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Hi @lesteve, this PR is ready for review – I pushed 84d2cc6 to trigger the wheel builder and the Azure Pyodide builds, just to confirm that they work as intended. Once this is reviewed and gets merged, I can rebase #29791. Thanks!

The wheels build fine, but the _build_utils/ folder still exists there :/ I'll take another look at this later in the day.

The wheels build fine, but the _build_utils/ folder still exists there :/ I'll take another look at this later in the day.

I pushed a commit that I think fixes it c5a71bf

Oops, yes – thanks!

Oh well not so simple, looks like this breaks the test discovery see build log ...

__________________ ERROR collecting _build_utils/__init__.py ___________________
ImportError while importing test module '/home/vsts/work/1/s/sklearn/_build_utils/__init__.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/share/miniconda/envs/testvenv/lib/python3.9/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
E   ModuleNotFoundError: No module named 'sklearn._build_utils'
___________________ ERROR collecting _build_utils/tempita.py ___________________
ImportError while importing test module '/home/vsts/work/1/s/sklearn/_build_utils/tempita.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/share/miniconda/envs/testvenv/lib/python3.9/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
E   ModuleNotFoundError: No module named 'sklearn._build_utils'
___________________ ERROR collecting _build_utils/version.py ___________________
ImportError while importing test module '/home/vsts/work/1/s/sklearn/_build_utils/version.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/share/miniconda/envs/testvenv/lib/python3.9/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
E   ModuleNotFoundError: No module named 'sklearn._build_utils'

I think there should be a way to manoeuvre around it for the tests. I guess it's because of the doctest_modules suggestion you mentioned in the other PR.

The solution to it is from my perspective will be to use install_tags. Add meson.build file inside sklearn/_build_utils and use install_tags. See my PRs on how we selectively install tests. You can use similiar logic to avoid installing sklearn/_build_utils maybe.

PRs - scipy/scipy#20712

Thanks for chiming in, @czgdp1807. I've experimented with adding install tags locally, and doing that seems to be a larger change which would need more consideration and reviewing effort in another PR (it's certainly useful to do, though); is there a more—for the lack of a better word—"organic" method to exclude files from sdists (and subsequently, wheels) in the meantime? In any case, I plan to revisit this PR next week.

Closing this PR as #31058 is now merged. Thank you!