Ticket #15791: do_not_call_in_templates.diff

docs/ref/templates/api.txt

@@ -195 +195 @@
     * A variable can only be called if it has no required arguments. Otherwise,
       the system will return an empty string.
 
+    * Occasionally you may want to turn off this feature, and tell the template
+      system to leave a variable un-called no matter what.  To disable this feature,
+      set a ``do_not_call_in_templates`` attribute on the callable variable.  The
+      template system then will act as if your variable is not callable.
+
     * Obviously, there can be side effects when calling some variables, and
       it'd be either foolish or a security hole to allow the template system
       to access them.
@@ -207 +212 @@
 
       To prevent this, set an ``alters_data`` attribute on the callable
       variable. The template system won't call a variable if it has
-      ``alters_data=True`` set. The dynamically-generated
+      ``alters_data=True`` set, and will instead replace the variable with an
+      empty string, unconditionally.  The dynamically-generated
       :meth:`~django.db.models.Model.delete` and
       :meth:`~django.db.models.Model.save` methods on Django model objects get
       ``alters_data=True`` automatically. Example::

django/template/base.py

@@ -692 +692 @@
                                 ):
                             raise VariableDoesNotExist("Failed lookup for key [%s] in %r", (bit, current)) # missing attribute
                 if callable(current):
-                    if getattr(current, 'alters_data', False):
+                    if getattr(current, 'do_not_call_in_templates', False):
+                        pass
+                    elif getattr(current, 'alters_data', False):
                         current = settings.TEMPLATE_STRING_IF_INVALID
                     else:
                         try: # method call (assuming no args required)