fix: not existing error type, add comments to JSI code

Author: NorbertKlockiewicz

packages/react-native-executorch/common/rnexecutorch/host_objects/ModelHostObject.h

@@ -46,13 +46,6 @@ template <typename Model> class ModelHostObject : public JsiHostObject {
           "getInputShape"));
     }
 
-    if constexpr (meta::HasGenerateFromString<Model>) {
-      addFunctions(
-          JSI_EXPORT_FUNCTION(ModelHostObject<Model>,
-                              promiseHostFunction<&Model::generateFromString>,
-                              "generateFromString"));
-    }
-
     if constexpr (meta::HasEncode<Model>) {
       addFunctions(JSI_EXPORT_FUNCTION(ModelHostObject<Model>,
                                        promiseHostFunction<&Model::encode>,
@@ -172,6 +165,13 @@ template <typename Model> class ModelHostObject : public JsiHostObject {
                                        "stream"));
     }
 
+    if constexpr (meta::HasGenerateFromString<Model>) {
+      addFunctions(
+          JSI_EXPORT_FUNCTION(ModelHostObject<Model>,
+                              promiseHostFunction<&Model::generateFromString>,
+                              "generateFromString"));
+    }
+
     if constexpr (meta::HasGenerateFromFrame<Model>) {
       addFunctions(JSI_EXPORT_FUNCTION(
           ModelHostObject<Model>, visionHostFunction<&Model::generateFromFrame>,
@@ -181,7 +181,7 @@ template <typename Model> class ModelHostObject : public JsiHostObject {
     if constexpr (meta::HasGenerateFromPixels<Model>) {
       addFunctions(
           JSI_EXPORT_FUNCTION(ModelHostObject<Model>,
-                              visionHostFunction<&Model::generateFromPixels>,
+                              promiseHostFunction<&Model::generateFromPixels>,
                               "generateFromPixels"));
     }
   }
@@ -233,47 +233,49 @@ template <typename Model> class ModelHostObject : public JsiHostObject {
     }
   }
 
+  /**
+   * Unlike promiseHostFunction, this runs synchronously on the JS thread,
+   * which is required for VisionCamera worklet frame processors.
+   *
+   * The key challenge is argument mapping: the C++ function takes
+   * (Runtime, frameData, Rest...) but from the JS side, Runtime is injected
+   * automatically and frameData is JS args[0]. The remaining args (Rest...)
+   * map to JS args[1..N].
+   *
+   * This is achieved via TailSignature: it extracts the Rest... parameter pack
+   * from the function pointer type, creates a dummy free function with only
+   * those types, then uses createArgsTupleFromJsi on that dummy to convert
+   * args[1..N] — bypassing the manually-handled frameData at args[0].
+   *
+   * Argument mapping:
+   *   C++ params:  (Runtime&,  frameData,  Rest[0],   Rest[1], ...)
+   *   JS args:     (           args[0],    args[1],   args[2], ...)
+   *   JS arg count = C++ arity - 1  (Runtime is injected, not counted)
+   *
+   */
   template <auto FnPtr> JSI_HOST_FUNCTION(visionHostFunction) {
-    // 1. Check Argument Count
-    // (We rely on our new FunctionTraits)
     constexpr std::size_t cppArgCount =
         meta::FunctionTraits<decltype(FnPtr)>::arity;
-
-    // We expect JS args = (Total C++ Args) - (2 injected args: Runtime + Value)
     constexpr std::size_t expectedJsArgs = cppArgCount - 1;
-    log(LOG_LEVEL::Debug, cppArgCount, count);
+
     if (count != expectedJsArgs) {
       throw jsi::JSError(runtime, "Argument count mismatch in vision function");
     }
 
     try {
-      // 2. The Magic Trick
-      // We get a pointer to a dummy function: void dummy(Rest...) {}
-      // This function has exactly the signature of the arguments we want to
-      // parse.
       auto dummyFuncPtr = &meta::TailSignature<decltype(FnPtr)>::dummy;
-
-      // 3. Let existing helpers do the work
-      // We pass the dummy pointer. The helper inspects its arguments (Rest...)
-      // and converts args[0]...args[N] accordingly.
-      // Note: We pass (args + 1) because JS args[0] is the PixelData, which we
-      // handle manually. Note: We use expectedJsArgs - 1 because we skipped one
-      // JS arg.
       auto tailArgsTuple =
           meta::createArgsTupleFromJsi(dummyFuncPtr, args + 1, runtime);
 
-      // 4. Invoke
       using ReturnType =
           typename meta::FunctionTraits<decltype(FnPtr)>::return_type;
 
       if constexpr (std::is_void_v<ReturnType>) {
         std::apply(
             [&](auto &&...tailArgs) {
               (model.get()->*FnPtr)(
-                  runtime,
-                  args[0], // 1. PixelData (Manually passed)
-                  std::forward<decltype(tailArgs)>(
-                      tailArgs)...); // 2. The rest (Auto parsed)
+                  runtime, args[0],
+                  std::forward<decltype(tailArgs)>(tailArgs)...);
             },
             std::move(tailArgsTuple));
         return jsi::Value::undefined();

packages/react-native-executorch/common/rnexecutorch/metaprogramming/FunctionHelpers.h

@@ -10,32 +10,6 @@
 namespace rnexecutorch::meta {
 using namespace facebook;
 
-// =========================================================================
-// 1. Function Traits (Extracts Arity, Return Type, Args)
-// =========================================================================
-
-template <typename T> struct FunctionTraits;
-
-// Specialization for Member Functions
-template <typename R, typename C, typename... Args>
-struct FunctionTraits<R (C::*)(Args...)> {
-  static constexpr std::size_t arity = sizeof...(Args);
-  using return_type = R;
-  using args_tuple = std::tuple<Args...>;
-};
-
-// Specialization for const Member Functions
-template <typename R, typename C, typename... Args>
-struct FunctionTraits<R (C::*)(Args...) const> {
-  static constexpr std::size_t arity = sizeof...(Args);
-  using return_type = R;
-  using args_tuple = std::tuple<Args...>;
-};
-
-// =========================================================================
-// 2. Argument Counting Helpers
-// =========================================================================
-
 template <typename Model, typename R, typename... Types>
 constexpr std::size_t getArgumentCount(R (Model::*f)(Types...)) {
   return sizeof...(Types);
@@ -46,10 +20,6 @@ constexpr std::size_t getArgumentCount(R (Model::*f)(Types...) const) {
   return sizeof...(Types);
 }
 
-// =========================================================================
-// 3. JSI -> Tuple Conversion Logic
-// =========================================================================
-
 template <typename... Types, std::size_t... I>
 std::tuple<Types...> fillTupleFromArgs(std::index_sequence<I...>,
                                        const jsi::Value *args,
@@ -62,6 +32,7 @@ std::tuple<Types...> fillTupleFromArgs(std::index_sequence<I...>,
  * arguments for method supplied with a pointer. The types in the tuple are
  * inferred from the method pointer.
  */
+
 template <typename Model, typename R, typename... Types>
 std::tuple<Types...> createArgsTupleFromJsi(R (Model::*f)(Types...),
                                             const jsi::Value *args,
@@ -78,7 +49,9 @@ std::tuple<Types...> createArgsTupleFromJsi(R (Model::*f)(Types...) const,
                                      runtime);
 }
 
-// Overload for free functions (used by TailSignature dummy)
+// Free function overload used by visionHostFunction: accepts a dummy free
+// function pointer whose parameter types (Rest...) are extracted by
+// TailSignature and converted from JSI args.
 template <typename... Types>
 std::tuple<Types...> createArgsTupleFromJsi(void (*f)(Types...),
                                             const jsi::Value *args,
@@ -87,27 +60,40 @@ std::tuple<Types...> createArgsTupleFromJsi(void (*f)(Types...),
                                      runtime);
 }
 
-// =========================================================================
-// 4. Tail Signature Helper (Crucial for Vision Functions)
-// =========================================================================
+// Extracts arity, return type, and argument types from a member function
+// pointer at compile time. Used by visionHostFunction to determine the expected
+// JS argument count and invoke the correct return path.
+template <typename T> struct FunctionTraits;
+
+template <typename R, typename C, typename... Args>
+struct FunctionTraits<R (C::*)(Args...)> {
+  static constexpr std::size_t arity = sizeof...(Args);
+  using return_type = R;
+  using args_tuple = std::tuple<Args...>;
+};
+
+template <typename R, typename C, typename... Args>
+struct FunctionTraits<R (C::*)(Args...) const> {
+  static constexpr std::size_t arity = sizeof...(Args);
+  using return_type = R;
+  using args_tuple = std::tuple<Args...>;
+};
 
-// Extracts the "Tail" arguments of a function signature, skipping the first
-// two arguments (Runtime and FrameValue).
+// Strips the first two parameters (Runtime& and jsi::Value&) from a member
+// function pointer and exposes the remaining types as a dummy free function.
+// Used by visionHostFunction to parse only the tail JS args via
+// createArgsTupleFromJsi, while frameData at args[0] is passed manually.
 template <typename T> struct TailSignature;
 
-// Non-const member function specialization
 template <typename R, typename C, typename Arg1, typename Arg2,
           typename... Rest>
 struct TailSignature<R (C::*)(Arg1, Arg2, Rest...)> {
-  // A dummy function that has the signature of just the "Rest" arguments.
   static void dummy(Rest...) {}
 };
 
-// Const member function specialization
 template <typename R, typename C, typename Arg1, typename Arg2,
           typename... Rest>
 struct TailSignature<R (C::*)(Arg1, Arg2, Rest...) const> {
   static void dummy(Rest...) {}
 };
-
 } // namespace rnexecutorch::meta

packages/react-native-executorch/common/rnexecutorch/utils/FrameExtractor.cpp

@@ -84,15 +84,14 @@ cv::Mat extractFromAHardwareBuffer(void *hardwareBuffer) {
     char errorMessage[100];
     std::snprintf(errorMessage, sizeof(errorMessage),
                   "Unsupported AHardwareBuffer format: %u", desc.format);
-    throw RnExecutorchError(RnExecutorchErrorCode::InvalidUserInput,
-                            errorMessage);
+    throw RnExecutorchError(RnExecutorchErrorCode::UnknownError, errorMessage);
   }
 
   // Note: We don't unlock here - Vision Camera manages the lifecycle
 
   return mat;
 #else
-  throw RnExecutorchError(RnExecutorchErrorCode::NotSupported,
+  throw RnExecutorchError(RnExecutorchErrorCode::UnknownError,
                           "AHardwareBuffer requires Android API 26+");
 #endif // __ANDROID_API__ >= 26
 }
@@ -106,7 +105,7 @@ cv::Mat extractFromNativeBuffer(uint64_t bufferPtr) {
 #elif defined(__ANDROID__)
   return extractFromAHardwareBuffer(reinterpret_cast<void *>(bufferPtr));
 #else
-  throw RnExecutorchError(RnExecutorchErrorCode::NotSupported,
+  throw RnExecutorchError(RnExecutorchErrorCode::UnknownError,
                           "NativeBuffer not supported on this platform");
 #endif
 }