Implement unions as members of structs.

mojo/public/cpp/bindings/lib/array_serialization.h

Index: mojo/public/cpp/bindings/lib/array_serialization.h
diff --git a/mojo/public/cpp/bindings/lib/array_serialization.h b/mojo/public/cpp/bindings/lib/array_serialization.h
index eacf298ec80ea46fffebe0afa499a32f83325316..154ac9f7662b346a3d287d56ee1b36cf8276a109 100644
--- a/mojo/public/cpp/bindings/lib/array_serialization.h
+++ b/mojo/public/cpp/bindings/lib/array_serialization.h
@@ -45,11 +45,16 @@ inline void Deserialize_(internal::Array_Data<F>* data, Array<E>* output);
 
 namespace internal {
 
-template <typename E, typename F, bool move_only = IsMoveOnlyType<E>::value>
+template <typename E,
+          typename F,
+          bool move_only = IsMoveOnlyType<E>::value,
+          bool is_union =
+              IsUnionDataType<typename RemovePointer<F>::type>::value>
 struct ArraySerializer;
 
+// Handles serialization and deserialization of arrays of pod types.
 template <typename E, typename F>
-struct ArraySerializer<E, F, false> {
+struct ArraySerializer<E, F, false, false> {
   static_assert(sizeof(E) == sizeof(F), "Incorrect array serializer");
   static size_t GetSerializedSize(const Array<E>& input) {
     return sizeof(Array_Data<F>) + Align(input.size() * sizeof(E));
@@ -74,8 +79,9 @@ struct ArraySerializer<E, F, false> {
   }
 };
 
+// Serializes and deserializes arrays of bools.
 template <>
-struct ArraySerializer<bool, bool, false> {
+struct ArraySerializer<bool, bool, false, false> {
   static size_t GetSerializedSize(const Array<bool>& input) {
     return sizeof(Array_Data<bool>) + Align((input.size() + 7) / 8);
   }
@@ -102,8 +108,9 @@ struct ArraySerializer<bool, bool, false> {
   }
 };
 
+// Serializes and deserializes arrays of handles.
 template <typename H>
-struct ArraySerializer<ScopedHandleBase<H>, H, true> {
+struct ArraySerializer<ScopedHandleBase<H>, H, true, false> {
   static size_t GetSerializedSize(const Array<ScopedHandleBase<H>>& input) {
     return sizeof(Array_Data<H>) + Align(input.size() * sizeof(H));
   }
@@ -142,7 +149,8 @@ struct ArraySerializer<S,
                            internal::IsPointer<typename internal::WrapperTraits<
                                S>::DataType>::value,
                            typename internal::WrapperTraits<S>::DataType>::type,
-                       true> {
+                       true,
+                       false> {
   typedef typename internal::RemovePointer<
       typename internal::WrapperTraits<S>::DataType>::type S_Data;
   static size_t GetSerializedSize(const Array<S>& input) {
@@ -172,9 +180,7 @@ struct ArraySerializer<S,
                                   Array<S>* output) {
     Array<S> result(input->size());
     for (size_t i = 0; i < input->size(); ++i) {
-      S element;
-      Deserialize_(input->at(i), &element);
-      result[i] = element.Pass();
+      Deserialize_(input->at(i), &result[i]);
     }
     output->Swap(&result);
   }
@@ -211,6 +217,44 @@ struct ArraySerializer<S,
   };
 };
 
+// Handles serialization and deserialization of arrays of unions.
+template <typename U, typename U_Data>
+struct ArraySerializer<U, U_Data, true, true> {
+  static size_t GetSerializedSize(const Array<U>& input) {
+    size_t size = sizeof(Array_Data<U_Data>);
+    for (size_t i = 0; i < input.size(); ++i) {
+      // GetSerializedSize_ will account for both the data in the union and the
+      // space in the array used to hold the union.
+      size += GetSerializedSize_(input[i]);
+    }
+    return size;
+  }
+
+  template <bool element_is_nullable, typename ElementValidateParams>
+  static void SerializeElements(Array<U> input,
+                                Buffer* buf,
+                                Array_Data<U_Data>* output) {
+    for (size_t i = 0; i < input.size(); ++i) {
+      U_Data* result = output->storage() + i;
+      SerializeUnion_(input[i].Pass(), buf, &result, true);
+      MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(
+          !element_is_nullable && output->at(i).is_null(),
+          VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,
+          MakeMessageWithArrayIndex("null in array expecting valid unions",
+                                    input.size(), i));
+    }
+  }
+
+  static void DeserializeElements(Array_Data<U_Data>* input, Array<U>* output) {
+    Array<U> result(input->size());
+    for (size_t i = 0; i < input->size(); ++i) {
+      Deserialize_(&input->at(i), &result[i]);
+    }
+    output->Swap(&result);
+  }
+};
+
+// Handles serialization and deserialization of arrays of strings.
 template <>
 struct ArraySerializer<String, String_Data*, false> {
   static size_t GetSerializedSize(const Array<String>& input) {