Make QSignalTransition take a pointer-to-const QObject

The obvious idea is that a connect() happens behind the scenes.
As QObject::connect takes a pointer-to-const, QSignalTransition should
do that as well.

TODO: the API becomes asymmetric in that it takes
a "const QObject *" but returns a "QObject *". Reasoning is needed.

Change-Id: I18d0436e7036eee851fd36d5b8ccda4a4757938f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>

src/corelib/statemachine/qsignaltransition.cpp

@@ -148,7 +148,7 @@ QSignalTransition::QSignalTransition(QState *sourceState)
   Constructs a new signal transition associated with the given \a signal of
   the given \a sender, and with the given \a sourceState.
 */
-QSignalTransition::QSignalTransition(QObject *sender, const char *signal,
+QSignalTransition::QSignalTransition(const QObject *sender, const char *signal,
                                      QState *sourceState)
     : QAbstractTransition(*new QSignalTransitionPrivate, sourceState)
 {
@@ -171,13 +171,13 @@ QSignalTransition::~QSignalTransition()
 QObject *QSignalTransition::senderObject() const
 {
     Q_D(const QSignalTransition);
-    return d->sender;
+    return const_cast<QObject *>(d->sender);
 }
 
 /*!
   Sets the \a sender object associated with this signal transition.
 */
-void QSignalTransition::setSenderObject(QObject *sender)
+void QSignalTransition::setSenderObject(const QObject *sender)
 {
     Q_D(QSignalTransition);
     if (sender == d->sender)

src/corelib/statemachine/qsignaltransition.h

@@ -59,12 +59,12 @@ class Q_CORE_EXPORT QSignalTransition : public QAbstractTransition
     Q_PROPERTY(QByteArray signal READ signal WRITE setSignal)
 public:
     QSignalTransition(QState *sourceState = 0);
-    QSignalTransition(QObject *sender, const char *signal,
+    QSignalTransition(const QObject *sender, const char *signal,
                       QState *sourceState = 0);
     ~QSignalTransition();
 
     QObject *senderObject() const;
-    void setSenderObject(QObject *sender);
+    void setSenderObject(const QObject *sender);
 
     QByteArray signal() const;
     void setSignal(const QByteArray &signal);

src/corelib/statemachine/qsignaltransition_p.h

@@ -71,7 +71,7 @@ public:
 
     virtual void callOnTransition(QEvent *e);
 
-    QObject *sender;
+    const QObject *sender;
     QByteArray signal;
     int signalIndex;
     int originalSignalIndex;

src/corelib/statemachine/qstate.cpp

@@ -348,7 +348,7 @@ void QState::addTransition(QAbstractTransition *transition)
   object, and returns the new QSignalTransition object. The transition has
   this state as the source, and the given \a target as the target state.
 */
-QSignalTransition *QState::addTransition(QObject *sender, const char *signal,
+QSignalTransition *QState::addTransition(const QObject *sender, const char *signal,
                                          QAbstractState *target)
 {
     if (!sender) {

src/corelib/statemachine/qstate.h

@@ -83,7 +83,7 @@ public:
     void setErrorState(QAbstractState *state);
 
     void addTransition(QAbstractTransition *transition);
-    QSignalTransition *addTransition(QObject *sender, const char *signal, QAbstractState *target);
+    QSignalTransition *addTransition(const QObject *sender, const char *signal, QAbstractState *target);
     QAbstractTransition *addTransition(QAbstractState *target);
     void removeTransition(QAbstractTransition *transition);
     QList<QAbstractTransition*> transitions() const;

src/corelib/statemachine/qstatemachine.cpp

@@ -1739,7 +1739,7 @@ void QStateMachinePrivate::registerSignalTransition(QSignalTransition *transitio
     Q_Q(QStateMachine);
     if (QSignalTransitionPrivate::get(transition)->signalIndex != -1)
         return; // already registered
-    QObject *sender = QSignalTransitionPrivate::get(transition)->sender;
+    const QObject *sender = QSignalTransitionPrivate::get(transition)->sender;
     if (!sender)
         return;
     QByteArray signal = QSignalTransitionPrivate::get(transition)->signal;