Fixed #27731 -- Implemented CreateModel/AlterFooOperation reduction.

This should alleviate the side effects of disabling the AlterFooOperation
reduction with RemoveField to fix refs #28862 during migration squashing
because CreateModel can perform a reduction with RemoveField.

Thanks Nick Pope for the review.

4 files changed, 95 insertions, 20 deletions

diff --git a/django/db/migrations/operations/models.py b/django/db/migrations/operations/models.py
index 549b2bfc62..8ae877b5fe 100644
--- a/django/db/migrations/operations/models.py
+++ b/django/db/migrations/operations/models.py
@@ -142,6 +142,17 @@ class CreateModel(ModelOperation):
                     managers=self.managers,
                 ),
             ]
+        elif isinstance(operation, FieldRelatedOptionOperation) and self.name_lower == operation.name_lower:
+            option_value = getattr(operation, operation.option_name)
+            return [
+                CreateModel(
+                    self.name,
+                    fields=self.fields,
+                    options={**self.options, **{operation.option_name: option_value}},
+                    bases=self.bases,
+                    managers=self.managers,
+                ),
+            ]
         elif isinstance(operation, FieldOperation) and self.name_lower == operation.model_name_lower:
             if isinstance(operation, AddField):
                 return [
@@ -167,6 +178,18 @@ class CreateModel(ModelOperation):
                     ),
                 ]
             elif isinstance(operation, RemoveField):
+                options = self.options.copy()
+                for option_name in ('unique_together', 'index_together'):
+                    option = options.pop(option_name, None)
+                    if option:
+                        option = set(filter(bool, (
+                            tuple(f for f in fields if f != operation.name_lower) for fields in option
+                        )))
+                        if option:
+                            options[option_name] = option
+                order_with_respect_to = options.get('order_with_respect_to')
+                if order_with_respect_to == operation.name_lower:
+                    del options['order_with_respect_to']
                 return [
                     CreateModel(
                         self.name,
@@ -175,12 +198,23 @@ class CreateModel(ModelOperation):
                             for n, v in self.fields
                             if n.lower() != operation.name_lower
                         ],
-                        options=self.options,
+                        options=options,
                         bases=self.bases,
                         managers=self.managers,
                     ),
                 ]
             elif isinstance(operation, RenameField):
+                options = self.options.copy()
+                for option_name in ('unique_together', 'index_together'):
+                    option = options.get(option_name)
+                    if option:
+                        options[option_name] = {
+                            tuple(operation.new_name if f == operation.old_name else f for f in fields)
+                            for fields in option
+                        }
+                order_with_respect_to = options.get('order_with_respect_to')
+                if order_with_respect_to == operation.old_name:
+                    options['order_with_respect_to'] = operation.new_name
                 return [
                     CreateModel(
                         self.name,
@@ -188,7 +222,7 @@ class CreateModel(ModelOperation):
                             (operation.new_name if n == operation.old_name else n, v)
                             for n, v in self.fields
                         ],
-                        options=self.options,
+                        options=options,
                         bases=self.bases,
                         managers=self.managers,
                     ),
@@ -568,6 +602,8 @@ class AlterIndexTogether(FieldRelatedOptionOperation):
 class AlterOrderWithRespectTo(FieldRelatedOptionOperation):
     """Represent a change with the order_with_respect_to option."""
 
+    option_name = 'order_with_respect_to'
+
     def __init__(self, name, order_with_respect_to):
         self.order_with_respect_to = order_with_respect_to
         super().__init__(name)
diff --git a/tests/migrations/test_autodetector.py b/tests/migrations/test_autodetector.py
index b181b084be..02b95b5458 100644
--- a/tests/migrations/test_autodetector.py
+++ b/tests/migrations/test_autodetector.py
@@ -2075,8 +2075,10 @@ class AutodetectorTests(TestCase):
         changes = self.get_changes([], [self.book, self.author_with_book_order_wrt])
         # Right number/type of migrations?
         self.assertNumberMigrations(changes, 'testapp', 1)
-        self.assertOperationTypes(changes, 'testapp', 0, ["CreateModel", "AlterOrderWithRespectTo"])
-        self.assertOperationAttributes(changes, 'testapp', 0, 1, name="author", order_with_respect_to="book")
+        self.assertOperationTypes(changes, 'testapp', 0, ["CreateModel"])
+        self.assertOperationAttributes(
+            changes, 'testapp', 0, 0, name="Author", options={'order_with_respect_to': 'book'}
+        )
         self.assertNotIn("_order", [name for name, field in changes['testapp'][0].operations[0].fields])
 
     def test_alter_model_managers(self):
diff --git a/tests/migrations/test_commands.py b/tests/migrations/test_commands.py
index 3c42755917..3408f2fefa 100644
--- a/tests/migrations/test_commands.py
+++ b/tests/migrations/test_commands.py
@@ -1335,7 +1335,7 @@ class SquashMigrationsTests(MigrationTestBase):
         out = io.StringIO()
         with self.temporary_migration_module(module="migrations.test_migrations"):
             call_command("squashmigrations", "migrations", "0002", interactive=False, verbosity=1, stdout=out)
-        self.assertIn("Optimized from 8 operations to 4 operations.", out.getvalue())
+        self.assertIn("Optimized from 8 operations to 2 operations.", out.getvalue())
 
     def test_ticket_23799_squashmigrations_no_optimize(self):
         """
diff --git a/tests/migrations/test_optimizer.py b/tests/migrations/test_optimizer.py
index b841b531b1..b2c7b062c6 100644
--- a/tests/migrations/test_optimizer.py
+++ b/tests/migrations/test_optimizer.py
@@ -594,8 +594,11 @@ class OptimizerTests(SimpleTestCase):
     def _test_create_alter_foo_field(self, alter):
         """
         CreateModel, AlterFooTogether/AlterOrderWithRespectTo followed by an
-        add/alter/rename field should optimize to CreateModel and the Alter*
+        add/alter/rename field should optimize to CreateModel with options.
         """
+        option_value = getattr(alter, alter.option_name)
+        options = {alter.option_name: option_value}
+
         # AddField
         self.assertOptimizesTo(
             [
@@ -611,13 +614,12 @@ class OptimizerTests(SimpleTestCase):
                     ("a", models.IntegerField()),
                     ("b", models.IntegerField()),
                     ("c", models.IntegerField()),
-                ]),
-                alter,
+                ], options=options),
             ],
         )
 
         # AlterField
-        self.assertDoesNotOptimize(
+        self.assertOptimizesTo(
             [
                 migrations.CreateModel("Foo", [
                     ("a", models.IntegerField()),
@@ -626,6 +628,12 @@ class OptimizerTests(SimpleTestCase):
                 alter,
                 migrations.AlterField("Foo", "b", models.CharField(max_length=255)),
             ],
+            [
+                migrations.CreateModel("Foo", [
+                    ("a", models.IntegerField()),
+                    ("b", models.CharField(max_length=255)),
+                ], options=options),
+            ],
         )
 
         self.assertOptimizesTo(
@@ -643,13 +651,20 @@ class OptimizerTests(SimpleTestCase):
                     ("a", models.IntegerField()),
                     ("b", models.IntegerField()),
                     ("c", models.CharField(max_length=255)),
-                ]),
-                alter,
+                ], options=options),
             ],
         )
 
         # RenameField
-        self.assertDoesNotOptimize(
+        if isinstance(option_value, str):
+            renamed_options = {alter.option_name: 'c'}
+        else:
+            renamed_options = {
+                alter.option_name: {
+                    tuple('c' if value == 'b' else value for value in item) for item in option_value
+                }
+            }
+        self.assertOptimizesTo(
             [
                 migrations.CreateModel("Foo", [
                     ("a", models.IntegerField()),
@@ -658,6 +673,12 @@ class OptimizerTests(SimpleTestCase):
                 alter,
                 migrations.RenameField("Foo", "b", "c"),
             ],
+            [
+                migrations.CreateModel("Foo", [
+                    ("a", models.IntegerField()),
+                    ("c", models.IntegerField()),
+                ], options=renamed_options),
+            ],
         )
 
         self.assertOptimizesTo(
@@ -673,10 +694,8 @@ class OptimizerTests(SimpleTestCase):
             [
                 migrations.CreateModel("Foo", [
                     ("a", models.IntegerField()),
-                    ("b", models.IntegerField()),
-                ]),
-                alter,
-                migrations.RenameField("Foo", "b", "c"),
+                    ("c", models.IntegerField()),
+                ], options=renamed_options),
             ],
         )
 
@@ -695,13 +714,20 @@ class OptimizerTests(SimpleTestCase):
                     ("a", models.IntegerField()),
                     ("b", models.IntegerField()),
                     ("d", models.IntegerField()),
-                ]),
-                alter,
+                ], options=options),
             ],
         )
 
         # RemoveField
-        self.assertDoesNotOptimize(
+        if isinstance(option_value, str):
+            removed_options = None
+        else:
+            removed_options = {
+                alter.option_name: {
+                    tuple(value for value in item if value != 'b') for item in option_value
+                }
+            }
+        self.assertOptimizesTo(
             [
                 migrations.CreateModel("Foo", [
                     ("a", models.IntegerField()),
@@ -710,9 +736,14 @@ class OptimizerTests(SimpleTestCase):
                 alter,
                 migrations.RemoveField("Foo", "b"),
             ],
+            [
+                migrations.CreateModel("Foo", [
+                    ("a", models.IntegerField()),
+                ], options=removed_options),
+            ]
         )
 
-        self.assertDoesNotOptimize(
+        self.assertOptimizesTo(
             [
                 migrations.CreateModel("Foo", [
                     ("a", models.IntegerField()),
@@ -722,6 +753,12 @@ class OptimizerTests(SimpleTestCase):
                 alter,
                 migrations.RemoveField("Foo", "c"),
             ],
+            [
+                migrations.CreateModel("Foo", [
+                    ("a", models.IntegerField()),
+                    ("b", models.IntegerField()),
+                ], options=options),
+            ],
         )
 
     def test_create_alter_unique_field(self):