Fixed #32316 -- Deferred accessing __file__.

Deferred accessing the module-global variable __file__ because the
Python import API does not guarantee it always exists—in particular, it
does not exist in certain "frozen" environments. The following changes
advanced this goal.

Thanks to Carlton Gibson, Tom Forbes, Mariusz Felisiak, and Shreyas
Ravi for review and feedback.

1 files changed, 13 insertions, 5 deletions

diff --git a/django/views/debug.py b/django/views/debug.py
index 1b8637874a..67bb5de20b 100644
--- a/django/views/debug.py
+++ b/django/views/debug.py
@@ -26,7 +26,15 @@ DEBUG_ENGINE = Engine(
     libraries={'i18n': 'django.templatetags.i18n'},
 )
 
-CURRENT_DIR = Path(__file__).parent
+
+def builtin_template_path(name):
+    """
+    Return a path to a builtin template.
+
+    Avoid calling this function at the module level or in a class-definition
+    because __file__ may not exist, e.g. in frozen environments.
+    """
+    return Path(__file__).parent / 'templates' / name
 
 
 class ExceptionCycleWarning(UserWarning):
@@ -248,11 +256,11 @@ class ExceptionReporter:
 
     @property
     def html_template_path(self):
-        return CURRENT_DIR / 'templates' / 'technical_500.html'
+        return builtin_template_path('technical_500.html')
 
     @property
     def text_template_path(self):
-        return CURRENT_DIR / 'templates' / 'technical_500.txt'
+        return builtin_template_path('technical_500.txt')
 
     def __init__(self, request, exc_type, exc_value, tb, is_email=False):
         self.request = request
@@ -534,7 +542,7 @@ def technical_404_response(request, exception):
             module = obj.__module__
             caller = '%s.%s' % (module, caller)
 
-    with Path(CURRENT_DIR, 'templates', 'technical_404.html').open(encoding='utf-8') as fh:
+    with builtin_template_path('technical_404.html').open(encoding='utf-8') as fh:
         t = DEBUG_ENGINE.from_string(fh.read())
     reporter_filter = get_default_exception_reporter_filter()
     c = Context({
@@ -553,7 +561,7 @@ def technical_404_response(request, exception):
 
 def default_urlconf(request):
     """Create an empty URLconf 404 error response."""
-    with Path(CURRENT_DIR, 'templates', 'default_urlconf.html').open(encoding='utf-8') as fh:
+    with builtin_template_path('default_urlconf.html').open(encoding='utf-8') as fh:
         t = DEBUG_ENGINE.from_string(fh.read())
     c = Context({
         'version': get_docs_version(),