bpo-39606: allow closing async generators that are already closed (GH-18475)

The fix for [bpo-39386](https://bugs.python.org/issue39386) attempted to make it so you couldn't reuse a
agen.aclose() coroutine object. It accidentally also prevented you
from calling aclose() at all on an async generator that was already
closed or exhausted. This commit fixes it so we're only blocking the
actually illegal cases, while allowing the legal cases.

The new tests failed before this patch. Also confirmed that this fixes
the test failures we were seeing in Trio with Python dev builds:
  https://github.com/python-trio/trio/pull/1396


https://bugs.python.org/issue39606

1 files changed, 11 insertions, 4 deletions

diff --git a/Objects/genobject.c b/Objects/genobject.c
index 576d685..0efd57d 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -1797,16 +1797,22 @@ async_gen_athrow_send(PyAsyncGenAThrow *o, PyObject *arg)
     PyFrameObject *f = gen->gi_frame;
     PyObject *retval;
 
-    if (f == NULL || f->f_stacktop == NULL ||
-            o->agt_state == AWAITABLE_STATE_CLOSED) {
+    if (o->agt_state == AWAITABLE_STATE_CLOSED) {
         PyErr_SetString(
             PyExc_RuntimeError,
             "cannot reuse already awaited aclose()/athrow()");
         return NULL;
     }
 
+    if (f == NULL || f->f_stacktop == NULL) {
+        o->agt_state = AWAITABLE_STATE_CLOSED;
+        PyErr_SetNone(PyExc_StopIteration);
+        return NULL;
+    }
+
     if (o->agt_state == AWAITABLE_STATE_INIT) {
         if (o->agt_gen->ag_running_async) {
+            o->agt_state = AWAITABLE_STATE_CLOSED;
             if (o->agt_args == NULL) {
                 PyErr_SetString(
                     PyExc_RuntimeError,
@@ -1878,7 +1884,6 @@ async_gen_athrow_send(PyAsyncGenAThrow *o, PyObject *arg)
         /* aclose() mode */
         if (retval) {
             if (_PyAsyncGenWrappedValue_CheckExact(retval)) {
-                o->agt_gen->ag_running_async = 0;
                 Py_DECREF(retval);
                 goto yield_close;
             }
@@ -1893,16 +1898,17 @@ async_gen_athrow_send(PyAsyncGenAThrow *o, PyObject *arg)
 
 yield_close:
     o->agt_gen->ag_running_async = 0;
+    o->agt_state = AWAITABLE_STATE_CLOSED;
     PyErr_SetString(
         PyExc_RuntimeError, ASYNC_GEN_IGNORED_EXIT_MSG);
     return NULL;
 
 check_error:
     o->agt_gen->ag_running_async = 0;
+    o->agt_state = AWAITABLE_STATE_CLOSED;
     if (PyErr_ExceptionMatches(PyExc_StopAsyncIteration) ||
             PyErr_ExceptionMatches(PyExc_GeneratorExit))
     {
-        o->agt_state = AWAITABLE_STATE_CLOSED;
         if (o->agt_args == NULL) {
             /* when aclose() is called we don't want to propagate
                StopAsyncIteration or GeneratorExit; just raise
@@ -1936,6 +1942,7 @@ async_gen_athrow_throw(PyAsyncGenAThrow *o, PyObject *args)
         /* aclose() mode */
         if (retval && _PyAsyncGenWrappedValue_CheckExact(retval)) {
             o->agt_gen->ag_running_async = 0;
+            o->agt_state = AWAITABLE_STATE_CLOSED;
             Py_DECREF(retval);
             PyErr_SetString(PyExc_RuntimeError, ASYNC_GEN_IGNORED_EXIT_MSG);
             return NULL;