panels(templates): avoid evaluating LazyObject

LazyObject is typically used for something expensive to evaluate, so avoid evaluating it just for showing it in the debug toolbar.

debug_toolbar/panels/templates/panel.py

@@ -133,10 +133,15 @@ def process_context_list(self, context_layers):
  if pformatted is None:
  temp_layer = {}
  for key, value in context_layer.items():
+ # Do not force evaluating LazyObject
+ if hasattr(value, "_wrapped"):
+ # SimpleLazyObject has __repr__ which includes actual value
+ # if it has been already evaluated
+ temp_layer[key] = repr(value)
  # Replace any request elements - they have a large
  # Unicode representation and the request data is
  # already made available from the Request panel.
- if isinstance(value, http.HttpRequest):
+ elif isinstance(value, http.HttpRequest):
  temp_layer[key] = "<<request>>"
  # Replace the debugging sql_queries element. The SQL
  # data is already made available from the SQL panel.

docs/changes.rst

@@ -7,6 +7,7 @@ Pending
 * Removed outdated third-party panels from the list.
 * Postponed context process in templates panel to include lazy evaluated
  content.
+* Fixed template panel to avoid evaluating ``LazyObject`` when not already evaluated.
 
 4.2.0 (2023-08-10)
 ------------------

tests/panels/test_template.py

@@ -2,6 +2,7 @@
 from django.contrib.auth.models import User
 from django.template import Context, RequestContext, Template
 from django.test import override_settings
+from django.utils.functional import SimpleLazyObject
 
 from ..base import BaseTestCase, IntegrationTestCase
 from ..forms import TemplateReprForm
@@ -113,6 +114,22 @@ def test_empty_context(self):
  ["{'False': False, 'None': None, 'True': True}"],
  )
 
+ def test_lazyobject(self):
+ response = self.panel.process_request(self.request)
+ t = Template("")
+ c = Context({"lazy": SimpleLazyObject(lambda: "lazy_value")})
+ t.render(c)
+ self.panel.generate_stats(self.request, response)
+ self.assertNotIn("lazy_value", self.panel.content)
+
+ def test_lazyobject_eval(self):
+ response = self.panel.process_request(self.request)
+ t = Template("{{lazy}}")
+ c = Context({"lazy": SimpleLazyObject(lambda: "lazy_value")})
+ self.assertEqual(t.render(c), "lazy_value")
+ self.panel.generate_stats(self.request, response)
+ self.assertIn("lazy_value", self.panel.content)
+
 
 @override_settings(
  DEBUG=True, DEBUG_TOOLBAR_PANELS=["debug_toolbar.panels.templates.TemplatesPanel"]