Fix backwards-compat for ModuleConstants<::Builder> (#54919)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/54919

Add a new `ResultT` to codegen and some C++ trickery so that `ModuleConstants<Type::Builder>` is equal to ModuleConstants<Type> and existing overrides of the module spec remain compatible.

Changelog: [Internal]

Reviewed By: cipolleschi

Differential Revision: D89373357

fbshipit-source-id: ac192e99e424a829668722722cf0c374172de48b

packages/react-native-codegen/e2e/deep_imports/__tests__/modules/__snapshots__/GenerateModuleObjCpp-test.js.snap

@@ -275,6 +275,9 @@ namespace JS {
     struct ConstantsEEE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsEEE;
+
         struct Input {
           RCTRequired<bool> D;
           RCTRequired<double> E;
@@ -304,6 +307,9 @@ namespace JS {
     struct ConstantsEE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsEE;
+
         struct Input {
           RCTRequired<bool> D;
           RCTRequired<JS::NativeObjectTurboModule::ConstantsEEE::Builder> E;
@@ -333,6 +339,9 @@ namespace JS {
     struct ConstantsE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsE;
+
         struct Input {
           RCTRequired<bool> D;
           RCTRequired<JS::NativeObjectTurboModule::ConstantsEE::Builder> E;
@@ -362,6 +371,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<bool> D;
           RCTRequired<JS::NativeObjectTurboModule::ConstantsE::Builder> E;
@@ -420,6 +432,9 @@ namespace JS {
     struct ConstantsEEE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsEEE;
+
         struct Input {
           std::optional<bool> D;
           std::optional<double> E;
@@ -449,6 +464,9 @@ namespace JS {
     struct ConstantsEE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsEE;
+
         struct Input {
           std::optional<bool> D;
           std::optional<JS::NativeOptionalObjectTurboModule::ConstantsEEE::Builder> E;
@@ -478,6 +496,9 @@ namespace JS {
     struct ConstantsE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsE;
+
         struct Input {
           std::optional<bool> D;
           std::optional<JS::NativeOptionalObjectTurboModule::ConstantsEE::Builder> E;
@@ -507,6 +528,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           std::optional<bool> D;
           id<NSObject> _Nullable A;
@@ -698,6 +722,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<bool> const1;
           RCTRequired<double> const2;
@@ -768,6 +795,9 @@ namespace JS {
     struct ConstantsIdElement {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsIdElement;
+
         struct Input {
           RCTRequired<double> prop;
         };
@@ -795,6 +825,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<std::vector<bool>> const1;
           RCTRequired<std::vector<double>> const2;
@@ -896,6 +929,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<std::optional<bool>> const1;
           RCTRequired<std::optional<double>> const2;
@@ -996,6 +1032,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           std::optional<bool> const1;
           std::optional<double> const2;
@@ -1096,6 +1135,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           std::optional<bool> const1;
           std::optional<double> const2;
@@ -1787,6 +1829,9 @@ namespace JS {
     struct ConstantsEEE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsEEE;
+
         struct Input {
           RCTRequired<bool> D;
           RCTRequired<double> E;
@@ -1816,6 +1861,9 @@ namespace JS {
     struct ConstantsEE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsEE;
+
         struct Input {
           RCTRequired<bool> D;
           RCTRequired<JS::NativeObjectTurboModule::ConstantsEEE::Builder> E;
@@ -1845,6 +1893,9 @@ namespace JS {
     struct ConstantsE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsE;
+
         struct Input {
           RCTRequired<bool> D;
           RCTRequired<JS::NativeObjectTurboModule::ConstantsEE::Builder> E;
@@ -1874,6 +1925,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<bool> D;
           RCTRequired<JS::NativeObjectTurboModule::ConstantsE::Builder> E;
@@ -1932,6 +1986,9 @@ namespace JS {
     struct ConstantsEEE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsEEE;
+
         struct Input {
           std::optional<bool> D;
           std::optional<double> E;
@@ -1961,6 +2018,9 @@ namespace JS {
     struct ConstantsEE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsEE;
+
         struct Input {
           std::optional<bool> D;
           std::optional<JS::NativeOptionalObjectTurboModule::ConstantsEEE::Builder> E;
@@ -1990,6 +2050,9 @@ namespace JS {
     struct ConstantsE {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsE;
+
         struct Input {
           std::optional<bool> D;
           std::optional<JS::NativeOptionalObjectTurboModule::ConstantsEE::Builder> E;
@@ -2019,6 +2082,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           std::optional<bool> D;
           id<NSObject> _Nullable A;
@@ -2210,6 +2276,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<bool> const1;
           RCTRequired<double> const2;
@@ -2280,6 +2349,9 @@ namespace JS {
     struct ConstantsIdElement {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ConstantsIdElement;
+
         struct Input {
           RCTRequired<double> prop;
         };
@@ -2307,6 +2379,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<std::vector<bool>> const1;
           RCTRequired<std::vector<double>> const2;
@@ -2408,6 +2483,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<std::optional<bool>> const1;
           RCTRequired<std::optional<double>> const2;
@@ -2508,6 +2586,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           std::optional<bool> const1;
           std::optional<double> const2;
@@ -2608,6 +2689,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           std::optional<bool> const1;
           std::optional<double> const2;

packages/react-native-codegen/src/generators/modules/GenerateModuleObjCpp/header/serializeConstantsStruct.js

@@ -35,6 +35,9 @@ const StructTemplate = ({
     struct ${structName} {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = ${structName};
+
         struct Input {
           ${builderInputProps}
         };

packages/react-native-codegen/src/generators/modules/__tests__/__snapshots__/GenerateModuleHObjCpp-test.js.snap

@@ -1008,6 +1008,9 @@ namespace JS {
     struct Constants {
 
       struct Builder {
+        // Backwards compat for RCTTypedModuleConstants
+        using ResultT = Constants;
+
         struct Input {
           RCTRequired<bool> const1;
           RCTRequired<double> const2;

packages/react-native/Libraries/TypeSafety/RCTTypedModuleConstants.h

@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <type_traits>
 #include <utility>
 
 #import <Foundation/Foundation.h>
@@ -32,10 +33,44 @@
 
 namespace facebook::react {
 
+namespace detail {
+
+// Helper to detect if T is a Builder type.
+// Builder types have: nested Input struct and buildUnsafeRawValue() method.
+template <typename T, typename = void>
+struct IsBuilder : std::false_type {};
+
+template <typename T>
+struct IsBuilder<T, std::void_t<typename T::Input, decltype(std::declval<T>().buildUnsafeRawValue())>>
+    : std::true_type {};
+
+// Resolve Builder to its parent Constants type.
+// For backwards compatibility: if T is a Builder type (e.g., JS::X::Constants::Builder),
+// we resolve to the parent Constants type (JS::X::Constants).
+//
+// This requires Builder to have a type alias `using ResultT = Constants;` defined by codegen.
+template <typename T, bool = IsBuilder<T>::value>
+struct ResolveConstantsType {
+  // Not a Builder, use T as-is
+  using type = T;
+};
+
+// Specialization for Builder types that have ResultT defined
+template <typename T>
+struct ResolveConstantsType<T, true> {
+  // Use T::ResultT which points to the parent Constants type (added by codegen)
+  using type = typename T::ResultT;
+};
+
+} // namespace detail
+
 // Objective-C doesn't allow arbitrary types in its lightweight generics, only object and block types. We can work
 // around that by having the struct type we care about be a block-argument. The block never exists at runtime.
+//
+// For backwards compatibility: if T is a Builder type (e.g., JS::Module::Constants::Builder),
+// ModuleConstants<Builder> resolves to the same type as ModuleConstants<Constants>.
 template <typename T>
-using ModuleConstants = _RCTTypedModuleConstants<void (^)(T)> *;
+using ModuleConstants = _RCTTypedModuleConstants<void (^)(typename detail::ResolveConstantsType<T>::type)> *;
 
 template <typename T>
 ModuleConstants<T> typedConstants(typename T::Builder::Input &&value)

packages/react-native/ReactCommon/react/nativemodule/samples/platform/ios/ReactCommon/RCTNativeSampleTurboModuleSpec.h

@@ -25,6 +25,8 @@ NS_ASSUME_NONNULL_BEGIN
 namespace JS::NativeSampleTurboModule {
 struct Constants {
   struct Builder {
+    using ResultT = Constants;
+
     struct Input {
       RCTRequired<bool> const1;
       RCTRequired<double> const2;