Use V4 double-to-string conversion instead of QVariant's

V4's version makes an effort to find the shortest possible
representation, which QVariant doesn't do.

Task-number: QTBUG-47070
Change-Id: I49ce130020496592325074e0db29a6984ee7649a
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

3 files changed, 39 insertions, 1 deletions

diff --git a/src/qml/qml/qqmlproperty.cpp b/src/qml/qml/qqmlproperty.cpp
index c1120b4542..d3f7070528 100644
--- a/src/qml/qml/qqmlproperty.cpp
+++ b/src/qml/qml/qqmlproperty.cpp
@@ -50,6 +50,7 @@
 #include "qqmlvaluetypeproxybinding_p.h"
 #include <private/qjsvalue_p.h>
 #include <private/qv4functionobject_p.h>
+#include <private/qv4runtime_p.h>
 
 #include <QStringList>
 #include <private/qmetaobject_p.h>
@@ -1350,7 +1351,12 @@ bool QQmlPropertyPrivate::write(QObject *object,
 
         if (!ok) {
             v = value;
-            if (v.convert(propertyType)) {
+            if (variantType == QVariant::Double && propertyType == QVariant::String) {
+                QString number;
+                QV4::RuntimeHelpers::numberToString(&number, v.toDouble());
+                v = number;
+                ok = true;
+            } else if (v.convert(propertyType)) {
                 ok = true;
             } else if (v.isValid() && value.isNull()) {
                 // For historical reasons converting a null QVariant to another type will do the trick
diff --git a/tests/auto/qml/qqmlproperty/data/floatToStringPrecision.qml b/tests/auto/qml/qqmlproperty/data/floatToStringPrecision.qml
new file mode 100644
index 0000000000..a0429e0cc8
--- /dev/null
+++ b/tests/auto/qml/qqmlproperty/data/floatToStringPrecision.qml
@@ -0,0 +1,10 @@
+import QtQuick 2.0
+
+QtObject {
+    property double a: 3.4
+    property string b: a
+
+    property double c: 0.035003945
+    property string d: c
+}
+
diff --git a/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp b/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
index d6b1c86b88..6ada14ce79 100644
--- a/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
+++ b/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
@@ -147,6 +147,7 @@ private slots:
     void registeredCompositeTypeProperty();
     void deeplyNestedObject();
     void readOnlyDynamicProperties();
+    void floatToStringPrecision();
 
     void copy();
 private:
@@ -2054,6 +2055,27 @@ void tst_qqmlproperty::readOnlyDynamicProperties()
     delete obj;
 }
 
+void tst_qqmlproperty::floatToStringPrecision()
+{
+    QQmlComponent comp(&engine, testFileUrl("floatToStringPrecision.qml"));
+    QObject *obj = comp.create();
+    QVERIFY(obj != 0);
+
+    QCOMPARE(obj->property("a").toDouble(), 3.4);
+    QEXPECT_FAIL("", "QVariant's double-to-string conversion is worse than V4's.", Continue);
+    QCOMPARE(obj->property("a").toString(), QLatin1String("3.4"));
+    QCOMPARE(obj->property("b").toDouble(), 3.4);
+    QCOMPARE(obj->property("b").toString(), QLatin1String("3.4"));
+
+    QCOMPARE(obj->property("c").toDouble(), 0.035003945);
+    QEXPECT_FAIL("", "QVariant's double-to-string conversion is worse than V4's.", Continue);
+    QCOMPARE(obj->property("c").toString(), QLatin1String("0.035003945"));
+    QCOMPARE(obj->property("d").toDouble(), 0.035003945);
+    QCOMPARE(obj->property("d").toString(), QLatin1String("0.035003945"));
+
+    delete obj;
+}
+
 void tst_qqmlproperty::initTestCase()
 {
     QQmlDataTest::initTestCase();