Fix throwing exceptions from asHostObject

Summary:
The current implementation of `throwJSError` places it in jsi.cpp, but
does not actually export it. This means that when JSI is being provided
by a dynamic library, `detail::throwJSError` will not be available.

To fix this, move the definition of `throwJSError` into jsi-inl.h,
similar to all of the other functions in the `detail` namespace. This
uses a roundabout implementation of `throwJSError` in order to avoid
directly using `throw`, which would fail to compile when exceptions are
turned off.

Changelog: [Internal]

Reviewed By: jpporto

Differential Revision: D36873154

fbshipit-source-id: bbea48e0d4d5fd65d67a029ba12e183128b96322

Author: neildhar

ReactCommon/jsi/jsi/jsi-inl.h

@@ -56,7 +56,12 @@ inline PropNameID&& toPropNameID(Runtime&, PropNameID&& name) {
   return std::move(name);
 }
 
-void throwJSError(Runtime&, const char* msg);
+/// Helper to throw while still compiling with exceptions turned off.
+template <typename E, typename... Args>
+[[noreturn]] inline void throwOrDie(Args&&... args) {
+  std::rethrow_exception(
+      std::make_exception_ptr(E{std::forward<Args>(args)...}));
+}
 
 } // namespace detail
 
@@ -184,7 +189,8 @@ inline std::shared_ptr<T> Object::getHostObject(Runtime& runtime) const {
 template <typename T>
 inline std::shared_ptr<T> Object::asHostObject(Runtime& runtime) const {
   if (!isHostObject<T>(runtime)) {
-    detail::throwJSError(runtime, "Object is not a HostObject of desired type");
+    detail::throwOrDie<JSError>(
+        runtime, "Object is not a HostObject of desired type");
   }
   return std::static_pointer_cast<T>(runtime.getHostObject(*this));
 }

ReactCommon/jsi/jsi/jsi.cpp

@@ -62,14 +62,6 @@ Value callGlobalFunction(Runtime& runtime, const char* name, const Value& arg) {
 
 } // namespace
 
-namespace detail {
-
-void throwJSError(Runtime& rt, const char* msg) {
-  throw JSError(rt, msg);
-}
-
-} // namespace detail
-
 Buffer::~Buffer() = default;
 
 PreparedJavaScript::~PreparedJavaScript() = default;

ReactCommon/react/renderer/runtimescheduler/tests/RuntimeSchedulerTest.cpp

@@ -453,7 +453,7 @@ TEST_F(RuntimeSchedulerTest, handlingError) {
   bool didRunTask = false;
   auto firstCallback = createHostFunctionFromLambda([this, &didRunTask](bool) {
     didRunTask = true;
-    jsi::detail::throwJSError(*runtime_, "Test error");
+    throw jsi::JSError(*runtime_, "Test error");
     return jsi::Value::undefined();
   });