Add 'self.order_tasks()' before getting 'output_task' (#873)

griptape/structures/workflow.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 import concurrent.futures as futures
 from graphlib import TopologicalSorter
-from typing import Any
+from typing import Any, Optional
 from attrs import define, field, Factory
 from griptape.artifacts import ErrorArtifact
 from griptape.structures import Structure
@@ -13,6 +13,10 @@
 class Workflow(Structure):
     futures_executor: futures.Executor = field(default=Factory(lambda: futures.ThreadPoolExecutor()), kw_only=True)
 
+    @property
+    def output_task(self) -> Optional[BaseTask]:
+        return self.order_tasks()[-1] if self.tasks else None
+
     def add_task(self, task: BaseTask) -> BaseTask:
         task.preprocess(self)
 

tests/unit/structures/test_workflow.py

@@ -637,6 +637,15 @@ def test_output_task(self):
 
         assert task4 == workflow.output_task
 
+        task4.add_parents([task2, task3])
+        task1.add_children([task2, task3])
+
+        # task4 is the final task, but its defined at index 0
+        workflow = Workflow(prompt_driver=MockPromptDriver(), tasks=[task4, task1, task2, task3])
+
+        # ouput_task topologically should be task4
+        assert task4 == workflow.output_task
+
     def test_to_graph(self):
         task1 = PromptTask("prompt1", id="task1")
         task2 = PromptTask("prompt2", id="task2")