[libdazzle] util: add helper to get relative widget

[Christian Hergert <chergert src gnome org>]

commit 9d5a95512fc38c5cd5764cd44bc480ae6d6108f1
Author: Christian Hergert <chergert redhat com>
Date:   Sun Jul 9 18:26:55 2017 -0700

    util: add helper to get relative widget
    
    This is useful when you want to look through the semantic
    hierarchy rather than the real ->parent hierarchy.

 src/util/dzl-gtk.c |   30 ++++++++++++++++++++++++++++++
 src/util/dzl-gtk.h |    2 ++
 2 files changed, 32 insertions(+), 0 deletions(-)
---
diff --git a/src/util/dzl-gtk.c b/src/util/dzl-gtk.c
index 107861d..ee4fbbf 100644
--- a/src/util/dzl-gtk.c
+++ b/src/util/dzl-gtk.c
@@ -648,3 +648,33 @@ dzl_gtk_widget_is_ancestor_or_relative (GtkWidget *widget,
 
   return FALSE;
 }
+
+/**
+ * dzl_gtk_widget_get_relative:
+ * @widget: a #GtkWidget
+ * @relative_type: the type of widget to locate
+ *
+ * This is similar to gtk_widget_get_ancestor(), but looks for relatives
+ * via properties such as #GtkPopover:relative-to and others.
+ *
+ * Returns: (transfer none) (nullable): A #GtkWidget or %NULL.
+ */
+GtkWidget *
+dzl_gtk_widget_get_relative (GtkWidget *widget,
+                             GType      relative_type)
+{
+  g_return_val_if_fail (!widget || GTK_IS_WIDGET (widget), NULL);
+  g_return_val_if_fail (g_type_is_a (relative_type, GTK_TYPE_WIDGET), NULL);
+
+  if (widget == NULL)
+    return FALSE;
+
+  do
+    {
+      if (g_type_is_a (G_OBJECT_TYPE (widget), relative_type))
+        return widget;
+    }
+  while (NULL != (widget = get_parent_or_relative (widget)));
+
+  return NULL;
+}
diff --git a/src/util/dzl-gtk.h b/src/util/dzl-gtk.h
index 4956fea..42a0a0f 100644
--- a/src/util/dzl-gtk.h
+++ b/src/util/dzl-gtk.h
@@ -56,6 +56,8 @@ void          dzl_gtk_list_store_insert_sorted       (GtkListStore            *s
                                                       guint                    compare_column,
                                                       GCompareDataFunc         compare_func,
                                                       gpointer                 compare_data);
+GtkWidget    *dzl_gtk_widget_get_relative            (GtkWidget               *widget,
+                                                      GType                    relative_type);
 gboolean      dzl_gtk_widget_is_ancestor_or_relative (GtkWidget               *widget,
                                                       GtkWidget               *ancestor);