Catch exceptions when error rendering templates

homeassistant/exceptions.py

@@ -14,3 +14,10 @@ class InvalidEntityFormatError(HomeAssistantError):
 class NoEntitySpecifiedError(HomeAssistantError):
     """ When no entity is specified. """
     pass
+
+
+class TemplateError(HomeAssistantError):
+    """ Error during template rendering. """
+    def __init__(self, exception):
+        super().__init__('{}: {}'.format(exception.__class__.__name__,
+                                         exception))

homeassistant/util/template.py

@@ -6,7 +6,12 @@ Template utility methods for rendering strings with HA data.
 """
 # pylint: disable=too-few-public-methods
 import json
+import logging
+import jinja2
 from jinja2.sandbox import ImmutableSandboxedEnvironment
+from homeassistant.exceptions import TemplateError
+
+_LOGGER = logging.getLogger(__name__)
 
 
 def render_with_possible_json_value(hass, template, value):
@@ -20,7 +25,11 @@ def render_with_possible_json_value(hass, template, value):
     except ValueError:
         pass
 
+    try:
         return render(hass, template, variables)
+    except TemplateError:
+        _LOGGER.exception('Error parsing value')
+        return value
 
 
 def render(hass, template, variables=None, **kwargs):
@@ -28,9 +37,12 @@ def render(hass, template, variables=None, **kwargs):
     if variables is not None:
         kwargs.update(variables)
 
+    try:
         return ENV.from_string(template, {
             'states': AllStates(hass)
         }).render(kwargs)
+    except jinja2.TemplateError as err:
+        raise TemplateError(err)
 
 
 class AllStates(object):

tests/util/test_template.py

@@ -7,7 +7,7 @@ Tests Home Assistant util methods.
 # pylint: disable=too-many-public-methods
 import unittest
 import homeassistant.core as ha
-
+from homeassistant.exceptions import TemplateError
 from homeassistant.util import template
 
 
@@ -84,3 +84,7 @@ class TestUtilTemplate(unittest.TestCase):
             '',
             template.render_with_possible_json_value(
                 self.hass, '{{ value_json }}', '{ I AM NOT JSON }'))
+
+    def test_raise_exception_on_error(self):
+        with self.assertRaises(TemplateError):
+            template.render(self.hass, '{{ invalid_syntax')