Expose Py_tp_vectorcall in the limited API

[encukou]

tp_vectorcall is somewhat tricky to understand, but can bring significant speedups to wrapper code.

In python/cpython#100554, pybind11 and PyO3 maintainers ask to expose it for use with PyType_FromSpec/PyType_GetSlot and in limited API, and Wenzel sent a PR recently.

tp_vectorcall needs to match the behavior of a metaclass call, so exposing tp_vectorcall limits future changes to PyType_Type->tp_call. But, I think that's already something we can't really change.

Does a Py_tp_vectorcall slot sound reasonable?

• @encukou
• @erlend-aasland
• @mdboom
• @serhiy-storchaka
• @vstinner
• @zooba

[vstinner]

Does a Py_tp_vectorcall slot sound reasonable?

We added vectorcall to multiple types successfully, it made creation of objects faster. So yes, it makes sense.

[zooba]

I disagree with vector call being part of the stable ABI at all, but since that's apparently already been done, then I see no reason to oppose adding a constant that should've been there from the start.

[encukou]

@erlend-aasland @mdboom @serhiy-storchaka, what's your opinion?

[encukou]

@serhiy-storchaka, do you have any reservations?

[serhiy-storchaka]

The vectorcall protocol was added to the Limited API in 3.12. It is too late to change anything here. Not exposing Py_tp_vectorcall looks like omission.

[encukou]

Thanks for the votes!