Fixed #31380 -- Added deployment system check for DJANGO_ALLOW_ASYNC_UNSAFE environment variable.

django/core/checks/__init__.py

@@ -5,6 +5,7 @@ from .messages import (
 from .registry import Tags, register, run_checks, tag_exists
 
 # Import these to force registration of checks
+import django.core.checks.async_checks  # NOQA isort:skip
 import django.core.checks.caches  # NOQA isort:skip
 import django.core.checks.database  # NOQA isort:skip
 import django.core.checks.model_checks  # NOQA isort:skip

django/core/checks/async_checks.py

@@ -0,0 +1,16 @@
+import os
+
+from . import Error, Tags, register
+
+E001 = Error(
+    'You should not set the DJANGO_ALLOW_ASYNC_UNSAFE environment variable in '
+    'deployment. This disables async safety protection.',
+    id='async.E001',
+)
+
+
+@register(Tags.async_support, deploy=True)
+def check_async_unsafe(app_configs, **kwargs):
+    if os.environ.get('DJANGO_ALLOW_ASYNC_UNSAFE'):
+        return [E001]
+    return []

django/core/checks/registry.py

@@ -8,6 +8,7 @@ class Tags:
     Built-in tags for internal checks.
     """
     admin = 'admin'
+    async_support = 'async_support'
     caches = 'caches'
     compatibility = 'compatibility'
     database = 'database'

docs/ref/checks.txt

@@ -74,6 +74,7 @@ Builtin tags
 Django's system checks are organized using the following tags:
 
 * ``admin``: Checks of any admin site declarations.
+* ``async_support``: Checks asynchronous-related configuration.
 * ``caches``: Checks cache related configuration.
 * ``compatibility``: Flags potential problems with version upgrades.
 * ``database``: Checks database-related configuration issues. Database checks
@@ -91,6 +92,10 @@ Django's system checks are organized using the following tags:
 
 Some checks may be registered with multiple tags.
 
+.. versionchanged:: 3.1
+
+    The ``async_support`` tag was added.
+
 .. versionchanged:: 3.1
 
     The ``database`` checks are now run only for database aliases specified
@@ -99,6 +104,17 @@ Some checks may be registered with multiple tags.
 Core system checks
 ==================
 
+Asynchronous support
+--------------------
+
+.. versionadded:: 3.1
+
+The following checks verify your setup for :doc:`/topics/async`:
+
+* **async.E001**: You should not set the ``DJANGO_ALLOW_ASYNC_UNSAFE``
+  environment variable in deployment. This disables :ref:`async safety
+  protection <async-safety>`.
+
 Backwards compatibility
 -----------------------
 

tests/check_framework/test_async_checks.py

@@ -0,0 +1,15 @@
+import os
+from unittest import mock
+
+from django.core.checks.async_checks import E001, check_async_unsafe
+from django.test import SimpleTestCase
+
+
+class AsyncCheckTests(SimpleTestCase):
+    @mock.patch.dict(os.environ, {'DJANGO_ALLOW_ASYNC_UNSAFE': ''})
+    def test_no_allowed_async_unsafe(self):
+        self.assertEqual(check_async_unsafe(None), [])
+
+    @mock.patch.dict(os.environ, {'DJANGO_ALLOW_ASYNC_UNSAFE': 'true'})
+    def test_allowed_async_unsafe_set(self):
+        self.assertEqual(check_async_unsafe(None), [E001])