Fixed #25791 -- Implement autoreload behaviour for cached template loader.

django/template/__init__.py

@@ -64,5 +64,8 @@ from .base import (                                                     # NOQA i
 # Library management
 from .library import Library                                            # NOQA isort:skip
 
+# Import the .autoreload module to trigger the registrations of signals.
+from . import autoreload                                                # NOQA isort:skip
+
 
 __all__ += ('Template', 'Context', 'RequestContext')

django/template/autoreload.py

@@ -0,0 +1,50 @@
+from django.dispatch import receiver
+from django.template import engines
+from django.template.backends.django import DjangoTemplates
+from django.utils.autoreload import (
+    autoreload_started, file_changed, is_django_path,
+)
+
+
+def get_template_directories():
+    # Iterate through each template backend and find
+    # any template_loader that has a 'get_dirs' method.
+    # Collect the directories, filtering out Django templates.
+    items = set()
+    for backend in engines.all():
+        if not isinstance(backend, DjangoTemplates):
+            continue
+
+        items.update(backend.engine.dirs)
+
+        for loader in backend.engine.template_loaders:
+            if not hasattr(loader, 'get_dirs'):
+                continue
+            items.update(
+                directory
+                for directory in loader.get_dirs()
+                if not is_django_path(directory)
+            )
+    return items
+
+
+def reset_loaders():
+    for backend in engines.all():
+        if not isinstance(backend, DjangoTemplates):
+            continue
+        for loader in backend.engine.template_loaders:
+            loader.reset()
+
+
+@receiver(autoreload_started, dispatch_uid='template_loaders_watch_changes')
+def watch_for_template_changes(sender, **kwargs):
+    for directory in get_template_directories():
+        sender.watch_dir(directory, '**/*')
+
+
+@receiver(file_changed, dispatch_uid='template_loaders_file_changed')
+def template_changed(sender, file_path, **kwargs):
+    for template_dir in get_template_directories():
+        if template_dir in file_path.parents:
+            reset_loaders()
+            return True

django/utils/autoreload.py

@@ -14,6 +14,7 @@ from pathlib import Path
 from types import ModuleType
 from zipimport import zipimporter
 
+import django
 from django.apps import apps
 from django.core.signals import request_finished
 from django.dispatch import Signal
@@ -45,6 +46,16 @@ except ImportError:
     pywatchman = None
 
 
+def is_django_module(module):
+    """Return True if the given module is nested under Django."""
+    return module.__name__.startswith('django.')
+
+
+def is_django_path(path):
+    """Return True if the given file path is nested under Django."""
+    return Path(django.__file__).parent in Path(path).parents
+
+
 def check_errors(fn):
     @functools.wraps(fn)
     def wrapper(*args, **kwargs):
@@ -431,8 +442,15 @@ class WatchmanReloader(BaseReloader):
 
     def _subscribe(self, directory, name, expression):
         root, rel_path = self._watch_root(directory)
+        # Only receive notifications of files changing, filtering out other types
+        # like special files: https://facebook.github.io/watchman/docs/type
+        only_files_expression = [
+            'allof',
+            ['anyof', ['type', 'f'], ['type', 'l']],
+            expression
+        ]
         query = {
-            'expression': expression,
+            'expression': only_files_expression,
             'fields': ['name'],
             'since': self._get_clock(root),
             'dedup_results': True,

django/utils/translation/reloader.py

@@ -3,11 +3,7 @@ from pathlib import Path
 from asgiref.local import Local
 
 from django.apps import apps
-
+from django.utils.autoreload import is_django_module
-
-def _is_django_module(module):
-    """Return True if the given module is nested under Django."""
-    return module.__name__.startswith('django.')
 
 
 def watch_for_translation_changes(sender, **kwargs):
@@ -19,7 +15,7 @@ def watch_for_translation_changes(sender, **kwargs):
         directories.extend(
             Path(config.path) / 'locale'
             for config in apps.get_app_configs()
-            if not _is_django_module(config.module)
+            if not is_django_module(config.module)
         )
         directories.extend(Path(p) for p in settings.LOCALE_PATHS)
         for path in directories:

docs/releases/3.2.txt

@@ -394,6 +394,9 @@ Templates
 * :tfilter:`floatformat` template filter now allows using the ``g`` suffix to
   force grouping by the :setting:`THOUSAND_SEPARATOR` for the active locale.
 
+* Templates cached with :ref:`Cached template loaders<template-loaders>` are
+  now correctly reloaded in development.
+
 Tests
 ~~~~~
 

tests/template_tests/test_autoreloader.py

@@ -0,0 +1,92 @@
+from pathlib import Path
+from unittest import mock
+
+from django.template import autoreload
+from django.test import SimpleTestCase, override_settings
+from django.test.utils import require_jinja2
+
+ROOT = Path(__file__).parent.absolute()
+EXTRA_TEMPLATES_DIR = ROOT / "templates_extra"
+
+
+@override_settings(
+    INSTALLED_APPS=['template_tests'],
+    TEMPLATES=[{
+        'BACKEND': 'django.template.backends.dummy.TemplateStrings',
+        'APP_DIRS': True,
+    }, {
+        'BACKEND': 'django.template.backends.django.DjangoTemplates',
+        'DIRS': [EXTRA_TEMPLATES_DIR],
+        'OPTIONS': {
+            'context_processors': [
+                'django.template.context_processors.request',
+            ],
+            'loaders': [
+                'django.template.loaders.filesystem.Loader',
+                'django.template.loaders.app_directories.Loader',
+            ]
+        },
+    }])
+class TemplateReloadTests(SimpleTestCase):
+    @mock.patch('django.template.autoreload.reset_loaders')
+    def test_template_changed(self, mock_reset):
+        template_path = Path(__file__).parent / 'templates' / 'index.html'
+        self.assertTrue(autoreload.template_changed(None, template_path))
+        mock_reset.assert_called_once()
+
+    @mock.patch('django.template.autoreload.reset_loaders')
+    def test_non_template_changed(self, mock_reset):
+        self.assertIsNone(autoreload.template_changed(None, Path(__file__)))
+        mock_reset.assert_not_called()
+
+    def test_watch_for_template_changes(self):
+        mock_reloader = mock.MagicMock()
+        autoreload.watch_for_template_changes(mock_reloader)
+        self.assertSequenceEqual(
+            sorted(mock_reloader.watch_dir.call_args_list),
+            [
+                mock.call(ROOT / 'templates', '**/*'),
+                mock.call(ROOT / 'templates_extra', '**/*')
+            ]
+        )
+
+    def test_get_template_directories(self):
+        self.assertSetEqual(
+            autoreload.get_template_directories(),
+            {
+                ROOT / 'templates_extra',
+                ROOT / 'templates',
+            }
+        )
+
+    @mock.patch('django.template.loaders.base.Loader.reset')
+    def test_reset_all_loaders(self, mock_reset):
+        autoreload.reset_loaders()
+        self.assertEqual(mock_reset.call_count, 2)
+
+
+@require_jinja2
+@override_settings(INSTALLED_APPS=['template_tests'])
+class Jinja2TemplateReloadTests(SimpleTestCase):
+    def test_watch_for_template_changes(self):
+        mock_reloader = mock.MagicMock()
+        autoreload.watch_for_template_changes(mock_reloader)
+        self.assertSequenceEqual(
+            sorted(mock_reloader.watch_dir.call_args_list),
+            [
+                mock.call(ROOT / 'templates', '**/*'),
+            ]
+        )
+
+    def test_get_template_directories(self):
+        self.assertSetEqual(
+            autoreload.get_template_directories(),
+            {
+                ROOT / 'templates',
+            }
+        )
+
+    @mock.patch('django.template.loaders.base.Loader.reset')
+    def test_reset_all_loaders(self, mock_reset):
+        autoreload.reset_loaders()
+        self.assertEqual(mock_reset.call_count, 0)

tests/utils_tests/test_autoreload.py

@@ -14,6 +14,8 @@ from pathlib import Path
 from subprocess import CompletedProcess
 from unittest import mock, skip, skipIf
 
+import pytz
+
 import django.__main__
 from django.apps.registry import Apps
 from django.test import SimpleTestCase
@@ -201,6 +203,26 @@ class TestChildArguments(SimpleTestCase):
             autoreload.get_child_arguments()
 
 
+class TestUtilities(SimpleTestCase):
+    def test_is_django_module(self):
+        for module, expected in (
+            (pytz, False),
+            (sys, False),
+            (autoreload, True)
+        ):
+            with self.subTest(module=module):
+                self.assertIs(autoreload.is_django_module(module), expected)
+
+    def test_is_django_path(self):
+        for module, expected in (
+            (pytz.__file__, False),
+            (contextlib.__file__, False),
+            (autoreload.__file__, True)
+        ):
+            with self.subTest(module=module):
+                self.assertIs(autoreload.is_django_path(module), expected)
+
+
 class TestCommonRoots(SimpleTestCase):
     def test_common_roots(self):
         paths = (