Fixed exception swallowing in a timed out cancel scope

Fixes #54.

anyio/_backends/asyncio.py

@@ -215,7 +215,8 @@ async def __aexit__(self, exc_type, exc_val, exc_tb):
         self._tasks.remove(host_task)
         _task_states[host_task].cancel_scope = self._parent_scope
 
-        if isinstance(exc_val, (asyncio.CancelledError, CancelledError)):
+        exceptions = exc_val.exceptions if isinstance(exc_val, ExceptionGroup) else [exc_val]
+        if all(isinstance(exc, (asyncio.CancelledError, CancelledError)) for exc in exceptions):
             if self._timeout_expired:
                 return True
             elif self._parent_scope is None or not self._parent_scope.cancel_called:

anyio/_backends/curio.py

@@ -108,7 +108,8 @@ async def __aexit__(self, exc_type, exc_val, exc_tb):
         self._tasks.remove(host_task)
         _task_states[host_task].cancel_scope = self._parent_scope
 
-        if isinstance(exc_val, (curio.TaskCancelled, CancelledError)):
+        exceptions = exc_val.exceptions if isinstance(exc_val, ExceptionGroup) else [exc_val]
+        if all(isinstance(exc, (curio.TaskCancelled, CancelledError)) for exc in exceptions):
             if self._timeout_expired:
                 return True
             elif self._parent_scope is None or not self._parent_scope.cancel_called:

docs/versionhistory.rst

@@ -11,6 +11,8 @@ This library adheres to `Semantic Versioning <http://semver.org/>`_.
   asyncio and curio
 - Fixed task cancellation not happening right away on asyncio and curio when a cancel scope is
   entered when the deadline has already passed
+- Fixed exception group containing only cancellation exceptions not being swallowed by a timed out
+  cancel scope on asyncio and curio
 - Added the ``current_time()`` function
 
 **1.0.0rc1**

tests/test_taskgroups.py

@@ -408,3 +408,12 @@ async def test_deadline_reached_on_start():
     async with move_on_after(0):
         await sleep(0)
         pytest.fail('Execution should not reach this point')
+
+
+@pytest.mark.anyio
+async def test_timeout_error_with_multiple_cancellations():
+    with pytest.raises(TimeoutError):
+        async with fail_after(0.1):
+            async with create_task_group() as tg:
+                await tg.spawn(sleep, 2)
+                await sleep(2)