Missing shared libraries for gdk-pixbuf break non-Guix applications on foreign distros

Hello,

When running an application that uses gdk-pixbuf as a library, the

GDK_PIXBUF_MODULE_FILE environment variable takes precedence over

build-time defaults (see for example [1]).

If a Guix user on a foreign distro installs in their main profile an

application that sets GDK_PIXBUF_MODULE_FILE, the variable will be used for

all applications, not only the ones installed by Guix (because it's

exported in the profile environment).

See for example when running Thunderbird on Debian when

GDK_PIXBUF_MODULE_FILE is set in the main Guix profile environment file

(note how it loads libgdk_pixbuf provided by Debian, but the PNG loader

provided by Guix):

"""

$ strace thunderbird 2>&1 | grep -E '^open(at)?\(.*\.so' | grep pixbuf

openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libgdk_pixbuf-2.0.so.0",

O_RDONLY|O_CLOEXEC) = 4

openat(AT_FDCWD,

"/gnu/store/5m25ni3hfvmqlsszvbkbz243avz78cb2-gdk-pixbuf-2.42.4/lib/gdk-pixbuf-2.0/2.10.0/loaders/libpixbufloader-png.so",

O_RDONLY|O_CLOEXEC) = 35

"""

This was not so much of a problem until the bump of gdk-pixbuf to version

2.42.8 (see commit 8b0565c07740167982e9cef3fc37359b25340d1b).

In gdkpixbuf 2.42.8, the support for PNG and JPEG is builtin (it's linked

statically, and not as shared libraries like it was the case in 2.42.4).

This also means that the shared libraries to be able to load such files are

not generated nor install by Guix at all anymore.

Applications that use the newer version of gdk-pixbuf will have no issue as

the gdk-pixbuf library already provides support for loading PNG files.

For non-Guix applications that have been linked against (or dlopen) a

previous version however, this becomes problematic as the support for PNG

files is not builtin anymore, so they will rely on loading the shared

library for it by looking at GDK_PIXBUF_MODULE_FILE, which no longer

contains the path to the lib for PNG files.

An example of such an application is Thunderbird when running on Debian:

with gdk-pixbuf 2.42.8 installed in the main Guix profile, it crashes

everytime the dialog to open a file is opened.

There could be multiple ways to solve it:

- Make sure the library for PNG support (and JPEG) is built as a shared

library again with the current gdk-pixbuf version. This would fix the

crashing apps, but is arguably more a workaround than a solution (do we

have any guarantee that the shared libraries are compatible with any

gdk-pixbuf version the foreign distro might have?).

- Set the GDK_PIXBUF_MODULE_FILE variable for all Guix applications that

need it, but do not export it for the whole profile. Since many other

variables are similarly exported in the profile environment I imagine there

is a good reason for it, so this might not be possible.

- Document as a limitation to not install applications that set

GDK_PIXBUF_MODULE_FILE in the main profile on foreign distros.

- Does anyone have any other idea?

Note that as a temporary fix for anyone affected by this issue, another

possiblity is to unset the GDK_PIXBUF_MODULE_FILE variable in a terminal

before starting the affected application.

Kind regards,

Raphaël

[1]:

Note that on Debian specifically, this is not so much of an issue after updating to Bookworm (Debian 12), as it itself ships gdk-pixbuf 2.42.10, which has the expected loaders builtin.