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
269017cec41350f30ac1e3edd644'>root</a>/<a href='/guix/log/build-aux?id=bb5c508c12db269017cec41350f30ac1e3edd644'>build-aux</a>/<a href='/guix/log/build-aux/cuirass?id=bb5c508c12db269017cec41350f30ac1e3edd644'>cuirass</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/build-aux/cuirass?id=bb5c508c12db269017cec41350f30ac1e3edd644&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-04-08 17:48:33 +0200'>2018-04-08</span></td><td><a href='/guix/commit/build-aux/cuirass?id=351f384e57939005b25fa976952e3a0e08785893'>cuirass: Add job specs for the modular Guix.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/cuirass/guix-modular.scm: New file.
* Makefile.am (EXTRA_DIST): Add it.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-04-08 17:48:33 +0200'>2018-04-08</span></td><td><a href='/guix/commit/build-aux/cuirass?id=a1ec7540be9b30593f5e83e36a0e83b1bcf337f1'>cuirass: Factorize hydra-to-cuirass CI job translation.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/cuirass/gnu-system.scm: Move code to...
* build-aux/cuirass/hydra-to-cuirass.scm: ... here, and include it.
* Makefile.am (EXTRA_DIST): Add 'build-aux/cuirass/hydra-to-cuirass.scm'
and 'build-aux/cuirass/gnu-system.scm'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-01-15 15:18:03 +0100'>2018-01-15</span></td><td><a href='/guix/commit/build-aux/cuirass?id=403f2dccfcf992573ceeeae7c76c71b4884d3cd4'>cuirass: Properly convert list of &lt;license&gt; objects.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes a bug whereby we would 'write' raw &lt;license&gt; objects when they
were in a list.

* build-aux/cuirass/gnu-system.scm (entry-&gt;sexp-entry): Add recursive
case when O is a list.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-09-27 22:19:28 +0200'>2017-09-27</span></td><td><a href='/guix/commit/build-aux/cuirass?id=66bc1d2aaf74fc7eb4ef9b3519c69bd37142ffb3'>cuirass: Add gnu-system build spec.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/hydra/gnu-system.scm (hydra-jobs): Support subset "hello".
* build-aux/cuirass/gnu-system.scm: New file.
* doc/guix.texi (Continuous Integration): Update example spec.
</span></span></td><td>Jan Nieuwenhuizen</td></tr>