add merge configs to allow merging lists between configuration layers (…

…aws-cloudformation#1915)

* Merge-configs parameter to merge lists

src/cfnlint/config.py

@@ -425,6 +425,10 @@ def __call__(self, parser, namespace, values, option_string=None):
             '--output-file', type=str, default=None,
             help='Writes the output to the specified file, ideal for producing reports'
         )
+        standard.add_argument(
+            '--merge-configs', default=False, action='store_true',
+            help='Merges lists between configuration layers'
+        )
 
         return parser
 
@@ -472,6 +476,7 @@ def set_template_args(self, template):
     template_args = property(get_template_args, set_template_args)
 
 
+# pylint: disable=too-many-public-methods
 class ConfigMixIn(TemplateArgs, CliArgs, ConfigFileArgs, object):
     """ Mixin for the Configs """
 
@@ -487,6 +492,22 @@ def _get_argument_value(self, arg_name, is_template, is_config_file):
         cli_value = getattr(self.cli_args, arg_name)
         template_value = self.template_args.get(arg_name)
         file_value = self.file_args.get(arg_name)
+
+        # merge list configurations
+        # make sure we don't do an infinite loop so skip this check for merge_configs
+        if arg_name != 'merge_configs':
+            if self.merge_configs:
+                # the CLI will always have an empty list when the item is a list
+                # we will use that to evaluate if we need to merge the lists
+                if isinstance(cli_value, list):
+                    result = cli_value
+                    if isinstance(template_value, list):
+                        result.extend(template_value)
+                    if isinstance(file_value, list):
+                        result.extend(file_value)
+                    return result
+
+        # return individual items
         if cli_value:
             return cli_value
         if template_value and is_template:
@@ -642,3 +663,7 @@ def output_file(self):
     @property
     def registry_schemas(self):
         return self._get_argument_value('registry_schemas', False, True)
+
+    @property
+    def merge_configs(self):
+        return self._get_argument_value('merge_configs', True, True)

src/cfnlint/data/CfnLintCli/config/schema.json

@@ -1,10 +1,8 @@
 {
   "$id": "https://github.com/aws-cloudformation/cfn-python-lint/blob/master/src/cfnlint/data/CfnLintCli/config/schema.json",
   "$schema": "http://json-schema.org/draft-07/schema#",
-  "description": "CFNLINTRC configuration schema",
-  "title": "CFNLINTRC JSON Schema",
-  "type": "object",
   "additionalProperties": false,
+  "description": "CFNLINTRC configuration schema",
   "properties": {
     "append_rules": {
       "description": "Location of directories to append rules from",
@@ -13,13 +11,45 @@
       },
       "type": "array"
     },
+    "configure_rules": {
+      "additionalProperties": false,
+      "description": "Configure rules",
+      "patternProperties": {
+        "^.*$": {
+          "patternProperties": {
+            "^.*$": {
+              "anyOf": [
+                {
+                  "type": "string"
+                },
+                {
+                  "type": "integer"
+                },
+                {
+                  "type": "boolean"
+                }
+              ]
+            }
+          },
+          "type": "object"
+        }
+      },
+      "type": "object"
+    },
     "ignore_checks": {
       "description": "List of checks to ignore",
       "items": {
         "type": "string"
       },
       "type": "array"
     },
+    "ignore_templates": {
+      "description": "Templates to ignore",
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
     "include_checks": {
       "description": "List of checks to include",
       "items": {
@@ -34,60 +64,40 @@
       },
       "type": "array"
     },
-    "override_spec": {
-      "description": "Path to spec file to override with",
-      "type": "string"
+    "merge_configs": {
+      "description": "Merges lists between configuration layers",
+      "type": "boolean"
     },
     "output_file": {
       "description": "Path to the file to write the main output to",
       "type": "string"
     },
+    "override_spec": {
+      "description": "Path to spec file to override with",
+      "type": "string"
+    },
     "regions": {
       "description": "Regions to test against",
       "items": {
         "type": "string"
       },
       "type": "array"
     },
-    "configure_rules": {
-      "description": "Configure rules",
-      "patternProperties": {
-        "^.*$": {
-          "type": "object",
-          "patternProperties": {
-            "^.*$": {
-              "anyOf": [
-                {"type": "string"},
-                {"type": "integer"},
-                {"type": "boolean"}
-              ]
-            }
-          }
-        }
-      },
-      "additionalProperties": false,
-      "type": "object"
-    },
-    "templates": {
-      "description": "Templates to lint",
+    "registry_schemas": {
+      "description": "One or more directories of CloudFormation Registry Resource Schemas",
       "items": {
         "type": "string"
       },
       "type": "array"
     },
-    "ignore_templates": {
-      "description": "Templates to ignore",
+    "templates": {
+      "description": "Templates to lint",
       "items": {
         "type": "string"
       },
       "type": "array"
-    },
-    "registry_schemas": {
-      "description": "One or more directories of CloudFormation Registry Resource Schemas",
-      "items": {
-        "type": "string"
-      },
-      "type": "array" 
     }
-  }
-}
+  },
+  "title": "CFNLINTRC JSON Schema",
+  "type": "object"
+}

test/unit/module/config/test_config_mixin.py

@@ -159,3 +159,29 @@ def test_config_expand_ignore_templates(self, yaml_mock):
         self.assertNotIn(
             'test/fixtures/templates/bad/resources/iam/resource_policy.yaml', config.templates)
         self.assertEqual(len(config.templates), 4)
+
+    @patch('cfnlint.config.ConfigFileArgs._read_config', create=True)
+    def test_config_merge(self, yaml_mock):
+        """ Test merging lists  """
+
+        yaml_mock.side_effect = [
+            {"include_checks": ["I"], "ignore_checks": ["E3001"], "regions": ["us-west-2"]},
+            {}
+        ]
+        config = cfnlint.config.ConfigMixIn(['--include-checks', 'I1234', 'I4321', '--merge-configs'])
+        config.template_args = {
+            'Metadata': {
+                'cfn-lint': {
+                    'config': {
+                        'include_checks': ['I9876'],
+                        'ignore_checks': ['W3001']
+                    }
+                }
+            }
+        }
+        # config files wins
+        self.assertEqual(config.regions, ['us-west-2'])
+        # CLI should win
+        self.assertEqual(config.include_checks, ['W', 'E', 'I1234', 'I4321', 'I9876', 'I'])
+        # template file wins over config file
+        self.assertEqual(config.ignore_checks, ['W3001', 'E3001'])