Avoided rewrapping Contexts in render_to_response.

This change preserves backwards-compatibility for a very common misuse
of render_to_response which even occurred in the official documentation.

It fixes that misuse wherever it happened in the code base and docs.

Context.__init__ is documented as accepting a dict and nothing else.
Since Context is dict-like, Context(Context({})) could work to some
extent. However, things get complicated with RequestContext and that
gets in the way of refactoring the template engine. This is the real
rationale for this change.

7 files changed, 36 insertions, 12 deletions

diff --git a/django/contrib/auth/tests/urls.py b/django/contrib/auth/tests/urls.py
index 7e9382fb56..8145f2f69c 100644
--- a/django/contrib/auth/tests/urls.py
+++ b/django/contrib/auth/tests/urls.py
@@ -28,7 +28,7 @@ def remote_user_auth_view(request):
 
 def auth_processor_no_attr_access(request):
     render_to_response('context_processors/auth_attrs_no_access.html',
-        RequestContext(request, {}, processors=[context_processors.auth]))
+        context_instance=RequestContext(request, {}, processors=[context_processors.auth]))
     # *After* rendering, we check whether the session was accessed
     return render_to_response('context_processors/auth_attrs_test_access.html',
         {'session_accessed': request.session.accessed})
@@ -36,30 +36,30 @@ def auth_processor_no_attr_access(request):
 
 def auth_processor_attr_access(request):
     render_to_response('context_processors/auth_attrs_access.html',
-        RequestContext(request, {}, processors=[context_processors.auth]))
+        context_instance=RequestContext(request, {}, processors=[context_processors.auth]))
     return render_to_response('context_processors/auth_attrs_test_access.html',
         {'session_accessed': request.session.accessed})
 
 
 def auth_processor_user(request):
     return render_to_response('context_processors/auth_attrs_user.html',
-        RequestContext(request, {}, processors=[context_processors.auth]))
+        context_instance=RequestContext(request, {}, processors=[context_processors.auth]))
 
 
 def auth_processor_perms(request):
     return render_to_response('context_processors/auth_attrs_perms.html',
-        RequestContext(request, {}, processors=[context_processors.auth]))
+        context_instance=RequestContext(request, {}, processors=[context_processors.auth]))
 
 
 def auth_processor_perm_in_perms(request):
     return render_to_response('context_processors/auth_attrs_perm_in_perms.html',
-        RequestContext(request, {}, processors=[context_processors.auth]))
+        context_instance=RequestContext(request, {}, processors=[context_processors.auth]))
 
 
 def auth_processor_messages(request):
     info(request, "Message 1")
     return render_to_response('context_processors/auth_attrs_messages.html',
-         RequestContext(request, {}, processors=[context_processors.auth]))
+         context_instance=RequestContext(request, {}, processors=[context_processors.auth]))
 
 
 def userpage(request):
diff --git a/django/template/loader.py b/django/template/loader.py
index 093d7d172b..be06d517d2 100644
--- a/django/template/loader.py
+++ b/django/template/loader.py
@@ -65,7 +65,12 @@ def render_to_string(template_name, dictionary=None, context_instance=None,
     else:
         t = get_template(template_name, dirs)
     if not context_instance:
-        return t.render(Context(dictionary))
+        # Django < 1.8 accepted a Context in `dictionary` even though that's
+        # unintended. Preserve this ability but don't rewrap `dictionary`.
+        if isinstance(dictionary, Context):
+            return t.render(dictionary)
+        else:
+            return t.render(Context(dictionary))
     if not dictionary:
         return t.render(context_instance)
     # Add the dictionary to the context stack, ensuring it gets removed again
diff --git a/docs/topics/i18n/translation.txt b/docs/topics/i18n/translation.txt
index 8ef9b89c6b..daf66d332b 100644
--- a/docs/topics/i18n/translation.txt
+++ b/docs/topics/i18n/translation.txt
@@ -860,9 +860,8 @@ If you do this in your view:
 
 .. code-block:: python
 
-    return render_to_response('mytemplate.html', {
-        'available_languages': ['en', 'es', 'fr'],
-    }, RequestContext(request))
+    context = {'available_languages': ['en', 'es', 'fr']}
+    return render(request, 'mytemplate.html', context)
 
 you can iterate over those languages in the template::
 
diff --git a/tests/context_processors/views.py b/tests/context_processors/views.py
index 7a00edab0a..077d722750 100644
--- a/tests/context_processors/views.py
+++ b/tests/context_processors/views.py
@@ -8,12 +8,13 @@ from .models import DebugObject
 def request_processor(request):
     return render_to_response(
         'context_processors/request_attrs.html',
-        RequestContext(request, {}, processors=[context_processors.request]))
+        context_instance=RequestContext(request, {}, processors=[context_processors.request]))
 
 
 def debug_processor(request):
+
     return render_to_response(
         'context_processors/debug.html',
-        RequestContext(request, {
+        context_instance=RequestContext(request, {
             'debug_objects': DebugObject.objects,
         }, processors=[context_processors.debug]))
diff --git a/tests/shortcuts/tests.py b/tests/shortcuts/tests.py
index 4835b40797..24a73d4ffd 100644
--- a/tests/shortcuts/tests.py
+++ b/tests/shortcuts/tests.py
@@ -32,6 +32,15 @@ class ShortcutTests(TestCase):
         self.assertEqual(response.content, b'spam eggs\n')
         self.assertEqual(response['Content-Type'], 'text/html; charset=utf-8')
 
+    def test_render_to_response_with_context_instance_misuse(self):
+        """
+        For backwards-compatibility, ensure that it's possible to pass a
+        RequestContext instance in the dictionary argument instead of the
+        context_instance argument.
+        """
+        response = self.client.get('/render_to_response/context_instance_misuse/')
+        self.assertContains(response, 'context processor output')
+
     def test_render(self):
         response = self.client.get('/render/')
         self.assertEqual(response.status_code, 200)
diff --git a/tests/shortcuts/urls.py b/tests/shortcuts/urls.py
index cd18c8a01b..f02e74a745 100644
--- a/tests/shortcuts/urls.py
+++ b/tests/shortcuts/urls.py
@@ -7,6 +7,7 @@ urlpatterns = [
     url(r'^render_to_response/request_context/$', views.render_to_response_view_with_request_context),
     url(r'^render_to_response/content_type/$', views.render_to_response_view_with_content_type),
     url(r'^render_to_response/dirs/$', views.render_to_response_view_with_dirs),
+    url(r'^render_to_response/context_instance_misuse/$', views.render_to_response_with_context_instance_misuse),
     url(r'^render/$', views.render_view),
     url(r'^render/base_context/$', views.render_view_with_base_context),
     url(r'^render/content_type/$', views.render_view_with_content_type),
diff --git a/tests/shortcuts/views.py b/tests/shortcuts/views.py
index afae78d4d8..c75d324a34 100644
--- a/tests/shortcuts/views.py
+++ b/tests/shortcuts/views.py
@@ -33,6 +33,15 @@ def render_to_response_view_with_dirs(request):
     return render_to_response('render_dirs_test.html', dirs=dirs)
 
 
+def context_processor(request):
+    return {'bar': 'context processor output'}
+
+
+def render_to_response_with_context_instance_misuse(request):
+    context_instance = RequestContext(request, {}, processors=[context_processor])
+    # Incorrect -- context_instance should be passed as a keyword argument.
+    return render_to_response('shortcuts/render_test.html', context_instance)
+
 def render_view(request):
     return render(request, 'shortcuts/render_test.html', {
         'foo': 'FOO',