Re: [PR PATCH] [Merged]: [RFC] common/build-helper/meson.sh: new build helper, used by meson build style

[ahesford <ahesford@users.noreply.github.com>]

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There's a merged pull request on the void-packages repository

[RFC] common/build-helper/meson.sh: new build helper, used by meson build style
https://github.com/void-linux/void-packages/pull/46117

Description:
The `python3-scipy` package now builds with `python3-meson-python`, with some more coming down the pike. The Python build process is necessary to include Python package metadata. For SciPy, this is accomplished by using the `meson` build style to configure a build directory, then overriding `do_build` and `do_install` to build things the PEP517 way (using the pre-configured build directory).

It might be helpful to define a `meson` build helper that can write out the standard cross file for builds, allowing packages like SciPy to use the `python3-pep517` build style with the `meson` helper. There are some issues to be worked out:
1. It seems like the `xbps_meson.cross` is written before `CFLAGS`, *et al.* are properly defined, so this cross file is actually broken. (This is the process by which the `qmake` helper writes its configurations, and they reference `CFLAGS` and others; is the `qmake` helper writing broken configs?)
2. The meson configuration (which would need to happen even with `python3-pep517` plus a `meson` helper) still includes a lot of magic that would have to be brought over to templates. This isn't really easier than the current practice of overriding the one-line `do_build` and `do_install`.

A possible solution would be to define a special-purpose function in the helper, called `vmesoncross` or somesuch, that will only write the configured when called---from a build function where these are properly defined (*e.g.*, `pre_configure`, `do_configure`). We could also define a special `do_configure`-like function in the helper that can be used by the `meson` style to actually do the configuration. This might be a bit ugly, but avoids repetition or violating the typical practice that the actual build functions are only defined in templates or build styles.

A third option is just defining a new `python3-meson` build style that mashes the meson `do_configure` bits from the `meson` style with the `do_build` and `do_install` bits from the `python3-pep517` style.

All of these options are sub-optimal, but I'm not sure which one is least offsensive.