meson detection broken (on Windows?) in latest release

[lucascolley]

see https://github.com/scipy/scipy/actions/runs/23884753200/job/69650276634?pr=24961

[lucascolley]

cc @rgommers

[rgommers]

I already just noticed, working on a fix. Due to #106 (comment).

[virtuald]

I made a fix for hatch-meson at virtuald/hatch-meson#14 -- a fix for meson-python would likely be very similar.

[rgommers]

Thanks for sharing @virtuald, that's a useful PR.

[rgommers]

@lucascolley my take is that:

1. For spin we'll want to do a similar thing as for hatch-meson, because that is the use case where we're already in the build environment. So it can continue to work without setting any environment variable.
2. For building with build isolation, this improves things. We already use export PKG_CONFIG_PATH there to point at a scipy_openblas in the root (rather than the isolated) environment.

[lucascolley]

sounds fine

[lucascolley]

any news here?

[mhsmith]

I think the actual reason meson fails to detect pkgconf might be that pkgconf --version gives no output when PKG_CONFIG_PATH is set:

(pkgconf) msmith@MacBook-Pro ~ % pip list
Package Version
------- -----------
pip     26.1.2
pkgconf 3.0.1.post0
(pkgconf) msmith@MacBook-Pro ~ % echo $PKG_CONFIG_PATH

(pkgconf) msmith@MacBook-Pro ~ % pkgconf --version                         
/Users/msmith/.venv/pkgconf/bin/pkgconf:6: UserWarning: PKG_CONFIG_PATH not specified, and the system is unavailable! The 'pkgconf' executable provided by pkgconf-pypi does not support searching for system-level .pc files, you must provide a search path instead. If you want the search path to be computed from the installed Python packages, please use the 'pkgconf-pypi' executable instead, or set FORCE_PKGCONF_PYPI.
  sys.exit(_vanilla_entrypoint())
3.0.1
(pkgconf) msmith@MacBook-Pro ~ % PKG_CONFIG_PATH=whatever pkgconf --version     
(pkgconf) msmith@MacBook-Pro ~ % pkgconf-pypi --version                         
3.0.1
(pkgconf) msmith@MacBook-Pro ~ % PKG_CONFIG_PATH=whatever pkgconf-pypi --version
3.0.1