* create config option for optional jinja2 extensions

* add comments & clarify code for jinja2 extensions

Conflicts:
	mediagoblin/config_spec.ini

mediagoblin/config_spec.ini

@@ -75,6 +75,12 @@ theme = string()
 plugin_web_path = string(default="/plugin_static/")
 plugin_linked_assets_dir = string(default="%(here)s/user_dev/plugin_static/")
 
+[jinja2]
+# Jinja2 supports more directives than the minimum required by mediagoblin. 
+# This setting allows users creating custom templates to specify a list of
+# additional extensions they want to use.  example value:
+# extensions = jinja2.ext.loopcontrols , jinja2.ext.with_
+extensions = string_list(default=list())
 
 [storage:publicstore]
 storage_class = string(default="mediagoblin.storage.filestorage:BasicFileStorage")

mediagoblin/tools/template.py

@@ -50,6 +50,12 @@ def get_jinja_env(template_loader, locale):
     if locale in SETUP_JINJA_ENVS:
         return SETUP_JINJA_ENVS[locale]
 
+    # The default config does not require a [jinja2] block.
+    # You may create one if you wish to enable additional jinja2 extensions,
+    # see example in config_spec.ini 
+    jinja2_config = mg_globals.global_config.get('jinja2', {})
+    local_exts = jinja2_config.get('extensions', [])
+
     # jinja2.StrictUndefined will give exceptions on references
     # to undefined/unknown variables in templates.
     template_env = jinja2.Environment(
@@ -57,7 +63,7 @@ def get_jinja_env(template_loader, locale):
         undefined=jinja2.StrictUndefined,
         extensions=[
             'jinja2.ext.i18n', 'jinja2.ext.autoescape',
-            TemplateHookExtension])
+            TemplateHookExtension] + local_exts)
 
     template_env.install_gettext_callables(
         mg_globals.thread_scope.translations.ugettext,