Use Q_STATIC_ASSERT to report error about missing Q_OBJECT

Q_STATIC_ASSERT gives better error with C++11 enabled.

Aslo the qt_check_for_QOBJECT_macro had warning on some compiler since
it used null reference

Change-Id: Ic6115da800064b00c50a5762f0b79f5f656bf750
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

5 files changed, 34 insertions, 13 deletions

diff --git a/src/corelib/kernel/qmetaobject.h b/src/corelib/kernel/qmetaobject.h
index 0c8ad8591f..818613195d 100644
--- a/src/corelib/kernel/qmetaobject.h
+++ b/src/corelib/kernel/qmetaobject.h
@@ -148,8 +148,8 @@ public:
     static inline QMetaMethod fromSignal(Func signal)
     {
         typedef QtPrivate::FunctionPointer<Func> SignalType;
-        reinterpret_cast<typename SignalType::Object *>(0)->qt_check_for_QOBJECT_macro(
-                    *reinterpret_cast<typename SignalType::Object *>(0));
+        Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value,
+                          "No Q_OBJECT in the class with the signal");
         return fromSignalImpl(&SignalType::Object::staticMetaObject,
                               reinterpret_cast<void **>(&signal));
     }
diff --git a/src/corelib/kernel/qobject.h b/src/corelib/kernel/qobject.h
index aaa09fac50..9d49bf26d2 100644
--- a/src/corelib/kernel/qobject.h
+++ b/src/corelib/kernel/qobject.h
@@ -217,7 +217,9 @@ public:
     {
         typedef QtPrivate::FunctionPointer<Func1> SignalType;
         typedef QtPrivate::FunctionPointer<Func2> SlotType;
-        reinterpret_cast<typename SignalType::Object *>(0)->qt_check_for_QOBJECT_macro(*reinterpret_cast<typename SignalType::Object *>(0));
+
+        Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value,
+                          "No Q_OBJECT in the class with the signal");
 
         //compilation error if the arguments does not match.
         Q_STATIC_ASSERT_X(int(SignalType::ArgumentCount) >= int(SlotType::ArgumentCount),
@@ -246,6 +248,9 @@ public:
         typedef QtPrivate::FunctionPointer<Func1> SignalType;
         typedef QtPrivate::FunctionPointer<Func2> SlotType;
 
+        Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value,
+                          "No Q_OBJECT in the class with the signal");
+
         //compilation error if the arguments does not match.
         Q_STATIC_ASSERT_X(int(SignalType::ArgumentCount) >= int(SlotType::ArgumentCount),
                           "The slot requires more arguments than the signal provides.");
@@ -307,6 +312,9 @@ public:
         Q_STATIC_ASSERT_X((QtPrivate::AreArgumentsCompatible<SlotReturnType, typename SignalType::ReturnType>::value),
                           "Return type of the slot is not compatible with the return type of the signal.");
 
+        Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value,
+                          "No Q_OBJECT in the class with the signal");
+
         return connectImpl(sender, reinterpret_cast<void **>(&signal), sender, 0,
                            new QtPrivate::QFunctorSlotObject<Func2, SlotArgumentCount,
                                 typename QtPrivate::List_Left<typename SignalType::Arguments, SlotArgumentCount>::Value,
@@ -335,7 +343,9 @@ public:
     {
         typedef QtPrivate::FunctionPointer<Func1> SignalType;
         typedef QtPrivate::FunctionPointer<Func2> SlotType;
-        reinterpret_cast<typename SignalType::Object *>(0)->qt_check_for_QOBJECT_macro(*reinterpret_cast<typename SignalType::Object *>(0));
+
+        Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value,
+                          "No Q_OBJECT in the class with the signal");
 
         //compilation error if the arguments does not match.
         Q_STATIC_ASSERT_X((QtPrivate::CheckCompatibleArguments<typename SignalType::Arguments, typename SlotType::Arguments>::value),
@@ -477,18 +487,18 @@ inline QT_DEPRECATED QList<T> qFindChildren(const QObject *o, const QRegExp &re)
 template <class T>
 inline T qobject_cast(QObject *object)
 {
-#if !defined(QT_NO_QOBJECT_CHECK)
-    reinterpret_cast<T>(object)->qt_check_for_QOBJECT_macro(*reinterpret_cast<T>(object));
-#endif
+    typedef typename QtPrivate::remove_cv<typename QtPrivate::remove_pointer<T>::type>::type ObjType;
+    Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<ObjType>::Value,
+                    "qobject_cast require the type to have a Q_OBJECT macro");
     return static_cast<T>(reinterpret_cast<T>(object)->staticMetaObject.cast(object));
 }
 
 template <class T>
 inline T qobject_cast(const QObject *object)
 {
-#if !defined(QT_NO_QOBJECT_CHECK)
-    reinterpret_cast<T>(object)->qt_check_for_QOBJECT_macro(*reinterpret_cast<T>(const_cast<QObject *>(object)));
-#endif
+    typedef typename QtPrivate::remove_cv<typename QtPrivate::remove_pointer<T>::type>::type ObjType;
+    Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<ObjType>::Value,
+                      "qobject_cast require the type to have a Q_OBJECT macro");
     return static_cast<T>(reinterpret_cast<T>(object)->staticMetaObject.cast(object));
 }
 
diff --git a/src/corelib/kernel/qobject_impl.h b/src/corelib/kernel/qobject_impl.h
index 0b5631f2a6..1bbd548be6 100644
--- a/src/corelib/kernel/qobject_impl.h
+++ b/src/corelib/kernel/qobject_impl.h
@@ -204,7 +204,6 @@ namespace QtPrivate {
     public:
         explicit QFunctorSlotObject(const Func &f) : QSlotObjectBase(&impl), function(f) {}
     };
-
 }
 
 
diff --git a/src/corelib/kernel/qobject_p.h b/src/corelib/kernel/qobject_p.h
index 3c43972ac9..562b0d24c7 100644
--- a/src/corelib/kernel/qobject_p.h
+++ b/src/corelib/kernel/qobject_p.h
@@ -316,7 +316,8 @@ inline QMetaObject::Connection QObjectPrivate::connect(const typename QtPrivate:
 {
     typedef QtPrivate::FunctionPointer<Func1> SignalType;
     typedef QtPrivate::FunctionPointer<Func2> SlotType;
-    reinterpret_cast<typename SignalType::Object *>(0)->qt_check_for_QOBJECT_macro(*reinterpret_cast<typename SignalType::Object *>(0));
+    Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value,
+                      "No Q_OBJECT in the class with the signal");
 
     //compilation error if the arguments does not match.
     Q_STATIC_ASSERT_X(int(SignalType::ArgumentCount) >= int(SlotType::ArgumentCount),
@@ -343,7 +344,8 @@ bool QObjectPrivate::disconnect(const typename QtPrivate::FunctionPointer< Func1
 {
     typedef QtPrivate::FunctionPointer<Func1> SignalType;
     typedef QtPrivate::FunctionPointer<Func2> SlotType;
-    reinterpret_cast<typename SignalType::Object *>(0)->qt_check_for_QOBJECT_macro(*reinterpret_cast<typename SignalType::Object *>(0));
+    Q_STATIC_ASSERT_X(QtPrivate::HasQ_OBJECT_Macro<typename SignalType::Object>::Value,
+                      "No Q_OBJECT in the class with the signal");
     //compilation error if the arguments does not match.
     Q_STATIC_ASSERT_X((QtPrivate::CheckCompatibleArguments<typename SignalType::Arguments, typename SlotType::Arguments>::value),
                       "Signal and slot arguments are not compatible.");
diff --git a/src/corelib/kernel/qobjectdefs.h b/src/corelib/kernel/qobjectdefs.h
index dd10e70609..7354c3f0d0 100644
--- a/src/corelib/kernel/qobjectdefs.h
+++ b/src/corelib/kernel/qobjectdefs.h
@@ -480,6 +480,16 @@ public:
 inline const QMetaObject *QMetaObject::superClass() const
 { return d.superdata; }
 
+namespace QtPrivate {
+    /* Trait that tells is a the Object has a Q_OBJECT macro */
+    template <typename Object> struct HasQ_OBJECT_Macro {
+        template <typename T>
+        static char test(int (T::*)(QMetaObject::Call, int, void **));
+        static int test(int (Object::*)(QMetaObject::Call, int, void **));
+        enum { Value =  sizeof(test(&Object::qt_metacall)) == sizeof(int) };
+    };
+}
+
 QT_END_NAMESPACE
 
 #endif // QOBJECTDEFS_H