Previously, mangleVarList would be used which would concatenate the
variables using a space as a separator. Paths are however separated by
`:` in PKG_CONFIG_PATH leading to entries being broken.
This is fixed by introducing mangleVarListGeneric which allows us to
specify the desired separator.
Reproducer for the issue prior to this change:
$ nix-shell -A pkgsLLVM.wayland
[nix-shell] $ pkg-config --libs expat
Package expat was not found in the pkg-config search path.
Perhaps you should add the directory containing `expat.pc'
to the PKG_CONFIG_PATH environment variable
No package 'expat' found
$ printf 'Host: %s\nBuild: %s' $PKG_CONFIG_PATH $PKG_CONFIG_PATH_FOR_BUILD
Host: /nix/store/5h308a4ab8w7prcp8iflh5pnl78mayi2-expat-2.2.10-x86_64-unknown-linux-gnu-dev/lib/pkgconfig:/nix/store/z3y9ska2h4l1map25m195iq577g7g3gz-libxml2-x86_64-unknown-linux-gnu-2.9.12-dev/lib/pkgconfig:/nix/store/lbz5m1s0r7zn0cxvl21czfspli6ribzb-zlib-1.2.11-x86_64-unknown-linux-gnu-dev/lib/pkgconfig:/nix/store/rfhvp8r8n3ygpzh8j0l34lk8hwwi3z0h-libffi-3.3-x86_64-unknown-linux-gnu-dev/lib/pkgconfig
Build: /nix/store/dw11ywy7qwfz53qisz0dggbgix88jah2-wayland-1.19.0-bin/lib/pkgconfig
strace reveals the issue:
stat("/nix/store/dw11ywy7qwfz53qisz0dggbgix88jah2-wayland-1.19.0-bin/lib/pkgconfig /nix/store/5h308a4ab8w7prcp8iflh5pnl78mayi2-expat-2.2.10-x86_64-unknown-linux-gnu-dev/lib/pkgconfig/expat-uninstalled.pc", 0x7fff49829fa0) = -1 ENOENT (No such file or directory)
In the pkg-config wrapper $PKG_CONFIG_PATH_FOR_BUILD and
$PKG_CONFIG_PATH are concatenated with a space which leads to two paths
being messed up. This issue likely only affects native cross
compilation.
This is much better because then we can freely keep the comments up to
date without causing mass rebuilds.
Someday, somebody should make the same change with `cc-wrapper` and
`bintools-wrapper`.
