fix: do not parse return value of errored tasks

When a task fails, the receiver stores a result with `is_err=True` and
`return_value=None`. `AsyncTaskiqTask.get_result` still tried to validate
that `None` against the task's return annotation, so every failed task
with a non-optional return type logged a misleading
"Cannot parse return type into ..." warning on the client side.

Skip the validation when the result is an error: there is no return value
to parse, and the actual failure is already available in `result.error`.

Closes: #479

Author: sinnercode228

taskiq/task.py

@@ -61,7 +61,9 @@ async def get_result(self, with_logs: bool = False) -> "TaskiqResult[_ReturnType
                 self.task_id,
                 with_logs=with_logs,
             )
-            if self.return_type is not None:
+            # Errored tasks have no return value to validate,
+            # so parsing would only produce a misleading warning.
+            if self.return_type is not None and not res.is_err:
                 try:
                     res.return_value = parse_obj_as(
                         self.return_type,

tests/test_task.py

@@ -1,5 +1,6 @@
+import logging
 import uuid
-from typing import TypeVar
+from typing import Any, TypeVar
 
 import pytest
 from pydantic import BaseModel
@@ -68,3 +69,41 @@ class MyResult(BaseModel):
     sent_task = AsyncTaskiqTask(test_id, res_back, MyResult)
     parsed = await sent_task.wait_result()
     assert isinstance(parsed.return_value, MyResult)
+
+
+async def test_res_parsing_skipped_on_error(caplog: pytest.LogCaptureFixture) -> None:
+    res_back: AsyncResultBackend[Any] = SerializingBackend(serializers.JSONSerializer())
+    test_id = str(uuid.uuid4())
+    await res_back.set_result(
+        test_id,
+        TaskiqResult(
+            is_err=True,
+            return_value=None,
+            execution_time=0.0,
+        ),
+    )
+    sent_task: AsyncTaskiqTask[Any] = AsyncTaskiqTask(test_id, res_back, int)
+    with caplog.at_level(logging.WARNING, logger="taskiq.task"):
+        parsed = await sent_task.wait_result()
+    assert parsed.is_err
+    assert parsed.return_value is None
+    assert "Cannot parse return type" not in caplog.text
+
+
+async def test_res_parsing_failure(caplog: pytest.LogCaptureFixture) -> None:
+    res_back: AsyncResultBackend[Any] = SerializingBackend(serializers.JSONSerializer())
+    test_id = str(uuid.uuid4())
+    await res_back.set_result(
+        test_id,
+        TaskiqResult(
+            is_err=False,
+            return_value="not-an-int",
+            execution_time=0.0,
+        ),
+    )
+    sent_task: AsyncTaskiqTask[Any] = AsyncTaskiqTask(test_id, res_back, int)
+    with caplog.at_level(logging.WARNING, logger="taskiq.task"):
+        parsed = await sent_task.wait_result()
+    assert not parsed.is_err
+    assert parsed.return_value == "not-an-int"
+    assert "Cannot parse return type" in caplog.text