[3.10] bpo-44490: Partially backport GH-26980's refactoring for easier bugfix backports

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(cherry picked from c45fa1a)

https://bugs.python.org/issue44490

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This is mainly for Serhiy's planned refactoring (see GH-27196). I did not backport any of the new features, only the code refactoring.

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Hmm I don't understand the failure in Tests / Check if the ABI has changed (pull_request):

2 Removed functions:
'function PyObject* _Py_make_parameters(PyObject*)' {_Py_make_parameters}
'function PyObject* _Py_subs_parameters(PyObject*, PyObject*, PyObject*, PyObject*)' {_Py_subs_parameters}

These functions are newly added, how can they be removed?

[serhiy-storchaka]

I do not think it is needed for backporting of GH-27196. GH-27196 almost do not touch genericaliasobject.c, so conflicts are minimal.

It would nice to backport indexing.

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I do not think it is needed for backporting of GH-27196. GH-27196 almost do not touch genericaliasobject.c, so conflicts are minimal.

You're right that most things should backport cleanly. It's only required if you want to backport shifting or using _Py_subs_parameters and _Py_make_parameters. Those don't exist in 3.10 currently.

It would nice to backport indexing.

Yup. Maybe if you review and approve GH-26980, Pablo will allow us to backport it to 3.10.

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Closing this since GH-27207 has been approved.