Don't clobber foreign exceptions even if timeout is expiring

(Includes test.)
python · gvanrossum · Mar 10, 2022 · Mar 2, 2022 · Mar 2, 2022 · Mar 2, 2022
commit fd2688da3c7817659b76bb7c1c0fa44ee99ef973
@@ -4,6 +4,7 @@
 from typing import final, Optional, Type
 
 from . import events
+from . import exceptions
 from . import tasks
 
 
@@ -91,7 +92,7 @@ async def __aexit__(
         if self._state is _State.EXPIRING:
             self._state = _State.EXPIRED
 
-            if self._task.uncancel() == 0:
+            if self._task.uncancel() == 0 and exc_type in (None, exceptions.CancelledError):
                 # Since there are no outstanding cancel requests, we're
                 # handling this.
                 raise TimeoutError

@@ -115,6 +115,15 @@ async def test_foreign_exception_passed(self):
                 raise KeyError
         self.assertFalse(cm.expired())
 
+        async def test_foreign_exception_on_timeout(self):
+        async def crash():
+            try:
+                await asyncio.sleep(1)
+            finally:
+                1/0
+        with self.assertRaises(ZeroDivisionError):
+            async with asyncio.timeout(0.01):
+                await crash()
     async def test_foreign_cancel_doesnt_timeout_if_not_expired(self):
         with self.assertRaises(asyncio.CancelledError):
             async with asyncio.timeout(10) as cm: