⚠️ CI failed on Wheel builder (last failure: Apr 28, 2025) ⚠️

[scikit-learn-bot]

CI is still failing on Wheel builder (Apr 28, 2025)

[ogrisel]

The nightly CI has discovered a Cython-related problem on all the free-threading builds:

   _______________ ERROR collecting utils/tests/test_cython_blas.py _______________
  ImportError while importing test module '/tmp/tmp.O8xqw5JN27/venv/lib/python3.13t/site-packages/sklearn/utils/tests/test_cython_blas.py'.
  Hint: make sure your test modules/packages have valid Python names.
  Traceback:
  /opt/_internal/cpython-3.13.3-nogil/lib/python3.13t/importlib/__init__.py:88: in import_module
      return _bootstrap._gcd_import(name[level:], package, level)
  ../venv/lib/python3.13t/site-packages/sklearn/utils/tests/test_cython_blas.py:4: in <module>
      from sklearn.utils._cython_blas import (
  E   ImportError: cannot import name 'ColMajor' from 'sklearn.utils._cython_blas' (/tmp/tmp.O8xqw5JN27/venv/lib/python3.13t/site-packages/sklearn/utils/_cython_blas.cpython-313t-x86_64-linux-gnu.so)

[ogrisel]

ColMajor comes from:

scikit-learn/sklearn/utils/_cython_blas.pxd

Lines 4 to 6 in 7131d94

	cpdef enum BLAS_Order:
	RowMajor # C contiguous
	ColMajor # Fortran contiguous

[ogrisel]

I am not sure exactly what caused this build to start failing 2 days ago. Here is the history of the runs:

https://github.com/scikit-learn/scikit-learn/actions/workflows/wheels.yml?query=branch%3Amain+event%3Aschedule

[ogrisel]

In the last successful run and the rist failing run, the Python versions were both:

3.13.2 experimental free-threading build (main, Mar 22 2025, 16:18:34) [GCC 10.2.1 20210130 (Red Hat 10.2.1-11)]

and the wheel was built with:

     Successfully installed Cython-3.1.0b1 meson-1.8.0rc2 meson-python-0.17.1 numpy-2.3.0.dev0 packaging-25.0 pyproject-metadata-0.9.1 scipy-1.16.0.dev0

in both cases. Maybe it's a side effect of a change in SciPy?

Anyway the fix in #31263 seems legit and I wonder why Cython does not complain at build time.