glib: add g_build_filename_valist()

A new public API convenience to build a filename from a va_list.

https://bugzilla.gnome.org/show_bug.cgi?id=788488

docs/reference/glib/glib-sections.txt

@@ -1851,6 +1851,7 @@ g_path_get_basename
 g_path_get_dirname
 g_build_filename
 g_build_filenamev
+g_build_filename_valist
 g_build_path
 g_build_pathv
 

glib/gfileutils.c

@@ -1981,6 +1981,28 @@ g_build_filename_va (const gchar  *first_argument,
   return str;
 }
 
+/**
+ * g_build_filename_valist:
+ * @first_element: (type filename): the first element in the path
+ * @args: va_list of remaining elements in path
+ *
+ * Behaves exactly like g_build_filename(), but takes the path elements
+ * as a va_list. This function is mainly meant for language bindings.
+ *
+ * Returns: (type filename): a newly-allocated string that must be freed
+ *     with g_free().
+ *
+ * Since: 2.56
+ */
+gchar *
+g_build_filename_valist (const gchar  *first_element,
+                         va_list      *args)
+{
+  g_return_val_if_fail (first_element != NULL, NULL);
+
+  return g_build_filename_va (first_element, args, NULL);
+}
+
 /**
  * g_build_filenamev:
  * @args: (array zero-terminated=1) (element-type filename): %NULL-terminated

glib/gfileutils.h

@@ -131,6 +131,9 @@ gchar   *g_build_filename     (const gchar *first_element,
                                ...) G_GNUC_MALLOC G_GNUC_NULL_TERMINATED;
 GLIB_AVAILABLE_IN_ALL
 gchar   *g_build_filenamev    (gchar      **args) G_GNUC_MALLOC;
+GLIB_AVAILABLE_IN_2_56
+gchar   *g_build_filename_valist (const gchar  *first_element,
+                                  va_list      *args) G_GNUC_MALLOC;
 
 GLIB_AVAILABLE_IN_ALL
 gint     g_mkdir_with_parents (const gchar *pathname,