Dart_SetReturnValue now accepts and propagates error handles.

runtime/vm/native_entry.cc

Index: runtime/vm/native_entry.cc
diff --git a/runtime/vm/native_entry.cc b/runtime/vm/native_entry.cc
index 2277319bb4d0e994804e5ccc14bfa656340a35a6..8523a272077b07b8a1fa57200fffa707d1dc1224 100644
--- a/runtime/vm/native_entry.cc
+++ b/runtime/vm/native_entry.cc
@@ -91,6 +91,26 @@ uword NativeEntry::NativeCallWrapperEntry() {
 }
 
 
+void NativeEntry::PropagateErrors(NativeArguments* arguments) {
+  RawObject* raw_retval = arguments->ReturnValue();
+  if (raw_retval->IsHeapObject() &&
+      RawObject::IsErrorClassId(raw_retval->GetClassId())) {
+    Thread* thread = arguments->thread();
+    const Object* error;
+    {
+      // We use a NoSafepointScope to make sure that the raw_retval
+      // is preserved while we are unwinding scopes.
+      NoSafepointScope no_safepoint;
+      thread->UnwindScopes(thread->top_exit_frame_info());
+      // The thread->zone() now is different here than before we unwound.
+      error = &Object::Handle(thread->zone(), raw_retval);
+    }

[siva, 2016/02/03 16:50:00]

Why do you declare it as:

const Object* error;

why not just:

NoSafepointScope no_safepoint;
thread->UnwindScopes(thread->top_exit_frame_info());
// We already have checked the type and know it is an Error object.
const Error& error = Error::Handle(thread->zone(), arguments->ReturnValue());
Exceptions::PropagateError(error);

[turnidge, 2016/02/03 19:13:46]

Done.

+    Exceptions::PropagateError(Error::Cast(*error));
+    UNREACHABLE();
+  }
+}
+
+
 void NativeEntry::NativeCallWrapper(Dart_NativeArguments args,
                                     Dart_NativeFunction func) {
   CHECK_STACK_ALIGNMENT;
@@ -102,6 +122,7 @@ void NativeEntry::NativeCallWrapper(Dart_NativeArguments args,
   if (!arguments->IsNativeAutoSetupScope()) {
     TransitionGeneratedToNative transition(thread);
     func(args);
+    PropagateErrors(arguments);

[siva, 2016/02/03 16:50:00]

Might be more efficient to have an inlinable function
if (ReturnValueIsError(arguments)) {
  PropagateError(arguments);
}

The current PropagateError seems too big to be inlined.

[turnidge, 2016/02/03 19:13:46]

Done.

   } else {
     Isolate* isolate = thread->isolate();
     ApiState* state = isolate->api_state();
@@ -123,6 +144,7 @@ void NativeEntry::NativeCallWrapper(Dart_NativeArguments args,
     thread->set_api_top_scope(scope);  // New scope is now the top scope.
 
     func(args);
+    PropagateErrors(arguments);
 
     ASSERT(current_top_scope == scope->previous());
     thread->set_api_top_scope(current_top_scope);  // Reset top scope to prev.