From 573f87d81363a303b7005f999a283db624201db8 Mon Sep 17 00:00:00 2001
From: Ulf Hermann <ulf.hermann@theqtcompany.com>
Date: Tue, 10 Nov 2015 15:41:01 +0100
Subject: [PATCH] Use "shortest" double conversion for JSON

Task-number: QTBUG-42419
Change-Id: I649c4de96a2e41078e139c0f382e5a6cf96d3bb9
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
---
 src/corelib/json/qjsonwriter.cpp       |  3 ++-
 tests/auto/corelib/json/json.pro       |  4 ++++
 tests/auto/corelib/json/tst_qtjson.cpp | 16 +++++++++++++---
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/corelib/json/qjsonwriter.cpp b/src/corelib/json/qjsonwriter.cpp
index 45a05e93a3..0ab8b2bb80 100644
--- a/src/corelib/json/qjsonwriter.cpp
+++ b/src/corelib/json/qjsonwriter.cpp
@@ -32,6 +32,7 @@
 **
 ****************************************************************************/
 
+#include <qlocale.h>
 #include "qjsonwriter_p.h"
 #include "qjson_p.h"
 #include "private/qutfcodec_p.h"
@@ -123,7 +124,7 @@ static void valueToJson(const QJsonPrivate::Base *b, const QJsonPrivate::Value &
     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', std::numeric_limits<double>::digits10 + 2); // ::digits10 is 15
+            json += QByteArray::number(d, 'g', QLocale::FloatingPointShortest);
         else
             json += "null"; // +INF || -INF || NaN (see RFC4627#section2.4)
         break;
diff --git a/tests/auto/corelib/json/json.pro b/tests/auto/corelib/json/json.pro
index a8224fd201..b3038d7ca1 100644
--- a/tests/auto/corelib/json/json.pro
+++ b/tests/auto/corelib/json/json.pro
@@ -6,4 +6,8 @@ CONFIG += testcase
 !android:TESTDATA += bom.json test.json test.bjson test3.json test2.json
     else:RESOURCES += json.qrc
 
+!contains(QT_CONFIG, doubleconversion):!contains(QT_CONFIG, system-doubleconversion) {
+    DEFINES += QT_NO_DOUBLECONVERSION
+}
+
 SOURCES += tst_qtjson.cpp
diff --git a/tests/auto/corelib/json/tst_qtjson.cpp b/tests/auto/corelib/json/tst_qtjson.cpp
index e8d836683e..aebf332fe3 100644
--- a/tests/auto/corelib/json/tst_qtjson.cpp
+++ b/tests/auto/corelib/json/tst_qtjson.cpp
@@ -1408,9 +1408,7 @@ void tst_QtJson::toJsonLargeNumericValues()
             "    \"Array\": [\n"
             "        1.234567,\n"
             "        1.7976931348623157e+308,\n"
-            //     ((4.9406564584124654e-324 == 5e-324) == true)
-            // I can only think JavaScript has a special formatter to
-            //  emit this value for this IEEE754 bit pattern.
+#ifdef QT_NO_DOUBLECONVERSION // "shortest" double conversion is not very short then
             "        4.9406564584124654e-324,\n"
             "        2.2250738585072014e-308,\n"
             "        1.7976931348623157e+308,\n"
@@ -1421,6 +1419,18 @@ void tst_QtJson::toJsonLargeNumericValues()
             "        -1.7976931348623157e+308,\n"
             "        -2.2204460492503131e-16,\n"
             "        -4.9406564584124654e-324,\n"
+#else
+            "        5e-324,\n"
+            "        2.2250738585072014e-308,\n"
+            "        1.7976931348623157e+308,\n"
+            "        2.220446049250313e-16,\n"
+            "        5e-324,\n"
+            "        0,\n"
+            "        -2.2250738585072014e-308,\n"
+            "        -1.7976931348623157e+308,\n"
+            "        -2.220446049250313e-16,\n"
+            "        -5e-324,\n"
+#endif
             "        0,\n"
             "        9007199254740992,\n"
             "        -9007199254740992\n"