json encoder: Harmonize number serialization with ES6

Ensures that numbers representable as 64-bit integer
are not printed using exponent notation.

Some JSON implementations such as the one of the Go
standard library expect this in the default
conversion to int.

Change-Id: Ic3ac718b7fd36462b4fcabbfb100a528a87798c8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 35 insertions, 3 deletions

diff --git a/src/corelib/json/qjsonwriter.cpp b/src/corelib/json/qjsonwriter.cpp
index b1544c749d..12ce20ef09 100644
--- a/src/corelib/json/qjsonwriter.cpp
+++ b/src/corelib/json/qjsonwriter.cpp
@@ -38,6 +38,7 @@
 **
 ****************************************************************************/
 
+#include <cmath>
 #include <qlocale.h>
 #include "qjsonwriter_p.h"
 #include "qjson_p.h"
@@ -129,10 +130,12 @@ static void valueToJson(const QJsonPrivate::Base *b, const QJsonPrivate::Value &
         break;
     case QJsonValue::Double: {
         const double d = v.toDouble(b);
-        if (qIsFinite(d)) // +2 to format to ensure the expected precision
-            json += QByteArray::number(d, 'g', QLocale::FloatingPointShortest);
-        else
+        if (qIsFinite(d)) { // +2 to format to ensure the expected precision
+            const double abs = std::abs(d);
+            json += QByteArray::number(d, abs == static_cast<quint64>(abs) ? 'f' : 'g', QLocale::FloatingPointShortest);
+        } else {
             json += "null"; // +INF || -INF || NaN (see RFC4627#section2.4)
+        }
         break;
     }
     case QJsonValue::String:
diff --git a/tests/auto/corelib/json/tst_qtjson.cpp b/tests/auto/corelib/json/tst_qtjson.cpp
index 6aa5165e24..b215364f0e 100644
--- a/tests/auto/corelib/json/tst_qtjson.cpp
+++ b/tests/auto/corelib/json/tst_qtjson.cpp
@@ -32,6 +32,7 @@
 #include "qjsonobject.h"
 #include "qjsonvalue.h"
 #include "qjsondocument.h"
+#include "qregularexpression.h"
 #include <limits>
 
 #define INVALID_UNICODE "\xCE\xBA\xE1"
@@ -49,6 +50,7 @@ private Q_SLOTS:
     void testNumbers();
     void testNumbers_2();
     void testNumbers_3();
+    void testNumbers_4();
 
     void testObjectSimple();
     void testObjectSmallKeys();
@@ -375,6 +377,33 @@ void tst_QtJson::testNumbers_3()
     QVERIFY(d1_1 != d2_1);
 }
 
+void tst_QtJson::testNumbers_4()
+{
+    // no exponent notation used to print numbers between -2^64 and 2^64
+    QJsonArray array;
+    array << QJsonValue(+1000000000000000.0);
+    array << QJsonValue(-1000000000000000.0);
+    array << QJsonValue(+9007199254740992.0);
+    array << QJsonValue(-9007199254740992.0);
+    array << QJsonValue(+9223372036854775808.0);
+    array << QJsonValue(-9223372036854775808.0);
+    array << QJsonValue(+18446744073709551616.0);
+    array << QJsonValue(-18446744073709551616.0);
+    const QByteArray json(QJsonDocument(array).toJson());
+    const QByteArray expected =
+            "[\n"
+            "    1000000000000000,\n"
+            "    -1000000000000000,\n"
+            "    9007199254740992,\n"
+            "    -9007199254740992,\n"
+            "    9223372036854776000,\n"
+            "    -9223372036854776000,\n"
+            "    18446744073709552000,\n"
+            "    -18446744073709552000\n"
+            "]\n";
+    QCOMPARE(json, expected);
+}
+
 void tst_QtJson::testObjectSimple()
 {
     QJsonObject object;