gnome: look up vapigen using pkg-config

[helmutg]

vapigen has architecture-dependent search path. In a cross build, using the native one cannot work as it cannot locate the host libraries it is supposed to use. On most distributions, vapigen.pc names location of vapigen (often suffixed with an appropriate version). On Debian, vapigen.pc points at an architecture-specific wrapper that adapts the search path for the desired architecture. It is never wrong to consult vapigen.pc and it also helps users with multiple vala installations selecting the right one. Thus prefer locating vapigen via its pc file over searching $PATH while retaining the override mechanisms available.

Link: https://bugs.debian.org/1061107
Link: https://salsa.debian.org/gnome-team/vala/-/merge_requests/3
Related: 62a5e3a ("env2mfile: Use a cross vapigen on Debian if available")
Thanks: Simon McVittie
Thanks: Eli Schwartz

[helmutg]

/cc @eli-schwartz
/cc @smcv

[smcv]

Not a maintainer, but LGTM

[eli-schwartz]

It is never wrong to consult vapigen.pc and it also helps users with multiple vala installations selecting the right one.

Slightly curious how this would work by the way. You'd need an unversioned pkgconfig file at the beginning of PKG_CONFIG_PATH instead of an unversioned binary at the beginning of PATH, and I think both are probably just as annoying.

[helmutg]

It is never wrong to consult vapigen.pc and it also helps users with multiple vala installations selecting the right one.

Slightly curious how this would work by the way. You'd need an unversioned pkgconfig file at the beginning of PKG_CONFIG_PATH instead of an unversioned binary at the beginning of PATH, and I think both are probably just as annoying.

One of the ways of managing custom environments is using dedicated pkgconf "personalities", so you'd supply a custom pkgconf to meson and that way query packages from a particular location. I am not using this approach myself, but my understanding is that sysroots tend to use this.