Gnome-tweaks does not look at GSETTINGS_SCHEMA_PATH or XDG_DATA_DIRS, it
assumes that schemas are installed in one global directory
(GSETTINGS_SCHEMA_DIR/gsettingsschemadir).

Guix/GuixSD uses a different directory for every gir package and has
packages pick-up files using XDG_DATA_DIRS.

Upstream ticket: https://bugzilla.gnome.org/show_bug.cgi?id=764537
janneke@gnu.org

--- gnome-tweak-3.18.1.orig/gtweak/gsettings.py	2015-04-08 15:21:32.000000000 +0200
+++ gnome-tweak-tool-3.18.1/gtweak/gsettings.py	2016-04-03 11:26:38.658482704 +0200
@@ -16,7 +16,8 @@
 # along with gnome-tweak-tool.  If not, see <http://www.gnu.org/licenses/>.
 
 import logging
-import os.path
+import os
+import sys
 import xml.dom.minidom
 import gettext
 
@@ -31,6 +32,13 @@
 class GSettingsMissingError(Exception):
     pass
 
+def file_from_path(path, file_name):
+    for dir in path:
+        f = os.path.join(dir, file_name)
+        if os.path.exists(f):
+            return f
+    return None
+
 class _GSettingsSchema:
     def __init__(self, schema_name, schema_dir=None, schema_filename=None, **options):
         if not schema_dir:
@@ -38,9 +46,14 @@
         if not schema_filename:
             schema_filename = schema_name + ".gschema.xml"
 
+        schema_prefix = os.path.join('glib-2.0', 'schemas')
         schema_path = os.path.join(schema_dir, schema_filename)
         if not os.path.exists(schema_path):
-            logging.critical("Could not find schema %s" % schema_path)
+            schema_path = file_from_path(os.environ.get ('GSETTINGS_SCHEMA_PATH', '').split(os.path.pathsep), schema_filename)
+        if not (schema_path and os.path.exists(schema_path)):
+            schema_path = file_from_path(os.environ.get ('XDG_DATA_DIRS', '').split(os.path.pathsep), os.path.join(schema_prefix, schema_filename))
+        if not (schema_path and os.path.exists(schema_path)):
+            logging.critical("Could not find schema %s" % schema_filename)
             assert(False)
 
         self._schema_name = schema_name
<a href='/guix/log/?id=822edbf08b754dfd1c9f25500c4e9490b99276f4'>root</a>/<a href='/guix/log/gnu?id=822edbf08b754dfd1c9f25500c4e9490b99276f4'>gnu</a>/<a href='/guix/log/gnu/services?id=822edbf08b754dfd1c9f25500c4e9490b99276f4'>services</a>/<a href='/guix/log/gnu/services/rsync.scm?id=822edbf08b754dfd1c9f25500c4e9490b99276f4'>rsync.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/services/rsync.scm?id=822edbf08b754dfd1c9f25500c4e9490b99276f4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-12-21 15:47:03 +0100'>2021-12-21</span></td><td><a href='/guix/commit/gnu/services/rsync.scm?id=c9d92409d4d3f587f73c6f48f845a913f7278ad1'>services: rsync: Allow configuring several rsync "modules".</a><span class='msg-avail'>...<span class='msg-tooltip'>Until now the rsync service would export a single module, named
"files".  This allows users to specify as many modules as they want, in
line with rsyncd.conf(5).

* gnu/services/rsync.scm (warn-share-field-deprecation): New procedure.
(&lt;rsync-configuration&gt;)[modules]: New field.
[share-path, share-comment, read-only?, timeout]: Mark as deprecated.
(&lt;rsync-module&gt;): New record type.
(%default-modules): New variable.
(rsync-configuration-modules): New procedure.
(rsync-activation): Create the directory of each module.
(rsync-config-file): Generate configuration for each module.
(rsync-service-type)[description]: New field.
* doc/guix.texi (Networking Services): Adjust documentation.  Augment
example.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-11-30 01:08:55 +0100'>2021-11-30</span></td><td><a href='/guix/commit/gnu/services/rsync.scm?id=892f1b7273d57b25940700877a02618fe826cc08'>services: Accept &lt;inferior-package&gt;s in lieu of &lt;package&gt;s.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/authentication.scm (fprintd-configuration)
(nslcd-configuration): Substitute file-like objects for package ones.
* gnu/services/cgit.scm (cgit-configuration, opaque-cgit-configuration):
Likewise.
* gnu/services/cups.scm (package-list?, cups-configuration): Likewise.
* gnu/services/dns.scm (verify-knot-configuration)
(ddclient-configuration): Likewise.
* gnu/services/docker.scm (docker-configuration): Likewise.
* gnu/services/file-sharing.scm (transmission-daemon-configuration): Likewise.
* gnu/services/getmail.scm (getmail-configuration): Likewise.
* gnu/services/mail.scm (dovecot-configuration)
(opaque-dovecot-configuration): Likewise.
* gnu/services/messaging.scm (prosody-configuration)
(opaque-prosody-configuration): Likewise.
* gnu/services/monitoring.scm (zabbix-server-configuration)
(zabbix-agent-configuration): Likewise.
* gnu/services/networking.scm (opendht-configuration): Likewise.
* gnu/services/pm.scm (tlp-configuration): Likewise.
* gnu/services/telephony.scm (jami-configuration): Likewise.
* gnu/services/virtualization.scm (libvirt-configuration)
(qemu-guest-agent-configuration): Likewise.
* gnu/services/vpn.scm (openvpn-client-configuration): Likewise.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-10-25 14:32:59 +0200'>2021-10-25</span></td><td><a href='/guix/commit/gnu/services/rsync.scm?id=1ea032fb5fc8dd6f7a10e5bc705e526d25fbe1b4'>services: rsync: support binding rsync to a specific IP address</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/rsync.scm (&lt;rsync-configuration&gt;)[address]: New field.
(rsync-config-file): Honor it.
* doc/guix.texi (Networking Services): Document new address rsync
configuration option.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Jacob Adams</td></tr>