[gtk/wip/otte/listmodel: 14/21] propertylookuplistmodel: Add

[Benjamin Otte <otte src gnome org>]

commit 416f8d59528ef82c78ef8bc7b348cedf84b2abc7
Author: Benjamin Otte <otte redhat com>
Date:   Mon Sep 10 17:01:57 2018 +0200

    propertylookuplistmodel: Add
    
    This model just takes an object and a property name and recursively
    looks it up. In particular, I want it for:
    
    widget, widget.parent, widget.parent.parent, ...

 gtk/gtkpropertylookuplistmodel.c        | 480 ++++++++++++++++++++++++++++++++
 gtk/gtkpropertylookuplistmodelprivate.h |  50 ++++
 gtk/meson.build                         |   1 +
 testsuite/gtk/meson.build               |   1 +
 testsuite/gtk/propertylookuplistmodel.c | 242 ++++++++++++++++
 5 files changed, 774 insertions(+)
---
diff --git a/gtk/gtkpropertylookuplistmodel.c b/gtk/gtkpropertylookuplistmodel.c
new file mode 100644
index 0000000000..0c0dc4ea91
--- /dev/null
+++ b/gtk/gtkpropertylookuplistmodel.c
@@ -0,0 +1,480 @@
+/*
+ * Copyright © 2018 Benjamin Otte
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Benjamin Otte <otte gnome org>
+ */
+
+
+/*
+ * SECTION:gtkpropertylookuplistmodel
+ * @Short_description: a List model for property lookups
+ * @Title: GtkPropertyLookupListModel
+ * @See_also: #GListModel
+ *
+ * #GtkPropertyLookupListModel is a #GListModel implementation that takes an
+ * object and a property and then recursively looks up the next element using
+ * the property on the previous object.
+ *
+ * For example, one could use this list model with the GtkWidget:parent property
+ * to get a list of a widgets and all its ancestors.
+ **/
+
+#include "config.h"
+
+#include "gtkpropertylookuplistmodelprivate.h"
+
+#include "gtkintl.h"
+#include "gtkprivate.h"
+
+enum {
+  PROP_0,
+  PROP_ITEM_TYPE,
+  PROP_OBJECT,
+  PROP_PROPERTY,
+  NUM_PROPERTIES
+};
+
+struct _GtkPropertyLookupListModel
+{
+  GObject parent_instance;
+
+  GType item_type;
+  char *property;
+  GPtrArray *items; /* list of items - lazily expanded if there's a NULL sentinel */
+};
+
+struct _GtkPropertyLookupListModelClass
+{
+  GObjectClass parent_class;
+};
+
+static GParamSpec *properties[NUM_PROPERTIES] = { NULL, };
+
+static GType
+gtk_property_lookup_list_model_get_item_type (GListModel *list)
+{
+  GtkPropertyLookupListModel *self = GTK_PROPERTY_LOOKUP_LIST_MODEL (list);
+
+  return self->item_type;
+}
+
+static gboolean
+gtk_property_lookup_list_model_is_infinite (GtkPropertyLookupListModel *self)
+{
+  if (self->items->len == 0)
+    return FALSE;
+
+  return g_ptr_array_index (self->items, self->items->len - 1) == NULL;
+}
+
+static void
+gtk_property_lookup_list_model_notify_cb (GObject                    *object,
+                                          GParamSpec                 *pspec,
+                                          GtkPropertyLookupListModel *self);
+
+static guint
+gtk_property_lookup_list_model_clear (GtkPropertyLookupListModel *self,
+                                      guint                       remaining)
+{
+  guint i;
+
+  for (i = remaining; i < self->items->len; i++)
+    {
+      gpointer object = g_ptr_array_index (self->items, i);
+      if (object == NULL)
+        break;
+
+      g_signal_handlers_disconnect_by_func (object, gtk_property_lookup_list_model_notify_cb, self);
+      g_object_unref (object);
+    }
+
+  /* keeps the sentinel, yay! */
+  g_ptr_array_remove_range (self->items, remaining, i - remaining);
+
+  return i - remaining;
+}
+
+static guint
+gtk_property_lookup_list_model_append (GtkPropertyLookupListModel *self,
+                                       guint                       n_items)
+{
+  gpointer last, next;
+  guint i, start;
+
+  g_assert (self->items->len > 0);
+  g_assert (!gtk_property_lookup_list_model_is_infinite (self));
+
+  last = g_ptr_array_index (self->items, self->items->len - 1);
+  start = self->items->len;
+  for (i = start; i < n_items; i++)
+    {
+      g_object_get (last, self->property, &next, NULL);
+      if (next == NULL)
+        return i - start;
+      
+      g_signal_connect_closure_by_id (next,
+                                      g_signal_lookup ("notify", G_OBJECT_TYPE (next)),
+                                      g_quark_from_static_string (self->property),
+                                      g_cclosure_new (G_CALLBACK (gtk_property_lookup_list_model_notify_cb), 
G_OBJECT (self), NULL),
+                                      FALSE);
+
+      g_ptr_array_add (self->items, next);
+      last = next;
+    }
+
+  return i - start;
+}
+
+static void
+gtk_property_lookup_list_model_ensure (GtkPropertyLookupListModel *self,
+                                       guint                       n_items)
+{
+  if (!gtk_property_lookup_list_model_is_infinite (self))
+    return;
+
+  if (self->items->len - 1 >= n_items)
+    return;
+  
+  /* remove NULL sentinel */
+  g_ptr_array_remove_index (self->items, self->items->len - 1);
+
+  if (self->items->len == 0)
+    return;
+
+  if (gtk_property_lookup_list_model_append (self, n_items) == n_items)
+    {
+      /* readd NULL sentinel */
+      g_ptr_array_add (self->items, NULL);
+    }
+}
+
+static void
+gtk_property_lookup_list_model_notify_cb (GObject                    *object,
+                                          GParamSpec                 *pspec,
+                                          GtkPropertyLookupListModel *self)
+{
+  guint position, removed, added;
+
+  if (!g_ptr_array_find (self->items, object, &position))
+    {
+      /* can only happen if we forgot to disconnect a signal handler */
+      g_assert_not_reached ();
+    }
+  /* we found the position of the item that notified, but the first change
+   * is its child.
+   */
+  position++;
+
+  removed = gtk_property_lookup_list_model_clear (self, position);
+
+  if (!gtk_property_lookup_list_model_is_infinite (self))
+    added = gtk_property_lookup_list_model_append (self, G_MAXUINT);
+  else
+    added = 0;
+
+  if (removed > 0 || added > 0)
+    g_list_model_items_changed (G_LIST_MODEL (self), position, removed, added);
+}
+
+static guint
+gtk_property_lookup_list_model_get_n_items (GListModel *list)
+{
+  GtkPropertyLookupListModel *self = GTK_PROPERTY_LOOKUP_LIST_MODEL (list);
+
+  gtk_property_lookup_list_model_ensure (self, G_MAXUINT);
+
+  return self->items->len;
+}
+
+static gpointer
+gtk_property_lookup_list_model_get_item (GListModel *list,
+                                         guint       position)
+{
+  GtkPropertyLookupListModel *self = GTK_PROPERTY_LOOKUP_LIST_MODEL (list);
+
+  gtk_property_lookup_list_model_ensure (self, position + 1);
+
+  if (position >= self->items->len)
+    return NULL;
+
+  return g_object_ref (g_ptr_array_index (self->items, position));
+}
+
+static void
+gtk_property_lookup_list_model_list_model_init (GListModelInterface *iface)
+{
+  iface->get_item_type = gtk_property_lookup_list_model_get_item_type;
+  iface->get_n_items = gtk_property_lookup_list_model_get_n_items;
+  iface->get_item = gtk_property_lookup_list_model_get_item;
+}
+
+G_DEFINE_TYPE_WITH_CODE (GtkPropertyLookupListModel, gtk_property_lookup_list_model,
+                         G_TYPE_OBJECT,
+                         G_IMPLEMENT_INTERFACE (G_TYPE_LIST_MODEL, 
gtk_property_lookup_list_model_list_model_init))
+
+static gboolean
+check_pspec (GType       type,
+             GParamSpec *pspec)
+{
+  if (pspec == NULL)
+    return FALSE;
+
+  if (!G_IS_PARAM_SPEC_OBJECT (pspec))
+    return FALSE;
+
+  if (!g_type_is_a (G_PARAM_SPEC (pspec)->value_type, type))
+    return FALSE;
+
+  return TRUE;
+}
+
+static gboolean
+lookup_pspec (GType       type,
+              const char *name)
+{
+  gboolean result;
+
+  if (g_type_is_a (type, G_TYPE_INTERFACE))
+    {
+      gpointer iface;
+      GParamSpec *pspec;
+
+      iface = g_type_default_interface_ref (type);
+      pspec = g_object_interface_find_property (iface, name);
+      result = check_pspec (type, pspec);
+      g_type_default_interface_unref (iface);
+    }
+  else
+    {
+      GObjectClass *klass;
+      GParamSpec *pspec;
+
+      klass = g_type_class_ref (type);
+      g_return_val_if_fail (klass != NULL, FALSE);
+      pspec = g_object_class_find_property (klass, name);
+      result = check_pspec (type, pspec);
+      g_type_class_unref (klass);
+    }
+
+  return result;
+}
+
+static void
+gtk_property_lookup_list_model_set_property (GObject      *object,
+                                             guint         prop_id,
+                                             const GValue *value,
+                                             GParamSpec   *pspec)
+{
+  GtkPropertyLookupListModel *self = GTK_PROPERTY_LOOKUP_LIST_MODEL (object);
+
+  switch (prop_id)
+    {
+    case PROP_ITEM_TYPE:
+      self->item_type = g_value_get_gtype (value);
+      g_return_if_fail (self->item_type != 0);
+      break;
+
+    case PROP_OBJECT:
+      gtk_property_lookup_list_model_set_object (self, g_value_get_object (value));
+      break;
+
+    case PROP_PROPERTY:
+      self->property = g_value_dup_string (value);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+
+  if (self->property && self->item_type &&
+      !lookup_pspec (self->item_type, self->property))
+    {
+      g_critical ("type %s has no property named \"%s\"", g_type_name (self->item_type), self->property);
+    }
+}
+
+static void 
+gtk_property_lookup_list_model_get_property (GObject     *object,
+                                             guint        prop_id,
+                                             GValue      *value,
+                                             GParamSpec  *pspec)
+{
+  GtkPropertyLookupListModel *self = GTK_PROPERTY_LOOKUP_LIST_MODEL (object);
+
+  switch (prop_id)
+    {
+    case PROP_ITEM_TYPE:
+      g_value_set_gtype (value, self->item_type);
+      break;
+
+    case PROP_OBJECT:
+      g_value_set_object (value, gtk_property_lookup_list_model_get_object (self));
+      break;
+
+    case PROP_PROPERTY:
+      g_value_set_object (value, self->property);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_property_lookup_list_model_dispose (GObject *object)
+{
+  GtkPropertyLookupListModel *self = GTK_PROPERTY_LOOKUP_LIST_MODEL (object);
+
+  gtk_property_lookup_list_model_clear (self, 0);
+
+  G_OBJECT_CLASS (gtk_property_lookup_list_model_parent_class)->dispose (object);
+}
+
+static void
+gtk_property_lookup_list_model_finalize (GObject *object)
+{
+  GtkPropertyLookupListModel *self = GTK_PROPERTY_LOOKUP_LIST_MODEL (object);
+
+  g_ptr_array_unref (self->items);
+  g_free (self->property);
+
+  G_OBJECT_CLASS (gtk_property_lookup_list_model_parent_class)->finalize (object);
+}
+
+static void
+gtk_property_lookup_list_model_class_init (GtkPropertyLookupListModelClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->get_property = gtk_property_lookup_list_model_get_property;
+  object_class->set_property = gtk_property_lookup_list_model_set_property;
+  object_class->dispose = gtk_property_lookup_list_model_dispose;
+  object_class->finalize = gtk_property_lookup_list_model_finalize;
+
+  /**
+   * GtkPropertyLookupListModel:item-type:
+   *
+   * The #GType for elements of this object
+   */
+  properties[PROP_ITEM_TYPE] =
+      g_param_spec_gtype ("item-type",
+                          P_("Item type"),
+                          P_("The type of elements of this object"),
+                          G_TYPE_OBJECT,
+                          GTK_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY | G_PARAM_EXPLICIT_NOTIFY);
+
+  /**
+   * GtkPropertyLookupListModel:property:
+   *
+   * Name of the property used for lookups
+   */
+  properties[PROP_PROPERTY] =
+      g_param_spec_string ("property",
+                           P_("type"),
+                           P_("Name of the property used for lookups"),
+                           NULL,
+                           GTK_PARAM_READWRITE | G_PARAM_CONSTRUCT_ONLY | G_PARAM_EXPLICIT_NOTIFY);
+
+  /**
+   * GtkPropertyLookupListModel:object:
+   *
+   * The root object
+   */
+  properties[PROP_OBJECT] =
+      g_param_spec_object ("object",
+                           P_("Object"),
+                           P_("The root object"),
+                           G_TYPE_LIST_MODEL,
+                           GTK_PARAM_READWRITE | G_PARAM_EXPLICIT_NOTIFY);
+
+  g_object_class_install_properties (object_class, NUM_PROPERTIES, properties);
+}
+
+static void
+gtk_property_lookup_list_model_init (GtkPropertyLookupListModel *self)
+{
+  self->items = g_ptr_array_new ();
+  /* add sentinel */
+  g_ptr_array_add (self->items, NULL);
+}
+
+GtkPropertyLookupListModel *
+gtk_property_lookup_list_model_new (GType       item_type,
+                                    const char *property_name)
+{
+  g_return_val_if_fail (g_type_is_a (item_type, G_TYPE_OBJECT), NULL);
+  g_return_val_if_fail (property_name != NULL, NULL);
+
+  return g_object_new (GTK_TYPE_PROPERTY_LOOKUP_LIST_MODEL,
+                       "item-type", item_type,
+                       "property", property_name,
+                       NULL);
+}
+
+void
+gtk_property_lookup_list_model_set_object (GtkPropertyLookupListModel *self,
+                                           gpointer                    object)
+{
+  guint removed, added;
+
+  g_return_if_fail (GTK_IS_PROPERTY_LOOKUP_LIST_MODEL (self));
+
+  if (object)
+    {
+      if (self->items->len != 0 &&
+          g_ptr_array_index (self->items, 0) == object)
+        return;
+
+      removed = gtk_property_lookup_list_model_clear (self, 0);
+
+      g_ptr_array_insert (self->items, 0, g_object_ref (object));
+      g_signal_connect_closure_by_id (object,
+                                      g_signal_lookup ("notify", G_OBJECT_TYPE (object)),
+                                      g_quark_from_static_string (self->property),
+                                      g_cclosure_new (G_CALLBACK (gtk_property_lookup_list_model_notify_cb), 
G_OBJECT (self), NULL),
+                                      FALSE);
+      added = 1;
+      if (!gtk_property_lookup_list_model_is_infinite (self))
+        added += gtk_property_lookup_list_model_append (self, G_MAXUINT);
+    }
+  else
+    {
+      if (self->items->len == 0 ||
+          g_ptr_array_index (self->items, 0) == NULL)
+        return;
+
+      removed = gtk_property_lookup_list_model_clear (self, 0);
+      added = 0;
+    }
+
+  g_assert (removed != 0 || added != 0);
+
+  g_list_model_items_changed (G_LIST_MODEL (self), 0, removed, added);
+}
+
+gpointer
+gtk_property_lookup_list_model_get_object (GtkPropertyLookupListModel *self)
+{
+  g_return_val_if_fail (GTK_IS_PROPERTY_LOOKUP_LIST_MODEL (self), NULL);
+
+  if (self->items->len == 0)
+    return NULL;
+  
+  return g_ptr_array_index (self->items, 0);
+}
+
diff --git a/gtk/gtkpropertylookuplistmodelprivate.h b/gtk/gtkpropertylookuplistmodelprivate.h
new file mode 100644
index 0000000000..fae9e239b2
--- /dev/null
+++ b/gtk/gtkpropertylookuplistmodelprivate.h
@@ -0,0 +1,50 @@
+/*
+ * Copyright © 2018 Benjamin Otte
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors: Benjamin Otte <otte gnome org>
+ */
+
+
+#ifndef __GTK_PROPERTY_LOOKUP_LIST_MODEL_H__
+#define __GTK_PROPERTY_LOOKUP_LIST_MODEL_H__
+
+#include <gio/gio.h>
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_PROPERTY_LOOKUP_LIST_MODEL         (gtk_property_lookup_list_model_get_type ())
+#define GTK_PROPERTY_LOOKUP_LIST_MODEL(o)           (G_TYPE_CHECK_INSTANCE_CAST ((o), 
GTK_TYPE_PROPERTY_LOOKUP_LIST_MODEL, GtkPropertyLookupListModel))
+#define GTK_PROPERTY_LOOKUP_LIST_MODEL_CLASS(k)     (G_TYPE_CHECK_CLASS_CAST ((k), 
GTK_TYPE_PROPERTY_LOOKUP_LIST_MODEL, GtkPropertyLookupListModelClass))
+#define GTK_IS_PROPERTY_LOOKUP_LIST_MODEL(o)        (G_TYPE_CHECK_INSTANCE_TYPE ((o), 
GTK_TYPE_PROPERTY_LOOKUP_LIST_MODEL))
+#define GTK_IS_PROPERTY_LOOKUP_LIST_MODEL_CLASS(k)  (G_TYPE_CHECK_CLASS_TYPE ((k), 
GTK_TYPE_PROPERTY_LOOKUP_LIST_MODEL))
+#define GTK_PROPERTY_LOOKUP_LIST_MODEL_GET_CLASS(o) (G_TYPE_INSTANCE_GET_CLASS ((o), 
GTK_TYPE_PROPERTY_LOOKUP_LIST_MODEL, GtkPropertyLookupListModelClass))
+
+typedef struct _GtkPropertyLookupListModel GtkPropertyLookupListModel;
+typedef struct _GtkPropertyLookupListModelClass GtkPropertyLookupListModelClass;
+
+GType                           gtk_property_lookup_list_model_get_type         (void) G_GNUC_CONST;
+
+GtkPropertyLookupListModel *    gtk_property_lookup_list_model_new              (GType                       
    item_type,
+                                                                                 const char                  
   *property_name);
+
+void                            gtk_property_lookup_list_model_set_object       (GtkPropertyLookupListModel  
   *self,
+                                                                                 gpointer                    
    object);
+gpointer                        gtk_property_lookup_list_model_get_object       (GtkPropertyLookupListModel  
   *self);
+
+
+G_END_DECLS
+
+#endif /* __GTK_PROPERTY_LOOKUP_LIST_MODEL_H__ */
diff --git a/gtk/meson.build b/gtk/meson.build
index dbdc455467..9d0f517b49 100644
--- a/gtk/meson.build
+++ b/gtk/meson.build
@@ -302,6 +302,7 @@ gtk_public_sources = files([
   'gtkprintoperationpreview.c',
   'gtkprintsettings.c',
   'gtkprogressbar.c',
+  'gtkpropertylookuplistmodel.c',
   'gtkradiobutton.c',
   'gtkradiomenuitem.c',
   'gtkradiotoolbutton.c',
diff --git a/testsuite/gtk/meson.build b/testsuite/gtk/meson.build
index 052de2abfa..e8171ea571 100644
--- a/testsuite/gtk/meson.build
+++ b/testsuite/gtk/meson.build
@@ -36,6 +36,7 @@ tests = [
   ['object'],
   ['objects-finalize'],
   ['papersize'],
+  ['propertylookuplistmodel', ['../../gtk/gtkpropertylookuplistmodel.c'], ['-DGTK_COMPILATION', 
'-UG_ENABLE_DEBUG']],
   ['rbtree', ['../../gtk/gtkrbtree.c'], ['-DGTK_COMPILATION', '-UG_ENABLE_DEBUG']],
   ['recentmanager'],
   ['regression-tests'],
diff --git a/testsuite/gtk/propertylookuplistmodel.c b/testsuite/gtk/propertylookuplistmodel.c
new file mode 100644
index 0000000000..21fa26445d
--- /dev/null
+++ b/testsuite/gtk/propertylookuplistmodel.c
@@ -0,0 +1,242 @@
+/* GtkRBTree tests.
+ *
+ * Copyright (C) 2011, Red Hat, Inc.
+ * Authors: Benjamin Otte <otte gnome org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <locale.h>
+
+#include <gtk/gtk.h>
+
+#include "gtk/gtkpropertylookuplistmodelprivate.h"
+
+GQuark changes_quark;
+
+static char *
+model_to_string (GListModel *model)
+{
+  GString *string = g_string_new (NULL);
+  gpointer item;
+  guint i;
+
+  for (i = 0; i < g_list_model_get_n_items (model); i++)
+    {
+      if (i > 0)
+        g_string_append (string, " ");
+      item = g_list_model_get_item (model, i);
+      g_string_append_printf (string, "%s", G_OBJECT_TYPE_NAME (item));
+      g_object_unref (item);
+    }
+
+  return g_string_free (string, FALSE);
+}
+
+#define assert_model(model, expected) G_STMT_START{ \
+  char *s = model_to_string (G_LIST_MODEL (model)); \
+  if (!g_str_equal (s, expected)) \
+     g_assertion_message_cmpstr (G_LOG_DOMAIN, __FILE__, __LINE__, G_STRFUNC, \
+         #model " == " #expected, s, "==", expected); \
+  g_free (s); \
+}G_STMT_END
+
+#define assert_changes(model, expected) G_STMT_START{ \
+  GString *changes = g_object_get_qdata (G_OBJECT (model), changes_quark); \
+  if (!g_str_equal (changes->str, expected)) \
+     g_assertion_message_cmpstr (G_LOG_DOMAIN, __FILE__, __LINE__, G_STRFUNC, \
+         #model " == " #expected, changes->str, "==", expected); \
+  g_string_set_size (changes, 0); \
+}G_STMT_END
+
+static void
+items_changed (GListModel *model,
+               guint       position,
+               guint       removed,
+               guint       added,
+               GString    *changes)
+{
+  g_assert (removed != 0 || added != 0);
+
+  if (changes->len)
+    g_string_append (changes, ", ");
+
+  if (removed == 1 && added == 0)
+    {
+      g_string_append_printf (changes, "-%u", position);
+    }
+  else if (removed == 0 && added == 1)
+    {
+      g_string_append_printf (changes, "+%u", position);
+    }
+  else
+    {
+      g_string_append_printf (changes, "%u", position);
+      if (removed > 0)
+        g_string_append_printf (changes, "-%u", removed);
+      if (added > 0)
+        g_string_append_printf (changes, "+%u", added);
+    }
+}
+
+static void
+free_changes (gpointer data)
+{
+  GString *changes = data;
+
+  /* all changes must have been checked via assert_changes() before */
+  g_assert_cmpstr (changes->str, ==, "");
+
+  g_string_free (changes, TRUE);
+}
+
+static GSList *widgets = NULL;
+
+static GtkWidget *
+create_widget_tree (void)
+{
+  GtkWidget *window, *box, *grid, *label;
+
+  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+  widgets = g_slist_prepend (widgets, window);
+
+  box = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 0);
+  gtk_container_add (GTK_CONTAINER (window), box);
+
+  grid = gtk_grid_new ();
+  gtk_container_add (GTK_CONTAINER (box), grid);
+
+  label = gtk_label_new ("Hello World");
+  gtk_container_add (GTK_CONTAINER (grid), label);
+
+  return label;
+}
+
+static void
+destroy_widgets (void)
+{
+  g_slist_free_full (widgets, (GDestroyNotify) gtk_widget_destroy);
+  widgets = NULL;
+}
+
+static GtkPropertyLookupListModel *
+new_model (gboolean fill)
+{
+  GtkPropertyLookupListModel *result;
+  GString *changes;
+
+  result = gtk_property_lookup_list_model_new (GTK_TYPE_WIDGET, "parent");
+  if (fill)
+    {
+      GtkWidget *widget = create_widget_tree ();
+      gtk_property_lookup_list_model_set_object (result, widget);
+    }
+  changes = g_string_new ("");
+  g_object_set_qdata_full (G_OBJECT(result), changes_quark, changes, free_changes);
+  g_signal_connect (result, "items-changed", G_CALLBACK (items_changed), changes);
+
+  return result;
+}
+
+static void
+test_create_empty (void)
+{
+  GtkPropertyLookupListModel *model;
+
+  model = new_model (FALSE);
+  assert_model (model, "");
+  assert_changes (model, "");
+
+  g_object_unref (model);
+}
+
+static void
+test_create (void)
+{
+  GtkPropertyLookupListModel *model;
+
+  model = new_model (TRUE);
+  assert_model (model, "GtkLabel GtkGrid GtkBox GtkWindow");
+  assert_changes (model, "");
+
+  g_object_unref (model);
+  destroy_widgets ();
+}
+
+static void
+test_set_object (void)
+{
+  GtkPropertyLookupListModel *model;
+  GtkWidget *widget;
+
+  widget = create_widget_tree ();
+
+  model = new_model (FALSE);
+  gtk_property_lookup_list_model_set_object (model, widget);
+  assert_model (model, "GtkLabel GtkGrid GtkBox GtkWindow");
+  assert_changes (model, "+0");
+  g_object_unref (model);
+
+  model = new_model (FALSE);
+  assert_model (model, "");
+  gtk_property_lookup_list_model_set_object (model, widget);
+  assert_model (model, "GtkLabel GtkGrid GtkBox GtkWindow");
+  assert_changes (model, "0+4");
+  g_object_unref (model);
+
+  destroy_widgets ();
+}
+
+static void
+test_change_property (void)
+{
+  GtkPropertyLookupListModel *model;
+  GtkWidget *widget, *parent, *grandparent;
+
+  widget = create_widget_tree ();
+  parent = gtk_widget_get_parent (widget);
+  grandparent = gtk_widget_get_parent (parent);
+
+  model = new_model (FALSE);
+  assert_model (model, ""); /* make sure the model has a definite size */
+  gtk_property_lookup_list_model_set_object (model, widget);
+  assert_model (model, "GtkLabel GtkGrid GtkBox GtkWindow");
+  assert_changes (model, "0+4");
+
+  gtk_container_remove (GTK_CONTAINER (parent), widget);
+  assert_model (model, "GtkLabel");
+  assert_changes (model, "1-3");
+
+  gtk_container_add (GTK_CONTAINER (grandparent), widget);
+  assert_model (model, "GtkLabel GtkBox GtkWindow");
+  assert_changes (model, "1+2");
+
+  g_object_unref (model);
+  destroy_widgets ();
+}
+
+int
+main (int argc, char *argv[])
+{
+  gtk_test_init (&argc, &argv);
+
+  changes_quark = g_quark_from_static_string ("What did I see? Can I believe what I saw?");
+
+  g_test_add_func ("/propertylookuplistmodel/create_empty", test_create_empty);
+  g_test_add_func ("/propertylookuplistmodel/create", test_create);
+  g_test_add_func ("/propertylookuplistmodel/set-object", test_set_object);
+  g_test_add_func ("/propertylookuplistmodel/change-property", test_change_property);
+
+  return g_test_run ();
+}