Make RuntimeHelpers::numberToString() comply with EcmaScript

We could use DoubleToStringConverter::EcmaScriptConverter().ToShortest()
here, but we'd have to #ifdef it for the case that we're using the libc
double conversion. As the formatting does not produce a lot of code I
decided against that.

Task-number: QTBUG-50131
Change-Id: If7a2ef8063b57ab35cda4a60d8ddd65442d70103
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

src/qml/jsruntime/qv4runtime.cpp

@@ -225,8 +225,36 @@ void RuntimeHelpers::numberToString(QString *result, double num, int radix)
     }
 
     if (radix == 10) {
-        const NumberLocale *locale = NumberLocale::instance();
-        *result = locale->toString(num, 'g', locale->defaultDoublePrecision);
+        // We cannot use our usual locale->toString(...) here, because EcmaScript has special rules
+        // about the longest permissible number, depending on if it's <0 or >0.
+        const int ecma_shortest_low = -6;
+        const int ecma_shortest_high = 21;
+
+        const QLatin1Char zero('0');
+        const QLatin1Char dot('.');
+
+        int decpt = 0;
+        int sign = 0;
+        *result = qdtoa(num, &decpt, &sign);
+
+        if (decpt <= ecma_shortest_low || decpt > ecma_shortest_high) {
+            if (result->length() > 1)
+                result->insert(1, dot);
+            result->append(QLatin1Char('e'));
+            if (decpt > 0)
+                result->append(QLatin1Char('+'));
+            result->append(QString::number(decpt - 1));
+        } else if (decpt <= 0) {
+            result->prepend(QString::fromLatin1("0.%1").arg(QString().fill(zero, -decpt)));
+        } else if (decpt < result->length()) {
+            result->insert(decpt, dot);
+        } else {
+            result->append(QString().fill(zero, decpt - result->length()));
+        }
+
+        if (sign)
+            result->prepend(QLatin1Char('-'));
+
         return;
     }
 

tests/auto/qml/qqmlproperty/data/floatToStringPrecision.qml

@@ -2,9 +2,27 @@ import QtQuick 2.0
 
 QtObject {
     property double a: 3.4
-    property string b: a
+    property string a1: a
+    property string a2: a + ""
 
-    property double c: 0.035003945
-    property string d: c
+    property double b: 0.035003945
+    property string b1: b
+    property string b2: b + ""
+
+    property double c: 0.0000012345
+    property string c1: c
+    property string c2: c + ""
+
+    property double d: 0.00000012345
+    property string d1: d
+    property string d2: d + ""
+
+    property double e: 100000000000000000000
+    property string e1: e
+    property string e2: e + ""
+
+    property double f: 1000000000000000000000
+    property string f1: f
+    property string f2: f + ""
 }
 

tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp

@@ -147,6 +147,8 @@ private slots:
     void registeredCompositeTypeProperty();
     void deeplyNestedObject();
     void readOnlyDynamicProperties();
+
+    void floatToStringPrecision_data();
     void floatToStringPrecision();
 
     void copy();
@@ -2055,21 +2057,43 @@ void tst_qqmlproperty::readOnlyDynamicProperties()
     delete obj;
 }
 
+void tst_qqmlproperty::floatToStringPrecision_data()
+{
+    QTest::addColumn<QString>("propertyName");
+    QTest::addColumn<double>("number");
+    QTest::addColumn<QString>("qtString");
+    QTest::addColumn<QString>("jsString");
+
+    QTest::newRow("3.4")           << "a" << 3.4           << "3.4"         << "3.4";
+    QTest::newRow("0.035003945")   << "b" << 0.035003945   << "0.035003945" << "0.035003945";
+    QTest::newRow("0.0000012345")  << "c" << 0.0000012345  << "1.2345e-6"   << "0.0000012345";
+    QTest::newRow("0.00000012345") << "d" << 0.00000012345 << "1.2345e-7"   << "1.2345e-7";
+    QTest::newRow("1e20")          << "e" << 1e20          << "1e+20"       << "100000000000000000000";
+    QTest::newRow("1e21")          << "f" << 1e21          << "1e+21"       << "1e+21";
+}
+
 void tst_qqmlproperty::floatToStringPrecision()
 {
     QQmlComponent comp(&engine, testFileUrl("floatToStringPrecision.qml"));
     QObject *obj = comp.create();
     QVERIFY(obj != 0);
 
-    QCOMPARE(obj->property("a").toDouble(), 3.4);
-    QCOMPARE(obj->property("a").toString(), QLatin1String("3.4"));
-    QCOMPARE(obj->property("b").toDouble(), 3.4);
-    QCOMPARE(obj->property("b").toString(), QLatin1String("3.4"));
+    QFETCH(QString, propertyName);
+    QFETCH(double, number);
+    QFETCH(QString, qtString);
+    QFETCH(QString, jsString);
 
-    QCOMPARE(obj->property("c").toDouble(), 0.035003945);
-    QCOMPARE(obj->property("c").toString(), QLatin1String("0.035003945"));
-    QCOMPARE(obj->property("d").toDouble(), 0.035003945);
-    QCOMPARE(obj->property("d").toString(), QLatin1String("0.035003945"));
+    const char *name = propertyName.toLatin1().constData();
+    QCOMPARE(obj->property(name).toDouble(), number);
+    QCOMPARE(obj->property(name).toString(), qtString);
+
+    const char *name1 = (propertyName + QLatin1Char('1')).toLatin1().constData();
+    QCOMPARE(obj->property(name1).toDouble(), number);
+    QCOMPARE(obj->property(name1).toString(), qtString);
+
+    const char *name2 = (propertyName + QLatin1Char('2')).toLatin1().constData();
+    QCOMPARE(obj->property(name2).toDouble(), number);
+    QCOMPARE(obj->property(name2).toString(), jsString);
 
     delete obj;
 }