inputmethod: improve the integration of the SNI

* Adds a context menu to choose virtual keyboards.
* Notifies when there is no virtual keyboard selected.

src/inputmethod.cpp

@@ -32,6 +32,7 @@
 #include <QDBusConnection>
 #include <QDBusPendingCall>
 #include <QDBusMessage>
+#include <QMenu>
 
 #include <linux/input-event-codes.h>
 #include <xkbcommon/xkbcommon-keysyms.h>
@@ -81,11 +82,20 @@ void InputMethod::init()
     }
 
     qCDebug(KWIN_VIRTUALKEYBOARD) << "Registering the SNI";
+
+    QMenu *sniMenu = new QMenu;
+    sniMenu->addAction(i18n("Configure virtual keyboards..."), this, [] {
+        QProcess::startDetached("systemsettings5", {"kcm_virtualkeyboard"});
+    });
+
     m_sni = new KStatusNotifierItem(QStringLiteral("kwin-virtual-keyboard"), this);
     m_sni->setStandardActionsEnabled(false);
     m_sni->setCategory(KStatusNotifierItem::Hardware);
     m_sni->setStatus(KStatusNotifierItem::Passive);
     m_sni->setTitle(i18n("Virtual Keyboard"));
+    m_sni->setToolTipTitle(i18n("Whether to show the virtual keyboard on demand."));
+    m_sni->setStandardActionsEnabled(false);
+    m_sni->setContextMenu(sniMenu);
     updateSni();
     connect(m_sni, &KStatusNotifierItem::activateRequested, this,
         [this] {
@@ -508,14 +518,19 @@ void InputMethod::updateSni()
     if (!m_sni) {
         return;
     }
-    if (m_enabled) {
+    if (m_inputMethodCommand.isEmpty()) {
+        m_sni->setIconByName(QStringLiteral("input-keyboard-virtual-on"));
+        m_sni->setOverlayIconByName(QStringLiteral("emblem-unavailable"));
+        m_sni->setTitle(i18n("No Virtual Keyboard configured"));
+    } else if (m_enabled) {
         m_sni->setIconByName(QStringLiteral("input-keyboard-virtual-on"));
         m_sni->setTitle(i18n("Virtual Keyboard: enabled"));
+        m_sni->setOverlayIconByName({});
     } else {
         m_sni->setIconByName(QStringLiteral("input-keyboard-virtual-off"));
         m_sni->setTitle(i18n("Virtual Keyboard: disabled"));
+        m_sni->setOverlayIconByName({});
     }
-    m_sni->setToolTipTitle(i18n("Whether to show the virtual keyboard on demand."));
 }
 
 void InputMethod::updateInputPanelState()
@@ -547,6 +562,7 @@ void InputMethod::setInputMethodCommand(const QString &command)
     if (m_enabled) {
         startInputMethod();
     }
+    updateSni();
 }
 
 void InputMethod::stopInputMethod()