Add option for detailed template error

Add option detailed_template_error for informative
error during template and environment parsing.

yaml.SafeLoader returns error with template snippet where
error has been occurred instead of CSafeLoader. But
CSafeLoader is faster. So, if user wants to get more
informative error, use slower but more detailed SafeLoader
for yaml loading.

Change-Id: Ied0a573a00eb5f564dea0c636da1301de5de9ea7
Closes-bug: #1496361

heatclient/common/environment_format.py

@@ -21,15 +21,21 @@ SECTIONS = (PARAMETER_DEFAULTS, PARAMETERS, RESOURCE_REGISTRY) = \
 
 
 def parse(env_str):
-    '''Takes a string and returns a dict containing the parsed structure.
+    """Takes a string and returns a dict containing the parsed structure.
 
     This includes determination of whether the string is using the
     YAML format.
-    '''
+    """
     try:
         env = yaml.load(env_str, Loader=template_format.yaml_loader)
-    except yaml.YAMLError as yea:
+    except yaml.YAMLError:
-        raise ValueError(yea)
+        # NOTE(prazumovsky): we need to return more informative error for
+        # user, so use SafeLoader, which return error message with template
+        # snippet where error has been occurred.
+        try:
+            env = yaml.load(env_str, Loader=yaml.SafeLoader)
+        except yaml.YAMLError as yea:
+            raise ValueError(yea)
     else:
         if env is None:
             env = {}

heatclient/common/template_format.py

@@ -40,18 +40,24 @@ yaml_loader.add_constructor(u'tag:yaml.org,2002:timestamp',
 
 
 def parse(tmpl_str):
-    '''Takes a string and returns a dict containing the parsed structure.
+    """Takes a string and returns a dict containing the parsed structure.
 
     This includes determination of whether the string is using the
     JSON or YAML format.
-    '''
+    """
     if tmpl_str.startswith('{'):
         tpl = json.loads(tmpl_str)
     else:
         try:
             tpl = yaml.load(tmpl_str, Loader=yaml_loader)
-        except yaml.YAMLError as yea:
+        except yaml.YAMLError:
-            raise ValueError(yea)
+            # NOTE(prazumovsky): we need to return more informative error for
+            # user, so use SafeLoader, which return error message with template
+            # snippet where error has been occurred.
+            try:
+                tpl = yaml.load(tmpl_str, Loader=yaml.SafeLoader)
+            except yaml.YAMLError as yea:
+                raise ValueError(yea)
         else:
             if tpl is None:
                 tpl = {}

heatclient/tests/unit/test_environment_format.py

@@ -13,6 +13,7 @@
 from heatclient.common import environment_format
 
 import mock
+import six
 import testscenarios
 import testtools
 import yaml
@@ -78,3 +79,14 @@ class YamlParseExceptions(testtools.TestCase):
 
             self.assertRaises(ValueError,
                               environment_format.parse, text)
+
+
+class DetailedYAMLParseExceptions(testtools.TestCase):
+
+    def test_parse_to_value_exception(self):
+        yaml = """not important
+but very:
+  - incorrect
+"""
+        ex = self.assertRaises(ValueError, environment_format.parse, yaml)
+        self.assertIn('but very:\n            ^', six.text_type(ex))

heatclient/tests/unit/test_template_format.py

@@ -11,6 +11,7 @@
 #    under the License.
 
 import mock
+import six
 import testscenarios
 import testtools
 import yaml
@@ -48,3 +49,14 @@ Resources: {}
 Outputs: {}
 '''
         self.assertRaises(ValueError, template_format.parse, yaml2)
+
+
+class DetailedYAMLParseExceptions(testtools.TestCase):
+
+    def test_parse_to_value_exception(self):
+        yaml = """not important
+but very:
+  - incorrect
+"""
+        ex = self.assertRaises(ValueError, template_format.parse, yaml)
+        self.assertIn('but very:\n            ^', six.text_type(ex))