[gtk/wip/ebassi/a11y-drop-atk: 17/24] Introduce GtkAccessible

[Emmanuele Bassi <ebassi src gnome org>]

commit 63cbfc06d49b962e66d48e18941e56ffef0e6997
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Tue Jun 16 17:40:14 2020 +0100

    Introduce GtkAccessible
    
    GtkAccessible is an interface for accessible UI elements.
    
    Currently, it doesn't do much except exist as a type; in the future, it
    will be the entry point for all accessible state in GTK.

 gtk/gtk.h           |  1 +
 gtk/gtkaccessible.c | 30 ++++++++++++++++++++++++++++++
 gtk/gtkaccessible.h | 39 +++++++++++++++++++++++++++++++++++++++
 gtk/gtkwidget.c     | 24 ++++++++++++++++++++++--
 gtk/meson.build     |  2 ++
 5 files changed, 94 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtk.h b/gtk/gtk.h
index c401443118..50c23caf26 100644
--- a/gtk/gtk.h
+++ b/gtk/gtk.h
@@ -34,6 +34,7 @@
 #include <gtk/gtkaboutdialog.h>
 #include <gtk/gtkaccelgroup.h>
 #include <gtk/gtkaccellabel.h>
+#include <gtk/gtkaccessible.h>
 #include <gtk/gtkactionable.h>
 #include <gtk/gtkactionbar.h>
 #include <gtk/gtkadjustment.h>
diff --git a/gtk/gtkaccessible.c b/gtk/gtkaccessible.c
new file mode 100644
index 0000000000..d8187b60c0
--- /dev/null
+++ b/gtk/gtkaccessible.c
@@ -0,0 +1,30 @@
+/* gtkaccessible.c: Accessible interface
+ *
+ * Copyright 2020  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * 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/>.
+ */
+
+#include "config.h"
+
+#include "gtkaccessible.h"
+
+G_DEFINE_INTERFACE (GtkAccessible, gtk_accessible, G_TYPE_OBJECT)
+
+static void
+gtk_accessible_default_init (GtkAccessibleInterface *iface)
+{
+}
diff --git a/gtk/gtkaccessible.h b/gtk/gtkaccessible.h
new file mode 100644
index 0000000000..d54d21a2d0
--- /dev/null
+++ b/gtk/gtkaccessible.h
@@ -0,0 +1,39 @@
+/* gtkaccessible.h: Accessible interface
+ *
+ * Copyright 2020  GNOME Foundation
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * 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/>.
+ */
+
+#pragma once
+
+#include <glib-object.h>
+#include <gtk/gtktypes.h>
+#include <gtk/gtkenums.h>
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_ACCESSIBLE (gtk_accessible_get_type())
+
+GDK_AVAILABLE_IN_ALL
+G_DECLARE_INTERFACE (GtkAccessible, gtk_accessible, GTK, ACCESSIBLE, GObject)
+
+struct _GtkAccessibleInterface
+{
+  GTypeInterface g_iface;
+};
+
+G_END_DECLS
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index e3da5273b9..00c7b8144b 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -27,6 +27,7 @@
 #include "gtkwidgetprivate.h"
 
 #include "gtkaccelgroupprivate.h"
+#include "gtkaccessible.h"
 #include "gtkapplicationprivate.h"
 #include "gtkbuildable.h"
 #include "gtkbuilderprivate.h"
@@ -598,6 +599,8 @@ static void             gtk_widget_real_measure                 (GtkWidget
 static void             gtk_widget_real_state_flags_changed     (GtkWidget        *widget,
                                                                  GtkStateFlags     old_state);
 
+static void             gtk_widget_accessible_interface_init    (GtkAccessibleInterface *iface);
+
 static void             gtk_widget_buildable_interface_init     (GtkBuildableIface  *iface);
 static void             gtk_widget_buildable_set_name           (GtkBuildable       *buildable,
                                                                  const gchar        *name);
@@ -679,6 +682,13 @@ gtk_widget_get_type (void)
        NULL,           /* value_table */
       };
 
+      const GInterfaceInfo accessible_info =
+      {
+        (GInterfaceInitFunc) gtk_widget_accessible_interface_init,
+        (GInterfaceFinalizeFunc) NULL,
+        NULL,
+      };
+
       const GInterfaceInfo buildable_info =
       {
        (GInterfaceInitFunc) gtk_widget_buildable_interface_init,
@@ -701,10 +711,12 @@ gtk_widget_get_type (void)
       GtkWidget_private_offset =
         g_type_add_instance_private (widget_type, sizeof (GtkWidgetPrivate));
 
+      g_type_add_interface_static (widget_type, GTK_TYPE_ACCESSIBLE,
+                                   &accessible_info);
       g_type_add_interface_static (widget_type, GTK_TYPE_BUILDABLE,
-                                   &buildable_info) ;
+                                   &buildable_info);
       g_type_add_interface_static (widget_type, GTK_TYPE_CONSTRAINT_TARGET,
-                                   &constraint_target_info) ;
+                                   &constraint_target_info);
     }
 
   return widget_type;
@@ -8046,6 +8058,14 @@ gtk_widget_set_vexpand_set (GtkWidget      *widget,
   gtk_widget_set_expand_set (widget, GTK_ORIENTATION_VERTICAL, set);
 }
 
+/*
+ * GtkAccessible implementation
+ */
+static void
+gtk_widget_accessible_interface_init (GtkAccessibleInterface *iface)
+{
+}
+
 /*
  * GtkBuildable implementation
  */
diff --git a/gtk/meson.build b/gtk/meson.build
index e6ecf867dc..fb0c7f9e41 100644
--- a/gtk/meson.build
+++ b/gtk/meson.build
@@ -149,6 +149,7 @@ gtk_public_sources = files([
   'gtkaboutdialog.c',
   'gtkaccelgroup.c',
   'gtkaccellabel.c',
+  'gtkaccessible.c',
   'gtkactionable.c',
   'gtkactionbar.c',
   'gtkadjustment.c',
@@ -435,6 +436,7 @@ gtk_public_headers = files([
   'gtkaboutdialog.h',
   'gtkaccelgroup.h',
   'gtkaccellabel.h',
+  'gtkaccessible.h',
   'gtkactionable.h',
   'gtkactionbar.h',
   'gtkadjustment.h',