Q(ObjectBindable)Property: Properly support comparisons

Before, it was possible to do some comparisons due to the implicit
conversion to T. However, that does not work in all contexts.

Fix this by explicitly declaring the comparison operators. We need to
a) use the helper macro directly, as the operartors are only available
   if the underlying type has them and
b) mark the operator as noexcept(false), as capturing a property in a
   binding might allocate.

Fixes: QTBUG-134921
Change-Id: I2855964ba481b9e7778a4a7076528593549910fe
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

src/corelib/kernel/qproperty.cpp

@@ -1277,6 +1277,9 @@ QString QPropertyBindingError::description() const
   \inmodule QtCore
   \brief The QProperty class is a template class that enables automatic property bindings.
   \since 6.0
+  \compares equality
+  \compareswith equality T
+  \endcompareswith
 
   \ingroup tools
 
@@ -1486,6 +1489,9 @@ QString QPropertyBindingError::description() const
          automatic property bindings for property data stored in QObject derived
          classes.
   \since 6.0
+  \compares equality
+  \compareswith equality T
+  \endcompareswith
 
   \ingroup tools
 

src/corelib/kernel/qproperty.h

@@ -384,6 +384,10 @@ public:
 #endif
     ~QProperty() = default;
 
+    QT_DECLARE_EQUALITY_OPERATORS_HELPER(QProperty, QProperty, /* non-constexpr */, noexcept(false), template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>)
+    QT_DECLARE_EQUALITY_OPERATORS_HELPER(QProperty, T, /* non-constexpr */, noexcept(false), template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>)
+    QT_DECLARE_EQUALITY_OPERATORS_REVERSED_HELPER(QProperty, T, /* non-constexpr */, noexcept(false), template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>)
+
     parameter_type value() const
     {
         d.registerWithCurrentlyEvaluatingBinding();
@@ -504,6 +508,18 @@ public:
 
     const QtPrivate::QPropertyBindingData &bindingData() const { return d; }
 private:
+    template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>
+    friend bool comparesEqual(const QProperty &lhs, const QProperty &rhs)
+    {
+        return lhs.value() == rhs.value();
+    }
+
+    template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>
+    friend bool comparesEqual(const QProperty &lhs, const T &rhs)
+    {
+        return lhs.value() == rhs;
+    }
+
     void notify()
     {
         d.notifyObservers(this);
@@ -1068,6 +1084,10 @@ public:
     explicit QObjectBindableProperty(Functor &&f);
 #endif
 
+    QT_DECLARE_EQUALITY_OPERATORS_HELPER(QObjectBindableProperty, QObjectBindableProperty, /* non-constexpr */, noexcept(false), template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>)
+    QT_DECLARE_EQUALITY_OPERATORS_HELPER(QObjectBindableProperty, T, /* non-constexpr */, noexcept(false), template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>)
+    QT_DECLARE_EQUALITY_OPERATORS_REVERSED_HELPER(QObjectBindableProperty, T, /* non-constexpr */, noexcept(false), template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>)
+
     parameter_type value() const
     {
         qGetBindingStorage(owner())->registerDependency(this);
@@ -1208,6 +1228,18 @@ public:
         return *storage->bindingData(const_cast<ThisType *>(this), true);
     }
 private:
+    template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>
+    friend bool comparesEqual(const QObjectBindableProperty &lhs, const QObjectBindableProperty &rhs)
+    {
+        return lhs.value() == rhs.value();
+    }
+
+    template <typename Ty = T, std::enable_if_t<QTypeTraits::has_operator_equal_v<Ty>>* = nullptr>
+    friend bool comparesEqual(const QObjectBindableProperty &lhs, const T &rhs)
+    {
+        return lhs.value() == rhs;
+    }
+
     void notify(const QtPrivate::QPropertyBindingData *binding)
     {
         if (binding)

tests/auto/corelib/kernel/qproperty/CMakeLists.txt

@@ -16,4 +16,5 @@ qt_internal_add_test(tst_qproperty
         tst_qproperty.cpp
     LIBRARIES
         Qt::CorePrivate
+        Qt::TestPrivate
 )

tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp

@@ -7,6 +7,7 @@
 #include <qproperty.h>
 #include <private/qproperty_p.h>
 #include <private/qobject_p.h>
+#include <private/qcomparisontesthelper_p.h>
 
 #if __has_include(<source_location>) && __cplusplus >= 202002L && !defined(Q_QDOC)
 #include <source_location>
@@ -82,6 +83,8 @@ private slots:
     void compatPropertyNoDobuleNotification();
     void compatPropertySignals();
 
+    void compareAgainstValueType();
+
     void noFakeDependencies();
 #if QT_CONFIG(thread)
     void threadSafety();
@@ -1735,6 +1738,39 @@ void tst_QProperty::compatPropertySignals()
     QCOMPARE(arguments.at(0).toInt(), 42);
 }
 
+struct CompareTestObject : QObject{
+    Q_OBJECT
+public:
+    CompareTestObject(const QVariantList &l) { varList = l; }
+    Q_OBJECT_BINDABLE_PROPERTY(CompareTestObject, QVariantList, varList)
+};
+
+
+void tst_QProperty::compareAgainstValueType()
+{
+    {
+        // compile time checks
+        QTestPrivate::testEqualityOperatorsCompile<QProperty<QVariantList>>();
+        QTestPrivate::testEqualityOperatorsCompile<QProperty<QVariantList>, QVariantList>();
+
+        using ObjectBindableProperty = decltype(std::declval<CompareTestObject>().varList);
+
+        QTestPrivate::testEqualityOperatorsCompile<ObjectBindableProperty>();
+        QTestPrivate::testEqualityOperatorsCompile<ObjectBindableProperty, QVariantList>();
+    }
+
+    QVariantList vl {1, QString(), QByteArray {}};
+    QProperty<QVariantList> vlProp { vl };
+    CompareTestObject o { vl };
+
+    QCOMPARE_EQ(vl, vlProp);
+    QCOMPARE_EQ(vl, o.varList);
+
+    vl.pop_back();
+    QCOMPARE_NE(vl, vlProp);
+    QCOMPARE_NE(vl, o.varList);
+}
+
 class FakeDependencyCreator : public QObject
 {
     Q_OBJECT