QVariant of nullptr should always be null

Implements isNull for QVariants of a nullptr so they always return
true to isNull(), instead of depending on how they were constructed.

Task-number: QTBUG-58296
Change-Id: Ibddec795cdadedef7e17d22c265c29e752d8f99f
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

2 files changed, 32 insertions, 1 deletions

diff --git a/src/corelib/kernel/qvariant_p.h b/src/corelib/kernel/qvariant_p.h
index bf88def438..487949431c 100644
--- a/src/corelib/kernel/qvariant_p.h
+++ b/src/corelib/kernel/qvariant_p.h
@@ -177,6 +177,26 @@ inline void v_clear(QVariant::Private *d, T* = 0)
 
 }
 
+template <typename T>
+struct PrimitiveIsNull
+{
+public:
+    static bool isNull(const QVariant::Private *d)
+    {
+        return d->is_null;
+    }
+};
+
+template <>
+struct PrimitiveIsNull<std::nullptr_t>
+{
+public:
+    static bool isNull(const QVariant::Private *)
+    {
+        return true;
+    }
+};
+
 template<class Filter>
 class QVariantComparator {
     template<typename T, bool IsAcceptedType = Filter::template Acceptor<T>::IsAccepted>
@@ -268,7 +288,7 @@ class QVariantIsNull
     {
         static bool isNull(const QVariant::Private *d)
         {
-            return d->is_null;
+            return PrimitiveIsNull<T>::isNull(d);
         }
     };
 
diff --git a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
index 75fa424ab1..3a51e67768 100644
--- a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
+++ b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
@@ -400,6 +400,17 @@ void tst_QVariant::isNull()
     QVERIFY( !varLL.isNull() );
     QVariant var7(QString::null);
     QVERIFY(var7.isNull());
+    var7 = QVariant::fromValue<QString>(QString::null);
+    QVERIFY(var7.isNull());
+
+    QVariant var8(QMetaType::Nullptr, nullptr);
+    QVERIFY(var8.isNull());
+    var8 = QVariant::fromValue<std::nullptr_t>(nullptr);
+    QVERIFY(var8.isNull());
+    QVariant var9 = QVariant(QJsonValue(QJsonValue::Null));
+    QVERIFY(var9.isNull());
+    var9 = QVariant::fromValue<QJsonValue>(QJsonValue(QJsonValue::Null));
+    QVERIFY(var9.isNull());
 }
 
 void tst_QVariant::swap()