Twist geometry_msg always read as all zeroes

[ssemenova]

Hey all, let me preface the question by thanking you for working on this, it's incredibly useful for a project I am working on and exciting to see Rust being used for robotics work.

I am running into an issue with sending a Twist message, where regardless of what actual vectors I send, the publisher always reads both angular and linear velocities as all zeroes.

I publish the message like this:

let linear = geometry_msgs::msg:Vector3 {x: 10.0, y: 0.0, z: 0.0};
let angular = geometry_msgs::msg:Vector3 {x: 0.0, y: 0.0, z: 0.0};

let message = geometry_msgs::msg::Twist {linear, angular};

let result = publisher.publish(&message);
match result {
   Ok(result) => println!("Publishing: {}", message.x.linear),
   Err(result) => println!("Could not publish velocity")
}

And read it like this:

let _subscription = node.create_subscription::<geometry_msgs::msg::Twist, _>(
   "cmd_vel",
   rclrs::QOS_PROFILE_DEFAULT,
   move |msg: &geometry_msgs:msg::Twist| {
      println!("I heard: {}", msg.linear.x);
   },
);

The output of my program always has the subscriber reading a 0 in the linear x velocity. So the output of the above two print statements ends up being:

Publishing: 10
I heard: 0

I can also verify this through ros2 topic echo cmd_vel:

linear:
   x: 0.0
   y: 0.0
   z: 0.0
angular:
   x: 0.0
   y: 0.0
   z: 0.0

I wonder if this is an issue with the generator for a geometry_msg in particular, or if I'm doing something wrong with sending the message. I don't understand how the ros2-rust code works perfectly so I'm having some difficulty digging into it to figure out what the problem is.

Thank you.

Edit
Actually, this seems to be happening with a Pose message as well (but not, for example, a Vector3). I wonder if the issue is a message type that has nested within it another message type?

[ssemenova]

Another update: The error is in the generated function get_native_message() and the internal C function it calls (e.g., geometry_msgs_msg_twist_get_native_message()) for any message type comprised of nested message types, in any of the generated msg.rs files. A message type that works (Vector3), has this function definition:

geometry_msgs_msg_vector3_get_native_message(
self.x,
self.y,
self.z,
) -> uintptr_t;

However, a message type that does not work (Twist), has this function definition:

geometry_msgs_msg_twist_get_native_message() -> uintptr_t;

I'm pretty sure that this function should take, as input, the data of the linear and angular velocities.

This all boils down to the msg.rs.em file, which generates these rust message files, on line 31 and line 55. Both these code blocks check for the member.type to be equal to Array, AbstractGenericString, and BasicType, but a member that is itself a message is of type NamespacedType and is never included!

I tried adding it in, but then I realized that even if I could generate Rust code that properly sends nested message contents, I have no idea how it's being handled on the C/C++ side. I started looking into rosidl message generation, but I think I'm a little in too deep here. With posts such as #27, I'm worried that there might not even be rosidl support for nested message types.

[nnmm]

Closed by #80.