Remove additional response.render() for tabs

Right now TabbedView has additional .render() call. Thus
get_context_data() for TabbedView returns already rendered response
with rendered=True flag, which makes it read-only.  This blocks
Profiler middleware in modifying the response. For example, we cannot
add any messages to response from tabbed view.

Simple views have no additional rendering. It was done because of
issues with raising redirect exceptions from tabbed views long
ago. Looks like now there is no such issues and raising redirects from
tabbed views is covered with unit tests. To ensure that nothing broke,
a test with a tab raising Http302 was added - it still redirects to
the url provided as before.

Change-Id: I37076abc15008a523f37da0d09b5b041ef77844e
Closes-Bug: #1595095

horizon/tabs/views.py

@@ -71,16 +71,6 @@ class TabView(views.HorizonTemplateView):
         context = self.get_context_data(**kwargs)
         return self.handle_tabbed_response(context["tab_group"], context)
 
-    def render_to_response(self, *args, **kwargs):
-        response = super(TabView, self).render_to_response(*args, **kwargs)
-        # Because Django's TemplateView uses the TemplateResponse class
-        # to provide deferred rendering (which is usually helpful), if
-        # a tab group raises an Http302 redirect (from exceptions.handle for
-        # example) the exception is actually raised *after* the final pass
-        # of the exception-handling middleware.
-        response.render()
-        return response
-
 
 class TabbedTableView(tables.MultiTableMixin, TabView):
     def __init__(self, *args, **kwargs):

horizon/test/tests/tabs.py

@@ -16,11 +16,13 @@
 
 import copy
 
+from django.conf import settings
 from django import http
 
 import six
 
 from horizon import exceptions
+from horizon import middleware
 from horizon import tabs as horizon_tabs
 from horizon.test import helpers as test
 
@@ -95,6 +97,19 @@ class RecoverableErrorTab(horizon_tabs.Tab):
         raise exc
 
 
+class RedirectExceptionTab(horizon_tabs.Tab):
+    name = "Redirect Exception Tab"
+    slug = "redirect_exception_tab"
+    template_name = "_tab.html"
+    url = settings.TESTSERVER + settings.LOGIN_URL
+
+    def get_context_data(self, request):
+        # Raise a known recoverable error.
+        exc = exceptions.Http302(self.url)
+        exc.silence_logging = True
+        raise exc
+
+
 class TableTabGroup(horizon_tabs.TabGroup):
     slug = "tab_group"
     tabs = [TabWithTable]
@@ -304,14 +319,26 @@ class TabExceptionTests(test.TestCase):
     def setUp(self):
         super(TabExceptionTests, self).setUp()
         self._original_tabs = copy.copy(TabWithTableView.tab_group_class.tabs)
-        TabWithTableView.tab_group_class.tabs.append(RecoverableErrorTab)
 
     def tearDown(self):
         super(TabExceptionTests, self).tearDown()
         TabWithTableView.tab_group_class.tabs = self._original_tabs
 
     def test_tab_view_exception(self):
+        TabWithTableView.tab_group_class.tabs.append(RecoverableErrorTab)
         view = TabWithTableView.as_view()
         req = self.factory.get("/")
         res = view(req)
         self.assertMessageCount(res, error=1)
+
+    def test_tab_302_exception(self):
+        TabWithTableView.tab_group_class.tabs.append(RedirectExceptionTab)
+        view = TabWithTableView.as_view()
+        req = self.factory.get("/")
+        mw = middleware.HorizonMiddleware()
+        try:
+            resp = view(req)
+        except Exception as e:
+            resp = mw.process_exception(req, e)
+            resp.client = self.client
+        self.assertRedirects(resp, RedirectExceptionTab.url)