SubParametersUsed.py

"""
Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
SPDX-License-Identifier: MIT-0
"""
import six
from cfnlint.rules import CloudFormationLintRule
from cfnlint.rules import RuleMatch


class SubParametersUsed(CloudFormationLintRule):
    """Check if Sub Parameters are used"""
    id = 'W1019'
    shortdesc = 'Sub validation of parameters'
    description = 'Validate that Fn::Sub Parameters are used'
    source_url = 'https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html'
    tags = ['functions', 'sub']

    def _test_parameters(self, cfn, sub_string, parameters, tree):
        """Test if sub parmaeters are in the string"""

        matches = []
        sub_string_parameters = cfn.get_sub_parameters(sub_string)

        for parameter_name, _ in parameters.items():
            if parameter_name not in sub_string_parameters:
                message = 'Parameter {0} not used in Fn::Sub at {1}'
                matches.append(RuleMatch(
                    tree, message.format(parameter_name, '/'.join(map(str, tree[:] + [parameter_name])))))

        return matches

    def match(self, cfn):
        matches = []

        sub_objs = cfn.search_deep_keys('Fn::Sub')

        for sub_obj in sub_objs:
            sub_value_obj = sub_obj[-1]
            tree = sub_obj[:-1]
            if isinstance(sub_value_obj, list):
                if len(sub_value_obj) == 2:
                    sub_string = sub_value_obj[0]
                    parameters = sub_value_obj[1]
                    if not isinstance(sub_string, six.string_types):
                        continue
                    if not isinstance(parameters, dict):
                        continue

                    matches.extend(self._test_parameters(cfn, sub_string, parameters, tree + [1]))

        return matches