From 8ad1fe069b9a0cfe87c28617aed6cde457b4a94e Mon Sep 17 00:00:00 2001
From: Simon Charette <simon.charette@zapier.com>
Date: Thu, 4 Mar 2021 23:08:01 -0500
Subject: [PATCH] Remove unnecessary elidable handling of operations.

As long as operations are reduceable to standard django.db.migrations
operations they should not require explicit elidable marking.
---
 syzygy/autodetector.py   | 11 +------
 syzygy/operations.py     |  3 --
 tests/test_operations.py | 62 ++++++++++++++++++----------------------
 3 files changed, 29 insertions(+), 47 deletions(-)

diff --git a/syzygy/autodetector.py b/syzygy/autodetector.py
index 0a78f69..2c5d36f 100644
--- a/syzygy/autodetector.py
+++ b/syzygy/autodetector.py
@@ -71,9 +71,6 @@ def _generate_added_field(self, app_label, model_name, field_name):
         post_add_field = PostAddField(
             model_name=model_name, name=field_name, field=add_field.field
         )
-        # Operation cannot be elided for the duration of the migration
-        # generation.
-        post_add_field.elidable = False
         self.add_operation(
             app_label,
             post_add_field,
@@ -121,13 +118,7 @@ def _generate_removed_field(self, app_label, model_name, field_name):
         pre_remove_field = PreRemoveField(
             model_name=model_name, name=field_name, field=field
         )
-        # Operation cannot be elided for the duration of the migration
-        # generation.
-        pre_remove_field.elidable = False
-        self.add_operation(
-            app_label,
-            PreRemoveField(model_name=model_name, name=field_name, field=field),
-        )
+        self.add_operation(app_label, pre_remove_field)
         stage = Stage()
         self.add_operation(
             self.STAGE_SPLIT,
diff --git a/syzygy/operations.py b/syzygy/operations.py
index 98f9c5f..3a40aa6 100644
--- a/syzygy/operations.py
+++ b/syzygy/operations.py
@@ -71,8 +71,6 @@ class PreRemoveField(migrations.AlterField):
     NULL'able if it's not already.
     """
 
-    elidable = True
-
     def state_forwards(self, app_label, state):
         pass
 
@@ -182,7 +180,6 @@ class PostAddField(migrations.AlterField):
     Elidable operation that drops a previously preserved database default.
     """
 
-    elidable = True
     stage = Stage.POST_DEPLOY
 
     def state_forwards(self, app_label, state):
diff --git a/tests/test_operations.py b/tests/test_operations.py
index 9ea8d64..cef6248 100644
--- a/tests/test_operations.py
+++ b/tests/test_operations.py
@@ -152,25 +152,6 @@ def test_database_backwards(self, preserve_default=True):
     def test_database_backwards_discard_default(self):
         self.test_database_backwards(preserve_default=False)
 
-    def test_elidable(self):
-        model_name = "TestModel"
-        field_name = "foo"
-        field = models.IntegerField(default=42)
-        operations = [
-            migrations.CreateModel(model_name, [("id", models.AutoField())]),
-            AddField(model_name, field_name, field),
-            PostAddField(model_name, field_name, field),
-        ]
-        self.maxDiff = None
-        self.assert_optimizes_to(
-            operations,
-            [
-                migrations.CreateModel(
-                    model_name, [("id", models.AutoField()), (field_name, field)]
-                ),
-            ],
-        )
-
     def test_stage(self):
         model_name = "TestModel"
         field_name = "foo"
@@ -210,6 +191,21 @@ def test_deconstruct(self):
             ),
         )
 
+    def test_reduce(self):
+        model_name = "TestModel"
+        field_name = "foo"
+        field = models.IntegerField(default=42)
+        operations = [
+            AddField(model_name, field_name, field),
+            PostAddField(model_name, field_name, field),
+        ]
+        self.assert_optimizes_to(
+            operations,
+            [
+                migrations.AddField(model_name, field_name, field),
+            ],
+        )
+
 
 class PreRemoveFieldTests(OperationTestCase):
     def test_database_forwards_null(self):
@@ -250,21 +246,6 @@ def test_database_forwards_default(self):
         post_model.objects.create()
         self.assertEqual(pre_model.objects.get().foo, 42)
 
-    def test_elidable(self):
-        model_name = "TestModel"
-        field_name = "foo"
-        field = models.IntegerField(default=42)
-        operations = [
-            migrations.CreateModel(model_name, [(field_name, field)]),
-            PreRemoveField(
-                model_name,
-                field_name,
-                field,
-            ),
-            migrations.RemoveField(model_name, field_name, field),
-        ]
-        self.assert_optimizes_to(operations, [migrations.CreateModel(model_name, [])])
-
     def test_migration_name_fragment(self):
         self.assertEqual(
             PreRemoveField(
@@ -309,3 +290,16 @@ def test_deconstruct(self):
             ),
         )
 
+    def test_elidable(self):
+        model_name = "TestModel"
+        field_name = "foo"
+        field = models.IntegerField(default=42)
+        operations = [
+            PreRemoveField(
+                model_name,
+                field_name,
+                field,
+            ),
+            migrations.RemoveField(model_name, field_name, field),
+        ]
+        self.assert_optimizes_to(operations, [operations[-1]])