Added a11y initialization code

This basically:
  * Checks a11y configuration properties
  * Checks if clutter has a11y enabled
  * Loads atk-bridge

It also ensure proper NO_GAIL and NO_AT_BRIDGE values on gnome-shell
startup script

https://bugzilla.gnome.org/show_bug.cgi?id=612599

src/Makefile.am

@@ -81,6 +81,8 @@ libgnome_shell_la_SOURCES =		\
 	shell-wm-private.h		\
 	gnome-shell-plugin.c		\
 	shell-app.c			\
+	shell-a11y.h			\
+	shell-a11y.c			\
 	shell-app-system.c		\
 	shell-app-usage.c		\
 	shell-arrow.c			\

src/gnome-shell-plugin.c

@@ -52,6 +52,7 @@
 #include "shell-perf-log.h"
 #include "shell-wm-private.h"
 #include "st.h"
+#include "shell-a11y.h"
 
 static void gnome_shell_plugin_dispose     (GObject *object);
 static void gnome_shell_plugin_finalize    (GObject *object);
@@ -420,6 +421,8 @@ gnome_shell_plugin_start (MetaPlugin *plugin)
   bindtextdomain (GETTEXT_PACKAGE, LOCALEDIR);
   bind_textdomain_codeset (GETTEXT_PACKAGE, "UTF-8");
 
+  shell_a11y_init ();
+
   settings = gtk_settings_get_default ();
   g_object_connect (settings,
                     "signal::notify::gtk-xft-dpi",

src/gnome-shell.in

@@ -219,12 +219,23 @@ def start_shell(perf_output=None):
         js_dir = os.path.join('@pkgdatadir@', 'js')
 
     # Set up environment
+
+    # About the value of NO_GAIL and NO_AT_BRIDGE: If a11y is enabled,
+    # gtk_init() will normally load gail and at-bridge. But we don't
+    # want at-bridge to be loaded until after clutter is initialized
+    # (which mutter does after initializing gtk) and we don't want
+    # gail to be loaded at all. So set these flags.  shell_a11y_init()
+    # will clear them so they don't get passed to gnome-shell's
+    # children.
+
     env = dict(os.environ)
     env.update({'GNOME_SHELL_JS'      : js_dir,
                 'PATH'                : '@MUTTER_BIN_DIR@:' + os.environ.get('PATH', ''),
                 'XDG_CONFIG_DIRS'     : '@sysconfdir@/xdg:' + (os.environ.get('XDG_CONFIG_DIRS') or '/etc/xdg'),
                 'XDG_DATA_DIRS'       : '@datadir@:' + (os.environ.get('XDG_DATA_DIRS') or '/usr/local/share:/usr/share'),
-                'GNOME_DISABLE_CRASH_DIALOG' : '1'})
+                'GNOME_DISABLE_CRASH_DIALOG' : '1',
+                'NO_GAIL'             : '1',
+                'NO_AT_BRIDGE'        : '1'})
 
     if running_from_source_tree:
         env.update({'GNOME_SHELL_DATADIR'  : data_dir,

src/shell-a11y.c

@@ -0,0 +1,165 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright (C) 2010 Igalia, S.L.
+ *
+ * Author: Alejandro Piñeiro Iglesias <apinheiro@igalia.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ */
+
+#include <string.h>
+#include <gmodule.h>
+#include <clutter/clutter.h>
+
+#include "shell-a11y.h"
+
+#define INIT_METHOD "gnome_accessibility_module_init"
+#define DESKTOP_SCHEMA "org.gnome.desktop.interface"
+#define ACCESSIBILITY_ENABLED_KEY "accessibility"
+#define AT_SPI_SCHEMA "org.a11y.atspi"
+#define ATK_BRIDGE_LOCATION_KEY "atk-bridge-location"
+
+static gboolean
+should_enable_a11y (void)
+{
+  GSettings *desktop_settings = NULL;
+  gboolean value = FALSE;
+
+  desktop_settings = g_settings_new (DESKTOP_SCHEMA);
+  value = g_settings_get_boolean (desktop_settings, ACCESSIBILITY_ENABLED_KEY);
+
+  g_object_unref (desktop_settings);
+
+  return value;
+}
+
+static char*
+get_atk_bridge_path (void)
+{
+  GSettings *atspi_settings = NULL;
+  char *value = NULL;
+  const char * const *schemas = NULL;
+  gboolean found = FALSE;
+  int i = 0;
+
+  schemas = g_settings_list_schemas ();
+
+  for (i = 0; schemas [i]; i++)
+    {
+      if (!strcmp (schemas[i], AT_SPI_SCHEMA))
+        {
+          found = TRUE;
+          break;
+        }
+    }
+
+  if (!found)
+    {
+      g_warning ("Accessibility: %s schema not found. Are you sure that at-spi or"
+                 " at-spi2 is installed on your system?", AT_SPI_SCHEMA);
+      return NULL;
+    }
+
+  atspi_settings = g_settings_new (AT_SPI_SCHEMA);
+  value = g_settings_get_string (atspi_settings, ATK_BRIDGE_LOCATION_KEY);
+
+  g_object_unref (atspi_settings);
+
+  return value;
+}
+
+static gboolean
+a11y_invoke_module (const char *module_path)
+{
+  GModule    *handle;
+  void      (*invoke_fn) (void);
+
+  if (!module_path)
+    {
+      g_warning ("Accessibility: invalid module path (NULL)");
+
+      return FALSE;
+    }
+
+  if (!(handle = g_module_open (module_path, 0)))
+    {
+      g_warning ("Accessibility: failed to load module '%s': '%s'",
+                 module_path, g_module_error ());
+
+      return FALSE;
+    }
+
+  if (!g_module_symbol (handle, INIT_METHOD, (gpointer *)&invoke_fn))
+    {
+      g_warning ("Accessibility: error library '%s' does not include "
+                 "method '%s' required for accessibility support",
+                 module_path, INIT_METHOD);
+      g_module_close (handle);
+
+      return FALSE;
+    }
+
+  invoke_fn ();
+
+  return TRUE;
+}
+
+/*
+ * It loads the atk-bridge if required. It checks:
+ *  * If the proper gsetting key is set
+ *  * If clutter has already enabled the accessibility
+ *
+ * You need to ensure that the atk-bridge was not loaded before this
+ * call, because in that case the application would be already
+ * registered on at-spi using the AtkUtil implementation on that
+ * moment (if any, although without anyone the application would
+ * crash). Anyway this is the reason of NO_AT_BRIDGE.
+ *
+ */
+void
+shell_a11y_init (void)
+{
+  char *bridge_path = NULL;
+
+  g_unsetenv ("NO_AT_BRIDGE");
+  g_unsetenv ("NO_GAIL");
+
+  if (!should_enable_a11y ())
+    return;
+
+  if (clutter_get_accessibility_enabled () == FALSE)
+    {
+      g_warning ("Accessibility: clutter has no accessibility enabled"
+                 " skipping the atk-bridge load");
+      return;
+    }
+
+  bridge_path = get_atk_bridge_path ();
+
+  if (a11y_invoke_module (bridge_path) == FALSE)
+    {
+      g_warning ("Accessibility: error loading the atk-bridge. Although the"
+                 " accessibility on the system is enabled and clutter"
+                 " accessibility is also enabled, accessibility support on"
+                 " GNOME Shell will not work");
+    }
+
+  /* NOTE: We avoid to load gail module, as gail-cally interaction is
+   * not fully supported right now.
+   */
+
+  g_free (bridge_path);
+}

src/shell-a11y.h

@@ -0,0 +1,32 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright (C) 2010 Igalia, S.L.
+ *
+ * Author: Alejandro Piñeiro Iglesias <apinheiro@igalia.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ */
+
+#ifndef __SHELL_A11Y_H_
+#define __SHELL_A11Y_H_
+
+G_BEGIN_DECLS
+
+void shell_a11y_init (void);
+
+G_END_DECLS
+
+#endif /* __SHELL_A11Y_H_ */