gh-117852: eagerly check arguments to asyncgen.athrow()

At present the arguments to asyncgen.athrow() are not checked until the
coroutine is awaited. Unpack them on coroutine creation instead, so they are
checked immediately.

Author: duaneg

Lib/test/test_asyncgen.py

@@ -2021,6 +2021,15 @@ async def gen():
             g.athrow(RuntimeError)
             gc_collect()
 
+    def test_athrow_throws_immediately(self):
+        async def gen():
+            yield 1
+
+        g = gen()
+        msg = "athrow expected at least 1 argument, got 0"
+        with self.assertRaisesRegex(TypeError, msg):
+            g.athrow()
+
     def test_aclose(self):
         async def gen():
             yield 1

Misc/NEWS.d/next/Core_and_Builtins/2025-05-28-23-58-50.gh-issue-117852.BO9g7z.rst

@@ -0,0 +1 @@
+Check :meth:`asyncgen.athrow` arguments immediately on instantiation.

Objects/genobject.c

@@ -1451,7 +1451,9 @@ typedef struct PyAsyncGenAThrow {
 
     /* Can be NULL, when in the "aclose()" mode
        (equivalent of "athrow(GeneratorExit)") */
-    PyObject *agt_args;
+    PyObject *agt_typ;
+    PyObject *agt_tb;
+    PyObject *agt_val;
 
     AwaitableState agt_state;
 } PyAsyncGenAThrow;
@@ -2078,7 +2080,9 @@ async_gen_athrow_dealloc(PyObject *self)
 
     _PyObject_GC_UNTRACK(self);
     Py_CLEAR(agt->agt_gen);
-    Py_CLEAR(agt->agt_args);
+    Py_XDECREF(agt->agt_typ);
+    Py_XDECREF(agt->agt_tb);
+    Py_XDECREF(agt->agt_val);
     PyObject_GC_Del(self);
 }
 
@@ -2088,7 +2092,9 @@ async_gen_athrow_traverse(PyObject *self, visitproc visit, void *arg)
 {
     PyAsyncGenAThrow *agt = _PyAsyncGenAThrow_CAST(self);
     Py_VISIT(agt->agt_gen);
-    Py_VISIT(agt->agt_args);
+    Py_VISIT(agt->agt_typ);
+    Py_VISIT(agt->agt_tb);
+    Py_VISIT(agt->agt_val);
     return 0;
 }
 
@@ -2116,7 +2122,7 @@ async_gen_athrow_send(PyObject *self, PyObject *arg)
     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) {
+            if (o->agt_typ == NULL) {
                 PyErr_SetString(
                     PyExc_RuntimeError,
                     "aclose(): asynchronous generator is already running");
@@ -2143,7 +2149,7 @@ async_gen_athrow_send(PyObject *self, PyObject *arg)
         o->agt_state = AWAITABLE_STATE_ITER;
         o->agt_gen->ag_running_async = 1;
 
-        if (o->agt_args == NULL) {
+        if (o->agt_typ == NULL) {
             /* aclose() mode */
             o->agt_gen->ag_closed = 1;
 
@@ -2157,19 +2163,10 @@ async_gen_athrow_send(PyObject *self, PyObject *arg)
                 goto yield_close;
             }
         } else {
-            PyObject *typ;
-            PyObject *tb = NULL;
-            PyObject *val = NULL;
-
-            if (!PyArg_UnpackTuple(o->agt_args, "athrow", 1, 3,
-                                   &typ, &val, &tb)) {
-                return NULL;
-            }
-
             retval = _gen_throw((PyGenObject *)gen,
                                 0,  /* Do not close generator when
                                        PyExc_GeneratorExit is passed */
-                                typ, val, tb);
+                                o->agt_typ, o->agt_val, o->agt_tb);
             retval = async_gen_unwrap_value(o->agt_gen, retval);
         }
         if (retval == NULL) {
@@ -2181,7 +2178,7 @@ async_gen_athrow_send(PyObject *self, PyObject *arg)
     assert(o->agt_state == AWAITABLE_STATE_ITER);
 
     retval = gen_send((PyObject *)gen, arg);
-    if (o->agt_args) {
+    if (o->agt_typ) {
         return async_gen_unwrap_value(o->agt_gen, retval);
     } else {
         /* aclose() mode */
@@ -2212,7 +2209,7 @@ async_gen_athrow_send(PyObject *self, PyObject *arg)
     if (PyErr_ExceptionMatches(PyExc_StopAsyncIteration) ||
             PyErr_ExceptionMatches(PyExc_GeneratorExit))
     {
-        if (o->agt_args == NULL) {
+        if (o->agt_typ == NULL) {
             /* when aclose() is called we don't want to propagate
                StopAsyncIteration or GeneratorExit; just raise
                StopIteration, signalling that this 'aclose()' await
@@ -2241,7 +2238,7 @@ async_gen_athrow_throw(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
     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) {
+            if (o->agt_typ == NULL) {
                 PyErr_SetString(
                     PyExc_RuntimeError,
                     "aclose(): asynchronous generator is already running");
@@ -2259,7 +2256,7 @@ async_gen_athrow_throw(PyObject *self, PyObject *const *args, Py_ssize_t nargs)
     }
 
     PyObject *retval = gen_throw((PyObject*)o->agt_gen, args, nargs);
-    if (o->agt_args) {
+    if (o->agt_typ) {
         retval = async_gen_unwrap_value(o->agt_gen, retval);
         if (retval == NULL) {
             o->agt_gen->ag_running_async = 0;
@@ -2334,7 +2331,7 @@ async_gen_athrow_finalize(PyObject *op)
 {
     PyAsyncGenAThrow *o = (PyAsyncGenAThrow*)op;
     if (o->agt_state == AWAITABLE_STATE_INIT) {
-        PyObject *method = o->agt_args ? &_Py_ID(athrow) : &_Py_ID(aclose);
+        PyObject *method = o->agt_typ ? &_Py_ID(athrow) : &_Py_ID(aclose);
         _PyErr_WarnUnawaitedAgenMethod(o->agt_gen, method);
     }
 }
@@ -2403,13 +2400,23 @@ PyTypeObject _PyAsyncGenAThrow_Type = {
 static PyObject *
 async_gen_athrow_new(PyAsyncGenObject *gen, PyObject *args)
 {
+    PyObject *typ = NULL;
+    PyObject *tb = NULL;
+    PyObject *val = NULL;
+    if (args && !PyArg_UnpackTuple(args, "athrow", 1, 3, &typ, &val, &tb)) {
+        return NULL;
+    }
+
     PyAsyncGenAThrow *o;
     o = PyObject_GC_New(PyAsyncGenAThrow, &_PyAsyncGenAThrow_Type);
     if (o == NULL) {
         return NULL;
     }
     o->agt_gen = (PyAsyncGenObject*)Py_NewRef(gen);
-    o->agt_args = Py_XNewRef(args);
+    o->agt_typ = Py_XNewRef(typ);
+    o->agt_tb = Py_XNewRef(tb);
+    o->agt_val = Py_XNewRef(val);
+
     o->agt_state = AWAITABLE_STATE_INIT;
     _PyObject_GC_TRACK((PyObject*)o);
     return (PyObject*)o;