Use OrderedDict to preserve elements order when parsing templates (#4)

Author: paoptu023

serverlessrepo/parser.py

@@ -6,6 +6,7 @@
 import six
 import yaml
 from yaml.resolver import ScalarNode, SequenceNode
+from collections import OrderedDict
 
 from .application_metadata import ApplicationMetadata
 from .exceptions import ApplicationMetadataNotFoundError
@@ -51,6 +52,10 @@ def intrinsics_multi_constructor(loader, tag_prefix, node):
     return {cfntag: value}
 
 
+def _dict_representer(dumper, data):
+    return dumper.represent_dict(data.items())
+
+
 def yaml_dump(dict_to_dump):
     """
     This function dumps the dictionary as a YAML document
@@ -59,9 +64,14 @@ def yaml_dump(dict_to_dump):
     :return: YAML document
     :rtype: str
     """
+    yaml.SafeDumper.add_representer(OrderedDict, _dict_representer)
     return yaml.safe_dump(dict_to_dump, default_flow_style=False)
 
 
+def _dict_constructor(loader, node):
+    return OrderedDict(loader.construct_pairs(node))
+
+
 def parse_template(template_str):
     """
     This function parses the SAM template
@@ -75,10 +85,11 @@ def parse_template(template_str):
         # PyYAML doesn't support json as well as it should, so if the input
         # is actually just json it is better to parse it with the standard
         # json parser.
-        return json.loads(template)
+        return json.loads(template_str)
     except ValueError:
+        yaml.SafeLoader.add_constructor(yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG, _dict_constructor)
         yaml.SafeLoader.add_multi_constructor('!', intrinsics_multi_constructor)
-        return yaml.safe_load(template)
+        return yaml.safe_load(template_str)
 
 
 def get_app_metadata(template_dict):
@@ -89,6 +100,7 @@ def get_app_metadata(template_dict):
     :type template_dict: dict
     :return: Application metadata as defined in the template
     :rtype: ApplicationMetadata
+    :raises ApplicationMetadataNotFoundError
     """
     if METADATA in template_dict and SERVERLESS_REPO_APPLICATION in template_dict[METADATA]:
         app_metadata_dict = template_dict[METADATA][SERVERLESS_REPO_APPLICATION]

tests/unit/test_parser.py

@@ -2,7 +2,7 @@
 
 from serverlessrepo.exceptions import ApplicationMetadataNotFoundError
 from serverlessrepo.application_metadata import ApplicationMetadata
-from serverlessrepo.parser import parse_sam_template, yaml_dump, get_app_metadata
+from serverlessrepo.parser import parse_template, yaml_dump, get_app_metadata
 
 
 class TestParser(TestCase):
@@ -46,12 +46,12 @@ class TestParser(TestCase):
     }
 
     def test_parse_yaml_with_tags(self):
-        output = parse_sam_template(self.yaml_with_tags)
+        output = parse_template(self.yaml_with_tags)
         self.assertEquals(self.parsed_yaml_dict, output)
 
         # Make sure formatter and parser work well with each other
         formatted_str = yaml_dump(output)
-        output_again = parse_sam_template(formatted_str)
+        output_again = parse_template(formatted_str)
         self.assertEquals(output, output_again)
 
     def test_yaml_getatt(self):
@@ -70,14 +70,44 @@ def test_yaml_getatt(self):
             }
         }
 
-        actual_output = parse_sam_template(input)
+        actual_output = parse_template(input)
         self.assertEquals(actual_output, output)
 
     def test_parse_json_with_tabs(self):
         template = '{\n\t"foo": "bar"\n}'
-        output = parse_sam_template(template)
+        output = parse_template(template)
         self.assertEqual(output, {'foo': 'bar'})
 
+    def test_parse_yaml_preserve_elements_order(self):
+        input_template = """
+        B_Resource:
+            Key2:
+                Name: name2
+            Key1:
+                Name: name1
+        A_Resource:
+            Key2:
+                Name: name2
+            Key1:
+                Name: name1
+        """
+        output_dict = parse_template(input_template)
+        expected_dict = {
+            'B_Resource': {
+                'Key2': {'Name': 'name2'},
+                'Key1': {'Name': 'name1'}
+            },
+            'A_Resource': {
+                'Key2': {'Name': 'name2'},
+                'Key1': {'Name': 'name1'}
+            }
+        }
+        self.assertEqual(expected_dict, output_dict)
+        output_template = yaml_dump(output_dict)
+        # yaml dump changes indentation, remove spaces and new line characters to just compare the text
+        self.assertEqual(input_template.translate(None, '\n '),
+                         output_template.translate(None, '\n '))
+
     def test_get_app_metadata_missing_metadata(self):
         template_dict_without_metadata = {
             'RandomKey': {
@@ -88,7 +118,7 @@ def test_get_app_metadata_missing_metadata(self):
             get_app_metadata(template_dict_without_metadata)
 
         message = str(context.exception)
-        expected = 'missing Metadata section'
+        expected = 'missing AWS::ServerlessRepo::Application section in template Metadata'
         self.assertTrue(expected in message)
 
     def test_get_app_metadata_missing_app_metadata(self):
@@ -101,7 +131,7 @@ def test_get_app_metadata_missing_app_metadata(self):
             get_app_metadata(template_dict_without_app_metadata)
 
         message = str(context.exception)
-        expected = 'missing AWS::ServerlessRepo::Application section'
+        expected = 'missing AWS::ServerlessRepo::Application section in template Metadata'
         self.assertTrue(expected in message)
 
     def test_get_app_metadata_return_metadata(self):