[gtk/matthiasc/atspi-child] a11y: Handle HIDDEN state changes

[Matthias Clasen <matthiasc src gnome org>]

commit b12992c1cbf96ed7b6c46caf0fc1de40a35b9c92
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Oct 24 11:14:18 2020 -0400

    a11y: Handle HIDDEN state changes
    
    Hidden elements are not presented in the accessible
    tree, so when then HIDDEN state changes, we should
    emit child-added or -removed signals.
    
    This commit does not yet handle all cases (HIDDEN
    toplevels or hidden stack pages are not handled),
    but it should cover the common case.

 gtk/a11y/gtkatspicontext.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)
---
diff --git a/gtk/a11y/gtkatspicontext.c b/gtk/a11y/gtkatspicontext.c
index be3cb128e6..18a1d7ff9c 100644
--- a/gtk/a11y/gtkatspicontext.c
+++ b/gtk/a11y/gtkatspicontext.c
@@ -34,7 +34,6 @@
 #include "gtkatspiutilsprivate.h"
 #include "gtkatspivalueprivate.h"
 #include "gtkatspicomponentprivate.h"
-
 #include "a11y/atspi/atspi-accessible.h"
 #include "a11y/atspi/atspi-action.h"
 #include "a11y/atspi/atspi-editabletext.h"
@@ -848,6 +847,29 @@ gtk_at_spi_context_state_change (GtkATContext                *ctx,
   if (!gtk_widget_get_realized (widget))
     return;
 
+  if (changed_states & GTK_ACCESSIBLE_STATE_CHANGE_HIDDEN)
+    {
+      GtkWidget *parent;
+      gboolean hidden;
+
+      value = gtk_accessible_attribute_set_get_value (states, GTK_ACCESSIBLE_STATE_HIDDEN);
+      hidden = gtk_boolean_accessible_value_get (value);
+
+      parent = gtk_widget_get_parent (widget);
+      if (parent)
+        {
+          if (GTK_IS_STACK (parent))
+            g_warning ("Setting GTK_ACCESSIBLE_STATE_HIDDEN on stack children is not supported");
+          else
+            gtk_at_context_child_changed (gtk_accessible_get_at_context (GTK_ACCESSIBLE (parent)),
+                                          hidden ? GTK_ACCESSIBLE_CHILD_CHANGE_REMOVED
+                                                 : GTK_ACCESSIBLE_CHILD_CHANGE_ADDED,
+                                          GTK_ACCESSIBLE (widget));
+        }
+      else
+        g_warning ("Setting GTK_ACCESSIBLE_STATE_HIDDEN on toplevels is not supported");
+    }
+
   if (changed_states & GTK_ACCESSIBLE_STATE_CHANGE_BUSY)
     {
       value = gtk_accessible_attribute_set_get_value (states, GTK_ACCESSIBLE_STATE_BUSY);