_PyEval_SetAsyncGenFinalizer() and _PyEval_SetAsyncGenFirstiter() don't include proper error handling for their PySys_Audit() calls. This could lead to leaked exceptions and fatal errors.

You're right, they need either your patch or PyErr_WriteUnraisable(NULL) before returning.

Łukasz - this needs a fix in 3.8, but we don't have to necessarily change the (internal, but exposed) ABI. For 3.9, we'll fix it properly, but for 3.8 I'll let you make the call whether we can also add a return value to these functions.

-PyAPI_FUNC(void) _PyEval_SetAsyncGenFirstiter(PyObject *);
+PyAPI_FUNC(int) _PyEval_SetAsyncGenFirstiter(PyObject *);
 PyAPI_FUNC(PyObject *) _PyEval_GetAsyncGenFirstiter(void);
-PyAPI_FUNC(void) _PyEval_SetAsyncGenFinalizer(PyObject *);
+PyAPI_FUNC(int) _PyEval_SetAsyncGenFinalizer(PyObject *);

Unfortunately at this point we will have to leave the ABI as is. We are in fact promising to lock it by Beta 3 so quite a long time ago.

In that case, the fix for 3.8 should be to call PyErr_WriteUnraisable(NULL) when an error occurs. This will report it through the new unraisable hook, and also prevent a fatal error if the exception escapes.

But I'm okay to defer it - this is still going to be obscure functionality for the time being, and it's possible to avoid the issue.

Why this ABI is exported at all? These functions are only used in the sys module, why they are defined in ceval.c instead of be static functions in sysmodule.c?

> Why this ABI is exported at all?

Great question for (probably) Yury, but it is exported and so we're stuck with it for 3.8 at least :(