Add enum support to ROSIDL

[r7vme]

Adds support for enums into ROSIDL. Only .idl files supported.

Example

module test_msgs {
  module idl {
    typedef SomeEnum SomeEnum__3[3];

    module EnumsMessage_Enums {
      enum SomeEnum {
        ENUMERATOR1,
        ENUMERATOR2
      };
    };

    struct EnumsMessage {
      SomeEnum enum_value;

      @default (value="ENUMERATOR2")
      SomeEnum enum_default_value;

      SomeEnum__3 static_array_values;

      sequence<SomeEnum, 3> bounded_array_values;

      sequence<SomeEnum> dynamic_array_values;
    };
  };
};

Fixes #260

List of related pull requests

ros2/test_interface_files#20
ros2/rosidl_python#170
ros2/rosidl_dds#58
ros2/rosidl_typesupport_fastrtps#89

TODO

• Add support to non-default RMWs
• Design document and documentation

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/need-reviewers-for-rosidl-related-change/26285/1

[methylDragon]

Hmm, CI is failing with

08:09:25 /tmp/ws/src/rosidl/rosidl_generator_c/test/test_interfaces.c:28:10: fatal error: rosidl_generator_c/idl/enums.h: No such file or directory
08:09:25    28 | #include "rosidl_generator_c/idl/enums.h"

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/why-did-ros2-keep-msg-interface-definitions/27631/2

[r7vme]

Closing as I have no plans to work on this in the near time (see more details here).