Ticket #4625: render-check-fix.2.patch

django/template/__init__.py

@@ -700 +700 @@
     return current
 
 class NodeBase(type):
+    """
+    Ensures that either a 'render' or 'render_iter' method is defined on
+    any Node sub-class. This avoids potential infinite loops at runtime.
+    """
     def __new__(cls, name, bases, attrs):
         """
-        Ensures that either a 'render' or 'render_iter' method is defined on
-        any Node sub-class. This avoids potential infinite loops at runtime.
+        iter_render/render checking, enabled form of __new__; initially disabled
         """
-        if not (isinstance(attrs.get('render'), types.FunctionType) or
-                isinstance(attrs.get('iter_render'), types.FunctionType)):
+        safeties_enabled = not attrs.pop("__disable_iter_render_safeties__", False)
+        new_cls = type.__new__(cls, name, bases, attrs)
+        if safeties_enabled and new_cls.render == Node.render and new_cls.iter_render == Node.iter_render:
             raise TypeError('Unable to create Node subclass without either "render" or "iter_render" method.')
-        return type.__new__(cls, name, bases, attrs)
+        return new_cls
 
 class Node(object):
     __metaclass__ = NodeBase
+    __disable_iter_render_safeties__ = True
 
     def iter_render(self, context):
         return (self.render(context),)