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
mitter'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=4e531e55dcdc99c83bcfe3eec67c3fd95c7b6ca7&amp;showmsg=1'>root</a>/<a href='/guix/log/doc?id=4e531e55dcdc99c83bcfe3eec67c3fd95c7b6ca7&amp;showmsg=1'>doc</a>/<a href='/guix/log/doc/images?id=4e531e55dcdc99c83bcfe3eec67c3fd95c7b6ca7&amp;showmsg=1'>images</a>/<a href='/guix/log/doc/images/gcc-core-mesboot0-graph.dot?id=4e531e55dcdc99c83bcfe3eec67c3fd95c7b6ca7&amp;showmsg=1'>gcc-core-mesboot0-graph.dot</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/doc/images/gcc-core-mesboot0-graph.dot?id=4e531e55dcdc99c83bcfe3eec67c3fd95c7b6ca7'>Collapse</a>)</th><th class='left'>Author</th></tr>
<tr class='logheader'><td><span title='2022-05-12 19:27:59 +0200'>2022-05-12</span></td><td class='logsubject'><a href='/guix/commit/doc/images/gcc-core-mesboot0-graph.dot?id=eeba993f570483345acd59c2d8709fd5d7ee7ae7'>doc: Add the "Full-source Bootstrap".</a></td><td>Jan (janneke) Nieuwenhuizen</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* doc/guix.texi (Reduced Binary Seed Bootstrap): Update and rename to...
(Full-Source Bootstrap): ...this.
* doc/images/gcc-core-mesboot0-graph.dot: Regenerate.


</td></tr>
<tr class='logheader'><td><span title='2020-05-22 16:11:52 +0200'>2020-05-22</span></td><td class='logsubject'><a href='/guix/commit/doc/images/gcc-core-mesboot0-graph.dot?id=cd5d5f53228fd5bf96d9f790aa2606ae71fa68d7'>doc: Update 'Bootstrapping' for further binary seed reduction.</a></td><td>Jan Nieuwenhuizen</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* doc/images/gcc-core-mesboot0-graph.dot: New image, replacing
* doc/images/gcc-mesboot0-bag-graph.dot: ... remove file.
* doc/local.mk (DOT_FILES): Update for new image file.
* doc/guix.texi (Reduced Binary Seed Bootstrap): Use it in updated description
of further reduction of the trusted computing base.


</td></tr>