Fixed #1780 -- Adjusted system check to allow for nested template loaders.

Django's cached loader wraps a list of child loaders, which may
correctly contain the required app directories loader.

Author: carltongibson

debug_toolbar/apps.py

@@ -32,8 +32,26 @@ def check_template_config(config):
     included in the loaders.
     If custom loaders are specified, then APP_DIRS must be True.
     """
+
+    def flat_loaders(loaders):
+        """
+        Recursively flatten the settings list of template loaders.
+
+        Check for (loader, [child_loaders]) tuples.
+        Django's default cached loader uses this pattern.
+        """
+        for loader in loaders:
+            if isinstance(loader, tuple):
+                yield loader[0]
+                yield from flat_loaders(loader[1])
+            else:
+                yield loader
+
     app_dirs = config.get("APP_DIRS", False)
     loaders = config.get("OPTIONS", {}).get("loaders", None)
+    if loaders:
+        loaders = list(flat_loaders(loaders))
+
     # By default the app loader is included.
     has_app_loaders = (
         loaders is None or "django.template.loaders.app_directories.Loader" in loaders

docs/changes.rst

@@ -4,6 +4,8 @@ Change log
 Pending
 -------
 
+* Adjusted app directories system check to allow for nested template loaders.
+
 4.1.0 (2023-05-15)
 ------------------
 

tests/test_checks.py

@@ -198,3 +198,32 @@ def test_check_w006_invalid(self):
     )
     def test_check_w006_valid(self):
         self.assertEqual(run_checks(), [])
+
+    @override_settings(
+        TEMPLATES=[
+            {
+                "NAME": "use_loaders",
+                "BACKEND": "django.template.backends.django.DjangoTemplates",
+                "APP_DIRS": False,
+                "OPTIONS": {
+                    "context_processors": [
+                        "django.template.context_processors.debug",
+                        "django.template.context_processors.request",
+                        "django.contrib.auth.context_processors.auth",
+                        "django.contrib.messages.context_processors.messages",
+                    ],
+                    "loaders": [
+                        (
+                            "django.template.loaders.cached.Loader",
+                            [
+                                "django.template.loaders.filesystem.Loader",
+                                "django.template.loaders.app_directories.Loader",
+                            ],
+                        ),
+                    ],
+                },
+            },
+        ]
+    )
+    def test_check_w006_valid_nested_loaders(self):
+        self.assertEqual(run_checks(), [])