Autodetect field renames. HAHAHA. AHAHAHAHA. YES.

django/db/migrations/autodetector.py

@@ -68,7 +68,26 @@ class MigrationAutodetector(object):
             old_field_names = set([x for x, y in old_model_state.fields])
             new_field_names = set([x for x, y in new_model_state.fields])
             for field_name in new_field_names - old_field_names:
-                field = [y for x, y in new_model_state.fields if x == field_name][0]
+                field = new_model_state.get_field_by_name(field_name)
+                # Scan to see if this is actually a rename!
+                field_dec = field.deconstruct()[1:]
+                found_rename = False
+                for removed_field_name in (old_field_names - new_field_names):
+                    if old_model_state.get_field_by_name(removed_field_name).deconstruct()[1:] == field_dec:
+                        self.add_to_migration(
+                            app_label,
+                            operations.RenameField(
+                                model_name = model_name,
+                                old_name = removed_field_name,
+                                new_name = field_name,
+                            )
+                        )
+                        old_field_names.remove(removed_field_name)
+                        new_field_names.remove(field_name)
+                        found_rename = True
+                        break
+                if found_rename:
+                    continue
                 # You can't just add NOT NULL fields with no default
                 if not field.null and not field.has_default():
                     field.default = self.questioner.ask_not_null_addition(field_name, model_name)

tests/migrations/test_autodetector.py

@@ -14,6 +14,7 @@ class AutodetectorTests(TestCase):
     author_empty = ModelState("testapp", "Author", [("id", models.AutoField(primary_key=True))])
     author_name = ModelState("testapp", "Author", [("id", models.AutoField(primary_key=True)), ("name", models.CharField(max_length=200))])
     author_name_longer = ModelState("testapp", "Author", [("id", models.AutoField(primary_key=True)), ("name", models.CharField(max_length=400))])
+    author_name_renamed = ModelState("testapp", "Author", [("id", models.AutoField(primary_key=True)), ("names", models.CharField(max_length=200))])
     other_pony = ModelState("otherapp", "Pony", [("id", models.AutoField(primary_key=True))])
     other_stable = ModelState("otherapp", "Stable", [("id", models.AutoField(primary_key=True))])
     third_thing = ModelState("thirdapp", "Thing", [("id", models.AutoField(primary_key=True))])
@@ -22,7 +23,7 @@ class AutodetectorTests(TestCase):
         "Shortcut to make ProjectStates from lists of predefined models"
         project_state = ProjectState()
         for model_state in model_states:
-            project_state.add_model_state(model_state)
+            project_state.add_model_state(model_state.clone())
         return project_state
 
     def test_arrange_for_graph(self):
@@ -148,3 +149,21 @@ class AutodetectorTests(TestCase):
         action = migration.operations[0]
         self.assertEqual(action.__class__.__name__, "AlterField")
         self.assertEqual(action.name, "name")
+
+    def test_rename_field(self):
+        "Tests autodetection of renamed fields"
+        # Make state
+        before = self.make_project_state([self.author_name])
+        after = self.make_project_state([self.author_name_renamed])
+        autodetector = MigrationAutodetector(before, after)
+        changes = autodetector.changes()
+        # Right number of migrations?
+        self.assertEqual(len(changes['testapp']), 1)
+        # Right number of actions?
+        migration = changes['testapp'][0]
+        self.assertEqual(len(migration.operations), 1)
+        # Right action?
+        action = migration.operations[0]
+        self.assertEqual(action.__class__.__name__, "RenameField")
+        self.assertEqual(action.old_name, "name")
+        self.assertEqual(action.new_name, "names")