Fixed #26039 -- Unwrapped nested partials in URL reversal.

Prior to Python 3.5 nested partials need to be fully "unfolded"
to get the actual function.

django/urls/resolvers.py

@@ -135,7 +135,9 @@ class RegexURLPattern(LocaleRegexProvider):
         'path.to.ClassBasedView').
         """
         callback = self.callback
-        if isinstance(callback, functools.partial):
+        # Python 3.5 collapses nested partials, so can change "while" to "if"
+        # when it's the minimum supported version.
+        while isinstance(callback, functools.partial):
             callback = callback.func
         if not hasattr(callback, '__name__'):
             return callback.__module__ + "." + callback.__class__.__name__

tests/urlpatterns_reverse/urls.py

 from django.conf.urls import include, url
 
 from .views import (
-    absolute_kwargs_view, defaults_view, empty_view, empty_view_partial,
-    empty_view_wrapped, nested_view,
+    absolute_kwargs_view, defaults_view, empty_view, empty_view_nested_partial,
+    empty_view_partial, empty_view_wrapped, nested_view,
 )
 
 other_patterns = [
@@ -62,6 +62,7 @@ urlpatterns = [
 
     # Partials should be fine.
     url(r'^partial/', empty_view_partial, name="partial"),
+    url(r'^partial_nested/', empty_view_nested_partial, name="partial_nested"),
     url(r'^partial_wrapped/', empty_view_wrapped, name="partial_wrapped"),
 
     # This is non-reversible, but we shouldn't blow up when parsing it.

tests/urlpatterns_reverse/views.py

@@ -55,8 +55,7 @@ def bad_view(request, *args, **kwargs):
 
 
 empty_view_partial = partial(empty_view, template_name="template.html")
-
-
+empty_view_nested_partial = partial(empty_view_partial, template_name="nested_partial.html")
 empty_view_wrapped = update_wrapper(
     partial(empty_view, template_name="template.html"), empty_view,
 )