[ghex] config: Add GNOME 42+ compatibility for dark mode

[Logan Rathbone <larathbone src gnome org>]

commit 2adb05ec282a5becdc4a1c22fe894b2f1cc5c130
Author: Logan Rathbone <poprocks gmail com>
Date:   Sun Jun 12 18:22:35 2022 -0400

    config: Add GNOME 42+ compatibility for dark mode
    
    It might work. Maybe.

 src/configuration.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 47 insertions(+), 5 deletions(-)
---
diff --git a/src/configuration.c b/src/configuration.c
index 9ecccba..f2fc627 100644
--- a/src/configuration.c
+++ b/src/configuration.c
@@ -78,12 +78,54 @@ dark_mode_changed_cb (GSettings   *settings,
 void
 get_sys_default_is_dark (void)
 {
+       /* NOTE: for GTK 4.0 backwards compatibility, we manually define these
+        * here. If we wish to add an additional dependency on
+        * gsettings-desktop-schemas >= 42, this can be eliminated.
+        */
+       enum {
+               SYSTEM_DEFAULT,
+               SYSTEM_PREFER_DARK,
+               SYSTEM_PREFER_LIGHT,
+       } color_scheme;
+       GSettings *set;
        GtkSettings *gtk_settings;
-
-       gtk_settings = gtk_settings_get_default ();
-       g_object_get (gtk_settings,
-                       "gtk-application-prefer-dark-theme", &sys_default_is_dark,
-                       NULL);
+       GSettingsSchemaSource *source;
+       GSettingsSchema *schema;
+       char *schema_id = NULL;
+
+       source = g_settings_schema_source_get_default ();
+       schema = g_settings_schema_source_lookup (source, "org.freedesktop.appearance", TRUE);
+
+       if (schema && g_settings_schema_has_key (schema, "color-scheme"))
+       {
+               schema_id = "org.freedesktop.appearance";
+               g_settings_schema_unref (schema);
+       }
+       else
+       {
+               schema = g_settings_schema_source_lookup (source, "org.gnome.desktop.appearance", TRUE);
+               if (schema && g_settings_schema_has_key (schema, "color-scheme"))
+               {
+                       schema_id = "org.gnome.desktop.appearance";
+                       g_settings_schema_unref (schema);
+               }
+       }
+
+       if (schema_id)
+       {
+               set = g_settings_new (schema_id);
+               color_scheme = g_settings_get_enum (set, "color-scheme");
+               if (color_scheme == SYSTEM_PREFER_DARK)
+                       sys_default_is_dark = TRUE;
+               g_object_unref (set);
+       }
+       else
+       {
+               gtk_settings = gtk_settings_get_default ();
+               g_object_get (gtk_settings,
+                               "gtk-application-prefer-dark-theme", &sys_default_is_dark,
+                               NULL);
+       }
 }
 
 static void