Support default values for POD struct fields in mojom IDL.

mojo/public/bindings/generators/cpp_templates/struct_builder_definition.tmpl

Index: mojo/public/bindings/generators/cpp_templates/struct_builder_definition.tmpl
diff --git a/mojo/public/bindings/generators/cpp_templates/struct_builder_definition.tmpl b/mojo/public/bindings/generators/cpp_templates/struct_builder_definition.tmpl
index d4e742786a57a1ba57f52cddc159701cc3b2a538..3841f4d912e4457261263ec275b142fcd9264933 100644
--- a/mojo/public/bindings/generators/cpp_templates/struct_builder_definition.tmpl
+++ b/mojo/public/bindings/generators/cpp_templates/struct_builder_definition.tmpl
@@ -6,8 +6,25 @@
 {%-   set _ = dtor_name.append("NULL") %}
 {%- endif %}
 
+{%- macro set_default(field) -%}
+{%-   if field.kind|is_string_kind -%}
+set_{{field.name}}(mojo::String({{field.default}}));
+{%-   elif field.kind|is_object_kind -%}
+{
+  {{field.kind|cpp_wrapper_type}}::Builder tmp;
+  // TODO
+  set_{{field.name}}(tmp.Finish());
+}
+{%-   else -%}
+set_{{field.name}}({{field.default}});
+{%-   endif %}
+{%- endmacro %}
+
 {{class_name}}::Builder::Builder(mojo::Buffer* buf)
     : data_(Data::New(buf, {{dtor_name[0]}})) {
+{%- for pf in struct.packed.packed_fields if pf.field.default %}
+  {{set_default(pf.field)|indent(2)}}

[darin (slow to review), 2014/01/21 23:47:20]

Perhaps we should defer setting default values until Finish() is called? That
way we don't waste memory writing default values for fields that the user sets?

Hmm, ah... but we don't keep track of what methods are called, so we can't know
if, for example, a null string field was intentional or not.

OK, nevermind.

+{%- endfor %}
 }
 
 {{class_name}} {{class_name}}::Builder::Finish() {