[User Switcher] Ungrab keyboard before trying to lock the screen

Otherwise it fails to lock the screen and since it waits for the lock screen to show up before switching, it never does it.

BUG: 375941
FIXED-IN: 5.9.1

Differential Revision: https://phabricator.kde.org/D4470

components/sessionsprivate/sessionsmodel.cpp

@@ -98,6 +98,8 @@ void SessionsModel::switchUser(int vt, bool shouldLock)
         } else {
             m_pendingReserve = false;
             m_pendingVt = vt;
+
+            emit aboutToLockScreen();
             m_screensaverInterface->Lock();
         }
     });
@@ -123,6 +125,8 @@ void SessionsModel::startNewSession(bool shouldLock)
         } else {
             m_pendingReserve = true;
             m_pendingVt = 0;
+
+            emit aboutToLockScreen();
             m_screensaverInterface->Lock();
         }
     });

components/sessionsprivate/sessionsmodel.h

@@ -95,6 +95,7 @@ signals:
 
     void switchedUser(int vt);
     void startedNewSession();
+    void aboutToLockScreen();
 
 private:
     void checkScreenLocked(const std::function<void (bool)> &cb);

ksmserver/switchuserdialog.cpp

@@ -112,6 +112,7 @@ void KSMSwitchUserDialog::init()
     }
 
     connect(rootObject(), SIGNAL(dismissed()), this, SIGNAL(dismissed()));
+    connect(rootObject(), SIGNAL(ungrab()), this, SLOT(ungrab()));
 
     connect(screen(), &QScreen::geometryChanged, this, [this] {
         setGeometry(screen()->geometry());
@@ -122,6 +123,7 @@ void KSMSwitchUserDialog::init()
 
     KWindowSystem::setState(winId(), NET::SkipTaskbar|NET::SkipPager);
 
+    // in case you change this make sure to adjust ungrab() also
     setKeyboardGrabEnabled(true);
 }
 
@@ -163,3 +165,8 @@ void KSMSwitchUserDialog::setupWaylandIntegration()
     // maybe we need a dedicated type for it?
     m_shellSurface->setPosition(geometry().topLeft());
 }
+
+void KSMSwitchUserDialog::ungrab()
+{
+    setKeyboardGrabEnabled(false);
+}

ksmserver/switchuserdialog.h

@@ -50,6 +50,9 @@ signals:
 protected:
     bool event(QEvent *e) override;
 
+private slots:
+    void ungrab();
+
 private:
     void setupWaylandIntegration();
 

lookandfeel/contents/userswitcher/UserSwitcher.qml

@@ -33,6 +33,7 @@ PlasmaCore.ColorScope {
     colorGroup: PlasmaCore.Theme.ComplementaryColorGroup
 
     signal dismissed
+    signal ungrab
 
     height:screenGeometry.height
     width: screenGeometry.width
@@ -52,6 +53,8 @@ PlasmaCore.ColorScope {
         // returned leaving us do nothing (Bug 356945)
         onStartedNewSession: root.dismissed()
         onSwitchedUser: root.dismissed()
+
+        onAboutToLockScreen: root.ungrab()
     }
 
     Controls.Action {