[mojo] Add pickling support for native-only structs

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

 {%- from "enum_macros.tmpl" import is_valid_enum_def %}
 
 {#--- Enums #}
 {%- for enum in struct.enums -%}
   {{is_valid_enum_def(enum, class_name=struct.name)}}
 {%- endfor %}
 
 // static
 {{struct.name}}Ptr {{struct.name}}::New() {
   {{struct.name}}Ptr rv;
   mojo::internal::StructHelper<{{struct.name}}>::Initialize(&rv);
   return rv.Pass();
 }
 
 {{struct.name}}::{{struct.name}}()
 {%- for field in struct.fields %}
     {% if loop.first %}:{% else %} {% endif %} {{field.name}}({{field|default_value}}){% if not loop.last %},{% endif %}
 {%- endfor %} {
 }
 
 {{struct.name}}::~{{struct.name}}() {
 }
 
 {%  if struct|is_cloneable_kind %}
 {{struct.name}}Ptr {{struct.name}}::Clone() const {
   {{struct.name}}Ptr rv(New());
 {%-   for field in struct.fields %}
-{%-     if field.kind|is_object_kind and not field.kind|is_string_kind %}
+{%-     if field.kind|is_typemapped_kind %}
+  NOTREACHED() << "Object cloning not supported with typemapped fields.";

[yzshen1, 2015/12/15 21:20:27]

It seems reasonable to add support if the typemapped object supports copy/clone,
right?
(No need to be in this CL though. Maybe a TODO.)

Besides, instead of adding a NOTREACHED() here, please consider changing the
definition of is_cloneable_kind.

If a struct is not cloneable (say, having handle fields), we don't generate this
method at all. 

[Ken Rockot(use gerrit already), 2015/12/15 23:31:08]

I agree we might want to, but I'd rather wait until we know for sure. It
complicates things a little, and the simplest path forward might be to add
explicit flags to typemaps (to mark types as copyable or move-only) so we can
get things like this right without piles of template voodoo.

Granted, detecting copyability at compile-time isn't very complex, but it would
make this code just that much harder to read.
Done.

+{%-     elif field.kind|is_object_kind and not field.kind|is_string_kind %}
   rv->{{field.name}} = {{field.name}}.Clone();
 {%-     else %}
   rv->{{field.name}} = {{field.name}};
 {%-     endif %}
 {%-   endfor %}
   return rv.Pass();
 }
 {%  endif %}
 
 bool {{struct.name}}::Equals(const {{struct.name}}& other) const {
 {%-  for field in struct.fields %}
+{%-    if field.kind|is_typemapped_kind %}
+  NOTREACHED() << "Equality testing not supported with typemapped fields.";

[yzshen1, 2015/12/15 21:20:27]

Similarly, seems reasonable to add support if the object supports equality
testing.

[Ken Rockot(use gerrit already), 2015/12/15 23:31:08]

Agreed

+{%-    else %}
   if (!mojo::internal::ValueTraits<{{field.kind|cpp_wrapper_type}}>::Equals(this->{{field.name}}, other.{{field.name}}))
     return false;
+{%-    endif %}
 {%-  endfor %}
   return true;
 }