Merge branch 'wip/chergert/fix-completion-snapshots'

6 files changed, 711 insertions, 29 deletions

diff --git a/gtksourceview/gtksourcecompletionlistbox.c b/gtksourceview/gtksourcecompletionlistbox.c
index a8f7d209..a7f6b810 100644
--- a/gtksourceview/gtksourcecompletionlistbox.c
+++ b/gtksourceview/gtksourcecompletionlistbox.c
@@ -27,12 +27,21 @@
 #include "gtksourcecompletionlistboxrow-private.h"
 #include "gtksourcecompletionproposal.h"
 #include "gtksourcecompletionprovider.h"
+#include "gtksourcelistsnapshot-private.h"
 #include "gtksourceview-private.h"
 
 struct _GtkSourceCompletionListBox
 {
 	GtkWidget parent_instance;
 
+	/* Used to snapshot a GListModel of the visible range during a
+	 * frame cycle, so that it cannot change underneath us. We hold()
+	 * and release() the snapshot from frame clock callbacks.
+	 */
+	GtkSourceListSnapshot *list_snapshot;
+	gulong update_handler;
+	gulong after_paint_handler;
+
 	/* The box containing the rows. */
 	GtkBox *box;
 
@@ -42,11 +51,6 @@ struct _GtkSourceCompletionListBox
 	/* The completion context that is being displayed. */
 	GtkSourceCompletionContext *context;
 
-	/* The handler for GtkSourceCompletionContext::items-chaged which should
-	 * be disconnected when no longer needed.
-	 */
-	gulong items_changed_handler;
-
 	/* The number of rows we expect to have visible to the user. */
 	guint n_rows;
 
@@ -116,12 +120,21 @@ enum {
 	N_SIGNALS
 };
 
-static void     gtk_source_completion_list_box_queue_update (GtkSourceCompletionListBox *self);
-static gboolean gtk_source_completion_list_box_update_cb    (GtkWidget                  *widget,
-                                                             GdkFrameClock              *frame_clock,
-                                                             gpointer                    user_data);
-static void     gtk_source_completion_list_box_do_update    (GtkSourceCompletionListBox *self,
-                                                             gboolean                    update_selection);
+static void     gtk_source_completion_list_box_queue_update     (GtkSourceCompletionListBox *self);
+static gboolean gtk_source_completion_list_box_update_cb        (GtkWidget                  *widget,
+                                                                 GdkFrameClock              *frame_clock,
+                                                                 gpointer                    user_data);
+static void     gtk_source_completion_list_box_after_update_cb  (GtkWidget                  *widget,
+                                                                 GdkFrameClock              *frame_clock);
+static void     gtk_source_completion_list_box_after_paint_cb   (GtkWidget                  *widget,
+                                                                 GdkFrameClock              *frame_clock);
+static void     gtk_source_completion_list_box_do_update        (GtkSourceCompletionListBox *self,
+                                                                 gboolean                    update_selection);
+static void     gtk_source_completion_list_box_items_changed_cb (GtkSourceCompletionListBox *self,
+                                                                 guint                       position,
+                                                                 guint                       removed,
+                                                                 guint                       added,
+                                                                 GListModel                 *model);
 
 G_DEFINE_TYPE_WITH_CODE (GtkSourceCompletionListBox, gtk_source_completion_list_box, GTK_TYPE_WIDGET,
                          G_IMPLEMENT_INTERFACE (GTK_TYPE_SCROLLABLE, NULL))
@@ -548,6 +561,42 @@ _gtk_source_completion_list_box_key_pressed_cb (GtkSourceCompletionListBox *self
 }
 
 static void
+gtk_source_completion_list_box_realize (GtkWidget *widget)
+{
+	GtkSourceCompletionListBox *self = GTK_SOURCE_COMPLETION_LIST_BOX (widget);
+	GdkFrameClock *frame_clock;
+
+	GTK_WIDGET_CLASS (gtk_source_completion_list_box_parent_class)->realize (widget);
+
+	frame_clock = gtk_widget_get_frame_clock (widget);
+
+	self->update_handler =
+		g_signal_connect_data (frame_clock,
+		                       "update",
+		                       G_CALLBACK (gtk_source_completion_list_box_after_update_cb),
+		                       self, NULL,
+		                       G_CONNECT_AFTER | G_CONNECT_SWAPPED);
+	self->after_paint_handler =
+		g_signal_connect_swapped (frame_clock,
+		                          "after-paint",
+		                          G_CALLBACK (gtk_source_completion_list_box_after_paint_cb),
+		                          self);
+}
+
+static void
+gtk_source_completion_list_box_unrealize (GtkWidget *widget)
+{
+	GtkSourceCompletionListBox *self = GTK_SOURCE_COMPLETION_LIST_BOX (widget);
+	GdkFrameClock *frame_clock;
+
+	frame_clock = gtk_widget_get_frame_clock (widget);
+	g_clear_signal_handler (&self->update_handler, frame_clock);
+	g_clear_signal_handler (&self->after_paint_handler, frame_clock);
+
+	GTK_WIDGET_CLASS (gtk_source_completion_list_box_parent_class)->unrealize (widget);
+}
+
+static void
 gtk_source_completion_list_box_constructed (GObject *object)
 {
 	GtkSourceCompletionListBox *self = (GtkSourceCompletionListBox *)object;
@@ -582,6 +631,7 @@ gtk_source_completion_list_box_dispose (GObject *object)
 		self->box = NULL;
 	}
 
+	g_clear_object (&self->list_snapshot);
 	g_clear_object (&self->before_size_group);
 	g_clear_object (&self->typed_text_size_group);
 	g_clear_object (&self->after_size_group);
@@ -693,6 +743,9 @@ gtk_source_completion_list_box_class_init (GtkSourceCompletionListBoxClass *klas
 	object_class->get_property = gtk_source_completion_list_box_get_property;
 	object_class->set_property = gtk_source_completion_list_box_set_property;
 
+	widget_class->realize = gtk_source_completion_list_box_realize;
+	widget_class->unrealize = gtk_source_completion_list_box_unrealize;
+
 	properties [PROP_ALTERNATE] =
 		g_param_spec_int ("alternate",
 		                  "Alternate",
@@ -804,6 +857,13 @@ gtk_source_completion_list_box_init (GtkSourceCompletionListBox *self)
 	                          self);
 	gtk_widget_add_controller (GTK_WIDGET (self), key);
 
+	self->list_snapshot = gtk_source_list_snapshot_new ();
+	g_signal_connect_object (self->list_snapshot,
+	                         "items-changed",
+	                         G_CALLBACK (gtk_source_completion_list_box_items_changed_cb),
+	                         self,
+	                         G_CONNECT_SWAPPED);
+
 	self->box = g_object_new (GTK_TYPE_BOX,
 				  "orientation", GTK_ORIENTATION_VERTICAL,
 				  "visible", TRUE,
@@ -1158,25 +1218,10 @@ _gtk_source_completion_list_box_set_context (GtkSourceCompletionListBox *self,
 	g_return_if_fail (GTK_SOURCE_IS_COMPLETION_LIST_BOX (self));
 	g_return_if_fail (!context || GTK_SOURCE_IS_COMPLETION_CONTEXT (context));
 
-	if (self->context == context)
-		return;
-
-	if (self->context != NULL && self->items_changed_handler != 0)
-	{
-		g_signal_handler_disconnect (self->context, self->items_changed_handler);
-		self->items_changed_handler = 0;
-	}
-
-	g_set_object (&self->context, context);
-
-	if (self->context != NULL)
+	if (g_set_object (&self->context, context))
 	{
-		self->items_changed_handler =
-			g_signal_connect_object (self->context,
-			                         "items-changed",
-			                         G_CALLBACK (gtk_source_completion_list_box_items_changed_cb),
-			                         self,
-			                         G_CONNECT_SWAPPED);
+		gtk_source_list_snapshot_set_model (self->list_snapshot,
+		                                    G_LIST_MODEL (context));
 	}
 
 	gtk_source_completion_list_box_set_selected (self, -1);
@@ -1340,3 +1385,32 @@ _gtk_source_completion_list_box_set_show_icons (GtkSourceCompletionListBox *self
 
 	gtk_source_completion_list_box_queue_update (self);
 }
+
+static void
+gtk_source_completion_list_box_after_update_cb (GtkWidget     *widget,
+                                                GdkFrameClock *frame_clock)
+{
+	GtkSourceCompletionListBox *self = (GtkSourceCompletionListBox *)widget;
+	double lower;
+	double page_size;
+
+	g_assert (GTK_SOURCE_IS_COMPLETION_LIST_BOX (self));
+	g_assert (GDK_IS_FRAME_CLOCK (frame_clock));
+
+	lower = gtk_adjustment_get_lower (self->vadjustment);
+	page_size = gtk_adjustment_get_page_size (self->vadjustment);
+
+	gtk_source_list_snapshot_hold (self->list_snapshot, lower, lower + page_size);
+}
+
+static void
+gtk_source_completion_list_box_after_paint_cb (GtkWidget     *widget,
+					       GdkFrameClock *frame_clock)
+{
+	GtkSourceCompletionListBox *self = (GtkSourceCompletionListBox *)widget;
+
+	g_assert (GTK_SOURCE_IS_COMPLETION_LIST_BOX (self));
+	g_assert (GDK_IS_FRAME_CLOCK (frame_clock));
+
+	gtk_source_list_snapshot_release (self->list_snapshot);
+}
diff --git a/gtksourceview/gtksourcelistsnapshot-private.h b/gtksourceview/gtksourcelistsnapshot-private.h
new file mode 100644
index 00000000..456f2592
--- /dev/null
+++ b/gtksourceview/gtksourcelistsnapshot-private.h
@@ -0,0 +1,40 @@
+/* gtksourcelistsnapshot-private.h
+ *
+ * Copyright 2022 Christian Hergert <chergert@redhat.com>
+ *
+ * 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 General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+#pragma once
+
+#include <gio/gio.h>
+
+G_BEGIN_DECLS
+
+#define GTK_SOURCE_TYPE_LIST_SNAPSHOT (gtk_source_list_snapshot_get_type())
+
+G_DECLARE_FINAL_TYPE (GtkSourceListSnapshot, gtk_source_list_snapshot, GTK_SOURCE, LIST_SNAPSHOT, GObject)
+
+GtkSourceListSnapshot *gtk_source_list_snapshot_new       (void);
+GListModel            *gtk_source_list_snapshot_get_model (GtkSourceListSnapshot *self);
+void                   gtk_source_list_snapshot_set_model (GtkSourceListSnapshot *self,
+                                                           GListModel            *model);
+void                   gtk_source_list_snapshot_hold      (GtkSourceListSnapshot *self,
+                                                           guint                  position,
+                                                           guint                  length);
+void                   gtk_source_list_snapshot_release   (GtkSourceListSnapshot *self);
+
+G_END_DECLS
diff --git a/gtksourceview/gtksourcelistsnapshot.c b/gtksourceview/gtksourcelistsnapshot.c
new file mode 100644
index 00000000..733d720a
--- /dev/null
+++ b/gtksourceview/gtksourcelistsnapshot.c
@@ -0,0 +1,406 @@
+/* gtksourcelistsnapshot.c
+ *
+ * Copyright 2022 Christian Hergert <chergert@redhat.com>
+ *
+ * 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 General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+#include "config.h"
+
+#include <gtk/gtk.h>
+
+#include "gtksourcelistsnapshot-private.h"
+
+/*
+ * GtkSourceListSnapshot:
+ *
+ * This classes purpose is to allow snapshoting a range of a GListModel
+ * and ensuring that no changes to the underlying model will cause that
+ * range to invalidate.
+ *
+ * The "hold" be done at the point where you want to avoid any model
+ * changes causing the widgetry to invalidate, and released after you've
+ * completed your snapshot work.
+ *
+ * If :model changes, or ::items-changed on the current model is emitted,
+ * that will be supressed until the hold is released. Objects for the
+ * hold range are retained so they may be returned from
+ * g_list_model_get_item().
+ */
+
+struct _GtkSourceListSnapshot
+{
+	GObject       parent_instance;
+	GListModel   *model;
+	GSignalGroup *signal_group;
+	GPtrArray    *held_items;
+	guint         held_position;
+	guint         held_n_items;
+	guint         real_n_items;
+	guint         invalid : 1;
+};
+
+enum {
+	PROP_0,
+	PROP_MODEL,
+	N_PROPS
+};
+
+static GType
+gtk_source_list_snapshot_get_item_type (GListModel *model)
+{
+	GtkSourceListSnapshot *self = GTK_SOURCE_LIST_SNAPSHOT (model);
+
+	if (self->model != NULL)
+	{
+		return g_list_model_get_item_type (self->model);
+	}
+
+	return G_TYPE_OBJECT;
+}
+
+static guint
+gtk_source_list_snapshot_get_n_items (GListModel *model)
+{
+	GtkSourceListSnapshot *self = GTK_SOURCE_LIST_SNAPSHOT (model);
+
+	if (self->held_position == GTK_INVALID_LIST_POSITION)
+	{
+		return self->real_n_items;
+	}
+
+	return self->held_n_items;
+}
+
+static gpointer
+gtk_source_list_snapshot_get_item (GListModel *model,
+				   guint       position)
+{
+	GtkSourceListSnapshot *self = GTK_SOURCE_LIST_SNAPSHOT (model);
+
+	if (self->held_position == GTK_INVALID_LIST_POSITION)
+	{
+		if (self->model == NULL)
+		{
+			return NULL;
+		}
+
+		return g_list_model_get_item (self->model, position);
+	}
+
+	if (position >= self->held_position &&
+	    position < self->held_position + self->held_items->len)
+	{
+		return g_object_ref (g_ptr_array_index (self->held_items, position - self->held_position));
+	}
+
+	return NULL;
+}
+
+static void
+list_model_iface_init (GListModelInterface *iface)
+{
+	iface->get_item_type = gtk_source_list_snapshot_get_item_type;
+	iface->get_n_items = gtk_source_list_snapshot_get_n_items;
+	iface->get_item = gtk_source_list_snapshot_get_item;
+}
+
+G_DEFINE_FINAL_TYPE_WITH_CODE (GtkSourceListSnapshot, gtk_source_list_snapshot, G_TYPE_OBJECT,
+                               G_IMPLEMENT_INTERFACE (G_TYPE_LIST_MODEL, list_model_iface_init))
+
+static GParamSpec *properties [N_PROPS];
+
+static void
+gtk_source_list_snapshot_bind_cb (GtkSourceListSnapshot *self,
+                                  GListModel            *model,
+                                  GSignalGroup          *signal_group)
+{
+	guint old_n_items;
+	guint new_n_items;
+
+	g_assert (GTK_SOURCE_IS_LIST_SNAPSHOT (self));
+	g_assert (G_IS_LIST_MODEL (model));
+	g_assert (G_IS_SIGNAL_GROUP (signal_group));
+
+	old_n_items = self->real_n_items;
+	new_n_items = g_list_model_get_n_items (model);
+
+	if (self->held_position == GTK_INVALID_LIST_POSITION)
+	{
+		if (old_n_items || new_n_items)
+		{
+			g_list_model_items_changed (G_LIST_MODEL (self), 0, old_n_items, new_n_items);
+		}
+	}
+	else
+	{
+		self->invalid = TRUE;
+	}
+
+	self->real_n_items = new_n_items;
+}
+
+static void
+gtk_source_list_snapshot_unbind_cb (GtkSourceListSnapshot *self,
+                                    GSignalGroup          *signal_group)
+{
+	guint old_n_items;
+	guint new_n_items;
+
+	g_assert (GTK_SOURCE_IS_LIST_SNAPSHOT (self));
+	g_assert (G_IS_SIGNAL_GROUP (signal_group));
+
+	old_n_items = self->real_n_items;
+	new_n_items = 0;
+
+	self->real_n_items = new_n_items;
+
+	if (self->held_position == GTK_INVALID_LIST_POSITION)
+	{
+		if (old_n_items || new_n_items)
+		{
+			g_list_model_items_changed (G_LIST_MODEL (self), 0, old_n_items, new_n_items);
+		}
+	}
+	else
+	{
+		self->invalid = TRUE;
+	}
+}
+
+static void
+gtk_source_list_snapshot_items_changed_cb (GtkSourceListSnapshot *self,
+                                           guint                  position,
+                                           guint                  removed,
+                                           guint                  added,
+                                           GListModel            *model)
+{
+	g_assert (GTK_SOURCE_IS_LIST_SNAPSHOT (self));
+	g_assert (G_IS_LIST_MODEL (model));
+
+	self->real_n_items -= removed;
+	self->real_n_items += added;
+
+	if (self->held_position == GTK_INVALID_LIST_POSITION)
+	{
+		if (removed || added)
+		{
+			g_list_model_items_changed (G_LIST_MODEL (self), position, removed, added);
+		}
+	}
+	else
+	{
+		self->invalid = TRUE;
+	}
+}
+
+static void
+gtk_source_list_snapshot_dispose (GObject *object)
+{
+	GtkSourceListSnapshot *self = (GtkSourceListSnapshot *)object;
+
+	g_clear_pointer (&self->held_items, g_ptr_array_unref);
+
+	if (self->signal_group != NULL)
+	{
+		g_signal_group_set_target (self->signal_group, NULL);
+		g_clear_object (&self->signal_group);
+	}
+
+	g_clear_object (&self->model);
+
+	G_OBJECT_CLASS (gtk_source_list_snapshot_parent_class)->dispose (object);
+}
+
+static void
+gtk_source_list_snapshot_get_property (GObject    *object,
+                                       guint       prop_id,
+                                       GValue     *value,
+                                       GParamSpec *pspec)
+{
+	GtkSourceListSnapshot *self = GTK_SOURCE_LIST_SNAPSHOT (object);
+
+	switch (prop_id)
+	{
+	case PROP_MODEL:
+		g_value_set_object (value, self->model);
+		break;
+
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+	}
+}
+
+static void
+gtk_source_list_snapshot_set_property (GObject      *object,
+                                       guint         prop_id,
+                                       const GValue *value,
+                                       GParamSpec   *pspec)
+{
+	GtkSourceListSnapshot *self = GTK_SOURCE_LIST_SNAPSHOT (object);
+
+	switch (prop_id)
+	{
+	case PROP_MODEL:
+		gtk_source_list_snapshot_set_model (self, g_value_get_object (value));
+		break;
+
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+	}
+}
+
+static void
+gtk_source_list_snapshot_class_init (GtkSourceListSnapshotClass *klass)
+{
+	GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+	object_class->dispose = gtk_source_list_snapshot_dispose;
+	object_class->get_property = gtk_source_list_snapshot_get_property;
+	object_class->set_property = gtk_source_list_snapshot_set_property;
+
+	properties [PROP_MODEL] =
+		g_param_spec_object ("model", NULL, NULL,
+		                     G_TYPE_LIST_MODEL,
+		                     (G_PARAM_READWRITE | G_PARAM_EXPLICIT_NOTIFY | G_PARAM_STATIC_STRINGS));
+
+	g_object_class_install_properties (object_class, N_PROPS, properties);
+}
+
+static void
+gtk_source_list_snapshot_init (GtkSourceListSnapshot *self)
+{
+	self->signal_group = g_signal_group_new (G_TYPE_LIST_MODEL);
+	self->held_items = g_ptr_array_new_with_free_func (g_object_unref);
+	self->held_position = GTK_INVALID_LIST_POSITION;
+
+	g_signal_connect_object (self->signal_group,
+	                         "bind",
+	                         G_CALLBACK (gtk_source_list_snapshot_bind_cb),
+	                         self,
+	                         G_CONNECT_SWAPPED);
+	g_signal_connect_object (self->signal_group,
+	                         "unbind",
+	                         G_CALLBACK (gtk_source_list_snapshot_unbind_cb),
+	                         self,
+	                         G_CONNECT_SWAPPED);
+	g_signal_group_connect_object (self->signal_group,
+	                               "items-changed",
+	                               G_CALLBACK (gtk_source_list_snapshot_items_changed_cb),
+	                               self,
+	                               G_CONNECT_SWAPPED);
+}
+
+GtkSourceListSnapshot *
+gtk_source_list_snapshot_new (void)
+{
+	return g_object_new (GTK_SOURCE_TYPE_LIST_SNAPSHOT, NULL);
+}
+
+/**
+ * gtk_source_list_snapshot_get_model:
+ * @self: a #GtkSourceListSnapshot
+ *
+ * Gets the underlying model, if any.
+ *
+ * Returns: (transfer none) (nullable): a #GListModel or %NULL
+ */
+GListModel *
+gtk_source_list_snapshot_get_model (GtkSourceListSnapshot *self)
+{
+	g_return_val_if_fail (GTK_SOURCE_IS_LIST_SNAPSHOT (self), NULL);
+
+	return self->model;
+}
+
+void
+gtk_source_list_snapshot_set_model (GtkSourceListSnapshot *self,
+                                    GListModel            *model)
+{
+	g_return_if_fail (GTK_SOURCE_IS_LIST_SNAPSHOT (self));
+	g_return_if_fail (!model || G_IS_LIST_MODEL (model));
+
+	if (g_set_object (&self->model, model))
+	{
+		g_signal_group_set_target (self->signal_group, model);
+		g_object_notify_by_pspec (G_OBJECT (self), properties [PROP_MODEL]);
+	}
+}
+
+void
+gtk_source_list_snapshot_hold (GtkSourceListSnapshot *self,
+                               guint                  position,
+                               guint                  length)
+{
+	g_return_if_fail (GTK_SOURCE_IS_LIST_SNAPSHOT (self));
+	g_return_if_fail (self->held_position == GTK_INVALID_LIST_POSITION);
+	g_return_if_fail (self->held_items != NULL);
+	g_return_if_fail (self->held_items->len == 0);
+	g_return_if_fail (self->held_n_items == 0);
+
+	self->held_position = position;
+
+	if (self->model != NULL)
+	{
+		self->held_n_items = g_list_model_get_n_items (self->model);
+	}
+
+	if (position > self->held_n_items)
+	{
+		position = self->held_n_items;
+	}
+
+	if (position + length > self->held_n_items)
+	{
+		length = self->held_n_items - position;
+	}
+
+	for (guint i = 0; i < length; i++)
+	{
+		g_ptr_array_add (self->held_items,
+		                 g_list_model_get_item (self->model, position + i));
+	}
+}
+
+void
+gtk_source_list_snapshot_release (GtkSourceListSnapshot *self)
+{
+	gboolean was_invalid;
+	guint old_n_items;
+	guint new_n_items;
+
+	g_return_if_fail (GTK_SOURCE_IS_LIST_SNAPSHOT (self));
+	g_return_if_fail (self->held_position != GTK_INVALID_LIST_POSITION);
+	g_return_if_fail (self->held_items != NULL);
+
+	was_invalid = self->invalid;
+	old_n_items = self->held_n_items;
+	new_n_items = self->model ? g_list_model_get_n_items (self->model) : 0;
+
+	self->invalid = FALSE;
+	self->held_n_items = 0;
+	self->held_position = GTK_INVALID_LIST_POSITION;
+
+	if (self->held_items->len > 0)
+	{
+		g_ptr_array_remove_range (self->held_items, 0, self->held_items->len);
+	}
+
+	if (was_invalid)
+	{
+		g_list_model_items_changed (G_LIST_MODEL (self), 0, old_n_items, new_n_items);
+	}
+}
diff --git a/gtksourceview/meson.build b/gtksourceview/meson.build
index 5ba8f20e..37a660f8 100644
--- a/gtksourceview/meson.build
+++ b/gtksourceview/meson.build
@@ -128,6 +128,7 @@ core_private_c = files([
   'gtksourceinformative.c',
   'gtksourceiter.c',
   'gtksourcelanguage-parser-2.c',
+  'gtksourcelistsnapshot.c',
   'gtksourcemarkssequence.c',
   'gtksourcepixbufhelper.c',
   'gtksourceregex.c',
diff --git a/testsuite/meson.build b/testsuite/meson.build
index 8195b14d..adbe140b 100644
--- a/testsuite/meson.build
+++ b/testsuite/meson.build
@@ -31,6 +31,7 @@ testsuite_sources = [
   ['test-language'],
   ['test-languagemanager'],
   ['test-language-specs', false],
+  ['test-listsnapshot'],
   ['test-mark'],
   ['test-printcompositor'],
   ['test-regex'],
diff --git a/testsuite/test-listsnapshot.c b/testsuite/test-listsnapshot.c
new file mode 100644
index 00000000..3edeaf38
--- /dev/null
+++ b/testsuite/test-listsnapshot.c
@@ -0,0 +1,160 @@
+/* test-listsnapshot.c
+ *
+ * Copyright 2022 Christian Hergert <chergert@redhat.com>
+ *
+ * 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 General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+#include <gtksourceview/gtksourcelistsnapshot-private.h>
+
+typedef struct
+{
+	guint call_count;
+	guint position;
+	guint removed;
+	guint added;
+} ItemsChanged;
+
+static void
+items_changed_cb (GListModel   *model,
+		  guint         position,
+		  guint         removed,
+		  guint         added,
+		  ItemsChanged *state)
+{
+#if 0
+	g_printerr ("%d %d %d\n", position, removed, added);
+#endif
+
+	state->call_count++;
+	state->position = position;
+	state->removed = removed;
+	state->added = added;
+}
+
+static void
+test_list_snapshot (void)
+{
+	GtkSourceListSnapshot *list_snapshot;
+	GListStore *store;
+	GMenu *menu;
+	ItemsChanged state = {0};
+
+	list_snapshot = gtk_source_list_snapshot_new ();
+	g_signal_connect (list_snapshot, "items-changed", G_CALLBACK (items_changed_cb), &state);
+	g_assert_cmpint (0, ==, g_list_model_get_n_items (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (G_TYPE_OBJECT, ==, g_list_model_get_item_type (G_LIST_MODEL (list_snapshot)));
+
+	store = g_list_store_new (G_TYPE_MENU_MODEL);
+
+	menu = g_menu_new ();
+	g_list_store_append (store, menu);
+
+	/* initial model set (with items) */
+	gtk_source_list_snapshot_set_model (list_snapshot, G_LIST_MODEL (store));
+	g_assert_cmpint (1, ==, g_list_model_get_n_items (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (G_TYPE_MENU_MODEL, ==, g_list_model_get_item_type (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (state.call_count, ==, 1);
+	g_assert_cmpint (state.position, ==, 0);
+	g_assert_cmpint (state.removed, ==, 0);
+	g_assert_cmpint (state.added, ==, 1);
+
+	/* try to reset, no changes/emission */
+	gtk_source_list_snapshot_set_model (list_snapshot, G_LIST_MODEL (store));
+	g_assert_cmpint (1, ==, g_list_model_get_n_items (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (G_TYPE_MENU_MODEL, ==, g_list_model_get_item_type (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (state.call_count, ==, 1);
+
+	/* clear model */
+	gtk_source_list_snapshot_set_model (list_snapshot, NULL);
+	g_assert_cmpint (0, ==, g_list_model_get_n_items (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (G_TYPE_OBJECT, ==, g_list_model_get_item_type (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (state.call_count, ==, 2);
+	g_assert_cmpint (state.position, ==, 0);
+	g_assert_cmpint (state.removed, ==, 1);
+	g_assert_cmpint (state.added, ==, 0);
+
+	/* set model again */
+	gtk_source_list_snapshot_set_model (list_snapshot, G_LIST_MODEL (store));
+	g_assert_cmpint (1, ==, g_list_model_get_n_items (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (G_TYPE_MENU_MODEL, ==, g_list_model_get_item_type (G_LIST_MODEL (list_snapshot)));
+	g_assert_cmpint (state.call_count, ==, 3);
+	g_assert_cmpint (state.position, ==, 0);
+	g_assert_cmpint (state.removed, ==, 0);
+	g_assert_cmpint (state.added, ==, 1);
+
+	/* Add some more items so we can hold a range */
+	for (guint i = 0; i < 100; i++)
+	{
+		GMenu *m = g_menu_new ();
+		state.call_count = 0;
+		g_list_store_append (store, m);
+		g_assert_cmpint (state.call_count, ==, 1);
+		g_assert_cmpint (state.position, ==, 1+i);
+		g_assert_cmpint (state.removed, ==, 0);
+		g_assert_cmpint (state.added, ==, 1);
+		g_object_unref (m);
+	}
+	g_assert_cmpint (101, ==, g_list_model_get_n_items (G_LIST_MODEL (store)));
+	g_assert_cmpint (101, ==, g_list_model_get_n_items (G_LIST_MODEL (list_snapshot)));
+
+	/* Hold a range so we can test changing things arround */
+	gtk_source_list_snapshot_hold (list_snapshot, 10, 20);
+	g_assert_cmpint (101, ==, g_list_model_get_n_items (G_LIST_MODEL (list_snapshot)));
+	for (guint i = 0; i <= 100; i++)
+	{
+		GMenu *item = g_list_model_get_item (G_LIST_MODEL (list_snapshot), i);
+
+		if (i < 10 || i >= 30)
+		{
+			g_assert_null (item);
+		}
+		else
+		{
+			g_assert_nonnull (item);
+			g_assert_true (G_IS_MENU (item));
+			g_object_unref (item);
+		}
+	}
+
+	/* Now remove everything and ensure we're still good */
+	state.call_count = 0;
+	while (g_list_model_get_n_items (G_LIST_MODEL (store)))
+	{
+		g_list_store_remove (store, 0);
+		g_assert_cmpint (state.call_count, ==, 0);
+	}
+
+	/* Now release our hold */
+	gtk_source_list_snapshot_release (list_snapshot);
+	g_assert_cmpint (state.call_count, ==, 1);
+	g_assert_cmpint (state.position, ==, 0);
+	g_assert_cmpint (state.removed, ==, 101);
+	g_assert_cmpint (state.added, ==, 0);
+
+	g_assert_finalize_object (list_snapshot);
+	g_assert_finalize_object (store);
+	g_assert_finalize_object (menu);
+}
+
+int
+main (int argc,
+      char *argv[])
+{
+	g_test_init (&argc, &argv, NULL);
+	g_test_add_func ("/GtkSource/ListSnapshot/basic", test_list_snapshot);
+	return g_test_run ();
+}