bpo-38248: Fix inconsistent immediate asyncio.Task cancellation (GH-16330) (GH-16383)

(cherry picked from commit edad4d89e357c92f70c0324b937845d652b20afd)

Co-authored-by: Yury Selivanov <yury@edgedb.com>

1 files changed, 8 insertions, 7 deletions

diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index 281161b..cea3aff 100644
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -2635,18 +2635,19 @@ task_step_impl(TaskObj *task, PyObject *exc)
         if (_PyGen_FetchStopIterationValue(&o) == 0) {
             /* The error is StopIteration and that means that
                the underlying coroutine has resolved */
+
+            PyObject *res;
             if (task->task_must_cancel) {
                 // Task is cancelled right before coro stops.
-                Py_DECREF(o);
                 task->task_must_cancel = 0;
-                et = asyncio_CancelledError;
-                Py_INCREF(et);
-                ev = NULL;
-                tb = NULL;
-                goto set_exception;
+                res = future_cancel((FutureObj*)task);
+            }
+            else {
+                res = future_set_result((FutureObj*)task, o);
             }
-            PyObject *res = future_set_result((FutureObj*)task, o);
+
             Py_DECREF(o);
+
             if (res == NULL) {
                 return NULL;
             }