Refs #28526 -- Provided URLResolver namespace in technical 404 template.

This avoids looking up the nonexistent "name" attribute on URLResolver,
which logs verbosely.

django/views/debug.py

@@ -11,7 +11,7 @@ from django.conf import settings
 from django.http import Http404, HttpResponse, HttpResponseNotFound
 from django.template import Context, Engine, TemplateDoesNotExist
 from django.template.defaultfilters import pprint
-from django.urls import resolve
+from django.urls import URLResolver, resolve
 from django.utils import timezone
 from django.utils.datastructures import MultiValueDict
 from django.utils.encoding import force_str
@@ -635,6 +635,20 @@ def technical_404_response(request, exception):
         ):
             return default_urlconf(request)
 
+    patterns_with_debug_info = []
+    for urlpattern in tried or ():
+        patterns = []
+        for inner_pattern in urlpattern:
+            wrapper = {"tried": inner_pattern}
+            if isinstance(inner_pattern, URLResolver):
+                wrapper["debug_key"] = "namespace"
+                wrapper["debug_val"] = inner_pattern.namespace
+            else:
+                wrapper["debug_key"] = "name"
+                wrapper["debug_val"] = inner_pattern.name
+            patterns.append(wrapper)
+        patterns_with_debug_info.append(patterns)
+
     urlconf = getattr(request, "urlconf", settings.ROOT_URLCONF)
     if isinstance(urlconf, types.ModuleType):
         urlconf = urlconf.__name__
@@ -647,7 +661,8 @@ def technical_404_response(request, exception):
             "urlconf": urlconf,
             "root_urlconf": settings.ROOT_URLCONF,
             "request_path": error_url,
-            "urlpatterns": tried,
+            "urlpatterns": tried,  # Unused, left for compatibility.
+            "urlpatterns_debug": patterns_with_debug_info,
             "resolved": resolved,
             "reason": str(exception),
             "request": request,

django/views/templates/technical_404.html

@@ -46,18 +46,18 @@
   </header>
 
   <main id="info">
-    {% if urlpatterns %}
+    {% if urlpatterns_debug %}
       <p>
       Using the URLconf defined in <code>{{ urlconf }}</code>,
       Django tried these URL patterns, in this order:
       </p>
       <ol>
-        {% for pattern in urlpatterns %}
+        {% for pattern in urlpatterns_debug %}
           <li>
             {% for pat in pattern %}
               <code>
-                {{ pat.pattern }}
-                {% if forloop.last and pat.name %}[name='{{ pat.name }}']{% endif %}
+                {{ pat.tried.pattern }}
+                {% if forloop.last and pat.debug_val %}[{{ pat.debug_key }}='{{ pat.debug_val }}']{% endif %}
               </code>
             {% endfor %}
           </li>

tests/view_tests/tests/test_debug.py

@@ -423,6 +423,16 @@ class DebugViewTests(SimpleTestCase):
             response, "<h1>The install worked successfully! Congratulations!</h1>"
         )
 
+    @override_settings(ROOT_URLCONF="view_tests.default_urls")
+    def test_default_urlconf_technical_404(self):
+        response = self.client.get("/favicon.ico")
+        self.assertContains(
+            response,
+            "<code>\nadmin/\n[namespace='admin']\n</code>",
+            status_code=404,
+            html=True,
+        )
+
     @override_settings(ROOT_URLCONF="view_tests.regression_21530_urls")
     def test_regression_21530(self):
         """