Use Jinja2 strict rendering.

For this I had to create an Jinja2 explicit environment, so I put a
function in `ihatemoney.utils.create_jinja2_env(strict_rendering=False)`.

When using this environment and if `strict_rendering` is activated,
templates using undefined variables will now error out rather than
failing silently.

ihatemoney/conf-templates/apache-vhost.conf.j2

@@ -1,8 +1,7 @@
 <VirtualHost *:80>
     ServerAdmin admin@example.com      # CUSTOMIZE
     ServerName ihatemoney.example.com  # CUSTOMIZE
-
-    WSGIDaemonProcess ihatemoney user=www-data group=www-data threads=5 python-path={{ pkg_path }} {% if venv_path %}python-home={{ venv_path }}{% endif %}
+    WSGIDaemonProcess ihatemoney user=www-data group=www-data threads=5 python-path={{ pkg_path }} {% if bin_path %}python-home={{ bin_path }}{% endif %}
     WSGIScriptAlias / {{ pkg_path }}/wsgi.py
     WSGIPassAuthorization On
 

ihatemoney/manage.py

@@ -1,18 +1,17 @@
 #!/usr/bin/env python
 
 import os
-import pkgutil
 import random
 import sys
 import getpass
 
 from flask_script import Manager, Command, Option
 from flask_migrate import Migrate, MigrateCommand
-from jinja2 import Template
 from werkzeug.security import generate_password_hash
 
 from ihatemoney.run import create_app
 from ihatemoney.models import db
+from ihatemoney.utils import create_jinja_env
 
 
 class GeneratePasswordHash(Command):
@@ -44,15 +43,14 @@ class GenerateConfig(Command):
             for i in range(50)])
 
     def run(self, config_file):
-        template_content = pkgutil.get_data(
-            'ihatemoney',
-            os.path.join('conf-templates/', config_file) + '.j2'
-        ).decode('utf-8')
+        env = create_jinja_env('conf-templates', strict_rendering=True)
+        template = env.get_template('%s.j2' % config_file)
 
         bin_path = os.path.dirname(sys.executable)
+        pkg_path = os.path.abspath(os.path.dirname(__file__))
 
-        print(Template(template_content).render(
-                pkg_path=os.path.abspath(os.path.dirname(__file__)),
+        print(template.render(
+                pkg_path=pkg_path,
                 bin_path=bin_path,
                 secret_key=self.gen_secret_key(),
         ))

ihatemoney/utils.py

@@ -2,7 +2,7 @@ import base64
 import re
 
 from io import BytesIO, StringIO
-from jinja2 import filters
+import jinja2
 from json import dumps
 from flask import redirect
 from werkzeug.routing import HTTPException, RoutingException
@@ -83,7 +83,7 @@ def minimal_round(*args, **kw):
     from http://stackoverflow.com/questions/28458524/
     """
     # Use the original round filter, to deal with the extra arguments
-    res = filters.do_round(*args, **kw)
+    res = jinja2.filters.do_round(*args, **kw)
     # Test if the result is equivalent to an integer and
     # return depending on it
     ires = int(res)
@@ -170,3 +170,18 @@ class LoginThrottler():
 
     def reset(self, ip):
         self._attempts.pop(ip, None)
+
+
+def create_jinja_env(folder, strict_rendering=False):
+    """Creates and return a Jinja2 Environment object, used, to load the
+    templates.
+
+    :param strict_rendering:
+        if set to `True`, all templates which use an undefined variable will
+        throw an exception (default to `False`).
+    """
+    loader = jinja2.PackageLoader('ihatemoney', folder)
+    kwargs = {'loader': loader}
+    if strict_rendering:
+        kwargs['undefined'] = jinja2.StrictUndefined
+    return jinja2.Environment(**kwargs)