gsettingsschema: Allow per-desktop overrides

Recognise a new 'd' option in schema keys which gives a dictionary of
per-desktop default values. This dictionary is searched for the items
found in XDG_CURRENT_DESKTOP, in the order. If nothing matches (or if
the option is missing) then the default value is used as before.

This feature was requested by Alberts Muktupāvels and this patch is
based on an approach devised by them.

https://bugzilla.gnome.org/show_bug.cgi?id=746592

gio/gsettings.c

@@ -1739,6 +1739,13 @@ g_settings_get_mapped (GSettings           *settings,
       if (okay) goto okay;
     }
 
+  if ((value = g_settings_schema_key_get_per_desktop_default (&skey)))
+    {
+      okay = mapping (value, &result, user_data);
+      g_variant_unref (value);
+      if (okay) goto okay;
+    }
+
   if (mapping (skey.default_value, &result, user_data))
     goto okay;
 
@@ -2646,6 +2653,20 @@ g_settings_binding_key_changed (GSettings   *settings,
         }
     }
 
+  if (variant == NULL)
+    {
+      variant = g_settings_schema_key_get_per_desktop_default (&binding->key);
+      if (variant &&
+          !binding->get_mapping (&value, variant, binding->user_data))
+        {
+          g_error ("Per-desktop default value for key '%s' in schema '%s' "
+                   "was rejected by the binding mapping function.",
+                   binding->key.name, g_settings_schema_get_id (binding->key.schema));
+          g_variant_unref (variant);
+          variant = NULL;
+        }
+    }
+
   if (variant == NULL)
     {
       variant = g_variant_ref (binding->key.default_value);

gio/gsettingsschema-internal.h

@@ -37,6 +37,7 @@ struct _GSettingsSchemaKey
   const GVariantType *type;
   GVariant *minimum, *maximum;
   GVariant *default_value;
+  GVariant *desktop_overrides;
 
   gint ref_count;
 };
@@ -58,6 +59,7 @@ gboolean                g_settings_schema_key_type_check                (GSettin
 GVariant *              g_settings_schema_key_range_fixup               (GSettingsSchemaKey *key,
                                                                          GVariant           *value);
 GVariant *              g_settings_schema_key_get_translated_default    (GSettingsSchemaKey *key);
+GVariant *              g_settings_schema_key_get_per_desktop_default   (GSettingsSchemaKey *key);
 
 gint                    g_settings_schema_key_to_enum                   (GSettingsSchemaKey *key,
                                                                          GVariant           *value);

gio/gsettingsschema.c

@@ -27,6 +27,7 @@
 #include <glibintl.h>
 #include <locale.h>
 #include <string.h>
+#include <stdlib.h>
 
 /**
  * SECTION:gsettingsschema
@@ -1283,6 +1284,11 @@ g_settings_schema_key_init (GSettingsSchemaKey *key,
           endian_fixup (&key->maximum);
           break;
 
+        case 'd':
+          g_variant_get (data, "@a{sv}", &key->desktop_overrides);
+          endian_fixup (&key->desktop_overrides);
+          break;
+
         default:
           g_warning ("unknown schema extension '%c'", code);
           break;
@@ -1303,6 +1309,9 @@ g_settings_schema_key_clear (GSettingsSchemaKey *key)
   if (key->maximum)
     g_variant_unref (key->maximum);
 
+  if (key->desktop_overrides)
+    g_variant_unref (key->desktop_overrides);
+
   g_variant_unref (key->default_value);
 
   g_settings_schema_unref (key->schema);
@@ -1410,6 +1419,35 @@ g_settings_schema_key_get_translated_default (GSettingsSchemaKey *key)
   return value;
 }
 
+GVariant *
+g_settings_schema_key_get_per_desktop_default (GSettingsSchemaKey *key)
+{
+  static const gchar * const *current_desktops;
+  GVariant *value = NULL;
+  gint i;
+
+  if (!key->desktop_overrides)
+    return NULL;
+
+  if (g_once_init_enter (&current_desktops))
+    {
+      const gchar *xdg_current_desktop = g_getenv ("XDG_CURRENT_DESKTOP");
+      gchar **tmp;
+
+      if (xdg_current_desktop != NULL && xdg_current_desktop[0] != '\0')
+        tmp = g_strsplit (xdg_current_desktop, G_SEARCHPATH_SEPARATOR_S, -1);
+      else
+        tmp = g_new0 (gchar *, 0 + 1);
+
+      g_once_init_leave (&current_desktops, (const gchar **) tmp);
+    }
+
+  for (i = 0; value == NULL && current_desktops[i] != NULL; i++)
+    value = g_variant_lookup_value (key->desktop_overrides, current_desktops[i], NULL);
+
+  return value;
+}
+
 gint
 g_settings_schema_key_to_enum (GSettingsSchemaKey *key,
                                GVariant           *value)
@@ -1698,6 +1736,9 @@ g_settings_schema_key_get_default_value (GSettingsSchemaKey *key)
 
   value = g_settings_schema_key_get_translated_default (key);
 
+  if (!value)
+    value = g_settings_schema_key_get_per_desktop_default (key);
+
   if (!value)
     value = g_variant_ref (key->default_value);