app: use GWeakRef instead of g_object_add_weak_pointer().

Other than multi-threading (which here is not the problem), using
GWeakRef has the other advantage that it makes the type of pointer
obvious, hence avoiding the kind of errors as fixed in commit 12df7960.
One can't just change the pointer value directly, and has to use
g_weak_ref_set(), so such problem won't happen again.

app/tools/gimpgegltool.c

@@ -392,6 +392,7 @@ gimp_gegl_tool_dialog (GimpFilterTool *filter_tool)
   GtkWidget         *main_vbox;
   GtkWidget         *hbox;
   GtkWidget         *combo;
+  GtkWidget         *options_gui;
   GList             *opclasses;
   GList             *iter;
 
@@ -474,17 +475,15 @@ gimp_gegl_tool_dialog (GimpFilterTool *filter_tool)
   gtk_box_reorder_child (GTK_BOX (main_vbox), tool->description_label, 1);
 
   /*  The options vbox  */
-  o_tool->options_gui =
-    gtk_label_new (_("Select an operation from the list above"));
-  g_object_add_weak_pointer (G_OBJECT (o_tool->options_gui),
-                             (gpointer) &o_tool->options_gui);
-  gimp_label_set_attributes (GTK_LABEL (o_tool->options_gui),
+  options_gui = gtk_label_new (_("Select an operation from the list above"));
+  gimp_label_set_attributes (GTK_LABEL (options_gui),
                              PANGO_ATTR_STYLE, PANGO_STYLE_ITALIC,
                              -1);
-  gtk_misc_set_padding (GTK_MISC (o_tool->options_gui), 0, 4);
+  gtk_misc_set_padding (GTK_MISC (options_gui), 0, 4);
   gtk_container_add (GTK_CONTAINER (o_tool->options_box),
-                     o_tool->options_gui);
-  gtk_widget_show (o_tool->options_gui);
+                     options_gui);
+  g_weak_ref_set (&o_tool->options_gui_ref, options_gui);
+  gtk_widget_show (options_gui);
 }
 
 static void

app/tools/gimpoperationtool.c

@@ -188,13 +188,19 @@ gimp_operation_tool_initialize (GimpTool     *tool,
 
       if (filter_tool->config)
         {
-          gimp_operation_tool_sync_op (op_tool, TRUE);
+          GtkWidget *options_gui;
 
-          if (! op_tool->options_gui)
+          gimp_operation_tool_sync_op (op_tool, TRUE);
+          options_gui = g_weak_ref_get (&op_tool->options_gui_ref);
+          if (! options_gui)
             {
               gimp_operation_tool_create_gui (op_tool);
               gimp_operation_tool_add_gui (op_tool);
             }
+          else
+            {
+              g_object_unref (options_gui);
+            }
         }
 
       return TRUE;
@@ -273,6 +279,7 @@ gimp_operation_tool_dialog (GimpFilterTool *filter_tool)
 {
   GimpOperationTool *op_tool = GIMP_OPERATION_TOOL (filter_tool);
   GtkWidget         *main_vbox;
+  GtkWidget         *options_gui;
 
   main_vbox = gimp_filter_tool_dialog_get_vbox (filter_tool);
 
@@ -285,8 +292,12 @@ gimp_operation_tool_dialog (GimpFilterTool *filter_tool)
   g_object_add_weak_pointer (G_OBJECT (op_tool->options_box),
                              (gpointer) &op_tool->options_box);
 
-  if (op_tool->options_gui)
-    gimp_operation_tool_add_gui (op_tool);
+  options_gui = g_weak_ref_get (&op_tool->options_gui_ref);
+  if (options_gui)
+    {
+      gimp_operation_tool_add_gui (op_tool);
+      g_object_unref (options_gui);
+    }
 }
 
 static void
@@ -497,13 +508,14 @@ static void
 gimp_operation_tool_create_gui (GimpOperationTool *op_tool)
 {
   GimpFilterTool *filter_tool = GIMP_FILTER_TOOL (op_tool);
+  GtkWidget      *options_gui;
   gint            off_x, off_y;
   GeglRectangle   area;
   gint            aux;
 
   gimp_filter_tool_get_drawable_area (filter_tool, &off_x, &off_y, &area);
 
-  op_tool->options_gui =
+  options_gui =
     gimp_prop_gui_new (G_OBJECT (filter_tool->config),
                        G_TYPE_FROM_INSTANCE (filter_tool->config), 0,
                        &area,
@@ -511,9 +523,7 @@ gimp_operation_tool_create_gui (GimpOperationTool *op_tool)
                        (GimpCreatePickerFunc) gimp_filter_tool_add_color_picker,
                        (GimpCreateControllerFunc) gimp_filter_tool_add_controller,
                        filter_tool);
-
-  g_object_add_weak_pointer (G_OBJECT (op_tool->options_gui),
-                             (gpointer) &op_tool->options_gui);
+  g_weak_ref_set (&op_tool->options_gui_ref, options_gui);
 
   for (aux = 1; ; aux++)
     {
@@ -554,8 +564,12 @@ static void
 gimp_operation_tool_add_gui (GimpOperationTool *op_tool)
 {
   GtkSizeGroup *size_group  = NULL;
+  GtkWidget    *options_gui;
   GList        *list;
 
+  options_gui = g_weak_ref_get (&op_tool->options_gui_ref);
+  g_return_if_fail (options_gui);
+
   for (list = op_tool->aux_inputs; list; list = g_list_next (list))
     {
       AuxInput  *input = list->data;
@@ -577,9 +591,10 @@ gimp_operation_tool_add_gui (GimpOperationTool *op_tool)
   if (size_group)
     g_object_unref (size_group);
 
-  gtk_box_pack_start (GTK_BOX (op_tool->options_box), op_tool->options_gui,
+  gtk_box_pack_start (GTK_BOX (op_tool->options_box), options_gui,
                       TRUE, TRUE, 0);
-  gtk_widget_show (op_tool->options_gui);
+  gtk_widget_show (options_gui);
+  g_object_unref (options_gui);
 }
 
 
@@ -682,6 +697,7 @@ gimp_operation_tool_set_operation (GimpOperationTool *op_tool,
 {
   GimpTool       *tool;
   GimpFilterTool *filter_tool;
+  GtkWidget      *options_gui;
 
   g_return_if_fail (GIMP_IS_OPERATION_TOOL (op_tool));
 
@@ -705,11 +721,12 @@ gimp_operation_tool_set_operation (GimpOperationTool *op_tool,
 
   gimp_filter_tool_set_widget (filter_tool, NULL);
 
-  if (op_tool->options_gui)
+  options_gui = g_weak_ref_get (&op_tool->options_gui_ref);
+  if (options_gui)
     {
       gimp_filter_tool_disable_color_picking (filter_tool);
-
-      gtk_widget_destroy (op_tool->options_gui);
+      g_object_unref (options_gui);
+      gtk_widget_destroy (options_gui);
     }
 
   if (! operation)

app/tools/gimpoperationtool.h

@@ -44,7 +44,7 @@ struct _GimpOperationTool
 
   /* dialog */
   GtkWidget      *options_box;
-  GtkWidget      *options_gui;
+  GWeakRef        options_gui_ref;
 };
 
 struct _GimpOperationToolClass