Migrate CoreDeveloper to StaffAreaAdministrator

Coupling of migrations to role classes (be the historic or current)
causes difficulties for future changes to role classes.

This migration therefore uses local classes which will match database
values created from the real role classes, and whose own corresponding
database values will parse to real role classes (if existing).

jobserver/migrations/0008_coredeveloper_to_staffareaadministrator.py

@@ -0,0 +1,50 @@
+# Generated by Django 5.1.1 on 2024-10-02 11:00
+
+from django.db import migrations
+
+
+# We have removed the "real" CoreDeveloper role so make a fake one here
+class CoreDeveloper:
+    __module__ = "jobserver.authorization.roles"
+
+
+# If we ever want to change StaffAreaAdministrator in future, coupling this migration
+# to that class would cause us problems, so use a local fake for this one as well
+class StaffAreaAdministrator:
+    __module__ = "jobserver.authorization.roles"
+
+
+def change_user_role(apps, from_role, to_role):
+    User = apps.get_model("jobserver", "User")
+    users = User.objects.filter(roles__contains=from_role)
+    for user in users:
+        for role in user.roles:
+            # we can't rely on vanilla python comparison of our fakes,
+            # so use RoleField.get_prep_value() for consistency with Django QuerySet
+            get_prep_value = User.roles.field.base_field.get_prep_value
+            from_path = get_prep_value(from_role)
+            if get_prep_value(role) == from_path:
+                user.roles.remove(role)
+        user.roles.append(to_role)
+    User.objects.bulk_update(users, ["roles"])
+
+
+def coredeveloper_to_staffadministrator(apps, schema_editor):
+    change_user_role(apps, CoreDeveloper, StaffAreaAdministrator)
+
+
+def staffadministrator_to_coredeveloper(apps, schema_editor):
+    change_user_role(apps, StaffAreaAdministrator, CoreDeveloper)
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("jobserver", "0007_remove_user_is_staff_remove_user_is_superuser"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            coredeveloper_to_staffadministrator,
+            reverse_code=staffadministrator_to_coredeveloper,
+        )
+    ]