Implement unions as members of structs.

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

Index: mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl
index 623ebb441c69938da26e8489662eb65641f82f5d..e457e61620658d3f00fd241d39a3fc2c21acb918 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl
@@ -14,7 +14,21 @@
 {%-   for packed_field in struct.packed.packed_fields %}
 {%-     set name = packed_field.field.name %}
 {%-     set kind = packed_field.field.kind %}
-{%-     if kind|is_object_kind %}
+{%-     if kind|is_union_kind %}
+{%-       if not kind|is_nullable_kind %}

[yzshen1, 2015/02/17 19:34:35]

(Please note that this part has been under significant change recently.
Especially after https://codereview.chromium.org/917333003/. Besides, I am
planning to move tmpl code into C++ template magic. :))

[azani, 2015/02/18 00:27:57]

Done.

+  if (object->{{name}}.is_null()) {
+    ReportValidationError(
+        mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,
+        "null {{name}} field in {{struct.name}} struct");
+    return false;
+  }
+{%-       endif %}
+  // We already claimed the union's memory as part of the struct, so we don't
+  // try to claim the union's memory when validating the union.
+  if (!{{kind.name}}::Data_::Validate(&object->{{name}}, bounds_checker, false)) {

[yzshen1, 2015/02/17 19:34:35]

Do you think it make sense to make |false| a template argument? That seems to be
more consistent with other Validate().

[azani, 2015/02/18 00:27:57]

It seems like we would just shift the inconsistency from the argument list to
the template arguments. I am somewhat disinclined to using templates for this
purpose, but only slightly so.

+    return false;
+  }
+{%-     elif kind|is_object_kind %}
 {%-       set wrapper_type = kind|cpp_wrapper_type %}
 {%-       if not kind|is_nullable_kind %}
   if (!object->{{name}}.offset) {
@@ -105,7 +119,9 @@
 
 {%- macro encodes(struct) -%}
 {%-   for pf in struct.packed.packed_fields %}
-{%-     if pf.field.kind|is_object_kind %}
+{%-     if pf.field.kind|is_union_kind %}
+// TODO(azani): Encode pointers and handles.
+{%-     elif pf.field.kind|is_object_kind %}
 mojo::internal::Encode(&{{pf.field.name}}, handles);
 {%-     elif pf.field.kind|is_any_handle_kind %}
 mojo::internal::EncodeHandle(&{{pf.field.name}}, handles);
@@ -115,7 +131,9 @@ mojo::internal::EncodeHandle(&{{pf.field.name}}, handles);
 
 {%- macro decodes(struct) -%}
 {%-   for pf in struct.packed.packed_fields %}
-{%-     if pf.field.kind|is_object_kind %}
+{%-     if pf.field.kind|is_union_kind %}
+// TODO(azani): Decode pointers and handles.
+{%-     elif pf.field.kind|is_object_kind %}
 mojo::internal::Decode(&{{pf.field.name}}, handles);
 {%-     elif pf.field.kind|is_any_handle_kind %}
 mojo::internal::DecodeHandle(&{{pf.field.name}}, handles);