XCB: Set WM_CLASS.

Set the instance name and class name of the application windows.

Task-number: QTBUG-29396

Change-Id: Ia1fb492ab169108c3779deb8964bb731b322dd89
Reviewed-by: Uli Schlachter <psychon@znc.in>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

src/plugins/platforms/xcb/qxcbconnection.cpp

@@ -1232,6 +1232,7 @@ static const char * xcb_atomnames = {
     // ICCCM window state
     "WM_STATE\0"
     "WM_CHANGE_STATE\0"
+    "WM_CLASS\0"
 
     // Session management
     "WM_CLIENT_LEADER\0"

src/plugins/platforms/xcb/qxcbconnection.h

@@ -102,6 +102,7 @@ namespace QXcbAtom {
         // ICCCM window state
         WM_STATE,
         WM_CHANGE_STATE,
+        WM_CLASS,
 
         // Session management
         WM_CLIENT_LEADER,

src/plugins/platforms/xcb/qxcbintegration.cpp

@@ -369,4 +369,48 @@ QVariant QXcbIntegration::styleHint(QPlatformIntegration::StyleHint hint) const
     return QPlatformIntegration::styleHint(hint);
 }
 
+static QString argv0BaseName()
+{
+    QString result;
+    const QStringList arguments = QCoreApplication::arguments();
+    if (!arguments.isEmpty() && !arguments.front().isEmpty()) {
+        result = arguments.front();
+        const int lastSlashPos = result.lastIndexOf(QLatin1Char('/'));
+        if (lastSlashPos != -1)
+            result.remove(0, lastSlashPos + 1);
+    }
+    return result;
+}
+
+static const char resourceNameVar[] = "RESOURCE_NAME";
+
+QByteArray QXcbIntegration::wmClass() const
+{
+    if (m_wmClass.isEmpty()) {
+        // Instance name according to ICCCM 4.1.2.5
+        QString name;
+        if (name.isEmpty() && qEnvironmentVariableIsSet(resourceNameVar))
+            name = QString::fromLocal8Bit(qgetenv(resourceNameVar));
+        if (name.isEmpty())
+            name = argv0BaseName();
+
+        // Note: QCoreApplication::applicationName() cannot be called from the QGuiApplication constructor,
+        // hence this delayed initialization.
+        QString className = QCoreApplication::applicationName();
+        if (className.isEmpty()) {
+            className = argv0BaseName();
+            if (!className.isEmpty() && className.at(0).isLower())
+                className[0] = className.at(0).toUpper();
+        }
+
+        if (!name.isEmpty() && !className.isEmpty()) {
+            m_wmClass = name.toLocal8Bit();
+            m_wmClass.append('\0');
+            m_wmClass.append(className.toLocal8Bit());
+            m_wmClass.append('\0');
+        }
+    }
+    return m_wmClass;
+}
+
 QT_END_NAMESPACE

src/plugins/platforms/xcb/qxcbintegration.h

@@ -99,6 +99,8 @@ public:
 
     QXcbConnection *defaultConnection() const { return m_connections.first(); }
 
+    QByteArray wmClass() const;
+
 private:
     QList<QXcbConnection *> m_connections;
 
@@ -115,6 +117,8 @@ private:
     QScopedPointer<QPlatformServices> m_services;
 
     friend class QXcbConnection; // access QPlatformIntegration::screenAdded()
+
+    mutable QByteArray m_wmClass;
 };
 
 QT_END_NAMESPACE

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -379,6 +379,13 @@ void QXcbWindow::create()
     m_syncValue.hi = 0;
     m_syncValue.lo = 0;
 
+    const QByteArray wmClass = static_cast<QXcbIntegration *>(QGuiApplicationPrivate::platformIntegration())->wmClass();
+    if (!wmClass.isEmpty()) {
+        Q_XCB_CALL(xcb_change_property(xcb_connection(), XCB_PROP_MODE_REPLACE,
+                                       m_window, atom(QXcbAtom::WM_CLASS),
+                                       XCB_ATOM_STRING, 8, wmClass.size(), wmClass.constData()));
+    }
+
     if (m_usingSyncProtocol) {
         m_syncCounter = xcb_generate_id(xcb_connection());
         Q_XCB_CALL(xcb_sync_create_counter(xcb_connection(), m_syncCounter, m_syncValue));