workaround for CallSpec2 attributes being frozen

[jammer87]

Fixes #251

In pytest 7, CallSpec2 was refactored and it made attributes read-only causing the issue from #251.

before this change, running pytest on the example from #251:

plugins: cases-3.6.8
collected 0 items / 1 error

=================================================================== ERRORS ===================================================================
__________________________________________________ ERROR collecting tests/issue_221_test.py __________________________________________________
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\pluggy\_hooks.py:265: in __call__
    return self._hookexec(self.name, self.get_hookimpls(), kwargs, firstresult)
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\pluggy\_manager.py:80: in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\_pytest\python.py:257: in pytest_pycollect_makeitem
    res = list(collector._genfunctions(name, obj))
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\_pytest\python.py:487: in _genfunctions
    fixtures.add_funcarg_pseudo_fixture_def(self, metafunc, fm)
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\_pytest\fixtures.py:164: in add_funcarg_pseudo_fixture_def
    if not metafunc._calls[0].funcargs:
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\pytest_cases\plugin.py:931: in __getitem__
    return self.calls_list[item]
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\pytest_cases\plugin.py:942: in calls_list
    self.create_call_list_from_pending_parametrizations()
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\pytest_cases\plugin.py:994: in create_call_list_from_pending_parametrizations
    remove_empty_ids(callspec)
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\pytest_cases\fixture_parametrize_plus.py:560: in remove_empty_ids
    callspec._idlist = [c for c in callspec._idlist if not c.startswith(EMPTY_ID)]
..\.virtualenvs\pytest-cases-test-aSbyvtak\lib\site-packages\attr\_make.py:642: in _frozen_setattrs
    raise FrozenInstanceError()
E   attr.exceptions.FrozenInstanceError
========================================================== short test summary info ===========================================================
ERROR tests/issue_221_test.py - attr.exceptions.FrozenInstanceError
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
============================================================== 1 error in 0.52s ==============================================================

With this change:

plugins: cases-3.6.8
collected 2 items

tests\issue_221_test.py ..                                                                                                              [100%]

============================================================= 2 passed in 0.05s ==============================================================

[saroad2]

This is a very needed PR!
One cannot use pytest 7.0 without it.

@smarie , can you publish a new pytest-cases version after merging this PR?

[smarie]

Thanks so much @jammer87 for this ! I'll check that PR builds ok and merge+release asap

[jammer87]

@smarie Besides the 2.7 failures for list not having the clear method, at first glance I'm not sure what's going wrong in the tests. Can you take over from here? You might also want to add pytest 6 checks as well now that the latest is 7.

[smarie]

Yes, I'll take over.

[smarie]

Merged through #255

A huge thanks to you @jammer87 !

[smarie]

Note: I thought that this would be marked as "merged" because I actually merged it in the branch that I used for the other PR #255. Strange that github did not realize it...