fix(migrations): Fail migrations that delete models if no historical_silo_assignment is found (#103702)

We have been silently failing the final deletion of tables for a while,
because we need to add them to `historical_silo_assignments` for it to
work correctly. This pr makes sure that we fail in CI if we aren't able
to find an entry there.

Author: wedamija

src/sentry/db/router.py

@@ -68,8 +68,13 @@ class SiloRouter:
     historical_silo_assignments = {
         "authidentity_duplicate": SiloMode.CONTROL,
         "authprovider_duplicate": SiloMode.CONTROL,
+        "feedback_feedback": SiloMode.REGION,
+        "releases_commit": SiloMode.REGION,
+        "releases_commitfilechange": SiloMode.REGION,
         "sentry_actor": SiloMode.REGION,
         "sentry_alertruleactivations": SiloMode.REGION,
+        "sentry_dashboardwidgetsnapshot": SiloMode.REGION,
+        "sentry_datasecrecywaiver": SiloMode.REGION,
         "sentry_incidentseen": SiloMode.REGION,
         "sentry_incidentsubscription": SiloMode.REGION,
         "sentry_monitorlocation": SiloMode.REGION,
@@ -78,6 +83,8 @@ class SiloRouter:
         "sentry_projectavatar": SiloMode.REGION,
         "sentry_scheduledjob": SiloMode.CONTROL,
         "sentry_teamavatar": SiloMode.REGION,
+        "uptime_projectuptimesubscription": SiloMode.REGION,
+        "workflow_engine_actiongroupstatus": SiloMode.REGION,
         "workflow_engine_workflowaction": SiloMode.REGION,
     }
     """

src/sentry/new_migrations/monkey/models.py

@@ -1,8 +1,10 @@
+from django.db import router
 from django.db.migrations import DeleteModel
 from django_zero_downtime_migrations.backends.postgres.schema import UnsafeOperationException
 
 from sentry.db.postgres.schema import SafePostgresDatabaseSchemaEditor
 from sentry.new_migrations.monkey.state import DeletionAction, SentryProjectState
+from sentry.utils.env import in_test_environment
 
 
 class SafeDeleteModel(DeleteModel):
@@ -35,6 +37,27 @@ def database_forwards(
             return
 
         model = from_state.get_pending_deletion_model(app_label, self.name)
+        table = model._meta.db_table
+
+        # Check if we can determine the model's database to detect missing
+        # historical_silo_assignments entries
+        resolved_db = None
+        for db_router in router.routers:
+            if hasattr(db_router, "_db_for_table"):
+                resolved_db = db_router._db_for_table(table, app_label)
+                if resolved_db is not None:
+                    break
+
+        # If we can't determine the database and we're in CI/tests, fail loudly
+        # This indicates the table is missing from historical_silo_assignments
+        if resolved_db is None and in_test_environment():
+            raise ValueError(
+                f"Cannot determine database for deleted model {app_label}.{self.name} "
+                f"(table: {table}). This table must be added to historical_silo_assignments "
+                f"in src/sentry/db/router.py (or getsentry/db/router.py for getsentry models) "
+                f"with the appropriate SiloMode before the deletion migration can run. "
+            )
+
         if self.allow_migrate_model(schema_editor.connection.alias, model):
             schema_editor.delete_model(model, is_safe=True)
 

tests/sentry/new_migrations/monkey/test_models.py

@@ -0,0 +1,59 @@
+"""
+Tests for SafeDeleteModel validation that ensures deleted models are added to
+historical_silo_assignments.
+"""
+
+from typing import cast
+from unittest.mock import Mock
+
+import pytest
+from django.db import connection
+
+from sentry.db.postgres.schema import SafePostgresDatabaseSchemaEditor
+from sentry.new_migrations.monkey.models import SafeDeleteModel
+from sentry.new_migrations.monkey.state import DeletionAction, SentryProjectState
+from sentry.testutils.cases import TestCase
+
+
+class SafeDeleteModelTest(TestCase):
+    """
+    Tests that SafeDeleteModel fails loudly when a deleted model is not in
+    historical_silo_assignments.
+    """
+
+    def test_delete_model_without_historical_assignment_fails(self) -> None:
+        """
+        When deleting a model that is not in historical_silo_assignments and
+        cannot be found, SafeDeleteModel should raise a ValueError in test
+        environments.
+        """
+        fake_meta = Mock()
+        fake_meta.db_table = "sentry_fake_deleted_table_not_in_router"
+        fake_meta.app_label = "sentry"
+        fake_meta.model_name = "fakedeletedmodel"
+
+        FakeDeletedModel = Mock()
+        FakeDeletedModel._meta = fake_meta
+
+        from_state = SentryProjectState()
+        to_state = SentryProjectState()
+
+        # Manually add the model to pending deletion in the from_state
+        # This simulates what happens when a model was marked for pending deletion
+        # and is now being deleted
+        from_state.pending_deletion_models[("sentry", "fakedeletedmodel")] = FakeDeletedModel
+
+        operation = SafeDeleteModel(name="FakeDeletedModel", deletion_action=DeletionAction.DELETE)
+
+        with connection.schema_editor() as schema_editor:
+            with pytest.raises(ValueError) as exc_info:
+                operation.database_forwards(
+                    "sentry",
+                    cast(SafePostgresDatabaseSchemaEditor, schema_editor),
+                    from_state,
+                    to_state,
+                )
+
+            assert "Cannot determine database for deleted model" in str(exc_info.value)
+            assert "sentry_fake_deleted_table_not_in_router" in str(exc_info.value)
+            assert "historical_silo_assignments" in str(exc_info.value)