Do not generate files for interfaces in rmw_dds_common

[ivanpauno]

Fixes ros2/rmw_dds_common#8.

There's no reason to generate files for the interfaces in rmw_dds_common, so I propose to skip them.

Another way to skip the package, is to avoid registering it as a rosidl_interfaces resource.
I can add an argument to rosidl_generate_interfaces to do that.

[dirk-thomas]

This package should not need to know about rmw_dds_common so this should not be merged

I don't know enough about how the interface in that package are needed to recommend an approach.

[ivanpauno]

Another way to skip the package, is to avoid registering it as a rosidl_interfaces resource.
I can add an argument to rosidl_generate_interfaces to do that.

Does this sound reasonable?

[dirk-thomas]

I don't understand why they must be installed but can't be registered at the index.

[ivanpauno]

I don't understand why they must be installed but can't be registered at the index.

They must be installed because rmw_fastrtps_cpp and rmw_fastrtps_dynamic_cpp use them.

They don't need to be registered at the index because they are not intended to be an interface used by the end user.

[ivanpauno]

See ros2/rmw_dds_common#11 and ros2/rosidl#454.

[dirk-thomas]

They don't need to be registered at the index because they are not intended to be an interface used by the end user.

The question remains: what is the problem for them being registered at the index?