Confusing behaviour when libfontconfig is missing

[brynedwards]

Hello,

No text appears when running a program using parley without libfontconfig in LD_LIBRARY_PATH. For example, here is how the hello-masonry example from Xilem appears:

I did not know why there was no text until I did a git bisect to find it started with #378. I realise that this might only affect unconventional setups (in my case I use Nix for development environments and my shell.nix did not include libfontconfig) but some kind of indication of this behaviour being due to libfontconfig missing would be very helpful. Thank you.

[DJMcNab]

Yeah, this is

parley/fontique/src/backend/fontconfig.rs

Lines 430 to 437 in 4f88757

	let library_exists = LIB_RESULT.as_ref().ok().is_some();
	// We couldn't find the fontconfig library; maybe it doesn't exist. Just
	// return a `SystemFonts` with no `config`. All our methods will return
	// `None` and shouldn't attempt any FFI calls because the first thing we
	// do is check for `config`.
	if !library_exists {
	return Self::default();
	}

.

At the very least, this should give an error! log. Although I do agree that the failure probably should be passed higher and handled by the app (although I'm not sure that there's any way to handle that error sensibly, given that your system can't actually display text!).

It seems surprising to me that every other application on your system doesn't use fontconfig.

[tronical]

I wonder if you folks would consider disabling the dlopen feature again and resort to regular dynamic linkage.

This would help identify such issues sooner, and it would simplify the setup needed in build environments for embedded systems that determine dependencies automatically by inspecting the binaries. If libfontconfig is in DT_NEEDED via regular linkage, the dependency is detected and fontconfig is included in the target system. If it's dynamically linked, one has to specify this run-time dependency by hand.

A related issue that we're facing in Slint is that we're building an example that integrates servo, which also uses yeslogic-fontconfig-sys without enabling the dlopen feature and relies on it. Unfortunately, fontique enabling it means the API is different and thus it can't be built.

[brynedwards]

(although I'm not sure that there's any way to handle that error sensibly, given that your system can't actually display text!)

It seems surprising to me that every other application on your system doesn't use fontconfig.

Applications on my system can and do display text, and my system does use fontconfig.

My original description was slightly inaccurate, it would be more correct to say that text does not appear if the dynamic loader (ld-linux) cannot find libfontconfig. In most Linux distributions, dynamic libraries are available globally in /lib or /usr/lib. I use NixOS which does not do this; it stores dependencies in unique paths to support reproducible builds (for example, libfontconfig is in /nix/store/37pqcmv5hn278m1anryngfnia3862iqc-fontconfig-2.17.1-lib/lib on my system) and then appends these paths to LD_LIBRARY_PATH for each application using a wrapper script. I realise this will only affect a tiny minority who use such unconventional setups but I figure I'd make an issue anyway as it might save someone else some time.

[DJMcNab]

What are the next steps for this issue now that #467 has landed?

[brynedwards]

I tried with #467 and now if fontconfig and pkg-config are missing this appears:

thread 'main' panicked at /home/bryn/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/yeslogic-fontconfig-sys-6.0.0/build.rs:8:48:
called Result::unwrap() on an Err value: "Could not run PKG_CONFIG_ALLOW_SYSTEM_LIBS=1 PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1 pkg-config --libs --cflags fontconfig\nThe pkg-config command could not be found.\n\nMost likely, you need to install a pkg-config package for your OS.\nTry apt install pkg-config, or yum install pkg-config, or brew install pkgconf\nor pkg install pkg-config, or apk add pkgconfig depending on your distribution.\n\nIf you've already installed it, ensure the pkg-config command is one of the\ndirectories in the PATH environment variable.\n\nIf you did not expect this build to link to a pre-installed system library,\nthen check documentation of the yeslogic-fontconfig-sys crate for an option to\nbuild the library from source, or disable features or dependencies\nthat require pkg-config."

Additionally, running e.g swash_render without libfontconfig available now shows:
target/debug/swash_render: error while loading shared libraries: libfontconfig.so.1: cannot open shared object file: No such file or directory

These errors make things much more obvious, thank you!