Fixed #33197 -- Made field rename with prior matching db_column change a noop.

Thanks Jacob Walls for the report.

3 files changed, 39 insertions, 12 deletions

diff --git a/django/db/migrations/autodetector.py b/django/db/migrations/autodetector.py
index 3cd8a43084..d3ac1c93ab 100644
--- a/django/db/migrations/autodetector.py
+++ b/django/db/migrations/autodetector.py
@@ -840,6 +840,20 @@ class MigrationAutodetector:
                             old_field_dec[0:2] == field_dec[0:2] and
                             dict(old_field_dec[2], db_column=old_db_column) == field_dec[2])):
                         if self.questioner.ask_rename(model_name, rem_field_name, field_name, field):
+                            # A db_column mismatch requires a prior noop
+                            # AlterField for the subsequent RenameField to be a
+                            # noop on attempts at preserving the old name.
+                            if old_field.db_column != field.db_column:
+                                altered_field = field.clone()
+                                altered_field.name = rem_field_name
+                                self.add_operation(
+                                    app_label,
+                                    operations.AlterField(
+                                        model_name=model_name,
+                                        name=rem_field_name,
+                                        field=altered_field,
+                                    ),
+                                )
                             self.add_operation(
                                 app_label,
                                 operations.RenameField(
@@ -970,7 +984,10 @@ class MigrationAutodetector:
                     new_field.remote_field.through = old_field.remote_field.through
             old_field_dec = self.deep_deconstruct(old_field)
             new_field_dec = self.deep_deconstruct(new_field)
-            if old_field_dec != new_field_dec:
+            # If the field was confirmed to be renamed it means that only
+            # db_column was allowed to change which generate_renamed_fields()
+            # already accounts for by adding an AlterField operation.
+            if old_field_dec != new_field_dec and old_field_name == field_name:
                 both_m2m = old_field.many_to_many and new_field.many_to_many
                 neither_m2m = not old_field.many_to_many and not new_field.many_to_many
                 if both_m2m or neither_m2m:
diff --git a/django/db/migrations/operations/fields.py b/django/db/migrations/operations/fields.py
index 641c142191..094c3e3cda 100644
--- a/django/db/migrations/operations/fields.py
+++ b/django/db/migrations/operations/fields.py
@@ -239,7 +239,11 @@ class AlterField(FieldOperation):
     def reduce(self, operation, app_label):
         if isinstance(operation, RemoveField) and self.is_same_field_operation(operation):
             return [operation]
-        elif isinstance(operation, RenameField) and self.is_same_field_operation(operation):
+        elif (
+            isinstance(operation, RenameField) and
+            self.is_same_field_operation(operation) and
+            self.field.db_column is None
+        ):
             return [
                 operation,
                 AlterField(
diff --git a/tests/migrations/test_autodetector.py b/tests/migrations/test_autodetector.py
index ed2398ebaf..8fb4897f0e 100644
--- a/tests/migrations/test_autodetector.py
+++ b/tests/migrations/test_autodetector.py
@@ -1001,14 +1001,17 @@ class AutodetectorTests(TestCase):
         ]
         changes = self.get_changes(before, after, MigrationQuestioner({'ask_rename': True}))
         self.assertNumberMigrations(changes, 'app', 1)
-        self.assertOperationTypes(changes, 'app', 0, ['RenameField', 'AlterField'])
+        self.assertOperationTypes(changes, 'app', 0, ['AlterField', 'RenameField'])
         self.assertOperationAttributes(
-            changes, 'app', 0, 0, model_name='foo', old_name='field', new_name='renamed_field',
+            changes, 'app', 0, 0, model_name='foo', name='field',
         )
-        self.assertOperationAttributes(changes, 'app', 0, 1, model_name='foo', name='renamed_field')
-        self.assertEqual(changes['app'][0].operations[-1].field.deconstruct(), (
-            'renamed_field', 'django.db.models.IntegerField', [], {'db_column': 'field'},
+        self.assertEqual(changes['app'][0].operations[0].field.deconstruct(), (
+            'field', 'django.db.models.IntegerField', [], {'db_column': 'field'},
         ))
+        self.assertOperationAttributes(
+            changes, 'app', 0, 1, model_name='foo', old_name='field',
+            new_name='renamed_field',
+        )
 
     def test_rename_related_field_preserved_db_column(self):
         before = [
@@ -1031,17 +1034,20 @@ class AutodetectorTests(TestCase):
         ]
         changes = self.get_changes(before, after, MigrationQuestioner({'ask_rename': True}))
         self.assertNumberMigrations(changes, 'app', 1)
-        self.assertOperationTypes(changes, 'app', 0, ['RenameField', 'AlterField'])
+        self.assertOperationTypes(changes, 'app', 0, ['AlterField', 'RenameField'])
         self.assertOperationAttributes(
-            changes, 'app', 0, 0, model_name='bar', old_name='foo', new_name='renamed_foo',
+            changes, 'app', 0, 0, model_name='bar', name='foo',
         )
-        self.assertOperationAttributes(changes, 'app', 0, 1, model_name='bar', name='renamed_foo')
-        self.assertEqual(changes['app'][0].operations[-1].field.deconstruct(), (
-            'renamed_foo',
+        self.assertEqual(changes['app'][0].operations[0].field.deconstruct(), (
+            'foo',
             'django.db.models.ForeignKey',
             [],
             {'to': 'app.foo', 'on_delete': models.CASCADE, 'db_column': 'foo_id'},
         ))
+        self.assertOperationAttributes(
+            changes, 'app', 0, 1, model_name='bar', old_name='foo',
+            new_name='renamed_foo',
+        )
 
     def test_rename_model(self):
         """Tests autodetection of renamed models."""