[Draft]Add structured parameter support

[Rahul-K-A]

Description

Adds additional API that allows the user to access structured YAML parameters as a YAML::Node (part of yaml-cpp in rclcpp. Original GSOC proposal can be found here
Essentially, given a parameter YAML file such as

<node>:
  ros__parameters:
    passenger_size:
      min:
        x: 0.6
        y: 0.4
        z: 0.17
      max:
        x: 0.850
        y: 0.65
        z: 0.47

In the code, the user can declare a structured yaml parameter as

this->declare_parameter("passenger_size", YAML::Node(""));

And get access to all the elements under passenger_size as

YAML::Node passenger_size = this->get_parameter("passenger_size").as_yaml();

They can then access individual fields using the standard dict() syntax

double max_x = passenger_size['max']['x'];
double_min_x = passenger_size['min']['x'];

Users can also now set yaml parameters through the ros2 CLI. The syntax is very similar to the one already used for setting messages. For example:

ros2 param set <node> passenger_size "{min: {x : 0.1, y: 0.2, z: 0.3}, max: [1, 2, "hello"] }"

will change passenger size as

min:
  x: 0.1
  y: 0.2
  z: 0.3
max:
  - 1
  - 2
  - hello

Fixes # (issue)

Is this user-facing behavior change?

Yes, it adds an additional parameter type that they can use. None of the existing parameter types are affected. Support for existing namespaced parameters is not affected. If required users will still be able to access individual namespaced parameters such as passenger_size.min.x, passenger_size.max.x, etc.

Did you use Generative AI?

No.

Additional Information

1. Companion rclpy PR: [Draft]Add structured parameter support rclpy#1494
2. Companion rcl PR: [Draft]Add structured parameter support rcl#1254
3. Compantion rcl_interfaces PR: Add structured parameter support  rcl_interfaces#183

[Rahul-K-A]

Tagging this as a draft, because Im yet to add in tests/ apply linter. Once done,will remove the draft tag. Maintainers are welcome to start reviewing it in the meantime

[Rahul-K-A]

Tagging this as a draft, because Im yet to add in tests/ apply linter. Once done,will remove the draft tag. Maintainers are welcome to start reviewing it in the meantime

[alsora]

CI for all the PRs involved

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[ahcorde]

uncrustify is failing. You might need to run

ament_uncrustify --reformat <filenames or directory>

[ahcorde]

Suggested change

	as_yaml() const;
	as_yaml() const;

[ahcorde]

Suggested change

	explicit ParameterValue(const std::vector<std::string> & string_array_value);
	/// Generate a parameter value with type PARAMETER_YAML
	explicit ParameterValue(const std::vector<std::string> & string_array_value);
	/// Generate a parameter value with type PARAMETER_YAML

[ahcorde]

include <type_traits>

[ahcorde]

don't change this number manually. Restore

[ahcorde]

Suggested change

	}
	}

[ahcorde]

move above <rcl_yaml_param_parser/parser.h> and use <>

[ahcorde]

Suggested change

	}
	RCLCPP_LOCAL
	}
	RCLCPP_LOCAL

[ahcorde]

lines < 100 characters

[asherikov]

hi, exposing third party library API (yaml-cpp) as a part of ROS api is not a good idea.

[Rahul-K-A]

Hi @asherikov , yaml-cpp is used by ROS2 on all platforms, as per my knowledge, since it's a dependency of rclcpp itself (yaml_cpp_vendor is just a wrapper). In that sense I do not consider it foreign to the ROS ecoyststem

[asherikov]

API dependency has more implications, e.g., a change in yaml-cpp API would imply a change in ROS2 public API affecting all user code.