.h` include is added to the templates in `scripts/featureflags/templates/common-cxx/` rather than to the headers themselves. `ReactNativeFeatureFlagsOverridesOSSStable.h` is the module's one hand-written header and is edited directly. The umbrella is not generated, and re-exports all eight of the module's headers.

The sibling `react/nativemodule/featureflags:featureflags` target is private under the same model.

The guards are inert unless a consumer defines `RN_STRICT_API`, so there is no behavior change.

Changelog:
[General][Added] - Add `<React/FeatureFlags.h>` umbrella header as the public entry point for `react/featureflags`

Reviewed By: cortinico

Differential Revision: D117172757

Author: j-piasecki

packages/react-native/ReactAndroid/build.gradle.kts

@@ -115,6 +115,7 @@ val preparePrefab by
                       Pair("../ReactCommon/cxxreact/", "cxxreact/"),
                       // react_featureflags
                       Pair("../ReactCommon/react/featureflags/", "react/featureflags/"),
+                      Pair("../ReactCommon/react/featureflags/React/", "React/"),
                       // react_devtoolsruntimesettings
                       Pair(
                           "../ReactCommon/react/devtoolsruntimesettings/",

packages/react-native/ReactCommon/react/featureflags/CMakeLists.txt

@@ -12,7 +12,8 @@ file(GLOB react_featureflags_SRC CONFIGURE_DEPENDS *.cpp)
 add_library(react_featureflags OBJECT ${react_featureflags_SRC})
 
 target_include_directories(react_featureflags PUBLIC ${REACT_COMMON_DIR})
+target_include_directories(react_featureflags INTERFACE ${REACT_COMMON_DIR}/react/featureflags)
 
-target_link_libraries(react_featureflags folly_runtime)
+target_link_libraries(react_featureflags folly_runtime react_cxxstableapi)
 target_compile_reactnative_options(react_featureflags PRIVATE)
 target_compile_options(react_featureflags PRIVATE -Wpedantic)

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

@@ -39,8 +39,15 @@ Pod::Spec.new do |s|
 
   resolve_use_frameworks(s, header_mappings_dir: "../..", module_name: "React_featureflags")
 
+  s.dependency "React-cxxstableapi"
   add_rn_third_party_dependencies(s)
   add_rncore_dependency(s)
 
+  s.subspec "featureflagsUmbrella" do |ss|
+    ss.source_files        = "React/*.h"
+    ss.header_dir          = "React"
+    ss.header_mappings_dir = "React"
+  end
+
   mark_as_react_native_build(s)
 end

packages/react-native/ReactCommon/react/featureflags/React/FeatureFlags.h

@@ -0,0 +1,40 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+// =============================================================================
+// Umbrella header for the `react/featureflags` module - public entry point.
+//
+//   #include <React/FeatureFlags.h>
+//
+// Re-exports the module's public interface headers. React Native's own code
+// should keep using the fine-grained `<react/featureflags/...>` includes; only
+// outside consumers use this umbrella.
+//
+// The headers below are generated from
+// `scripts/featureflags/ReactNativeFeatureFlags.config.js`, but this file is
+// not - keep it in sync by hand when the set of generated headers in
+// `scripts/featureflags/generateCommonCxxModules.js` changes.
+// =============================================================================
+
+// Marks that the following headers are pulled in through the umbrella, so their
+// shared guard (<react/cxxstableapi/UmbrellaGuard.h>) accepts them. Scoped to
+// this block so later *direct* includes in the same translation unit are still
+// caught.
+#define RN_UMBRELLA_CONTEXT
+
+#include <react/featureflags/ReactNativeFeatureFlags.h>
+#include <react/featureflags/ReactNativeFeatureFlagsAccessor.h>
+#include <react/featureflags/ReactNativeFeatureFlagsDefaults.h>
+#include <react/featureflags/ReactNativeFeatureFlagsDynamicProvider.h>
+#include <react/featureflags/ReactNativeFeatureFlagsOverridesOSSCanary.h>
+#include <react/featureflags/ReactNativeFeatureFlagsOverridesOSSExperimental.h>
+#include <react/featureflags/ReactNativeFeatureFlagsOverridesOSSStable.h>
+#include <react/featureflags/ReactNativeFeatureFlagsProvider.h>
+
+#undef RN_UMBRELLA_CONTEXT

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlags.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<2d59cf5ea42847d6174fc433ba5a6fe4>>
+ * @generated SignedSource<<414b7a90eeecd2abe9849955131fb122>>
  */
 
 /**
@@ -19,6 +19,8 @@
 
 #pragma once
 
+#include <react/cxxstableapi/UmbrellaGuard.h>
+
 #include <react/featureflags/ReactNativeFeatureFlagsAccessor.h>
 #include <react/featureflags/ReactNativeFeatureFlagsProvider.h>
 #include <memory>

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlagsAccessor.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<55f19e7a0d7fbbda3aa131a74909ec07>>
+ * @generated SignedSource<<c1b8add7c4f70f65e71ff2742a7f5427>>
  */
 
 /**
@@ -19,6 +19,8 @@
 
 #pragma once
 
+#include <react/cxxstableapi/UmbrellaGuard.h>
+
 #include <react/featureflags/ReactNativeFeatureFlagsProvider.h>
 #include <array>
 #include <atomic>

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlagsDefaults.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<8e00ed57e2faa8e13ae2eb58afd64962>>
+ * @generated SignedSource<<9e798b7ae2a2f26097359ca37fa99d04>>
  */
 
 /**
@@ -19,6 +19,8 @@
 
 #pragma once
 
+#include <react/cxxstableapi/UmbrellaGuard.h>
+
 #include <react/featureflags/ReactNativeFeatureFlagsProvider.h>
 
 namespace facebook::react {

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlagsDynamicProvider.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<9c0b6df9433a5696f5eacf47713b9040>>
+ * @generated SignedSource<<3429660cde44d793af0e86ff425b1094>>
  */
 
 /**
@@ -19,6 +19,8 @@
 
 #pragma once
 
+#include <react/cxxstableapi/UmbrellaGuard.h>
+
 #include <folly/dynamic.h>
 #include <react/featureflags/ReactNativeFeatureFlagsDefaults.h>
 

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlagsOverridesOSSCanary.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<70297dc6230d386e556c82860cbf9985>>
+ * @generated SignedSource<<650cb266846c66577dde6d7c7a703af1>>
  */
 
 /**
@@ -19,6 +19,8 @@
 
 #pragma once
 
+#include <react/cxxstableapi/UmbrellaGuard.h>
+
 #include <react/featureflags/ReactNativeFeatureFlagsOverridesOSSStable.h>
 
 namespace facebook::react {

packages/react-native/ReactCommon/react/featureflags/ReactNativeFeatureFlagsOverridesOSSExperimental.h

@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @generated SignedSource<<dc6298e569276bf047951a8e4105aa96>>
+ * @generated SignedSource<<5c7271fe5fcdd90f61a5a07772b820e5>>
  */
 
 /**
@@ -19,6 +19,8 @@
 
 #pragma once
 
+#include <react/cxxstableapi/UmbrellaGuard.h>
+
 #include <react/featureflags/ReactNativeFeatureFlagsOverridesOSSCanary.h>
 
 namespace facebook::react {