Recently I’ve come across the Field Monitor project, designated as “Remote-desktop client designed for the GNOME platform.” using GTK 4. I thought this would perform better than Virt Manager due to how GTK 3 and 4 differs from fractional scaling and hardware rendering. So packaging it was the next thing to do.

The first step was obviously to create a standard meson PKGBUILD for it and include all necessary dependencies, but package() is failing with error:

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failed to parse config file: invalid configuration key (in /root/.gitconfig)...

This makes no sense. Why would meson install look up a gitconfig? Worse yet, it’s reading root’s gitconfig which completely makes no sense even in a chroot build, as the HOME should be /build. And it seems that meson install is fetching something via cargo?

Getto way

As the error clearly deviates from the package() function, what if we just use bubblewrap to hide and create a tmpfs over /root? This sounds doable, but in reality due to various restrictions, bwrap inside fakeroot always fails with

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bwrap: Creating new namespace failed: Operation not permitted

Okay then, we just search online for existing bugs. And it appears that cargo/#9854 is the root cause. Reading through the issue it seems that env variable GIT_CONFIG_GLOBAL="" should be enough…?

Nope! cargo invokes git using libgit2, and it does not honor this specific environment variable… So after some thinking, a possible explanation finally comes into my mind:

  1. The upstream did some bizzare things and it downloads something when meson install is executed.
  2. Arch fakeroot makes cargo think it is running as root, and it’s home lies in /root.
  3. Git assumes /root/.gitconfig as it’s config file, and fails reading it, causing the entire build to fall apart.

The stars have aligned perfectly, that is to say: A) Upstream downloads stuff in meson install, B) We are building this package on Arch using makepkg or makechrootpkg, C) /root/.gitconfig happens to be inaccessible. Now we know how this happened, is there a way to fix it?

The getto way is to just run meson install in build(), and copy the contents in package(), which should look like this:

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function build() {
	export RUSTFLAGS="${RUSTFLAGS} --remap-path-prefix $srcdir=src"
	export RUST_BACKTRACE=1
	arch-meson "${srcdir}/field-monitor" build
	meson compile -C build
}

function package() {
	cp -a \
		"${srcdir}/install"/* \
		"${pkgdir}/"
}

But maybe a proper fix is either cargo or libgit2 detects whether such config is available, and skip it in case inaccessible, or libgit2 may honor the GIT_CONFIG_GLOBAL environment variable. And the upstream should not download any crates during installation phases. Maybe we should track cargo/#9854 for more up-to-date changes.

That’s all for today, see you in the next blog!