Add a jinja2 syntax checker for Travis

.travis.yml

@@ -24,6 +24,16 @@ script:
       fi
     done
   - |
+    pushd playbooks
+    for j2 in $(find ../ -name "*.j2" -o -name "*.yml"); do
+      python ../util/jinja_check.py $j2
+      if [[ $? -ne 0 ]]; then
+          echo "Jinja parsing error on $j2"
+          exit 1
+      fi
+    done
+    popd
+  - |
     set -e
     cd playbooks/edx-east
     ROLE_DIRS=$(/bin/ls -d roles/*)

util/jinja_check.py

+#!/usr/bin/env python
+import os
+import sys
+from jinja2 import FileSystemLoader
+from jinja2 import Environment as j
+from jinja2.exceptions import UndefinedError
+from ansible.utils.template import _get_filters, _get_extensions
+from yaml.representer import RepresenterError
+
+input_file = sys.argv[1]
+
+# Setup jinja to include ansible filters
+j_e = j(trim_blocks=True, extensions=_get_extensions())
+j_e.loader = FileSystemLoader(['.', os.path.dirname(input_file)])
+j_e.filters.update(_get_filters())
+
+# Go ahead and catch errors for undefined variables and bad yaml
+# from `to_nice_yaml` ansible filter
+try:
+    j_e.from_string(file((input_file)).read()).render(func=lambda: None)
+except (UndefinedError, RepresenterError), ex:
+    pass
+except TypeError, ex:
+    if ex.message != 'Undefined is not JSON serializable':
+        raise Exception(ex.message)
+    pass
+print('{}: ok'.format(input_file))