glib: Add helpers for finding schema datadir

It is commonly needed for test environments.

pkgs/desktops/gnome/apps/seahorse/default.nix

@@ -73,7 +73,7 @@ stdenv.mkDerivation rec {
     # Add “org.gnome.crypto.pgp” GSettings schema to path
     # to make it available for “gpgme-backend” test.
     # It is used by Seahorse’s internal “common” library.
-    addToSearchPath XDG_DATA_DIRS "${glib.getSchemaPath gcr}/../.."
+    addToSearchPath XDG_DATA_DIRS "${glib.getSchemaDataDirPath gcr}"
     # The same test also requires home directory so that it can store settings.
     export HOME=$TMPDIR
   '';

pkgs/development/libraries/glib/default.nix

@@ -191,8 +191,12 @@ stdenv.mkDerivation rec {
 
   passthru = rec {
     gioModuleDir = "lib/gio/modules";
-    makeSchemaPath = dir: name: "${dir}/share/gsettings-schemas/${name}/glib-2.0/schemas";
+
+    makeSchemaDataDirPath = dir: name: "${dir}/share/gsettings-schemas/${name}";
+    makeSchemaPath = dir: name: "${makeSchemaDataDirPath dir name}/glib-2.0/schemas";
     getSchemaPath = pkg: makeSchemaPath pkg pkg.name;
+    getSchemaDataDirPath = pkg: makeSchemaDataDirPath pkg pkg.name;
+
     inherit flattenInclude;
     updateScript = gnome.updateScript { packageName = "glib"; };
   };

pkgs/development/libraries/libadwaita/default.nix

@@ -73,7 +73,7 @@ stdenv.mkDerivation rec {
       # AdwSettings needs to be initialized from “org.gnome.desktop.interface” GSettings schema when portal is not used for color scheme.
       # It will not actually be used since the “color-scheme” key will only have been introduced in GNOME 42, falling back to detecting theme name.
       # See adw_settings_constructed function in https://gitlab.gnome.org/GNOME/libadwaita/commit/60ec69f0a5d49cad8a6d79e4ecefd06dc6e3db12
-      "XDG_DATA_DIRS=${glib.getSchemaPath gsettings-desktop-schemas}/../.."
+      "XDG_DATA_DIRS=${glib.getSchemaDataDirPath gsettings-desktop-schemas}"
 
       # Tests need a cache directory
       "HOME=$TMPDIR"

pkgs/development/libraries/libhandy/default.nix

@@ -94,7 +94,7 @@ stdenv.mkDerivation rec {
         # HdySettings needs to be initialized from “org.gnome.desktop.interface” GSettings schema when portal is not used for color scheme.
         # It will not actually be used since the “color-scheme” key will only have been introduced in GNOME 42, falling back to detecting theme name.
         # See hdy_settings_constructed function in https://gitlab.gnome.org/GNOME/libhandy/-/commit/bb68249b005c445947bfb2bee66c91d0fe9c41a4
-        "${glib.getSchemaPath gsettings-desktop-schemas}/../.."
+        (glib.getSchemaDataDirPath gsettings-desktop-schemas)
 
         # Some tests require icons
         "${hicolor-icon-theme}/share"