Mark H Weaver <mhw@netris.org> writes:

> I can confirm that the problem does not occur on Debian, and I've not
> found reports of it happening on any other mainstream distro.  I would
> guess that our unusual filesystem layout prevents GNOME Shell from
> finding something that it's looking for, and that the error handling in
> that case is deficient or non-existent.

Hi,

I think I understand what's going on, and I may even have a solution ;-)

What's happening is that gnome-shell wants certain cursors, but can't
find them.  These cursors are provided by Adwaita icon theme, but
gnome-shell somehow isn't looking in Adwaita's location (unless you
symlink adwaita's icons into ${HOME}/.icons as I mentioned before).
I've attached an strace from gnome-shell, the relevant part is here:

open("/home/thomas/.icons/Adwaita/cursors/dnd-none", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/home/thomas/.icons/Adwaita/index.theme", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/gnu/store/14f4vh3y3wdf3rfpzkpqfqbl9i81hyw8-libxcursor-1.1.14/share/icons/Adwaita/cursors/dnd-none", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/gnu/store/14f4vh3y3wdf3rfpzkpqfqbl9i81hyw8-libxcursor-1.1.14/share/icons/Adwaita/index.theme", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/gnu/store/14f4vh3y3wdf3rfpzkpqfqbl9i81hyw8-libxcursor-1.1.14/share/pixmaps/Adwaita/cursors/dnd-none", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/gnu/store/14f4vh3y3wdf3rfpzkpqfqbl9i81hyw8-libxcursor-1.1.14/share/pixmaps/Adwaita/index.theme", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/home/thomas/.icons/default/cursors/dnd-none", O_RDONLY) = -1
ENOENT (No such file or directory)
[...]
--- SIGTRAP {si_signo=SIGTRAP, si_code=SI_KERNEL} ---
+++ killed by SIGTRAP +++

I've been looking through the sources, and
gtk+-3.22.15/gdk/x11/gdkcursor-x11.c makes me think that cursor lookup
in our case is ultimately done by libxcursor.

libxcursor's configure script has an option "--with-cursorpath=<paths>"
to set a default search path for cursors.  If no option is given (as is
the case with our package), the default is
DEF_CURSORPATH="~/.icons:${datadir}/icons:${datadir}/pixmaps", which is
exactly the set of directories in the strace (${HOME}/.icons and
${INSTALLPREFIX}/share/icons).

So I guess that adding relevant directories to the libxcursor search
path would solve the problem.  For Guix, it'd be useful to add
/run/current-system/profile/share/icons, as well as
~/.guix-profile/share/icons (for users installing other icon themes in
their profile).  Would this be ok?

I'll go and test this, but building everything from libxcursor up to gnome-desktop
will probably take a while :).

Comments are welcome!

Thomas