[gtk/matthiasc/for-master: 2/6] checkbutton: Add a warning about cyclic groups

[Matthias Clasen <matthiasc src gnome org>]

commit ee837dfc1230f0a5cc398c3e2bfb32aac369dadd
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Mar 17 07:37:33 2021 -0400

    checkbutton: Add a warning about cyclic groups
    
    Setting up check or toggle button group relationships
    in a cycle will lead to lockups. Add a warning about
    this, and catch the simplest case with a precondition
    check.
    
    Fixes: #3763

 gtk/gtkcheckbutton.c  | 3 +++
 gtk/gtktogglebutton.c | 3 +++
 2 files changed, 6 insertions(+)
---
diff --git a/gtk/gtkcheckbutton.c b/gtk/gtkcheckbutton.c
index 366fd2398c..e9a30a1ce3 100644
--- a/gtk/gtkcheckbutton.c
+++ b/gtk/gtkcheckbutton.c
@@ -913,6 +913,8 @@ gtk_check_button_set_label (GtkCheckButton *self,
  * Setting the group of a check button also changes the css name of the
  * indicator widget's CSS node to 'radio'.
  *
+ * Setting up groups in a cycle leads to undefined behavior.
+ *
  * Note that the same effect can be achieved via the [interface@Gtk.Actionable]
  * API, by using the same action with parameter type and state type 's'
  * for all buttons in the group, and giving each button its own target
@@ -926,6 +928,7 @@ gtk_check_button_set_group (GtkCheckButton *self,
   GtkCheckButtonPrivate *group_priv = gtk_check_button_get_instance_private (group);
 
   g_return_if_fail (GTK_IS_CHECK_BUTTON (self));
+  g_return_if_fail (self != group);
 
   if (!group)
     {
diff --git a/gtk/gtktogglebutton.c b/gtk/gtktogglebutton.c
index 6ae96fc8af..1e53a896c6 100644
--- a/gtk/gtktogglebutton.c
+++ b/gtk/gtktogglebutton.c
@@ -473,6 +473,8 @@ gtk_toggle_button_toggled (GtkToggleButton *toggle_button)
  * In a group of multiple toggle buttons, only one button can be active
  * at a time.
  *
+ * Setting up groups in a cycle leads to undefined behavior.
+ *
  * Note that the same effect can be achieved via the [interface@Gtk.Actionable]
  * API, by using the same action with parameter type and state type 's'
  * for all buttons in the group, and giving each button its own target
@@ -486,6 +488,7 @@ gtk_toggle_button_set_group (GtkToggleButton *toggle_button,
   GtkToggleButtonPrivate *group_priv = gtk_toggle_button_get_instance_private (group);
 
   g_return_if_fail (GTK_IS_TOGGLE_BUTTON (toggle_button));
+  g_return_if_fail (toggle_button != group);
 
   if (!group)
     {