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
='/guix/log/?id=807bd1ac449373c1da6feedc392ea7ca495b44f4'>root</a>/<a href='/guix/log/gnu?id=807bd1ac449373c1da6feedc392ea7ca495b44f4'>gnu</a>/<a href='/guix/log/gnu/packages?id=807bd1ac449373c1da6feedc392ea7ca495b44f4'>packages</a>/<a href='/guix/log/gnu/packages/time.scm?id=807bd1ac449373c1da6feedc392ea7ca495b44f4'>time.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/packages/time.scm?id=807bd1ac449373c1da6feedc392ea7ca495b44f4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-06-21 00:10:50 +0200'>2023-06-21</span></td><td><a href='/guix/commit/gnu/packages/time.scm?id=da4305e9b3d65cf698a6987bd7be7905785bf06c'>gnu: go-github-com-mattn-go-runewidth: Update to 0.0.14.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/golang.scm (go-github-com-mattn-go-runewidth): Update to 0.0.14.
(go-github.com-mattn-go-runewidth): Remove, and change users to to refer
to 'go-github-com-mattn-go-runewidth'.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Nguyễn Gia Phong</td></tr>
<tr><td><span title='2023-05-10 19:27:08 +0200'>2023-05-10</span></td><td><a href='/guix/commit/gnu/packages/time.scm?id=452fec7226bc697a71caa7ca1667ef6601d79245'>gnu: python-arrow: Update to 1.2.3.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/time.scm (python-arrow): Update to 1.2.3.
</span></span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2023-05-10 19:27:07 +0200'>2023-05-10</span></td><td><a href='/guix/commit/gnu/packages/time.scm?id=ff3c55bb98c1b9629061af8f8d3848bc6faea064'>gnu: Add python-dateutils.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/time.scm (python-dateutils): New variable.
</span></span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2023-05-08 12:42:09 +0300'>2023-05-08</span></td><td><a href='/guix/commit/gnu/packages/time.scm?id=5a70b9b924444f8e238c546116045f4992faeffe'>gnu: Add python-timezonefinder.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/time.scm (python-timezonefinder): New variable.
* gnu/packages/geo.scm (h3-3, python-h3-3): New variables. The latest
compatible versions to build python-timezonefinder.

Signed-off-by: Efraim Flashner &lt;efraim@flashner.co.il&gt;
</span></span></td><td>Sharlatan Hellseher</td></tr>
<tr><td><span title='2023-03-27 16:40:58 +0100'>2023-03-27</span></td><td><a href='/guix/commit/gnu/packages/time.scm?id=3547ecc3fa478d076faea79112758154c8bb8c9b'>gnu: python-isodate: Update to 0.6.1.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/time.scm (python-isodate): Update to 0.6.1.

Signed-off-by: Christopher Baines &lt;mail@cbaines.net&gt;
</span></span></td><td>Greg Hogan</td></tr>