Autoreload crashes with FORM_RENDERER="django.forms.renderers.TemplatesSetting".

[danjac]

Running Python 3.11 and Django 5.0a1.

I have the following settings:

DEBUG = True

FORM_RENDERER = "django.forms.renderers.TemplatesSetting"

TEMPLATES = [
    {
        "BACKEND": "django.template.backends.django.DjangoTemplates",
        "DIRS": [BASE_DIR / "templates"],
        "OPTIONS": {
            "debug": True,
            "context_processors": [
                "django.template.context_processors.debug",
                "django.template.context_processors.request",
                "django.contrib.auth.context_processors.auth",
                "django.template.context_processors.i18n",
                "django.template.context_processors.media",
                "django.template.context_processors.static",
                "django.template.context_processors.tz",
                "django.contrib.messages.context_processors.messages",
            ],
        },
    }
]

This causes the development server (i.e. manage.py runserver) to crash whenever a template is saved:

  File "python-path/lib/python3.11/site-packages/django/template/autoreload.py", line 60, in template_changed
    reset_loaders()
  File "python-path/lib/python3.11/site-packages/django/template/autoreload.py", line 42, in reset_loaders
    backend = get_default_renderer().engine
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'TemplatesSetting' object has no attribute 'engine'

[Mariusz Felisiak]

Thanks for the report. Would you like to prepare a patch? (a regression test is required, sth similar to the template_tests.test_autoreloader.TemplateReloadTests.test_form_template_reset_template_change_reset_call but with changed FORM_RENDERER).
The following works for me:

django/template/autoreload.py

@@ -39 +39 @@
         for loader in backend.engine.template_loaders:
             loader.reset()
 
-    backend = get_default_renderer().engine
-    if isinstance(backend, DjangoTemplates):
-        for loader in backend.engine.template_loaders:
+    renderer = get_default_renderer()
+    if hasattr(renderer, "engine") and isinstance(renderer.engine, DjangoTemplates):
+        for loader in renderer.engine.engine.template_loaders:
             loader.reset()
 
 

Regression in 439242c5943e16dd5a3a68fadac76e5e723eb323.

[Mariusz Felisiak]

The following could be a regression test:

tests/template_tests/test_autoreloader.py

@@ -1 +1 @@
 from pathlib import Path
 from unittest import mock
 
+from django.forms.renderers import get_default_renderer
 from django.template import autoreload
 from django.test import SimpleTestCase, override_settings
 from django.test.utils import require_jinja2
@@ -68 +69 @@
         self.assertIs(autoreload.template_changed(None, template_path), True)
         mock_loader_reset.assert_called_once()
 
+    @override_settings(FORM_RENDERER="django.forms.renderers.TemplatesSetting")
+    @mock.patch("django.template.loaders.cached.Loader.reset")
+    def test_form_template_reset_template_change_no_djangotemplates(
+        self, mock_loader_reset,
+    ):
+        get_default_renderer.cache_clear()
+        template_path = Path(__file__).parent / "templates" / "index.html"
+        self.assertIs(autoreload.template_changed(None, template_path), True)
+        mock_loader_reset.assert_not_called()
+        get_default_renderer.cache_clear()
+
     @mock.patch("django.forms.renderers.get_default_renderer")
     def test_form_template_reset_non_template_change(self, mock_renderer):
         self.assertIsNone(autoreload.template_changed(None, Path(__file__)))

[danjac]

I've submitted a PR as per suggestions:

​https://github.com/django/django/pull/17318

[Mariusz Felisiak <felisiak.mariusz@…>]

In fe835c23:

Fixed #34878 -- Fixed autoreloader crash when FORM_RENDERER is set to TemplatesSetting.

Regression in 439242c5943e16dd5a3a68fadac76e5e723eb323.

[Mariusz Felisiak <felisiak.mariusz@…>]

In e60fe3b:

[5.0.x] Fixed #34878 -- Fixed autoreloader crash when FORM_RENDERER is set to TemplatesSetting.

Regression in 439242c5943e16dd5a3a68fadac76e5e723eb323.

Backport of fe835c2355072fc2b7a0fbbc57d05477c7ee6ce9 from main