bug#21842: Brasero fails to start on foreign distros

[Federico Beffa <beffa@ieee.org>]

On Fri, Nov 6, 2015 at 3:49 PM, Ludovic Courtès <ludo@gnu.org> wrote:
> As Andy notes on IRC, Brasero currently fails to start:
>
> --8<---------------cut here---------------start------------->8---
> $  /gnu/store/dq3817g8w80c9hffbgzspslqjy7szq35-brasero-3.12.1/bin/brasero
>
> ** (brasero:21487): WARNING **: Error retrieving accessibility bus address: org.freedesktop.DBus.Error.ServiceUnknown: The name org.a11y.Bus was not provided by any .service files
>
> (brasero:21487): GLib-GIO-ERROR **: Settings schema 'org.gnome.brasero.config' is not installed
>
> Trace/breakpoint trap (core dumped)
> --8<---------------cut here---------------end--------------->8---
>
> On GuixSD, it starts just fine *if* it is installed in ~/.guix-profile,
> because XDG_DATA_DIRS and XDG_CONFIG_DIRS are appropriately set.
>
> However, on foreign distros, it doesn’t work out of the box.
>
> Andy suggests using ‘glib-or-gtk-build-system’ for Brasero, which
> appears to solve the problem.
>
> WDYT?

I think that using the 'glib-or-gtk-build-system' is the right thing
to do. It will create a wrapper with the correct value of some
environment variables, enabling the program to find its schema.

>
> Should we add a profile hook similar to ‘gtk-icon-themes’ in (guix
> profiles) but for schemas?

I do not think so because if a program gets the wrong schema (say, a
different incompatible version) then it may crash. With the
'glib-or-gtk-build-system' it is guaranteed that it will find the
schema used at build time.

Speaking of GTK+ applications: I think that removing the generation of
'icon-theme.cache' from the 'glib-or-gtk-build-system' was a mistake
(I may even have suggested this). It is my understanding (see [1, 2])
that this file is not strictly necessary, however it speeds up things
and is therefore useful. Having the cache generated by the
build-system allows one to use the program optimally without having to
install it into a profile.

The icon profile hook is still useful because it allows one to add
icon themes a posteriori, that is after having build a program
derivation and without having to rebuild it. The wrapper created by
'glib-or-gtk-build-system' still looks in the directories listed in
XDG_DATA_DIRS (similarly for some other variables). See also the
discussion at [3].

The reason for removing the phase from the build system was to
suppress annoying collision warnings, but in my opinion it would be
better to suppress them in a different way. As long as the profile
hook is the last derivation being installed in a profile, such
collisions are harmless and should just be masked.

Regards,
Fede

[1] https://developer.gnome.org/gtk3/stable/gtk-update-icon-cache.html
[2] http://standards.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html
[3] https://lists.gnu.org/archive/html/guix-devel/2015-01/msg00108.html