gh-148736: Use ag_frame when walking async generators in asyncio.graph

_build_graph_for_future appended FrameCallGraphEntry(coro.cr_frame) in
the ag_await branch; async generators expose ag_frame. The line is
unreachable via standard async-for (async_generator_asend has neither
cr_await nor ag_await) but is reachable from duck-typed chains.

Author: rajkripal

Lib/asyncio/graph.py

@@ -62,7 +62,7 @@ def _build_graph_for_future(
             coro = coro.cr_await
         elif hasattr(coro, 'ag_await'):
             # A native async generator or duck-type compatible iterator
-            st.append(FrameCallGraphEntry(coro.cr_frame))
+            st.append(FrameCallGraphEntry(coro.ag_frame))
             coro = coro.ag_await
         else:
             break

Lib/test/test_asyncio/test_graph.py

@@ -1,6 +1,8 @@
 import asyncio
 import io
+import sys
 import unittest
+import unittest.mock
 
 
 # To prevent a warning "test altered the execution environment"
@@ -146,6 +148,28 @@ async def main():
             'async generator CallStackTestBase.test_stack_async_gen.<locals>.gen()',
             stack_for_gen_nested_call[1])
 
+    def test_ag_frame_used_for_async_generator(self):
+        # Regression test for gh-148736: the ag_await branch of
+        # _build_graph_for_future must read ag_frame, not cr_frame.
+        from asyncio.graph import _build_graph_for_future
+
+        sentinel_frame = sys._getframe()
+
+        class FakeAsyncGen:
+            ag_await = None
+            ag_frame = sentinel_frame
+
+        class FakeCoro:
+            cr_frame = sentinel_frame
+            cr_await = FakeAsyncGen()
+
+        fut = unittest.mock.Mock()
+        fut.get_coro = lambda: FakeCoro()
+        fut._asyncio_awaited_by = None
+
+        result = _build_graph_for_future(fut)
+        self.assertEqual(len(result.call_stack), 2)
+
     async def test_stack_gather(self):
 
         stack_for_deep = None

Misc/NEWS.d/next/Library/2026-04-18-12-00-00.gh-issue-148736.ag-frame.rst

@@ -0,0 +1,3 @@
+Fix a latent :exc:`AttributeError` in :mod:`asyncio` call-graph capture when
+walking an async generator's ``ag_await`` chain: the walker referenced
+``cr_frame`` instead of ``ag_frame``.