Incorrect service autocompletion

It seems that the service autocomplete is not behaving entirely correctly. I have moved this issue from https://github.com/ros/ros_tutorials/issues/136#issue-1040427338, opened by @kurshakuz.

Typing following command and trying autocompletion (tab) produces following output:

ros2 service call /spawn turtlesim/srv/Spawn 

-r
--rate
x:\ 0.0\^Jy:\ 0.0\^Jtheta:\ 0.0\^Jname:\ \'\'\

However, adding an x after above statement, produces different output:

ros2 service call /spawn turtlesim/srv/Spawn x

ros2 service call /spawn turtlesim/srv/Spawn x:\ 0.0\
y:\ 0.0\
theta:\ 0.0\
name:\ \'\'\ 

Executing any of them produces errors:

yaml.scanner.ScannerError: mapping values are not allowed here
  in "<unicode string>", line 1, column 8:
    x: 0.0y: 0.0theta: 0.0name: '' 
           ^

The expected and working example should look like the one below.

ros2 service call /spawn turtlesim/srv/Spawn "{x: 0.0, y: 0.0, theta: 0.0, name: ''}"

Start with the ros2 service call autocompletion path described in the issue and reproduce the tab-completion commands using turtlesim/srv/Spawn. Compare the generated multiline output with the expected quoted mapping, and verify that the corrected command executes without the reported YAML scanner error.