cli: Add support for auto-completing artifact ref names

    return complete_list

def complete_artifact(args, incomplete):

    from .._context import Context

    ctx = Context()

    config = None

    for i, arg in enumerate(args):

        if arg in ('-c', '--config'):

            config = args[i + 1]

    ctx.load(config)

    # element targets are valid artifact names

    complete_list = complete_target(args, incomplete)

    complete_list.extend(ref for ref in ctx.artifactcache.cas.list_refs() if ref.startswith(incomplete))

    return complete_list

def override_completions(cmd, cmd_param, args, incomplete):

    """

    :param cmd_param: command definition

    # We can't easily extend click's data structures without

    # modifying click itself, so just do some weak special casing

    # right here and select which parameters we want to handle specially.

    if isinstance(cmd_param.type, click.Path) and \

       (cmd_param.name == 'elements' or

    if isinstance(cmd_param.type, click.Path):

        if (cmd_param.name == 'elements' or

                cmd_param.name == 'element' or

                cmd_param.name == 'except_' or

                cmd_param.opts == ['--track'] or

                cmd_param.opts == ['--track-except']):

            return complete_target(args, incomplete)

        if cmd_param.name == 'artifacts':

            return complete_artifact(args, incomplete)

    raise CompleteUnhandled()