gh-96037: Always insert TimeoutError when exit an expired asyncio.timeout() block (GH-113819)

If other exception was raised during exiting an expired
asyncio.timeout() block, insert TimeoutError in the exception context
just above the CancelledError.

1 files changed, 17 insertions, 2 deletions

diff --git a/Lib/asyncio/timeouts.py b/Lib/asyncio/timeouts.py
index 2c5dd29..e6f5100 100644
--- a/Lib/asyncio/timeouts.py
+++ b/Lib/asyncio/timeouts.py
@@ -110,10 +110,15 @@ class Timeout:
             self._state = _State.EXPIRED
 
             if self._task.uncancel() <= self._cancelling and exc_type is not None:
+                # Since there are no new cancel requests, we're
+                # handling this.
                 if issubclass(exc_type, exceptions.CancelledError):
-                    # Since there are no new cancel requests, we're
-                    # handling this.
                     raise TimeoutError from exc_val
+                elif exc_val is not None:
+                    self._insert_timeout_error(exc_val)
+                    if isinstance(exc_val, ExceptionGroup):
+                        for exc in exc_val.exceptions:
+                            self._insert_timeout_error(exc)
         elif self._state is _State.ENTERED:
             self._state = _State.EXITED
 
@@ -126,6 +131,16 @@ class Timeout:
         # drop the reference early
         self._timeout_handler = None
 
+    @staticmethod
+    def _insert_timeout_error(exc_val: BaseException) -> None:
+        while exc_val.__context__ is not None:
+            if isinstance(exc_val.__context__, exceptions.CancelledError):
+                te = TimeoutError()
+                te.__context__ = te.__cause__ = exc_val.__context__
+                exc_val.__context__ = te
+                break
+            exc_val = exc_val.__context__
+
 
 def timeout(delay: Optional[float]) -> Timeout:
     """Timeout async context manager.