prefs: Track the XKB 'grp:' option in gsettings as a keybinding pref

We'll use the value of this option to establish a passive grab on the
keycode/modifier combos generating XK_ISO_Next_Group.

https://bugzilla.gnome.org/show_bug.cgi?id=697002

src/core/prefs.c

@@ -55,6 +55,7 @@
 #define KEY_GNOME_ANIMATIONS "enable-animations"
 #define KEY_GNOME_CURSOR_THEME "cursor-theme"
 #define KEY_GNOME_CURSOR_SIZE "cursor-size"
+#define KEY_XKB_OPTIONS "xkb-options"
 
 #define KEY_OVERLAY_KEY "overlay-key"
 #define KEY_WORKSPACES_ONLY_ON_PRIMARY "workspaces-only-on-primary"
@@ -65,6 +66,7 @@
 #define SCHEMA_GENERAL         "org.gnome.desktop.wm.preferences"
 #define SCHEMA_MUTTER          "org.gnome.mutter"
 #define SCHEMA_INTERFACE       "org.gnome.desktop.interface"
+#define SCHEMA_INPUT_SOURCES   "org.gnome.desktop.input-sources"
 
 #define SETTINGS(s) g_hash_table_lookup (settings_schemas, (s))
 
@@ -115,6 +117,7 @@ static gboolean workspaces_only_on_primary = FALSE;
 
 static gboolean no_tab_popup = FALSE;
 
+static char *iso_next_group_option = NULL;
 
 static void handle_preference_update_enum (GSettings *settings,
                                            gchar     *key);
@@ -139,6 +142,7 @@ static gboolean theme_name_handler (GVariant*, gpointer*, gpointer);
 static gboolean mouse_button_mods_handler (GVariant*, gpointer*, gpointer);
 static gboolean button_layout_handler (GVariant*, gpointer*, gpointer);
 static gboolean overlay_key_handler (GVariant*, gpointer*, gpointer);
+static gboolean iso_next_group_handler (GVariant*, gpointer*, gpointer);
 
 static void     do_override               (char *key, char *schema);
 
@@ -451,6 +455,14 @@ static MetaStringArrayPreference preferences_string_array[] =
       NULL,
       &workspace_names,
     },
+    {
+      { KEY_XKB_OPTIONS,
+        SCHEMA_INPUT_SOURCES,
+        META_PREF_KEYBINDINGS,
+      },
+      iso_next_group_handler,
+      NULL,
+    },
     { { NULL, 0, 0 }, NULL },
   };
 
@@ -961,6 +973,11 @@ meta_prefs_init (void)
                     G_CALLBACK (settings_changed), NULL);
   g_hash_table_insert (settings_schemas, g_strdup (SCHEMA_INTERFACE), settings);
 
+  settings = g_settings_new (SCHEMA_INPUT_SOURCES);
+  g_signal_connect (settings, "changed::" KEY_XKB_OPTIONS,
+                    G_CALLBACK (settings_changed), NULL);
+  g_hash_table_insert (settings_schemas, g_strdup (SCHEMA_INPUT_SOURCES), settings);
+
 
   for (tmp = overridden_keys; tmp; tmp = tmp->next)
     {
@@ -1652,6 +1669,39 @@ overlay_key_handler (GVariant *value,
   return TRUE;
 }
 
+static gboolean
+iso_next_group_handler (GVariant *value,
+                        gpointer *result,
+                        gpointer  data)
+{
+  const char **xkb_options, **p;
+  const char *option = NULL;
+  gboolean changed = FALSE;
+
+  *result = NULL; /* ignored */
+  xkb_options = g_variant_get_strv (value, NULL);
+
+  for (p = xkb_options; p && *p; ++p)
+    if (g_str_has_prefix (*p, "grp:"))
+      {
+        option = (*p + 4);
+        break;
+      }
+
+  changed = (g_strcmp0 (option, iso_next_group_option) != 0);
+
+  if (changed)
+    {
+      g_free (iso_next_group_option);
+      iso_next_group_option = g_strdup (option);
+      queue_changed (META_PREF_KEYBINDINGS);
+    }
+
+  g_free (xkb_options);
+
+  return TRUE;
+}
+
 const PangoFontDescription*
 meta_prefs_get_titlebar_font (void)
 {
@@ -2155,6 +2205,12 @@ meta_prefs_get_overlay_binding (MetaKeyCombo *combo)
   *combo = overlay_key_combo;
 }
 
+const char *
+meta_prefs_get_iso_next_group_option (void)
+{
+  return iso_next_group_option;
+}
+
 GDesktopTitlebarAction
 meta_prefs_get_action_double_click_titlebar (void)
 {

src/meta/prefs.h

@@ -353,6 +353,7 @@ typedef enum _MetaKeyBindingAction
   META_KEYBINDING_ACTION_MOVE_TO_SIDE_W,
   META_KEYBINDING_ACTION_MOVE_TO_CENTER,
   META_KEYBINDING_ACTION_OVERLAY_KEY,
+  META_KEYBINDING_ACTION_ISO_NEXT_GROUP,
 
   META_KEYBINDING_ACTION_LAST
 } MetaKeyBindingAction;
@@ -442,6 +443,7 @@ void meta_prefs_get_window_binding (const char          *name,
                                     MetaVirtualModifier *modifiers);
 
 void meta_prefs_get_overlay_binding (MetaKeyCombo *combo);
+const char *meta_prefs_get_iso_next_group_option (void);
 
 gboolean           meta_prefs_get_visual_bell      (void);
 gboolean           meta_prefs_bell_is_audible      (void);