Refs #26421 -- Refactored Apps.lazy_model_operation() for better checks and tests

3 files changed, 68 insertions, 11 deletions

diff --git a/tests/migrations/test_commands.py b/tests/migrations/test_commands.py
index cc655f112f..c9efa09667 100644
--- a/tests/migrations/test_commands.py
+++ b/tests/migrations/test_commands.py
@@ -449,6 +449,12 @@ class MigrateTests(MigrationTestBase):
         """
         call_command("migrate", "migrated_unapplied_app", stdout=six.StringIO())
 
+        # unmigrated_app.SillyModel has a foreign key to 'migrations.Tribble',
+        # but that model is only defined in a migration, so the global app
+        # registry never sees it and the reference is left dangling. Remove it
+        # to avoid problems in subsequent tests.
+        del apps._pending_operations[('migrations', 'tribble')]
+
     @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations_squashed"})
     def test_migrate_record_replaced(self):
         """
diff --git a/tests/migrations/test_state.py b/tests/migrations/test_state.py
index f2e91267e9..2e53e4f825 100644
--- a/tests/migrations/test_state.py
+++ b/tests/migrations/test_state.py
@@ -661,9 +661,10 @@ class StateTests(SimpleTestCase):
         project_state = ProjectState()
         project_state.add_model(ModelState.from_model(Book))
         msg = (
-            "Unhandled pending operations for models:\n"
-            "  migrations.author (referred to by fields: migrations.Book.author)\n"
-            "  migrations.publisher (referred to by fields: migrations.Book.publisher)"
+            "The field migrations.Book.author was declared with a lazy reference "
+            "to 'migrations.author', but app 'migrations' doesn't provide model 'author'.\n"
+            "The field migrations.Book.publisher was declared with a lazy reference "
+            "to 'migrations.publisher', but app 'migrations' doesn't provide model 'publisher'."
         )
         with self.assertRaisesMessage(ValueError, msg):
             project_state.apps
@@ -672,9 +673,10 @@ class StateTests(SimpleTestCase):
         project_state = ProjectState()
         project_state.add_model(ModelState.from_model(Magazine))
         msg = (
-            "Unhandled pending operations for models:\n"
-            "  migrations.author (referred to by fields: "
-            "migrations.Magazine.authors, migrations.Magazine_authors.author)"
+            "The field migrations.Magazine.authors was declared with a lazy reference "
+            "to 'migrations.author\', but app 'migrations' doesn't provide model 'author'.\n"
+            "The field migrations.Magazine_authors.author was declared with a lazy reference "
+            "to \'migrations.author\', but app 'migrations' doesn't provide model 'author'."
         )
         with self.assertRaisesMessage(ValueError, msg):
             project_state.apps
@@ -682,10 +684,14 @@ class StateTests(SimpleTestCase):
         # And now with multiple models and multiple fields.
         project_state.add_model(ModelState.from_model(Book))
         msg = (
-            "Unhandled pending operations for models:\n"
-            "  migrations.author (referred to by fields: migrations.Book.author, "
-            "migrations.Magazine.authors, migrations.Magazine_authors.author)\n"
-            "  migrations.publisher (referred to by fields: migrations.Book.publisher)"
+            "The field migrations.Book.author was declared with a lazy reference "
+            "to 'migrations.author', but app 'migrations' doesn't provide model 'author'.\n"
+            "The field migrations.Book.publisher was declared with a lazy reference "
+            "to 'migrations.publisher', but app 'migrations' doesn't provide model 'publisher'.\n"
+            "The field migrations.Magazine.authors was declared with a lazy reference "
+            "to 'migrations.author', but app 'migrations' doesn't provide model 'author'.\n"
+            "The field migrations.Magazine_authors.author was declared with a lazy reference "
+            "to 'migrations.author', but app 'migrations' doesn't provide model 'author'."
         )
         with self.assertRaisesMessage(ValueError, msg):
             project_state.apps
diff --git a/tests/model_validation/tests.py b/tests/model_validation/tests.py
index 3d079d5bef..b98fd2ddac 100644
--- a/tests/model_validation/tests.py
+++ b/tests/model_validation/tests.py
@@ -1,8 +1,10 @@
 from django.core import management
 from django.core.checks import Error, run_checks
+from django.core.checks.model_checks import _check_lazy_references
+from django.db import models
 from django.db.models.signals import post_init
 from django.test import SimpleTestCase
-from django.test.utils import override_settings
+from django.test.utils import isolate_apps, override_settings
 from django.utils import six
 
 
@@ -15,6 +17,10 @@ def on_post_init(**kwargs):
     pass
 
 
+def dummy_function(model):
+    pass
+
+
 @override_settings(
     INSTALLED_APPS=['django.contrib.auth', 'django.contrib.contenttypes'],
     SILENCED_SYSTEM_CHECKS=['fields.W342'],  # ForeignKey(unique=True)
@@ -54,3 +60,42 @@ class ModelValidationTest(SimpleTestCase):
         self.assertEqual(errors, expected)
 
         post_init.unresolved_references = unresolved_references
+
+    @isolate_apps('django.contrib.auth', kwarg_name='apps')
+    def test_lazy_reference_checks(self, apps):
+
+        class DummyModel(models.Model):
+            author = models.ForeignKey('Author', models.CASCADE)
+
+            class Meta:
+                app_label = "model_validation"
+
+        apps.lazy_model_operation(dummy_function, ('auth', 'imaginarymodel'))
+        apps.lazy_model_operation(dummy_function, ('fanciful_app', 'imaginarymodel'))
+
+        errors = _check_lazy_references(apps)
+
+        expected = [
+            Error(
+                "%r contains a lazy reference to auth.imaginarymodel, "
+                "but app 'auth' doesn't provide model 'imaginarymodel'." % dummy_function,
+                obj=dummy_function,
+                id='models.E022',
+            ),
+            Error(
+                "%r contains a lazy reference to fanciful_app.imaginarymodel, "
+                "but app 'fanciful_app' isn't installed." % dummy_function,
+                obj=dummy_function,
+                id='models.E022',
+            ),
+            Error(
+                "The field model_validation.DummyModel.author was declared "
+                "with a lazy reference to 'model_validation.author', but app "
+                "'model_validation' isn't installed.",
+                hint=None,
+                obj=DummyModel.author.field,
+                id='fields.E307',
+            ),
+        ]
+
+        self.assertEqual(errors, expected)