Parse an annotation function.
    Return the value of `name` keyword argument and the AST Call node.
    func_name: expected function name

def parse_annotation_function(code, func_name):
    """Parse an annotation function.
    Return the value of `name` keyword argument and the AST Call node.
    func_name: expected function name
    """
    expr = parse_annotation(code)
    call = expr.value
    assert type(call) is ast.Call, 'Annotation is not a function call'

    assert type(call.func) is ast.Attribute, 'Unexpected annotation function'
    assert type(call.func.value) is ast.Name, 'Invalid annotation function name'
    assert call.func.value.id == 'nni', 'Annotation is not a NNI function'
    assert call.func.attr == func_name, 'internal error #2'

    assert len(call.keywords) == 1, 'Annotation function contains more than one keyword argument'
    assert call.keywords[0].arg == 'name', 'Annotation keyword argument is not "name"'
    name = call.keywords[0].value

    return name, call