Fix API break coming from ChainableControllerInterface @ Iron

[ArthurVal]

Inside the ros2_control repo, since Iron (branch iron), and therefore Jazzy (tag 4.16.0), the ChainableControllerInterface interface changes its definition:

-  virtual return_type update_reference_from_subscribers() = 0;
+  virtual return_type update_reference_from_subscribers(
+    const rclcpp::Time & time, const rclcpp::Duration & period) = 0;

Complete diff output from ros_control chainable_controller_interface.hpp repo:

$ git diff humble...4.16.0 -- controller_interface/include/controller_interface/chainable_controller_interface.hpp
diff --git a/controller_interface/include/controller_interface/chainable_controller_interface.hpp b/controller_interface/include/controller_interface/chainable_controller_interface.hpp
index 5008a1b5..2e39f038 100644
--- a/controller_interface/include/controller_interface/chainable_controller_interface.hpp
+++ b/controller_interface/include/controller_interface/chainable_controller_interface.hpp
@@ -15,6 +15,7 @@
 #ifndef CONTROLLER_INTERFACE__CHAINABLE_CONTROLLER_INTERFACE_HPP_
 #define CONTROLLER_INTERFACE__CHAINABLE_CONTROLLER_INTERFACE_HPP_

+#include <string>
 #include <vector>

 #include "controller_interface/controller_interface_base.hpp"
@@ -41,7 +42,8 @@ public:
   virtual ~ChainableControllerInterface() = default;

   /**
-   * Control step update. Command interfaces are updated based on on reference inputs and current states.
+   * Control step update. Command interfaces are updated based on on reference inputs and current
+   * states.
    * **The method called in the (real-time) control loop.**
    *
    * \param[in] time The time at the start of this control loop iteration
@@ -54,6 +56,9 @@ public:
   CONTROLLER_INTERFACE_PUBLIC
   bool is_chainable() const final;

+  CONTROLLER_INTERFACE_PUBLIC
+  std::vector<hardware_interface::StateInterface> export_state_interfaces() final;
+
   CONTROLLER_INTERFACE_PUBLIC
   std::vector<hardware_interface::CommandInterface> export_reference_interfaces() final;

@@ -64,8 +69,19 @@ public:
   bool is_in_chained_mode() const final;

 protected:
-  /// Virtual method that each chainable controller should implement to export its chainable
-  /// interfaces.
+  /// Virtual method that each chainable controller should implement to export its read-only
+  /// chainable interfaces.
+  /**
+   * Each chainable controller implements this methods where all its state(read only) interfaces are
+   * exported. The method has the same meaning as `export_state_interfaces` method from
+   * hardware_interface::SystemInterface or hardware_interface::ActuatorInterface.
+   *
+   * \returns list of StateInterfaces that other controller can use as their inputs.
+   */
+  virtual std::vector<hardware_interface::StateInterface> on_export_state_interfaces();
+
+  /// Virtual method that each chainable controller should implement to export its read/write
+  /// chainable interfaces.
   /**
    * Each chainable controller implements this methods where all input (command) interfaces are
    * exported. The method has the same meaning as `export_command_interface` method from
@@ -73,7 +89,7 @@ protected:
    *
    * \returns list of CommandInterfaces that other controller can use as their outputs.
    */
-  virtual std::vector<hardware_interface::CommandInterface> on_export_reference_interfaces() = 0;
+  virtual std::vector<hardware_interface::CommandInterface> on_export_reference_interfaces();

   /// Virtual method that each chainable controller should implement to switch chained mode.
   /**
@@ -83,7 +99,9 @@ protected:
    *
    * \param[in] flag marking a switch to or from chained mode.
    *
-   * \returns true if controller successfully switched between "chained" and "external" mode. \default returns true so the method don't have to be overridden if controller can always switch chained mode.
+   * \returns true if controller successfully switched between "chained" and "external" mode.
+   * \default returns true so the method don't have to be overridden if controller can always switch
+   * chained mode.
    */
   virtual bool on_set_chained_mode(bool chained_mode);

@@ -94,7 +112,8 @@ protected:
    *
    * \returns return_type::OK if update is successfully, otherwise return_type::ERROR.
    */
-  virtual return_type update_reference_from_subscribers() = 0;
+  virtual return_type update_reference_from_subscribers(
+    const rclcpp::Time & time, const rclcpp::Duration & period) = 0;

   /// Execute calculations of the controller and update command interfaces.
   /**
@@ -110,7 +129,12 @@ protected:
   virtual return_type update_and_write_commands(
     const rclcpp::Time & time, const rclcpp::Duration & period) = 0;

+  /// Storage of values for state interfaces
+  std::vector<std::string> exported_state_interface_names_;
+  std::vector<double> state_interfaces_values_;
+
   /// Storage of values for reference interfaces
+  std::vector<std::string> exported_reference_interface_names_;
   std::vector<double> reference_interfaces_;

 private:

[ArthurVal]

I highly recommend to not merge this until the humble-devel stuffs are sorted out.
After the humble branch is clean we will be able to rebase the jazzy-devel into humble-devel and merge this afterwards.

[MaximilienNaveau]

Actually there another major change I would like to do with these changes.
In practice the reference_interface implemented in humble are nothing but states coming from a state_estimator.
In the case of a fixed robot, I implemented a dummy joint_state_estimator that simply forward the state of the joints.
Ideally we would modify the joint_state_estimator to export the state_interfaces (optionally filtered).
And we would only use the state_interfaces with a prefix inside the linear_feedback_controller to either use the raw state or the one from another state_estimator.

What do you think?