[mutter] window-props: Don't look for parent multiple times

[Marco Trevisan <marcotrevi src gnome org>]

commit c85fb107c0556283062f2bf9b8d990f1e2c0acae
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Tue Oct 29 17:14:43 2019 +0100

    window-props: Don't look for parent multiple times
    
    Once we set the transient_for, we look for parent MetaWindow, so instead
    of overwriting this value for loops check, just use another function
    and avoid to look for the xwindow again when setting the MetaWindow parent.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/895

 src/x11/window-props.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)
---
diff --git a/src/x11/window-props.c b/src/x11/window-props.c
index 48454befe..2564909a9 100644
--- a/src/x11/window-props.c
+++ b/src/x11/window-props.c
@@ -1625,6 +1625,22 @@ reload_wm_hints (MetaWindow    *window,
   meta_window_queue (window, META_QUEUE_UPDATE_ICON | META_QUEUE_MOVE_RESIZE);
 }
 
+static gboolean
+check_xtransient_for_loop (MetaWindow *window,
+                           MetaWindow *parent)
+{
+  while (parent)
+    {
+      if (parent == window)
+        return TRUE;
+
+      parent = meta_x11_display_lookup_x_window (parent->display->x11_display,
+                                                 parent->xtransient_for);
+    }
+
+  return FALSE;
+}
+
 static void
 reload_transient_for (MetaWindow    *window,
                       MetaPropValue *value,
@@ -1647,18 +1663,11 @@ reload_transient_for (MetaWindow    *window,
         }
 
       /* Make sure there is not a loop */
-      while (parent)
+      if (check_xtransient_for_loop (window, parent))
         {
-          if (parent == window)
-            {
-              meta_warning ("WM_TRANSIENT_FOR window 0x%lx for %s would create loop.\n",
-                            transient_for, window->desc);
-              transient_for = None;
-              break;
-            }
-
-          parent = meta_x11_display_lookup_x_window (parent->display->x11_display,
-                                                     parent->xtransient_for);
+          meta_warning ("WM_TRANSIENT_FOR window 0x%lx for %s would create a "
+                        "loop.\n", transient_for, window->desc);
+          transient_for = None;
         }
     }
   else
@@ -1679,8 +1688,6 @@ reload_transient_for (MetaWindow    *window,
     meta_window_set_transient_for (window, NULL);
   else
     {
-      parent = meta_x11_display_lookup_x_window (window->display->x11_display,
-                                                 window->xtransient_for);
       meta_window_set_transient_for (window, parent);
     }
 }