client: reimplement QPlatformIntegration::possibleKeys()

This is required to trigger more complex shortcut sequences. For
example, with 'us' keyboard layout to enter '%' or '+' you have to
press 'Shift' button. Previosly the following shortcuts could not be
triggered:

'Shift' + '5'
'%'

'Ctrl' + '+'
'Ctrl' + 'Shift' + '='

The same function also ensures that these shortcuts work with non-latin
keyboard layouts.

Change-Id: Id50c7bb28cf76b9f7a861ced7894b2cacae6ed65
Reviewed-by: David Edmundson <davidedmundson@kde.org>
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>
Reviewed-by: Johan Helsing <johan.helsing@qt.io>

src/plugins/platforms/wayland/qwaylandinputdevice.cpp

@@ -476,6 +476,17 @@ QPointF QWaylandInputDevice::pointerSurfacePosition() const
     return mPointer ? mPointer->mSurfacePos : QPointF();
 }
 
+QList<int> QWaylandInputDevice::possibleKeys(const QKeyEvent *event) const
+{
+#if QT_CONFIG(xkbcommon)
+    if (mKeyboard && mKeyboard->mXkbState)
+        return QXkbCommon::possibleKeys(mKeyboard->mXkbState.get(), event);
+#else
+    Q_UNUSED(event);
+#endif
+    return {};
+}
+
 Qt::KeyboardModifiers QWaylandInputDevice::modifiers() const
 {
     if (!mKeyboard)

src/plugins/platforms/wayland/qwaylandinputdevice_p.h

@@ -124,6 +124,8 @@ public:
     QWaylandWindow *keyboardFocus() const;
     QWaylandWindow *touchFocus() const;
 
+    QList<int> possibleKeys(const QKeyEvent *event) const;
+
     QPointF pointerSurfacePosition() const;
 
     Qt::KeyboardModifiers modifiers() const;
@@ -245,6 +247,7 @@ private:
     QXkbCommon::ScopedXKBKeymap mXkbKeymap;
     QXkbCommon::ScopedXKBState mXkbState;
 #endif
+    friend class QWaylandInputDevice;
 };
 
 class Q_WAYLAND_CLIENT_EXPORT QWaylandInputDevice::Pointer : public QObject, public QtWayland::wl_pointer

src/plugins/platforms/wayland/qwaylandintegration.cpp

@@ -293,6 +293,13 @@ QWaylandDisplay *QWaylandIntegration::display() const
     return mDisplay.data();
 }
 
+QList<int> QWaylandIntegration::possibleKeys(const QKeyEvent *event) const
+{
+    if (auto *seat = mDisplay->currentInputDevice())
+        return seat->possibleKeys(event);
+    return {};
+}
+
 QStringList QWaylandIntegration::themeNames() const
 {
     return GenericWaylandTheme::themeNames();

src/plugins/platforms/wayland/qwaylandintegration_p.h

@@ -106,6 +106,8 @@ public:
 
     QWaylandDisplay *display() const;
 
+    QList<int> possibleKeys(const QKeyEvent *event) const override;
+
     QStringList themeNames() const override;
 
     QPlatformTheme *createPlatformTheme(const QString &name) const override;