media-keys: Handle 'Above_Tab' fake key

Mutter supports the 'Above_Tab' fake keysym that refers to the key
that is physically located above the tab key. It is used in the default
shortcut of the "Switch windows of an application" action.

As gtk_accelerator_parse() doesn't recognize the keysym, we display
the shortcut incorrectly as "disabled", and it is not taken into account
for conflict resolution.

Address this by translating binding that contains the 'Above_Tab' string
to bindings where the string is replaced with each possible keysym that
corresponds to the fixed keycode of KEY_GRAVE + 8.

https://gitlab.gnome.org/GNOME/gnome-control-center/issues/581

panels/keyboard/cc-keyboard-item.c

@@ -424,11 +424,119 @@ cc_keyboard_item_new (CcKeyboardItemType type)
   return CC_KEYBOARD_ITEM (object);
 }
 
+static guint *
+get_above_tab_keysyms (void)
+{
+  GdkKeymap *keymap = gdk_keymap_get_for_display (gdk_display_get_default ());
+  guint keycode = 0x29 /* KEY_GRAVE */ + 8;
+  g_autofree guint *keyvals = NULL;
+  GArray *keysyms;
+  int n_entries, i, j;
+
+  keysyms = g_array_new (TRUE, FALSE, sizeof (guint));
+
+  if (!gdk_keymap_get_entries_for_keycode (keymap, keycode, NULL, &keyvals, &n_entries))
+    goto out;
+
+  for (i = 0; i < n_entries; i++)
+    {
+      gboolean found = FALSE;
+
+      for (j = 0; j < keysyms->len; j++)
+        if (g_array_index (keysyms, guint, j) == keyvals[i])
+          {
+            found = TRUE;
+            break;
+          }
+
+      if (!found)
+        g_array_append_val (keysyms, keyvals[i]);
+    }
+
+out:
+  return (guint *)g_array_free (keysyms, FALSE);
+}
+
+/*
+ * translate_above_tab:
+ *
+ * @original_bindings: A list of accelerator strings
+ * @new_bindings: (out): Translated bindings if translation is needed
+ *
+ * Translate accelerator strings that contain the Above_Tab fake keysym
+ * used by mutter to strings that use the real keysyms that correspond
+ * to the key that is located physically above the tab key.
+ *
+ * Returns: %TRUE if strings were translated, %FALSE if @original_bindings
+ *   can be used unmodified
+ */
+static gboolean
+translate_above_tab (char **original_bindings,
+                     char ***new_bindings)
+{
+  GPtrArray *replaced_bindings;
+  g_autofree guint *above_tab_keysyms = NULL;
+  gboolean needs_translation = FALSE;
+  char **str;
+
+  for (str = original_bindings; *str && !needs_translation; str++)
+    needs_translation = strstr (*str, "Above_Tab") != NULL;
+
+  if (!needs_translation)
+    return FALSE;
+
+  above_tab_keysyms = get_above_tab_keysyms ();
+
+  replaced_bindings = g_ptr_array_new ();
+
+  for (str = original_bindings; *str; str++)
+    {
+      if (strstr (*str, "Above_Tab") == NULL)
+        {
+          g_ptr_array_add (replaced_bindings, g_strdup (*str));
+        }
+      else
+        {
+          g_auto (GStrv) split_str = g_strsplit (*str, "Above_Tab", -1);
+          int i;
+
+          for (i = 0; above_tab_keysyms[i]; i++)
+            {
+              g_autofree char *sym = NULL;
+
+              sym = gtk_accelerator_name (above_tab_keysyms[i], 0);
+              g_ptr_array_add (replaced_bindings, g_strjoinv (sym, split_str));
+            }
+        }
+      g_ptr_array_add (replaced_bindings, NULL);
+    }
+
+  *new_bindings = (char **)g_ptr_array_free (replaced_bindings, FALSE);
+  return TRUE;
+}
+
+static char *
+translate_binding_string (const char *str)
+{
+  g_autofree guint *above_tab_keysyms = NULL;
+  g_autofree char *symname = NULL;
+  g_auto (GStrv) split_str = NULL;
+
+  if (str == NULL || strstr (str, "Above_Tab") == NULL)
+    return g_strdup (str);
+
+  above_tab_keysyms = get_above_tab_keysyms ();
+  symname = gtk_accelerator_name (above_tab_keysyms[0], 0);
+
+  split_str = g_strsplit (str, "Above_Tab", -1);
+  return g_strjoinv (symname, split_str);
+}
+
 static GList *
 variant_get_key_combos (GVariant *variant)
 {
   GList *combos = NULL;
-  char **bindings = NULL, **str;
+  char **bindings = NULL, **translated_bindings, **str;
 
   if (g_variant_is_of_type (variant, G_VARIANT_TYPE_STRING))
     {
@@ -440,6 +548,12 @@ variant_get_key_combos (GVariant *variant)
       bindings = g_variant_dup_strv (variant, NULL);
     }
 
+  if (translate_above_tab (bindings, &translated_bindings))
+    {
+      g_strfreev (bindings);
+      bindings = translated_bindings;
+    }
+
   for (str = bindings; *str; str++)
     {
       CcKeyCombo *combo = g_new (CcKeyCombo, 1);
@@ -480,13 +594,13 @@ settings_get_binding (GSettings  *settings,
 
   variant = g_settings_get_value (settings, key);
   if (g_variant_is_of_type (variant, G_VARIANT_TYPE_STRING))
-    value = g_variant_dup_string (variant, NULL);
+    value = translate_binding_string (g_variant_get_string (variant, NULL));
   else if (g_variant_is_of_type (variant, G_VARIANT_TYPE_STRING_ARRAY))
     {
       const char **str_array;
 
       str_array = g_variant_get_strv (variant, NULL);
-      value = g_strdup (str_array[0]);
+      value = translate_binding_string (str_array[0]);
       g_free (str_array);
     }
   g_variant_unref (variant);