Only allow tasks in a final state to have a finished date

Closes #1884 (closed)

arkindex/ponos/migrations/0014_task_task_finished_requires_final_state.py

+# Generated by Django 5.0.8 on 2025-01-07 10:11
+
+from django.db import migrations, models
+
+from arkindex.ponos.models import State
+
+# Copy the FINAL_STATES here so that if we ever change them,
+# Django will detect it and require a new migration
+FINAL_STATES = (
+    State.Completed,
+    State.Failed,
+    State.Error,
+    State.Stopped,
+    State.Cancelled,
+)
+
+def clear_unexpected_finish_dates(apps, schema_editor):
+    Task = apps.get_model("ponos", "Task")
+    Task.objects.exclude(state__in=FINAL_STATES).exclude(finished=None).update(finished=None)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("ponos", "0013_task_ttl"),
+        ("process", "0046_workerrun_ttl"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            clear_unexpected_finish_dates,
+            reverse_code=migrations.RunPython.noop,
+            elidable=True,
+        ),
+        migrations.AddConstraint(
+            model_name="task",
+            constraint=models.CheckConstraint(
+                check=models.Q(finished=None) | models.Q(state__in=FINAL_STATES),
+                name="task_finished_requires_final_state",
+                violation_error_message="Only tasks in a final state can have a finish date set.",
+            ),
+        ),
+    ]