Fixed #27367 -- Doc'd and tested reversing of URLs with the same name.

Thanks Reinout van Rees for contributing to the patch.

docs/topics/http/urls.txt

@@ -597,15 +597,28 @@ In order to perform URL reversing, you'll need to use **named URL patterns**
 as done in the examples above. The string used for the URL name can contain any
 characters you like. You are not restricted to valid Python names.
 
-When you name your URL patterns, make sure you use names that are unlikely
-to clash with any other application's choice of names. If you call your URL
-pattern ``comment``, and another application does the same thing, there's
-no guarantee which URL will be inserted into your template when you use
-this name.
+When naming URL patterns, choose names that are unlikely to clash with other
+applications' choice of names. If you call your URL pattern ``comment``
+and another application does the same thing, the URL that
+:func:`~django.urls.reverse()` finds depends on whichever pattern is last in
+your project's ``urlpatterns`` list.
 
 Putting a prefix on your URL names, perhaps derived from the application
-name, will decrease the chances of collision. We recommend something like
-``myapp-comment`` instead of ``comment``.
+name (such as ``myapp-comment`` instead of ``comment``), decreases the chance
+of collision.
+
+You can deliberately choose the *same URL name* as another application if you
+want to override a view. For example, a common use case is to override the
+:class:`~django.contrib.auth.views.LoginView`. Parts of Django and most
+third-party apps assume that this view has a URL pattern with the name
+``login``. If you have a custom login view and give its URL the name ``login``,
+:func:`~django.urls.reverse()` will find your custom view as long as it's in
+``urlpatterns`` after ``django.contrib.auth.urls`` is included (if that's
+included at all).
+
+You may also use the same name for multiple URL patterns if they differ in
+their arguments. In addition to the URL name, :func:`~django.urls.reverse()`
+matches the number of arguments and the names of the keyword arguments.
 
 .. _topics-http-defining-url-namespaces:
 

tests/urlpatterns_reverse/named_urls_conflict.py

@@ -0,0 +1,17 @@
+from django.conf.urls import url
+
+from .views import empty_view
+
+urlpatterns = [
+    # No kwargs
+    url(r'^conflict/cannot-go-here/$', empty_view, name='name-conflict'),
+    url(r'^conflict/$', empty_view, name='name-conflict'),
+    # One kwarg
+    url(r'^conflict-first/(?P<first>\w+)/$', empty_view, name='name-conflict'),
+    url(r'^conflict-cannot-go-here/(?P<middle>\w+)/$', empty_view, name='name-conflict'),
+    url(r'^conflict-middle/(?P<middle>\w+)/$', empty_view, name='name-conflict'),
+    url(r'^conflict-last/(?P<last>\w+)/$', empty_view, name='name-conflict'),
+    # Two kwargs
+    url(r'^conflict/(?P<another>\w+)/(?P<extra>\w+)/cannot-go-here/$', empty_view, name='name-conflict'),
+    url(r'^conflict/(?P<extra>\w+)/(?P<another>\w+)/$', empty_view, name='name-conflict'),
+]

tests/urlpatterns_reverse/tests.py

@@ -386,6 +386,23 @@ class ResolverTests(SimpleTestCase):
         self.assertEqual(resolver.reverse('named-url2', 'arg'), 'extra/arg/')
         self.assertEqual(resolver.reverse('named-url2', extra='arg'), 'extra/arg/')
 
+    def test_resolver_reverse_conflict(self):
+        """
+        url() name arguments don't need to be unique. The last registered
+        pattern takes precedence for conflicting names.
+        """
+        resolver = get_resolver('urlpatterns_reverse.named_urls_conflict')
+        # Without arguments, the last URL in urlpatterns has precedence.
+        self.assertEqual(resolver.reverse('name-conflict'), 'conflict/')
+        # With an arg, the last URL in urlpatterns has precedence.
+        self.assertEqual(resolver.reverse('name-conflict', 'arg'), 'conflict-last/arg/')
+        # With a kwarg, other url()s can be reversed.
+        self.assertEqual(resolver.reverse('name-conflict', first='arg'), 'conflict-first/arg/')
+        self.assertEqual(resolver.reverse('name-conflict', middle='arg'), 'conflict-middle/arg/')
+        self.assertEqual(resolver.reverse('name-conflict', last='arg'), 'conflict-last/arg/')
+        # The number and order of the arguments don't interfere with reversing.
+        self.assertEqual(resolver.reverse('name-conflict', 'arg', 'arg'), 'conflict/arg/arg/')
+
     def test_non_regex(self):
         """
         A Resolver404 is raised if resolving doesn't meet the basic