[oe-core] [RFC] meson.bbclass: pkg-config vs pkgconf

[Randolph Sapp <rs@ti.com>]

Hello,

Forgive my ignorance, but is there any particular reason why pkg-config 
is preferred over pkgconf for meson related recipes? It seems the two 
treat the usage of the PKG_CONFIG_SYSROOT_DIR variable differently, 
resulting in issues when build scripts attempting to use package config 
variables directly.

It seems that pkgconf respects PKG_CONFIG_SYSROOT_DIR by prepending that 
path to all variables queried, where as pkg-config just populates an 
internal global variable that the *.pc file must then use (pc_sysrootdir).

The global variable method would work, if any package config generating 
scripts used it by default. Unfortunately the only use I've been able to 
find comes from Yocto related patches specifically added to work around 
this difference in behavior.

You can see some of the attempts to work around this discrepancy here:
recipes-graphics/xorg-proto/xcb-proto/0001-xcb-proto.pc.in-reinstate-libdir.patch
recipes-graphics/wayland/wayland/0002-Consider-pkgconfig-sysroot-for-pkgdatadir.patch
meta-openembedded/meta-oe/recipes-extended/flatpak/flatpak_1.15.6.bb

If there's not an explicit reason we're preferring pkg-config, would 
anyone be opposed to switching it out for pkgconf for meson related 
packages? Of course, with a note about this behavior discrepancy. It 
would reduce these Yocto specific patches and align meson behavior with 
distros that currently default to pkgconf.

Regards,
Randolph