[1.10.x] Fixed #24931 -- Made namespaced RegexURLResolvers populate callback strings.

Fixed a regression in 2f16ff5a6c.

Thanks Tim Graham for the review.

Backport of 625b8e9295 from master

tests/admin_docs/namespace_urls.py

@@ -0,0 +1,14 @@
+from django.conf.urls import include, url
+from django.contrib import admin
+
+from . import views
+
+backend_urls = ([
+    url(r'^something/$', views.XViewClass.as_view(), name='something'),
+], 'backend')
+
+urlpatterns = [
+    url(r'^admin/doc/', include('django.contrib.admindocs.urls')),
+    url(r'^admin/', admin.site.urls),
+    url(r'^api/backend/', include(backend_urls, namespace='backend')),
+]

tests/admin_docs/tests.py

@@ -88,6 +88,12 @@ class AdminDocViewTests(TestDataMixin, AdminDocsTestCase):
         # View docstring
         self.assertContains(response, 'Base view for admindocs views.')
 
+    @override_settings(ROOT_URLCONF='admin_docs.namespace_urls')
+    def test_namespaced_view_detail(self):
+        url = reverse('django-admindocs-views-detail', args=['admin_docs.views.XViewClass'])
+        response = self.client.get(url)
+        self.assertContains(response, '<h1>admin_docs.views.XViewClass</h1>')
+
     def test_view_detail_illegal_import(self):
         """
         #23601 - Ensure the view exists in the URLconf.