From 3a23fd070a61d97ba08564688a4a82064002ac7a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christoph=20Fr=C3=B6hlich?=
 <christophfroehlich@users.noreply.github.com>
Date: Mon, 16 Oct 2023 12:58:44 +0200
Subject: [PATCH] Update requirements of state interfaces (backport #798)

---
 joint_trajectory_controller/doc/userdoc.rst            | 10 ++++++++--
 .../validate_jtc_parameters.hpp                        |  4 ++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/joint_trajectory_controller/doc/userdoc.rst b/joint_trajectory_controller/doc/userdoc.rst
index cdc734500a..b6c4c1ecf3 100644
--- a/joint_trajectory_controller/doc/userdoc.rst
+++ b/joint_trajectory_controller/doc/userdoc.rst
@@ -17,7 +17,7 @@ Waypoints consist of positions, and optionally velocities and accelerations.
 Hardware interface types
 -------------------------------
 
-Currently, joints with hardware interface types ``position``, ``velocity``, ``acceleration``, and ``effort`` (defined `here <https://github.com/ros-controls/ros2_control/blob/{REPOS_FILE_BRANCH}/hardware_interface/include/hardware_interface/types/hardware_interface_type_values.hpp>`_) are supported in the following combinations:
+Currently, joints with hardware interface types ``position``, ``velocity``, ``acceleration``, and ``effort`` (defined `here <https://github.com/ros-controls/ros2_control/blob/{REPOS_FILE_BRANCH}/hardware_interface/include/hardware_interface/types/hardware_interface_type_values.hpp>`_) are supported in the following combinations as command interfaces:
 
 * ``position``
 * ``position``, ``velocity``
@@ -37,10 +37,16 @@ This leads to the following allowed combinations of command and state interfaces
 * With command interface ``velocity``:
 
   * if command interface ``velocity`` is the only one, state interfaces must include  ``position, velocity`` .
-  * no restrictions otherwise.
 
 * With command interface ``effort``, state interfaces must include  ``position, velocity``.
 
+* With command interface ``acceleration``, state interfaces must include  ``position, velocity``.
+
+Further restrictions of state interfaces exist:
+
+* ``velocity`` state interface cannot be used if ``position`` interface  is missing.
+* ``acceleration`` state interface cannot be used if ``position`` and ``velocity`` interfaces are not present."
+
 Example controller configurations can be found :ref:`below <ROS 2 interface>`.
 
 Other features
diff --git a/joint_trajectory_controller/include/joint_trajectory_controller/validate_jtc_parameters.hpp b/joint_trajectory_controller/include/joint_trajectory_controller/validate_jtc_parameters.hpp
index 6c909e3278..0b22c7cdd9 100644
--- a/joint_trajectory_controller/include/joint_trajectory_controller/validate_jtc_parameters.hpp
+++ b/joint_trajectory_controller/include/joint_trajectory_controller/validate_jtc_parameters.hpp
@@ -42,7 +42,7 @@ tl::expected<void, std::string> command_interface_type_combinations(
   {
     return tl::make_unexpected(
       "'velocity' command interface can be used either alone or 'position' "
-      "interface has to be present");
+      "command interface has to be present");
   }
 
   if (
@@ -52,7 +52,7 @@ tl::expected<void, std::string> command_interface_type_combinations(
   {
     return tl::make_unexpected(
       "'acceleration' command interface can only be used if 'velocity' and "
-      "'position' interfaces are present");
+      "'position' command interfaces are present");
   }
 
   if (