Test that TaskStatus.started() does not allow teleporting Cancelled(s) around the tree

Author: gschaffner

src/trio/_core/_tests/test_run.py

@@ -40,6 +40,7 @@
         Callable,
         Generator,
     )
+from exceptiongroup import catch
 
 if sys.version_info < (3, 11):
     from exceptiongroup import BaseExceptionGroup, ExceptionGroup
@@ -1845,7 +1846,59 @@ async def no_checkpoint_before_started(
                     raise AssertionError() from exc  # pragma: no cover
             assert not cs.cancelled_caught
 
-    # trying to start in a closed nursery raises an error immediately
+    # calling started() while handling a Cancelled raises an error immediately.
+    async def started_while_handling_cancelled(
+        task_status: _core.TaskStatus[None] = _core.TASK_STATUS_IGNORED,
+    ) -> None:
+        try:
+            await _core.checkpoint()
+        except _core.Cancelled:
+            task_status.started()
+        raise AssertionError()  # pragma: no cover
+
+    async with _core.open_nursery() as nursery:
+        with _core.CancelScope() as cs:
+            cs.cancel()
+            with pytest.raises(RuntimeError):
+                await nursery.start(started_while_handling_cancelled)
+
+    # calling started() while handling multiple Cancelleds raises an error
+    # immediately.
+    async def started_while_handling_multiple_cancelled(
+        task_status: _core.TaskStatus[None] = _core.TASK_STATUS_IGNORED,
+    ) -> None:
+        with catch({_core.Cancelled: lambda _: task_status.started()}):
+            async with _core.open_nursery() as nursery:
+                nursery.start_soon(_core.checkpoint)
+                nursery.start_soon(_core.checkpoint)
+        raise AssertionError()  # pragma: no cover
+
+    async with _core.open_nursery() as nursery:
+        with _core.CancelScope() as cs:
+            cs.cancel()
+            with pytest.raises(RuntimeError):
+                await nursery.start(started_while_handling_multiple_cancelled)
+
+    # calling started() while handling an exception while handling Cancelled(s) raises an error immediately.
+    async def started_while_handling_exc_while_handling_cancelled(
+        task_status: _core.TaskStatus[None] = _core.TASK_STATUS_IGNORED,
+    ) -> None:
+        try:
+            await _core.checkpoint()
+        except _core.Cancelled:
+            try:
+                raise ValueError
+            except ValueError:
+                task_status.started()
+        raise AssertionError()  # pragma: no cover
+
+    async with _core.open_nursery() as nursery:
+        with _core.CancelScope() as cs:
+            cs.cancel()
+            with pytest.raises(RuntimeError):
+                await nursery.start(started_while_handling_exc_while_handling_cancelled)
+
+    # trying to start in a closed nursery raises an error immediately.
     async with _core.open_nursery() as closed_nursery:
         pass
     t0 = _core.current_time()

test-requirements.in

@@ -30,4 +30,4 @@ sortedcontainers
 idna
 outcome
 sniffio
-exceptiongroup >= 1.0.0rc9; python_version < "3.11"
+exceptiongroup >= 1.0.0rc9

test-requirements.txt

@@ -36,7 +36,7 @@ cryptography==41.0.5
     #   types-pyopenssl
 dill==0.3.7
     # via pylint
-exceptiongroup==1.1.3 ; python_version < "3.11"
+exceptiongroup==1.1.3
     # via
     #   -r test-requirements.in
     #   pytest