Fixed #29945 -- Moved contrib.postgres uninstallation logic to the app config.

django/contrib/postgres/apps.py

@@ -2,17 +2,38 @@ from django.apps import AppConfig
 from django.db import connections
 from django.db.backends.signals import connection_created
 from django.db.models import CharField, TextField
+from django.test.signals import setting_changed
 from django.utils.translation import gettext_lazy as _
 
 from .lookups import SearchLookup, TrigramSimilar, Unaccent
 from .signals import register_type_handlers
 
 
+def uninstall_if_needed(setting, value, enter, **kwargs):
+    """
+    Undo the effects of PostgresConfig.ready() when django.contrib.postgres
+    is "uninstalled" by override_settings().
+    """
+    if not enter and setting == 'INSTALLED_APPS' and 'django.contrib.postgres' not in set(value):
+        connection_created.disconnect(register_type_handlers)
+        CharField._unregister_lookup(Unaccent)
+        TextField._unregister_lookup(Unaccent)
+        CharField._unregister_lookup(SearchLookup)
+        TextField._unregister_lookup(SearchLookup)
+        CharField._unregister_lookup(TrigramSimilar)
+        TextField._unregister_lookup(TrigramSimilar)
+        # Disconnect this receiver until the next time this app is installed
+        # and ready() connects it again to prevent unnecessary processing on
+        # each setting change.
+        setting_changed.disconnect(uninstall_if_needed)
+
+
 class PostgresConfig(AppConfig):
     name = 'django.contrib.postgres'
     verbose_name = _('PostgreSQL extensions')
 
     def ready(self):
+        setting_changed.connect(uninstall_if_needed)
         # Connections may already exist before we are called.
         for conn in connections.all():
             if conn.vendor == 'postgresql':

tests/postgres_tests/__init__.py

@@ -3,19 +3,12 @@ import unittest
 from forms_tests.widget_tests.base import WidgetTest
 
 from django.db import connection
-from django.db.backends.signals import connection_created
 from django.test import TestCase, modify_settings
 
 
 @unittest.skipUnless(connection.vendor == 'postgresql', "PostgreSQL specific tests")
 class PostgreSQLTestCase(TestCase):
-    @classmethod
+    pass
-    def tearDownClass(cls):
-        # No need to keep that signal overhead for non PostgreSQL-related tests.
-        from django.contrib.postgres.signals import register_type_handlers
-
-        connection_created.disconnect(register_type_handlers)
-        super().tearDownClass()
 
 
 @unittest.skipUnless(connection.vendor == 'postgresql', "PostgreSQL specific tests")

tests/postgres_tests/test_apps.py

@@ -0,0 +1,13 @@
+from django.db.backends.signals import connection_created
+from django.test.utils import modify_settings
+
+from . import PostgreSQLTestCase
+
+
+class PostgresConfigTests(PostgreSQLTestCase):
+    def test_register_type_handlers_connection(self):
+        from django.contrib.postgres.signals import register_type_handlers
+        self.assertNotIn(register_type_handlers, connection_created._live_receivers(None))
+        with modify_settings(INSTALLED_APPS={'append': 'django.contrib.postgres'}):
+            self.assertIn(register_type_handlers, connection_created._live_receivers(None))
+        self.assertNotIn(register_type_handlers, connection_created._live_receivers(None))