fix: keep the original error when a curator run fails inside a running event loop

src/bespokelabs/curator/request_processor/event_loop.py

@@ -27,18 +27,17 @@ def run_in_event_loop(coroutine):
     try:
         # This call will raise an RuntimError if there is no event loop running.
         asyncio.get_running_loop()
-
+    except RuntimeError:
+        # If no event loop is running, asyncio will
+        # return a RuntimeError (https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.get_running_loop).
+        # In that case, we can just use asyncio.run.
+        pass
+    else:
         # If there is an event loop running (the call
         # above doesn't raise an exception), we can
         # use nest_asyncio to patch the event loop.
         nest_asyncio.apply()
 
-        return asyncio.run(coroutine)
-    except RuntimeError:
-        # Explicitly pass, since we want to fallback to asyncio.run
-        pass
-
-    # If no event loop is running, asyncio will
-    # return a RuntimeError (https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.get_running_loop).
-    # In that case, we can just use asyncio.run.
+    # Run the coroutine once, outside the except block, so its own errors (including
+    # RuntimeErrors) propagate unchanged and aren't chained to the error above.
     return asyncio.run(coroutine)

tests/unittests/test_event_loop.py

@@ -0,0 +1,45 @@
+import asyncio
+
+import pytest
+
+from bespokelabs.curator.request_processor.event_loop import run_in_event_loop
+
+
+async def _fail(calls):
+    calls.append(1)
+    raise RuntimeError("original error")
+
+
+async def _answer():
+    return 42
+
+
+def test_coroutine_error_is_raised_without_a_running_loop():
+    calls = []
+
+    with pytest.raises(RuntimeError, match="original error") as exc_info:
+        run_in_event_loop(_fail(calls))
+
+    assert calls == [1]
+    # Not chained to the "no running event loop" RuntimeError used to detect the loop.
+    assert exc_info.value.__context__ is None
+
+
+def test_coroutine_error_is_raised_inside_a_running_loop():
+    """In Jupyter or Colab an event loop is already running when curator is called."""
+    calls = []
+
+    async def notebook_cell():
+        with pytest.raises(RuntimeError, match="original error"):
+            run_in_event_loop(_fail(calls))
+
+    asyncio.run(notebook_cell())
+
+    assert calls == [1]
+
+
+def test_result_is_returned_inside_a_running_loop():
+    async def notebook_cell():
+        return run_in_event_loop(_answer())
+
+    assert asyncio.run(notebook_cell()) == 42