Fix weird planning issues when already fully migrated.

3 files changed, 54 insertions, 1 deletions

diff --git a/tests/migrations/test_executor.py b/tests/migrations/test_executor.py
index ddbfa78db7..5167f428d1 100644
--- a/tests/migrations/test_executor.py
+++ b/tests/migrations/test_executor.py
@@ -12,7 +12,7 @@ class ExecutorTests(TransactionTestCase):
     test failures first, as they may be propagating into here.
     """
 
-    available_apps = ["migrations"]
+    available_apps = ["migrations", "django.contrib.sessions"]
 
     @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations"})
     def test_run(self):
@@ -38,3 +38,35 @@ class ExecutorTests(TransactionTestCase):
         # Are the tables there now?
         self.assertIn("migrations_author", connection.introspection.get_table_list(connection.cursor()))
         self.assertIn("migrations_book", connection.introspection.get_table_list(connection.cursor()))
+
+    @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations", "sessions": "migrations.test_migrations_2"})
+    def test_empty_plan(self):
+        """
+        Tests that re-planning a full migration of a fully-migrated set doesn't
+        perform spurious unmigrations and remigrations.
+
+        There was previously a bug where the executor just always performed the
+        backwards plan for applied migrations - which even for the most recent
+        migration in an app, might include other, dependent apps, and these
+        were being unmigrated.
+        """
+        # Make the initial plan, check it
+        # We use 'sessions' here as the second app as it's always present
+        # in INSTALLED_APPS, so we can happily assign it test migrations.
+        executor = MigrationExecutor(connection)
+        plan = executor.migration_plan([("migrations", "0002_second"), ("sessions", "0001_initial")])
+        self.assertEqual(
+            plan,
+            [
+                (executor.loader.graph.nodes["migrations", "0001_initial"], False),
+                (executor.loader.graph.nodes["migrations", "0002_second"], False),
+                (executor.loader.graph.nodes["sessions", "0001_initial"], False),
+            ],
+        )
+        # Fake-apply all migrations
+        executor.migrate([("migrations", "0002_second"), ("sessions", "0001_initial")], fake=True)
+        # Now plan a second time and make sure it's empty
+        plan = executor.migration_plan([("migrations", "0002_second"), ("sessions", "0001_initial")])
+        self.assertEqual(plan, [])
+        # Erase all the fake records
+        executor.recorder.flush()
diff --git a/tests/migrations/test_migrations_2/0001_initial.py b/tests/migrations/test_migrations_2/0001_initial.py
new file mode 100644
index 0000000000..94c4bc0746
--- /dev/null
+++ b/tests/migrations/test_migrations_2/0001_initial.py
@@ -0,0 +1,21 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [("migrations", "0002_second")]
+    
+    operations = [
+
+        migrations.CreateModel(
+            "OtherAuthor",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=255)),
+                ("slug", models.SlugField(null=True)),
+                ("age", models.IntegerField(default=0)),
+                ("silly_field", models.BooleanField(default=False)),
+            ],
+        ),
+        
+    ]
diff --git a/tests/migrations/test_migrations_2/__init__.py b/tests/migrations/test_migrations_2/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/migrations/test_migrations_2/__init__.py