[2.2.x] Fixed #30318 -- Added check for importability of arguments of custom error handler views.

Thanks to Jon on Stack Overflow for reporting the issue.

Backport of a5accc0368c6575b55976c06af36ed399c85c781 from master

1 files changed, 10 insertions, 2 deletions

diff --git a/django/urls/resolvers.py b/django/urls/resolvers.py
index 8f59313c93..9d3379a821 100644
--- a/django/urls/resolvers.py
+++ b/django/urls/resolvers.py
@@ -15,7 +15,7 @@ from urllib.parse import quote
 from django.conf import settings
 from django.core.checks import Error, Warning
 from django.core.checks.urls import check_resolver
-from django.core.exceptions import ImproperlyConfigured
+from django.core.exceptions import ImproperlyConfigured, ViewDoesNotExist
 from django.utils.datastructures import MultiValueDict
 from django.utils.functional import cached_property
 from django.utils.http import RFC3986_SUBDELIMS, escape_leading_slashes
@@ -405,7 +405,15 @@ class URLResolver:
         # All handlers take (request, exception) arguments except handler500
         # which takes (request).
         for status_code, num_parameters in [(400, 2), (403, 2), (404, 2), (500, 1)]:
-            handler, param_dict = self.resolve_error_handler(status_code)
+            try:
+                handler, param_dict = self.resolve_error_handler(status_code)
+            except (ImportError, ViewDoesNotExist) as e:
+                path = getattr(self.urlconf_module, 'handler%s' % status_code)
+                msg = (
+                    "The custom handler{status_code} view '{path}' could not be imported."
+                ).format(status_code=status_code, path=path)
+                messages.append(Error(msg, hint=str(e), id='urls.E008'))
+                continue
             signature = inspect.signature(handler)
             args = [None] * num_parameters
             try: