Be able to obtain list of possible key combinations in platform integration

As there is no way to obtain the list of possible keys for a shortcut
in a platform independent way there needs to be a way to get that
from the platform integration.

Task-number: QTBUG-26902
Change-Id: I520add56ee09d5c3c58709fb29dad2fbfe4c9d0b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/gui/kernel/qkeymapper_qpa.cpp

@@ -43,6 +43,8 @@
 #include <qdebug.h>
 #include <private/qevent_p.h>
 #include <private/qlocale_p.h>
+#include <private/qguiapplication_p.h>
+#include <qpa/qplatformintegration.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -66,7 +68,10 @@ void QKeyMapperPrivate::clearMappings()
 
 QList<int> QKeyMapperPrivate::possibleKeys(QKeyEvent *e)
 {
-    QList<int> result;
+    QList<int> result = QGuiApplicationPrivate::platformIntegration()->possibleKeys(e);
+    if (!result.isEmpty())
+        return result;
+
     if (e->key() && (e->key() != Qt::Key_unknown))
         result << int(e->key() + e->modifiers());
     else if (!e->text().isEmpty())

src/gui/kernel/qplatformintegration.cpp

@@ -312,6 +312,20 @@ Qt::KeyboardModifiers QPlatformIntegration::queryKeyboardModifiers() const
     return QGuiApplication::keyboardModifiers();
 }
 
+/*!
+  Should be used to obtain a list of possible shortcuts for the given key
+  event. As that needs system functionality it cannot be done in qkeymapper.
+
+  One example for more than 1 possibility is the key combination of Shift+5.
+  That one might trigger a shortcut which is set as "Shift+5" as well as one
+  using %. These combinations depend on the currently set keyboard layout
+  which cannot be obtained by Qt functionality.
+*/
+QList<int> QPlatformIntegration::possibleKeys(const QKeyEvent *) const
+{
+    return QList<int>();
+}
+
 /*!
   Should be called by the implementation whenever a new screen is added.
 

src/gui/kernel/qplatformintegration.h

@@ -76,6 +76,7 @@ class QPlatformTheme;
 class QPlatformDialogHelper;
 class QPlatformSharedGraphicsCache;
 class QPlatformServices;
+class QKeyEvent;
 
 class Q_GUI_EXPORT QPlatformIntegration
 {
@@ -141,6 +142,7 @@ public:
     virtual QVariant styleHint(StyleHint hint) const;
 
     virtual Qt::KeyboardModifiers queryKeyboardModifiers() const;
+    virtual QList<int> possibleKeys(const QKeyEvent *) const;
 
     virtual QStringList themeNames() const;
     virtual QPlatformTheme *createPlatformTheme(const QString &name) const;