fix: Callback Error Handling

rigging/chat.py

@@ -1845,13 +1845,12 @@ async def _step(  # noqa: PLR0915, PLR0912
                         *[state.ready_event.wait() for state in states if not state.completed],
                     )
 
-                    # TODO(nick): Are we good to throw exceptions here?
-                    for task in tasks:
+                    for state, task in zip(states, tasks, strict=True):
                         if task.done() and (exception := task.exception()):
-                            raise exception
+                            state.chat.error = exception
+                            state.chat.failed = True
 
-                    for state in states:
-                        if state.ready_event.is_set() and state.step:
+                        elif state.ready_event.is_set() and state.step:
                             step = state.step.with_parent(current_step)
 
                             if step.depth > max_depth:
@@ -1875,10 +1874,12 @@ async def _step(  # noqa: PLR0915, PLR0912
                     for task in tasks:
                         if not task.done():
                             task.cancel()
-                    await asyncio.gather(*tasks)  # TODO(nick): return_exceptions=True ?
+                    await asyncio.gather(*tasks, return_exceptions=True)
 
             chats = ChatList([state.chat for state in states if state.chat])
 
+            self._raise_if_failed(chats, on_failed)
+
             current_step = PipelineStep(
                 state="callback",
                 chats=chats,
@@ -1917,9 +1918,18 @@ async def _step(  # noqa: PLR0915, PLR0912
             )
 
             async with contextlib.AsyncExitStack() as exit_stack:
-                result = map_task(chats)
-                if inspect.isawaitable(result):
-                    result = await result
+                try:
+                    result = map_task(chats)
+                    if inspect.isawaitable(result):
+                        result = await result
+                except Exception as e:  # noqa: BLE001
+                    # If the map raised an exception, assign it to all the chats
+                    for chat in chats:
+                        chat.error = e
+                        chat.failed = True
+
+                    self._raise_if_failed(chats, on_failed)
+                    continue
 
                 if isinstance(result, contextlib.AbstractAsyncContextManager):
                     result = await exit_stack.enter_async_context(result)

tests/test_chat_pipeline.py

@@ -233,3 +233,59 @@ async def watch_function(chats: list[Chat]) -> None:
     # Watch should be called at least once
     assert len(watch_calls) >= 1
     assert all(calls >= 1 for calls in watch_calls)
+
+
+@pytest.mark.asyncio
+async def test_map_callback_exception_handling() -> None:
+    """Test that exceptions in map callback functions are properly caught and assigned to chat.error and chat.failed."""
+
+    generator = FixedGenerator(model="fixed", text="Response", params=GenerateParams())
+
+    async def failing_map_callback(chats: list[Chat]) -> list[Chat]:
+        # Simulate an exception in the map callback
+        raise RuntimeError("Map callback failure")
+
+    pipeline = generator.chat("test").map(failing_map_callback)
+
+    # Test with default on_failed behavior (should raise)
+    with pytest.raises(RuntimeError):
+        await pipeline.run()
+
+    # Should still raise as RuntimeError is not in the default catch list
+    with pytest.raises(RuntimeError):
+        await pipeline.run(on_failed="include")
+
+    # Should capture now
+    chat = await pipeline.catch(RuntimeError, on_failed="include").run()
+
+    assert chat.failed is True
+    assert isinstance(chat.error, RuntimeError)
+    assert str(chat.error) == "Map callback failure"
+
+
+@pytest.mark.asyncio
+async def test_then_callback_exception_handling() -> None:
+    """Test that exceptions in then callback functions are properly caught and assigned to chat.error and chat.failed."""
+
+    generator = FixedGenerator(model="fixed", text="Response", params=GenerateParams())
+
+    async def failing_then_callback(chat: Chat) -> PipelineStepContextManager:
+        # Simulate an exception in the then callback
+        raise RuntimeError("Then callback failure")
+
+    pipeline = generator.chat("test").then(failing_then_callback)
+
+    # Test with default on_failed behavior (should raise)
+    with pytest.raises(RuntimeError):
+        await pipeline.run()
+
+    # Should still raise as RuntimeError is not in the default catch list
+    with pytest.raises(RuntimeError):
+        await pipeline.run(on_failed="include")
+
+    # Should capture now
+    chat = await pipeline.catch(RuntimeError, on_failed="include").run()
+
+    assert chat.failed is True
+    assert isinstance(chat.error, RuntimeError)
+    assert str(chat.error) == "Then callback failure"