Add type & value fields to primitive json types

[dyackzan]

Before these changes, primitive types do not have a "__type" field when the blackboard is converted to json like in the screenshot:

After these changes:

  "View Workspace": {
    "acceleration_scale_factor": {
      "type": "string",
      "value": "1.0"
    },
    "controller_action_server": {
      "type": "string",
      "value": "/joint_trajectory_controller/follow_joint_trajectory"
    },
...                                                                                                                                                                                                                                                
    "pose_count": {                                                                                                                                                                                                                                                   
      "type": "int64_t",                                                                                                                                                                                                                                              
      "value": 2                                                                                                                                                                                                                                                      
    }
  }

resolves https://github.com/PickNikRobotics/moveit_pro/issues/10488

[dsobek]

For custom types, I take it that the value and type fields must be added in the custom converter function then?

Happy to approve once tests are updated.

[dsobek]

Might be good to pull out "type" and "value" as constants here.

(I've been paranoid about typoing things in situations like this recently)

[dsobek]

Also should "type" be "__type"? Or is the difference in name so that you know to pick out the "value" json field?

[dyackzan]

Good calls, it should be __type to align

[dsobek]

For custom types, I take it that the value and type fields must be added in the custom converter function then?

Happy to approve once tests are updated.

I see, calling add_field in the body of BT_JSON_CONVERTER takes care of this already.

[dsobek]

Ok some more questions:
Would it be helpful to have boolean support? (Do these get encoded as string types?)
Does the add_field function when defining a custom converter take care of converting primitives to this format? (I suppose this could be answered with a test case).

[dyackzan]

Many objects are just strings on the blackboard and then get converted when they are loaded with getInput. Bools are always strings on the blackboard and get converted here

[dyackzan]

Now that I'm adding tests, I went ahead and tried to add one for a bool, and it turns out that the behavior tree implementation of Any just casts bools to int64_ts so it's not possible to to have a type == typeid(bool) case here

[dsobek]

I believe I saw that nlohmann::json has a find function.

Suggested change

	if(!source.contains("__type"))
	auto source_type_it = source.find(kTypeField);
	if(source_type_it == source.end())

Then you can replace usage of source[kTypeField] with source_type_it below.

[dyackzan]

Looks like the only other usage of kTypeField in this function is to lookup if the type is in the available converters (type_names_) so I wouldn't be able to reuse this iterator. But yeah definitely better to reuse the kTypeField const than re-write the string again