efl_ui_relative_layout: prevent infinite loop in chain calculation

Test Plan:
test code
```
EAPI_MAIN int
elm_main(int argc, char **argv)
{
   Eo *win, *layout, *btn1, *btn2, *btn3;

   win =  efl_add(EFL_UI_WIN_CLASS, efl_main_loop_get());
   layout = efl_add(EFL_UI_RELATIVE_LAYOUT_CLASS, win,
                    efl_content_set(win, efl_added));

   btn1 = efl_add(EFL_UI_BUTTON_CLASS, layout);
   btn2 = efl_add(EFL_UI_BUTTON_CLASS, layout);

   efl_ui_relative_layout_relation_right_set(layout, btn1, btn2, 0.0);
   efl_ui_relative_layout_relation_right_set(layout, btn2, btn1, 0.0);

   efl_ui_relative_layout_relation_left_set(layout, btn2, btn1, 1.0);
   efl_ui_relative_layout_relation_left_set(layout, btn1, btn2, 1.0);

   elm_run();
   return 0;
}
ELM_MAIN()
```

Reviewers: Jaehyun_Cho

Reviewed By: Jaehyun_Cho

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D9032

1 files changed, 9 insertions, 1 deletions

diff --git a/src/lib/elementary/efl_ui_relative_layout.c b/src/lib/elementary/efl_ui_relative_layout.c
index a0814cebad..7e8b6f3c01 100644
--- a/src/lib/elementary/efl_ui_relative_layout.c
+++ b/src/lib/elementary/efl_ui_relative_layout.c
@@ -218,7 +218,15 @@ _child_chain_calc(Efl_Ui_Relative_Layout_Child *child, Eina_Bool axis)
    // find head
    head = child;
    while (head == head->calc.to[START]->calc.to[END])
-     head = head->calc.to[START];
+     {
+        head = head->calc.to[START];
+        if (head == child)
+          {
+             ERR("%c-axis circular dependency when calculating \"%s\"(%p).",
+                 axis ? 'Y' : 'X', efl_class_name_get(child->obj), child->obj);
+             return EINA_TRUE;
+          }
+     }
 
    //calculate weight_sum
    aspect_type = !axis ? EFL_GFX_HINT_ASPECT_VERTICAL : EFL_GFX_HINT_ASPECT_HORIZONTAL;