a11y atspi: Watch for enabled status change

On log-in this may be disabled and only enabled later; that prevents
clients like plasmashell to enable a11y features.
We need to watch changes to the org.a11y.Status properties and enable
the a11y integration on-demand.

As the in-line comment said, qdbusxml2cpp does not generate NOTIFY
signals for DBus properties, so use the raw PropertiesChanged signal
to receive those notifications.

Downstream bugs:
- https://bugs.kde.org/show_bug.cgi?id=495096
- https://bugs.kde.org/show_bug.cgi?id=495098

Pick-to: 6.7
Pick-to: 6.7
Change-Id: I4d0adf61af875464d3cd47759631d2a3aac664f0
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
(cherry picked from commit 38251c36edf11316a2467169b1d491bf13520fd3)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/CMakeLists.txt

@@ -565,6 +565,7 @@ qt_internal_extend_target(Gui CONDITION atspi_accessibility
     DBUS_INTERFACE_SOURCES
         accessible/linux/dbusxml/Bus.xml
         accessible/linux/dbusxml/Socket.xml
+        accessible/linux/dbusxml/org.freedesktop.DBus.Properties.xml
     DBUS_INTERFACE_FLAGS
         "-i" "QtGui/private/qspi_struct_marshallers_p.h"
 )

src/gui/accessible/linux/dbusconnection.cpp

@@ -10,7 +10,6 @@
 #include <qdebug.h>
 
 #include <QDBusConnectionInterface>
-#include "bus_interface.h"
 
 #include <QtGui/qguiapplication.h>
 #include <qpa/qplatformnativeinterface.h>
@@ -49,12 +48,22 @@ QAtSpiDBusConnection::QAtSpiDBusConnection(QObject *parent)
         return;
     }
 
+    m_a11yStatus = new OrgA11yStatusInterface(A11Y_SERVICE, A11Y_PATH, c, this);
+    m_dbusProperties = new OrgFreedesktopDBusPropertiesInterface(A11Y_SERVICE, A11Y_PATH, c, this);
+
     dbusWatcher = new QDBusServiceWatcher(A11Y_SERVICE, c, QDBusServiceWatcher::WatchForRegistration, this);
-    connect(dbusWatcher, SIGNAL(serviceRegistered(QString)), this, SLOT(serviceRegistered()));
+    connect(dbusWatcher, SIGNAL(checkEnabledState(QString)), this, SLOT(checkEnabledState()));
 
     // If it is registered already, setup a11y right away
     if (c.interface()->isServiceRegistered(A11Y_SERVICE))
-        serviceRegistered();
+        checkEnabledState();
+
+    // Subscribe to updates about a11y enabled state.
+    connect(m_dbusProperties, &OrgFreedesktopDBusPropertiesInterface::PropertiesChanged,
+            this, [this](const QString &interface_name) {
+        if (interface_name == QLatin1StringView(OrgA11yStatusInterface::staticInterfaceName()))
+            checkEnabledState();
+    });
 
     if (QGuiApplication::platformName().startsWith("xcb"_L1)) {
         // In addition try if there is an xatom exposing the bus address, this allows applications run as root to work
@@ -82,21 +91,14 @@ QString QAtSpiDBusConnection::getAddressFromXCB()
     return QString();
 }
 
-// We have the a11y registry on the session bus.
+void QAtSpiDBusConnection::checkEnabledState()
-// Subscribe to updates about a11y enabled state.
-// Find out the bus address
-void QAtSpiDBusConnection::serviceRegistered()
 {
-    // listen to enabled changes
-    QDBusConnection c = QDBusConnection::sessionBus();
-    OrgA11yStatusInterface *a11yStatus = new OrgA11yStatusInterface(A11Y_SERVICE, A11Y_PATH, c, this);
-
     //The variable was introduced because on some embedded platforms there are custom accessibility
     //clients which don't set Status.ScreenReaderEnabled to true. The variable is also useful for
     //debugging.
     static const bool a11yAlwaysOn = qEnvironmentVariableIsSet("QT_LINUX_ACCESSIBILITY_ALWAYS_ON");
 
-    bool enabled = a11yAlwaysOn || a11yStatus->screenReaderEnabled() || a11yStatus->isEnabled();
+    bool enabled = a11yAlwaysOn || m_a11yStatus->screenReaderEnabled() || m_a11yStatus->isEnabled();
 
     if (enabled != m_enabled) {
         m_enabled = enabled;
@@ -109,8 +111,6 @@ void QAtSpiDBusConnection::serviceRegistered()
             c.callWithCallback(m, this, SLOT(connectA11yBus(QString)), SLOT(dbusError(QDBusError)));
         }
     }
-
-    //    connect(a11yStatus, ); QtDbus doesn't support notifications for property changes yet
 }
 
 void QAtSpiDBusConnection::serviceUnregistered()

src/gui/accessible/linux/dbusconnection_p.h

@@ -23,6 +23,9 @@
 #include <QtCore/private/qglobal_p.h>
 Q_MOC_INCLUDE(<QtDBus/QDBusError>)
 
+#include "bus_interface.h"
+#include "properties_interface.h"
+
 QT_BEGIN_NAMESPACE
 
 class QDBusServiceWatcher;
@@ -42,7 +45,7 @@ Q_SIGNALS:
 
 private Q_SLOTS:
     QString getAddressFromXCB();
-    void serviceRegistered();
+    void checkEnabledState();
     void serviceUnregistered();
     void connectA11yBus(const QString &address);
 
@@ -52,6 +55,8 @@ private:
     QString getAccessibilityBusAddress() const;
 
     QDBusServiceWatcher *dbusWatcher;
+    OrgFreedesktopDBusPropertiesInterface *m_dbusProperties;
+    OrgA11yStatusInterface *m_a11yStatus;
     QDBusConnection m_a11yConnection;
     bool m_enabled;
 };

src/gui/accessible/linux/dbusxml/org.freedesktop.DBus.Properties.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" ?>
+<node>
+  <interface name="org.freedesktop.DBus.Properties">
+    <method name="Get">
+      <arg type="s" name="interface_name" direction="in"/>
+      <arg type="s" name="property_name" direction="in"/>
+      <arg type="v" name="value" direction="out"/>
+    </method>
+    <method name="GetAll">
+      <arg type="s" name="interface_name" direction="in"/>
+      <arg type="a{sv}" name="properties" direction="out"/>
+      <annotation name="org.qtproject.QtDBus.QtTypeName.Out0" value="QVariantMap"/>
+    </method>
+    <method name="Set">
+      <arg type="s" name="interface_name" direction="in"/>
+      <arg type="s" name="property_name" direction="in"/>
+      <arg type="v" name="value" direction="in"/>
+    </method>
+    <signal name="PropertiesChanged">
+      <arg type="s" name="interface_name"/>
+      <arg type="a{sv}" name="changed_properties"/>
+      <arg type="as" name="invalidated_properties"/>
+      <annotation name="org.qtproject.QtDBus.QtTypeName.Out1" value="QVariantMap"/>
+    </signal>
+  </interface>
+</node>