Cloudformation: Fix - validate template yml fixes

This change fixes:
* Replace call to non-existent exception yaml.ParserError
* Catches yaml scanner error for valid json with tabs
* Supply yaml loader to ensure yaml loading throws exception validly for json with tabs and doesn't try to load the json incorrectly

moto/cloudformation/responses.py

@@ -365,8 +365,8 @@ class CloudFormationResponse(BaseResponse):
         except (ValueError, KeyError):
             pass
         try:
-            description = yaml.load(template_body)["Description"]
-        except (yaml.ParserError, KeyError):
+            description = yaml.load(template_body, Loader=yaml.Loader)["Description"]
+        except (yaml.parser.ParserError, yaml.scanner.ScannerError, KeyError):
             pass
         template = self.response_template(VALIDATE_STACK_RESPONSE_TEMPLATE)
         return template.render(description=description)

tests/test_cloudformation/test_validate.py

@@ -40,6 +40,16 @@ json_template = {
     },
 }
 
+json_valid_template_with_tabs = """
+{
+\t"AWSTemplateFormatVersion": "2010-09-09",
+\t"Description": "Stack 2",
+\t"Resources": {
+\t\t"Queue": {"Type": "AWS::SQS::Queue", "Properties": {"VisibilityTimeout": 60}}
+\t}
+}
+"""
+
 # One resource is required
 json_bad_template = {"AWSTemplateFormatVersion": "2010-09-09", "Description": "Stack 1"}
 
@@ -56,6 +66,15 @@ def test_boto3_json_validate_successful():
     assert response["ResponseMetadata"]["HTTPStatusCode"] == 200
 
 
+@mock_cloudformation
+def test_boto3_json_with_tabs_validate_successful():
+    cf_conn = boto3.client("cloudformation", region_name="us-east-1")
+    response = cf_conn.validate_template(TemplateBody=json_valid_template_with_tabs)
+    assert response["Description"] == "Stack 2"
+    assert response["Parameters"] == []
+    assert response["ResponseMetadata"]["HTTPStatusCode"] == 200
+
+
 @mock_cloudformation
 def test_boto3_json_invalid_missing_resource():
     cf_conn = boto3.client("cloudformation", region_name="us-east-1")