[rclc] Implementation of "client with context" should be improved

[JanStaschulat]

Missing condition to call client callback with context:

@norro. It looks like that the implementation of the client callback with context is not properly called: In case the client would have a context (which is not possible now), it will call the normal callback function and not the callback function with context:

rclc/rclc/src/rclc/executor.c

Line 976 in 0263722

handle->client_callback(handle->data);

You never use a client callback with context?

[BrettRD]

I don't think this is a bug

There is no way to add a client with a context pointer, and there is no typedef for a client callback to receive a context pointer.
https://github.com/ros2/rclc/blob/master/rclc/include/rclc/executor_handle.h#L130-L138

I think there is a subtle bug in the conditions to execute the callback (WITH_CONTEXT should throw an error instead of executing the callback), but not one that could cause a crash, and I can't see a way of even running that execution pathway.

This will disappear after #116
Maybe mark it as a feature request?

[norro]

Agreed, the WITH_CONTEXT callback shouldn't be silently handled without context. Since I don't know any use case for a client with context, I suggest aborting with a warning/error, if a client callback is called WITH_CONTEXT.