nanobind/scikit-build-core/vcpkg/windows: how to find cibuildwheel's python?

[nilsnolde]

I'm having a very high level of frustration trying to build windows wheels for a project in this PR switching pybind to nanobind.

I tried tons of things in CI but scikit/cmake keeps finding the wrong Python libraries because vcpkg does its own CMake config (nanobind vcpkg unfortunately pulls in Python). I won't list everything I tried, but this I would've expected to work in the worst case:

      - uses: pypa/[email protected]
        env:
          CIBW_BEFORE_BUILD_WINDOWS: |
             $env:PY_EXE  = & python -c "import sys; print(sys.executable)"
             $env:PY_ROOT = Split-Path -Parent $env:PY_EXE

          CIBW_ENVIRONMENT_WINDOWS: >-
            CMAKE_ARGS="-DPython_EXECUTABLE=$env:PY_EXE -DPython_ROOT_DIR=$PY_ROOT"

I didn't expect $env:PY_EXE to work and it doesn't but when I look at scikit logs, the 2025-10-25 19:03:07,586 - scikit_build_core - DEBUG - RUNENV: section doesn't list any of them and then the cmake configure misses the values (and it does contain all others I set via GITHUB_ENV, so the system env vars are taken into account during scikit build)

2025-10-25 19:03:07,617 - scikit_build_core - INFO - RUN: C:\Program Files\CMake\bin\cmake.EXE -S. <...> -DPython_EXECUTABLE=:PY_EXE -DPython_ROOT_DIR=

`
Does anyone know how to pass the right python paths to the scikit cmake bulid with this software combo on Windows GHA?

[nilsnolde]

see #2641