public: do not redirect if template rendering is empty (#29763)

Also, on template error, raise a 404 with a debug message.

combo/public/views.py

@@ -446,8 +446,12 @@ def publish_page(request, page, status=200, template_name=None):
         raise PermissionDenied()
 
     if page.redirect_url:
-        return HttpResponseRedirect(
-                    page.get_redirect_url(context=request.extra_context_data))
+        try:
+            redirect_url = page.get_redirect_url(context=request.extra_context_data)
+        except utils.TemplateError:
+            raise Http404("combo: can't compute redirect URL (template error).")
+        if redirect_url:
+            return HttpResponseRedirect(redirect_url)
 
     cells = CellBase.get_cells(page=page)
     extend_with_parent_cells(cells, hierarchy=pages)

tests/test_public.py

@@ -197,6 +197,19 @@ def test_page_templated_redirect(app):
         resp = app.get('/elsewhere/', status=302)
         assert resp.location == 'http://example.net'
 
+        page.redirect_url = '{{test_url}}/ok'
+        page.save()
+        resp = app.get('/elsewhere/', status=302)
+        assert resp.location == 'http://example.net/ok'
+
+        page.redirect_url = '{{unknown_variable}}'
+        page.save()
+        resp = app.get('/elsewhere/', status=200)
+
+        page.redirect_url = '{% if error %}'
+        page.save()
+        resp = app.get('/elsewhere/', status=404)
+
 def test_page_private_unlogged(app):
     Page.objects.all().delete()
     page = Page(title='Home', slug='index', template_name='standard', public=False)