ci: support Python 3.14

[henryiii]

Description

Let's try beta 1!

Suggested changelog entry:

* Support Python 3.14 (beta 1)

[henryiii]

FAILED test_methods_and_attributes.py::test_dynamic_attributes - AssertionError: assert not True
 +  where True = hasattr(<pybind11_tests.methods_and_attributes.DynamicClass object at 0x7f3c250dd750>, 'foo')
FAILED test_operator_overloading.py::test_return_set_of_unhashable - assert False
 +  where False = <built-in method startswith of str object at 0x7f3c252b3030>('unhashable type:')
 +    where <built-in method startswith of str object at 0x7f3c252b3030> = "cannot use 'pybind11_tests.operators.HashMe' as a set element (unhashable type: 'pybind11_tests.operators.HashMe')".startswith
 +      where "cannot use 'pybind11_tests.operators.HashMe' as a set element (unhashable type: 'pybind11_tests.operators.HashMe')" = str(TypeError("cannot use 'pybind11_tests.operators.HashMe' as a set element (unhashable type: 'pybind11_tests.operators.HashMe')"))
 +        where TypeError("cannot use 'pybind11_tests.operators.HashMe' as a set element (unhashable type: 'pybind11_tests.operators.HashMe')") = TypeError('Unable to convert function return value to a Python type! The signature was\n\t() -> set[pybind11_tests.operators.HashMe]').__cause__
 +          where TypeError('Unable to convert function return value to a Python type! The signature was\n\t() -> set[pybind11_tests.operators.HashMe]') = <ExceptionInfo TypeError('Unable to convert function return value to a Python type! The signature was\n\t() -> set[pybind11_tests.operators.HashMe]') tblen=1>.value
FAILED test_pickling.py::test_roundtrip_with_dict[PickleableWithDict] - AttributeError: 'pybind11_tests.pickling.PickleableWithDict' object has no attribute 'dynamic'
FAILED test_pickling.py::test_roundtrip_with_dict[PickleableWithDictNew] - AttributeError: 'pybind11_tests.pickling.PickleableWithDictNew' object has no attribute 'dynamic'

[rwgk]

The tests/test_operator_overloading.py failure is a trivial fix, but I'm not sure about the other two. They could easily steal a couple hours each to take care of...

[henryiii]

Looks like two errors: py::hash isn’t working, and dynamic attributes are broken. @vstinner I don’t see anything in https://docs.python.org/3.14/whatsnew/3.14.html#id11 that would seem to indicate changes here.

I can try bisecting later.

[vstinner]

• where <built-in method startswith of str object at 0x7f3c252b3030> = "cannot use 'pybind11_tests.operators.HashMe' as a set element (unhashable type: 'pybind11_tests.operators.HashMe')".startswith

Yeah, I changed the error message in: python/cpython#132825

You may be able to fix your test by replacing "startswith" with "contains" ("in").

[henryiii]

Wow, that's a huge improvement:

Love the syntax highlighting in the REPL now, too. :)

I thought there was another issue with py::hash, but I see it's just that, so it's only the dynamic change now. I still don't see anything in the upgrade guide. But one issue should be easy to bisect.

[vstinner]

I still don't see anything in the upgrade guide

The change was documented 1h ago: python/cpython@de28651.

[henryiii]

BTW, we are also running into https://gitlab.kitware.com/cmake/cmake/-/issues/26926 on Windows, CMake is confused and trying to use a free-threaded lib. I've seen that with scikit-build-core, too, in scikit-build/scikit-build-core#1074.

[henryiii]

Bisecting this shows it was broken by python/cpython#123192. I've commented on python/cpython#115776.