feat(migrations): Add in SafeDeleteColumn migration operation (#81098)

This builds on #81063

This adds in `SafeDeleteColumn`, which works the same way as
`SafeDeleteModel`, except on database columns.

It performs checks that the column doesn't have a db constraint set, and
also that it is either nullable or has a db_default set.

Similarly to `SafeDeleteModel` we still need to be careful to make sure
that the pending deletion merges and deploys first, and then the real
deletion.

Author: wedamija

fixtures/safe_migrations_apps/bad_flow_delete_field_double_pending_app/__init__.py

@@ -0,0 +1,27 @@
+# Generated by Django 3.1 on 2019-09-22 21:47
+
+from django.db import migrations, models
+
+from sentry.new_migrations.migrations import CheckedMigration
+
+
+class Migration(CheckedMigration):
+
+    initial = True
+
+    dependencies = []
+
+    operations = [
+        migrations.CreateModel(
+            name="TestTable",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+                    ),
+                ),
+                ("field", models.IntegerField(null=True)),
+            ],
+        ),
+    ]

fixtures/safe_migrations_apps/bad_flow_delete_field_double_pending_app/migrations/0001_initial.py

@@ -0,0 +1,18 @@
+from sentry.new_migrations.migrations import CheckedMigration
+from sentry.new_migrations.monkey.fields import SafeRemoveField
+from sentry.new_migrations.monkey.state import DeletionAction
+
+
+class Migration(CheckedMigration):
+
+    dependencies = [
+        ("bad_flow_delete_field_double_pending_app", "0001_initial"),
+    ]
+
+    operations = [
+        SafeRemoveField(
+            model_name="testtable",
+            name="field",
+            deletion_action=DeletionAction.MOVE_TO_PENDING,
+        ),
+    ]

fixtures/safe_migrations_apps/bad_flow_delete_field_double_pending_app/migrations/0002_delete_pending.py

@@ -0,0 +1,18 @@
+from sentry.new_migrations.migrations import CheckedMigration
+from sentry.new_migrations.monkey.fields import SafeRemoveField
+from sentry.new_migrations.monkey.state import DeletionAction
+
+
+class Migration(CheckedMigration):
+
+    dependencies = [
+        ("bad_flow_delete_field_double_pending_app", "0002_delete_pending"),
+    ]
+
+    operations = [
+        SafeRemoveField(
+            model_name="testtable",
+            name="field",
+            deletion_action=DeletionAction.MOVE_TO_PENDING,
+        ),
+    ]

fixtures/safe_migrations_apps/bad_flow_delete_field_double_pending_app/migrations/0003_double_pending.py

@@ -0,0 +1,5 @@
+from django.db import models
+
+
+class TestTable(models.Model):
+    field = models.IntegerField(default=0, null=False)

fixtures/safe_migrations_apps/bad_flow_delete_field_double_pending_app/migrations/__init__.py

@@ -0,0 +1,45 @@
+import django
+from django.db import migrations, models
+
+import sentry
+from sentry.new_migrations.migrations import CheckedMigration
+
+
+class Migration(CheckedMigration):
+
+    initial = True
+
+    dependencies = []
+
+    operations = [
+        migrations.CreateModel(
+            name="FkTable",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+                    ),
+                ),
+            ],
+        ),
+        migrations.CreateModel(
+            name="TestTable",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+                    ),
+                ),
+                (
+                    "fk_table",
+                    sentry.db.models.fields.foreignkey.FlexibleForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        to="bad_flow_delete_field_pending_with_fk_constraint_app.fktable",
+                        db_index=False,
+                    ),
+                ),
+            ],
+        ),
+    ]

fixtures/safe_migrations_apps/bad_flow_delete_field_double_pending_app/models.py

@@ -0,0 +1,19 @@
+from sentry.new_migrations.migrations import CheckedMigration
+from sentry.new_migrations.monkey.fields import SafeRemoveField
+from sentry.new_migrations.monkey.state import DeletionAction
+
+
+class Migration(CheckedMigration):
+    atomic = False
+
+    dependencies = [
+        ("bad_flow_delete_field_pending_with_fk_constraint_app", "0001_initial"),
+    ]
+
+    operations = [
+        SafeRemoveField(
+            model_name="testtable",
+            name="fk_table",
+            deletion_action=DeletionAction.MOVE_TO_PENDING,
+        ),
+    ]