[2.2.x] Fixed #30324 -- Forced utf-8 encoding when loading the template for the technical 500 debug page.

Regression in 50b8493.
Related to ea542a9.

Backport of efb257a017 from master

django/views/debug.py

@@ -328,14 +328,14 @@ class ExceptionReporter:
 
     def get_traceback_html(self):
         """Return HTML version of debug 500 HTTP error page."""
-        with Path(CURRENT_DIR, 'templates', 'technical_500.html').open() as fh:
+        with Path(CURRENT_DIR, 'templates', 'technical_500.html').open(encoding='utf-8') as fh:
             t = DEBUG_ENGINE.from_string(fh.read())
         c = Context(self.get_traceback_data(), use_l10n=False)
         return t.render(c)
 
     def get_traceback_text(self):
         """Return plain text version of debug 500 HTTP error page."""
-        with Path(CURRENT_DIR, 'templates', 'technical_500.txt').open() as fh:
+        with Path(CURRENT_DIR, 'templates', 'technical_500.txt').open(encoding='utf-8') as fh:
             t = DEBUG_ENGINE.from_string(fh.read())
         c = Context(self.get_traceback_data(), autoescape=False, use_l10n=False)
         return t.render(c)

docs/releases/2.2.1.txt

@@ -14,3 +14,6 @@ Bugfixes
   (:ticket:`30307`).
 
 * Added compatibility for ``psycopg2`` 2.8 (:ticket:`30331`).
+
+* Fixed a regression in Django 2.2 that caused a crash when loading the
+  template for the technical 500 debug page (:ticket:`30324`).

tests/view_tests/tests/test_debug.py

@@ -6,6 +6,7 @@ import sys
 import tempfile
 from io import StringIO
 from pathlib import Path
+from unittest import mock
 
 from django.core import mail
 from django.core.files.uploadedfile import SimpleUploadedFile
@@ -20,7 +21,8 @@ from django.utils.safestring import mark_safe
 from django.utils.version import PY36
 from django.views.debug import (
     CLEANSED_SUBSTITUTE, CallableSettingWrapper, ExceptionReporter,
-    cleanse_setting, technical_500_response,
+    Path as DebugPath, cleanse_setting, default_urlconf,
+    technical_404_response, technical_500_response,
 )
 
 from ..views import (
@@ -610,6 +612,20 @@ class ExceptionReporterTests(SimpleTestCase):
         text = reporter.get_traceback_text()
         self.assertIn('USER: [unable to retrieve the current user]', text)
 
+    def test_template_encoding(self):
+        """
+        The templates are loaded directly, not via a template loader, and
+        should be opened as utf-8 charset as is the default specified on
+        template engines.
+        """
+        reporter = ExceptionReporter(None, None, None, None)
+        with mock.patch.object(DebugPath, 'open') as m:
+            reporter.get_traceback_html()
+            m.assert_called_once_with(encoding='utf-8')
+            m.reset_mock()
+            reporter.get_traceback_text()
+            m.assert_called_once_with(encoding='utf-8')
+
 
 class PlainTextReportTests(SimpleTestCase):
     rf = RequestFactory()