Currently there is a contradiction between suggested completion and constrain check for source interface name.

To demonstrate this first create any VRF e.g.:

set vrf name red table 1000
commit

Now try to see completion for command:

vyos@r1# set system flow-accounting netflow server 10.1.0.2 source-interface
Possible completions:

interface            Interface name
dum0
eth0
eth1
lo

Though red is not shown, it can be set without error unlike non-existing interface like blabla:

vyos@r1# set system flow-accounting netflow server 10.1.0.2 source-interface blabla

Incorrect path /sys/class/net/blabla: no such file or directory



Invalid value
Value validation failed
Set failed

[edit]
vyos@r1# set system flow-accounting netflow server 10.1.0.2 source-interface red
[edit]

Either completion should show VRFs, or constrains check should refuse to accept VRFs.

Part of interface definition in interface-definitions/include/source-interface.xml.i:

<completionHelp>
  <script>${vyos_completion_dir}/list_interfaces</script>
</completionHelp>
<constraint>
  #include <include/constraint/interface-name.xml.i>
</constraint>