[rolling] Combined Parameter Files

[DLu]

Description

Fixes #517 in Rolling - Combined parameter files.

Is this user-facing behavior change?

Yes, adds a new way to combine parameter files in launch files.

Did you use Generative AI?

No.

Additional Information

After getting a little annoyed at #518, I decided to try another approach I mentioned in #517 where we add a new parameter type to parameter_descriptions.

Current State:

• I developed this in jazzy. It should eventually go in rolling but I wanted to get feedback before I committed to it. Now its rolling
• New description: CombinedParameterFiles allows for combining multiple yaml files and writing into a temp yaml file.
  • Issue: I'm not sure if I have the typing correct on the param_files argument
• TempYamlFile class consolidates the functionality for maybe writing to a temp yaml file between this and ParameterFile
• Updated the typing in parameters_type.py and added CombinedParameterFiles as a valid type in a couple of spots.
• Added new parsing logic in Node.parse
• Tests for core Python functionality in test_combined_param_files.py
• Tests for parsing Yaml and XML in test_node_with_combo_file_params.py
  • Issue: I got the XML to work the way I wanted, but didn't get the YAML to parse the way I wanted. That test currently fails. Figured it out with @christophebedard

[DLu]

I have updated this PR to be based on rolling, and removed the draft status.

@christophebedard @emersonknapp I would welcome your feedback on the proper YAML format to mimic the XML test.

[christophebedard]

Taking a look!

[christophebedard]

This works:

Suggested change

	param:
	- file:
	- path: {}
	- file:
	- path: {}
	param:
	- file:
	- path: {}
	- path: {}

The key is that param.get_attr('file', data_type=List[Entity], optional=True) is expected to be:

1. In XML: a list of (i.e., multiple)<file .../> nested within <param>...</param>.
2. In YAML: a single file with a list of dictionaries (- ...) under it.

For reference, look at how XML <let> and YAML let: are handled in IncludeLaunchDescription: https://github.com/ros2/launch/blob/a5a6dd7eb7865dbc64d0e18f0229b0ebad826082/launch/launch/actions/include_launch_description.py#L96-L116. I'm not entirely sure why it's

        launch:
            - node:
                # ...
                param:
                    - file:
                        - path: {}
                        - path: {}

and not

        launch:
            - node:
                # ...
                param:
                    file:
                        - path: {}
                        - path: {}

like param: is to node: here or how let: is to include: in IncludeLaunchDescription, but the parsing works 🤷 . Maybe because we have an extra nesting level here (all under param and not directly under node).

[christophebedard]

Maybe because we have an extra nesting level here (all under param and not directly under node).

ah, that is probably because where you put your new parsing code is supposed to handle a single param out of a list of param. YAML param: expects a list under it (and we can have multiple XML <param> under a <node>), hence the - file:. In other words, you need - file: here because you can have multiple params 🤯 totally not confusing