QML: Collapse all NaNs into one single (encoded) NaN

The idea of NaN boxing is to use one single NaN as a "true" NaN, and all
others as a boxed value. So when encoding some NaN, be sure to use that
one "true" NaN. Otherwise, it will be interpreted as an encoded value.

Task-number: QTBUG-65998
Change-Id: Ia6e4641be180f3d626c40a57b473f181358e04db
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/qml/jsruntime/qv4value_p.h

@@ -56,6 +56,8 @@
 #include "qv4global_p.h"
 #include <private/qv4heap_p.h>
 
+#include <private/qnumeric_p.h>
+
 #if QT_POINTER_SIZE == 8
 #define QV4_USE_64_BIT_VALUE_ENCODING
 #endif
@@ -362,6 +364,8 @@ struct Q_QML_PRIVATE_EXPORT Value
         return d;
     }
     QML_NEARLY_ALWAYS_INLINE void setDouble(double d) {
+        if (qt_is_nan(d))
+            d = qt_qnan();
         memcpy(&_val, &d, 8);
 #ifdef QV4_USE_64_BIT_VALUE_ENCODING
         _val ^= NaNEncodeMask;

tests/auto/qml/qqmlecmascript/data/nans.qml

@@ -0,0 +1,5 @@
+import QtQuick 2.0
+
+QtObject {
+    property var prop: undefined
+}

tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp

@@ -338,6 +338,7 @@ private slots:
     void freeze_empty_object();
     void singleBlockLoops();
     void qtbug_60547();
+    void anotherNaN();
 
 private:
 //    static void propertyVarWeakRefCallback(v8::Persistent<v8::Value> object, void* parameter);
@@ -8266,6 +8267,20 @@ void tst_qqmlecmascript::qtbug_60547()
     QCOMPARE(object->property("counter"), QVariant(int(1)));
 }
 
+void tst_qqmlecmascript::anotherNaN()
+{
+    QQmlComponent component(&engine, testFileUrl("nans.qml"));
+    QScopedPointer<QObject> object(component.create());
+    QVERIFY2(!object.isNull(), qPrintable(component.errorString()));
+    object->setProperty("prop", std::numeric_limits<double>::quiet_NaN()); // don't crash
+
+    std::uint64_t anotherNaN = 0xFFFFFF01000000F7ul;
+    double d;
+    std::memcpy(&d, &anotherNaN, sizeof(d));
+    QVERIFY(std::isnan(d));
+    object->setProperty("prop", d);  // don't crash
+}
+
 QTEST_MAIN(tst_qqmlecmascript)
 
 #include "tst_qqmlecmascript.moc"