System library target - pkg-config argument format

Hello.

TL;DR What is the correct format of pkgConfig String argument when creating Target.systemLibray? Is it allowed to pass more then one package at a time?

Full story:
I'm currently working on improving rhx's implementation of Swift wrapper around GTK. There are a lot of things I want to achieve to make the library as easy to use as possible.

The issue I am currently focused on is having the ability to build a project with simple swift build command (assuming wrapper was already generated). I hope this should improve experience with Sourcekit which is imo essential for comfortable development in Swift.
I've started with GitHub - rhx/SwiftGLib: A Swift wrapper around glib-2.x that is largely auto-generated from gobject-introspection package. This package should wrap GLib for Swift. However, in order to build the project, provided build.sh script calls swift build with c++ and linker arguments. For my system, those arguments are generated as follows:
swift build --build-path /home/mikolas/Developer/SwiftGLib/.build -Xcc -pthread -Xcc -I/usr/include/gio-unix-2.0 -Xcc -I/usr/include/libmount -Xcc -I/usr/include/blkid -Xcc -I/usr/include/glib-2.0 -Xcc -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -Xlinker -lgio-2.0 -Xlinker -lgobject-2.0 -Xlinker -lglib-2.0

Using this command results in successful build. However I've the noticed, that those exact paths and linker commands should be emitted already, since glib-2.0 and gio-unix-2.0 are passed as a argument to the target via pkgConfig argument in the Package.swift.

My first naive attempt to solve the issue by removing one of the packages (that being glib-2.0) resulted in successful clean build (assuming generated code was still present) using nothing more than swift build.

Therefore I am wondering, is it required to have only one package passed to the pkgConfig at the time? Is it a bug? What is the correct format if more than one package could be passed to a pkgConfig argument? ... :thinking:

I've done some research into this and found this documentation in the SPM repo https://github.com/apple/swift-package-manager/blob/7afc6e22bb7b957b7d212fea31cf0f9132513bc0/Sources/PackageDescription/Target.swift#L111.

Is it correct to assume that multiple package names do not work because SPM searches for *.po file which contains name of all listed packages? Are there any workarounds?