Fixed #29245 -- Made autodetector treat field renames + db_column addition as RenameField.

django/db/migrations/autodetector.py

@@ -797,12 +797,19 @@ class MigrationAutodetector:
             field_dec = self.deep_deconstruct(field)
             for rem_app_label, rem_model_name, rem_field_name in sorted(self.old_field_keys - self.new_field_keys):
                 if rem_app_label == app_label and rem_model_name == model_name:
-                    old_field_dec = self.deep_deconstruct(old_model_state.get_field_by_name(rem_field_name))
+                    old_field = old_model_state.get_field_by_name(rem_field_name)
+                    old_field_dec = self.deep_deconstruct(old_field)
                     if field.remote_field and field.remote_field.model and 'to' in old_field_dec[2]:
                         old_rel_to = old_field_dec[2]['to']
                         if old_rel_to in self.renamed_models_rel:
                             old_field_dec[2]['to'] = self.renamed_models_rel[old_rel_to]
-                    if old_field_dec == field_dec:
+                    old_field.set_attributes_from_name(rem_field_name)
+                    old_db_column = old_field.get_attname_column()[1]
+                    if (old_field_dec == field_dec or (
+                            # Was the field renamed and db_column equal to the
+                            # old field's column added?
+                            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):
                             self.add_operation(
                                 app_label,

tests/migrations/test_autodetector.py

@@ -921,6 +921,67 @@ class AutodetectorTests(TestCase):
             changes, 'app', 0, 1, model_name='bar', old_name='second', new_name='second_renamed',
         )
 
+    def test_rename_field_preserved_db_column(self):
+        """
+        RenameField is used if a field is renamed and db_column equal to the
+        old field's column is added.
+        """
+        before = [
+            ModelState('app', 'Foo', [
+                ('id', models.AutoField(primary_key=True)),
+                ('field', models.IntegerField()),
+            ]),
+        ]
+        after = [
+            ModelState('app', 'Foo', [
+                ('id', models.AutoField(primary_key=True)),
+                ('renamed_field', models.IntegerField(db_column='field')),
+            ]),
+        ]
+        changes = self.get_changes(before, after, MigrationQuestioner({'ask_rename': True}))
+        self.assertNumberMigrations(changes, 'app', 1)
+        self.assertOperationTypes(changes, 'app', 0, ['RenameField', 'AlterField'])
+        self.assertOperationAttributes(
+            changes, 'app', 0, 0, model_name='foo', old_name='field', new_name='renamed_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'},
+        ))
+
+    def test_rename_related_field_preserved_db_column(self):
+        before = [
+            ModelState('app', 'Foo', [
+                ('id', models.AutoField(primary_key=True)),
+            ]),
+            ModelState('app', 'Bar', [
+                ('id', models.AutoField(primary_key=True)),
+                ('foo', models.ForeignKey('app.Foo', models.CASCADE)),
+            ]),
+        ]
+        after = [
+            ModelState('app', 'Foo', [
+                ('id', models.AutoField(primary_key=True)),
+            ]),
+            ModelState('app', 'Bar', [
+                ('id', models.AutoField(primary_key=True)),
+                ('renamed_foo', models.ForeignKey('app.Foo', models.CASCADE, db_column='foo_id')),
+            ]),
+        ]
+        changes = self.get_changes(before, after, MigrationQuestioner({'ask_rename': True}))
+        self.assertNumberMigrations(changes, 'app', 1)
+        self.assertOperationTypes(changes, 'app', 0, ['RenameField', 'AlterField'])
+        self.assertOperationAttributes(
+            changes, 'app', 0, 0, model_name='bar', old_name='foo', new_name='renamed_foo',
+        )
+        self.assertOperationAttributes(changes, 'app', 0, 1, model_name='bar', name='renamed_foo')
+        self.assertEqual(changes['app'][0].operations[-1].field.deconstruct(), (
+            'renamed_foo',
+            'django.db.models.ForeignKey',
+            [],
+            {'to': 'app.Foo', 'on_delete': models.CASCADE, 'db_column': 'foo_id'},
+        ))
+
     def test_rename_model(self):
         """Tests autodetection of renamed models."""
         changes = self.get_changes(