Make the fuchsia mojo/public repo the source of truth.

mojo/public/tools/bindings/generators/cpp_templates/union_definition.tmpl

-{%- import "validation_macros.tmpl" as validation_macros %}
-{%- set class_name = union.name ~ "_Data" %}
-{%- set enum_name = union.name ~ "_Tag" -%}
-
-// static
-{{class_name}}* {{class_name}}::New(mojo::internal::Buffer* buf) {
-  return new (buf->Allocate(sizeof({{class_name}}))) {{class_name}}();
-}
-
-{# TODO(vardhan): Set error messages here for the remaining validation
-   errors. #}
-// static
-mojo::internal::ValidationError {{class_name}}::Validate(
-    const void* data,
-    mojo::internal::BoundsChecker* bounds_checker,
-    bool inlined,
-    std::string* err) {
-  if (!data)
-    return mojo::internal::ValidationError::NONE;
-
-  if (!mojo::internal::IsAligned(data)) {
-    MOJO_INTERNAL_DEBUG_SET_ERROR_MSG(err) << "";
-    return mojo::internal::ValidationError::MISALIGNED_OBJECT;
-  }
-
-  // If the union is inlined in another structure its memory was already claimed.
-  // This ONLY applies to the union itself, NOT anything which the union points
-  // to.
-  if (!inlined && !bounds_checker->ClaimMemory(data, sizeof({{class_name}}))) {
-    MOJO_INTERNAL_DEBUG_SET_ERROR_MSG(err) << "";
-    return mojo::internal::ValidationError::ILLEGAL_MEMORY_RANGE;
-  }
-
-  const {{class_name}}* object = static_cast<const {{class_name}}*>(data);
-  MOJO_ALLOW_UNUSED_LOCAL(object);
-
-  if (object->is_null())
-    return mojo::internal::ValidationError::NONE;
-
-  switch (object->tag) {
-{%  for field in union.fields %}
-    case {{enum_name}}::{{field.name|upper}}: {
-{{ validation_macros.validate_union_field(field, union, "err")|indent(8) }}
-    }
-{%- endfor %}
-    default:
-      // Unknown tags should not cause validation to fail.
-      break;
-  }
-  return mojo::internal::ValidationError::NONE;
-}
-
-void {{class_name}}::set_null() {
-  size = 0U;
-  tag = static_cast<{{enum_name}}>(0);
-  data.unknown = 0U;
-}
-
-{{class_name}}::{{class_name}}() {
-}
-
-void {{class_name}}::EncodePointersAndHandles(
-    std::vector<mojo::Handle>* handles) {
-  switch (tag) {
-{%- for field in union.fields %}
-    case {{enum_name}}::{{field.name|upper}}: {
-{%-   if field.kind|is_object_kind %}
-      mojo::internal::Encode(&data.f_{{field.name}}, handles);
-{%-   elif field.kind|is_any_handle_kind %}
-      mojo::internal::EncodeHandle(&data.f_{{field.name}}, handles);
-{%-   elif field.kind|is_interface_kind %}
-      mojo::internal::EncodeHandle(
-          reinterpret_cast<mojo::internal::Interface_Data*>(
-              &data.f_{{field.name}}), handles);
-{%-   endif %}
-      return;
-    }
-{%- endfor %}
-    case {{enum_name}}::__UNKNOWN__: {
-      MOJO_DCHECK(false) << "No sane way to serialize a union with an unknown tag.";
-      break;
-    }
-  }
-}
-
-void {{class_name}}::DecodePointersAndHandles(
-    std::vector<mojo::Handle>* handles) {
-  switch (tag) {
-{%- for field in union.fields %}
-    case {{enum_name}}::{{field.name|upper}}: {
-{%-   if field.kind|is_object_kind %}
-      mojo::internal::Decode(&data.f_{{field.name}}, handles);
-{%-   elif field.kind|is_any_handle_kind %}
-      mojo::internal::DecodeHandle(&data.f_{{field.name}}, handles);
-{%-   elif field.kind|is_interface_kind %}
-      mojo::internal::DecodeHandle(
-          reinterpret_cast<mojo::internal::Interface_Data*>(
-              &data.f_{{field.name}}), handles);
-{%-   endif %}
-      return;
-    }
-{%- endfor %}
-    default:
-      return;
-  }
-}