Fixed #27882 -- Allowed {% cache %} to cache indefinitely.

django/templatetags/cache.py

@@ -20,6 +20,7 @@ class CacheNode(Node):
             expire_time = self.expire_time_var.resolve(context)
         except VariableDoesNotExist:
             raise TemplateSyntaxError('"cache" tag got an unknown variable: %r' % self.expire_time_var.var)
+        if expire_time is not None:
             try:
                 expire_time = int(expire_time)
             except (ValueError, TypeError):

docs/topics/cache.txt

@@ -659,8 +659,9 @@ the ``cache`` template tag. To give your template access to this tag, put
 
 The ``{% cache %}`` template tag caches the contents of the block for a given
 amount of time. It takes at least two arguments: the cache timeout, in seconds,
-and the name to give the cache fragment. The name will be taken as is, do not
-use a variable. For example:
+and the name to give the cache fragment. The fragment is cached forever if
+timeout is ``None``. The name will be taken as is, do not use a variable. For
+example:
 
 .. code-block:: html+django
 
@@ -669,6 +670,10 @@ use a variable. For example:
         .. sidebar ..
     {% endcache %}
 
+.. versionchanged:: 2.0
+
+    Older versions don't allow a ``None`` timeout.
+
 Sometimes you might want to cache multiple copies of a fragment depending on
 some dynamic data that appears inside the fragment. For example, you might want a
 separate cached copy of the sidebar used in the previous example for every user

tests/template_tests/syntax_tests/test_cache.py

@@ -122,6 +122,17 @@ class CacheTagTests(SimpleTestCase):
         output = self.engine.render_to_string('cache18')
         self.assertEqual(output, 'cache18')
 
+    @setup({
+        'first': '{% load cache %}{% cache None fragment19 %}content{% endcache %}',
+        'second': '{% load cache %}{% cache None fragment19 %}not rendered{% endcache %}'
+    })
+    def test_none_timeout(self):
+        """A timeout of None means "cache forever"."""
+        output = self.engine.render_to_string('first')
+        self.assertEqual(output, 'content')
+        output = self.engine.render_to_string('second')
+        self.assertEqual(output, 'content')
+
 
 class CacheTests(SimpleTestCase):