Fix optional fields in proto3

[adamwhats]

Proposed changes

I think I've found an issue with handling optional fields. To replicate, add an optional field to a message in test.proto:

// A control request for an HVAC system.
message HVACControlRequest {
    double air_flow_rate = 1;
    Temperature temperature_setpoint = 2;
+   optional double humidity_setpoint = 3;
}

After building this gives the following error:

  File "/workspaces/proto2ros/install/proto2ros/lib/python3.12/site-packages/proto2ros/equivalences.py", line 379, in compute_equivalence_for_message
    oneof_type = Type(f"{ros_package_name}/{oneof_type_name}")
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/parser.py", line 278, in __init__
    super(Type, self).__init__(
  File "/opt/ros/jazzy/lib/python3.12/site-packages/rosidl_adapter/parser.py", line 206, in __init__
    raise InvalidResourceName(
rosidl_adapter.parser.InvalidResourceName: 'HVACControlRequestOneOf_humiditySetpoint' is an invalid message name. It should have the pattern '^[A-Z][A-Za-z0-9]*$'

I think this is due to proto3 internally rewriting optional fields as a 'synthetic oneof' with a leading underscore, as documented here. This then causes issues with this line line, as .camelize() doesn't handle double underscores, hence we get oneof_type_name = HVACControlRequestOneOf_humiditySetpoint.

My fix has is a small change to equivalences.py where we only add oneof field descriptors without a leading underscore to oneof_field_sets, then a little bit of handling in the next loop below. I'm very open to feedback on this, there may well be a more elegant solution.

Checklist

• Lint and unit tests pass locally
• I have added tests that prove my changes are effective
• I have added necessary documentation to communicate the changes

[adamwhats]

Edited to add commit signoffs

[mhidalgo-rai]

@adamwhats great catch, and thanks for the contribution 😃

Would you mind adding a test for Python conversion APIs too?