Fixed #23516 -- Added caching of include tag Template objects

This also speeds up for loops that render the same template
multiple times.

django/template/loader_tags.py

@@ -171,6 +171,8 @@ class ExtendsNode(Node):
 
 
 class IncludeNode(Node):
+    context_key = '__include_context'
+
     def __init__(self, template, *args, **kwargs):
         self.template = template
         self.extra_context = kwargs.pop('extra_context', {})
@@ -178,12 +180,22 @@ class IncludeNode(Node):
         super(IncludeNode, self).__init__(*args, **kwargs)
 
     def render(self, context):
+        """
+        Render the specified template and context. Cache the template object
+        in render_context to avoid reparsing and loading when used in a for
+        loop.
+        """
         try:
             template = self.template.resolve(context)
             # Does this quack like a Template?
             if not callable(getattr(template, 'render', None)):
-                # If not, we'll try get_template
+                # If not, we'll try our cache, and get_template()
-                template = context.template.engine.get_template(template)
+                template_name = template
+                cache = context.render_context.setdefault(self.context_key, {})
+                template = cache.get(template_name)
+                if template is None:
+                    template = context.template.engine.get_template(template_name)
+                    cache[template_name] = template
             values = {
                 name: var.resolve(context)
                 for name, var in six.iteritems(self.extra_context)

docs/releases/1.9.txt

@@ -314,6 +314,9 @@ Templates
 * The ``timesince`` and ``timeuntil`` filters were improved to deal with leap
   years when given large time spans.
 
+* The ``include`` tag now caches parsed templates objects during template
+  rendering, speeding up reuse in places such as for loops.
+
 Requests and Responses
 ^^^^^^^^^^^^^^^^^^^^^^
 

tests/template_tests/syntax_tests/test_if_changed.py

@@ -196,3 +196,17 @@ class IfChangedTests(SimpleTestCase):
         template = self.engine.from_string('{% ifchanged %}{% cycle "1st time" "2nd time" %}{% endifchanged %}')
         output = template.render(Context({}))
         self.assertEqual(output, '1st time')
+
+    def test_include(self):
+        """
+        #23516 -- This works as a regression test only if the cached loader
+        isn't used. Hence we don't use the @setup decorator.
+        """
+        engine = Engine(loaders=[
+            ('django.template.loaders.locmem.Loader', {
+                'template': '{% for x in vars %}{% include "include" %}{% endfor %}',
+                'include': '{% ifchanged %}{{ x }}{% endifchanged %}',
+            }),
+        ])
+        output = engine.render_to_string('template', dict(vars=[1, 1, 2, 2, 3, 3]))
+        self.assertEqual(output, "123")