Fix behavior change QStringList::join() for null

Before 4.6.2 both str.isNull() and str.isEmpty() return true for the
following code.

    QStringList list;
    QString str = list.join(QString());

This commit revert the behavior change introduced by
7461ed5227e3002c4a6f74d458aa0255b7c1217d. Joining null
QString was giving a empty string instead of a null
string.

Reviewed-by: Benjamin Poulain <benjamin.poulain@nokia.com>

2 files changed, 12 insertions, 0 deletions

diff --git a/src/corelib/tools/qstringlist.cpp b/src/corelib/tools/qstringlist.cpp
index e9bdf57..32a0b1e 100644
--- a/src/corelib/tools/qstringlist.cpp
+++ b/src/corelib/tools/qstringlist.cpp
@@ -414,6 +414,8 @@ QString QtPrivate::QStringList_join(const QStringList *that, const QString &sep)
         totalLength += sep.size() * (size - 1);
 
     QString res;
+    if (totalLength == 0)
+	return res;
     res.reserve(totalLength);
     for (int i = 0; i < that->size(); ++i) {
         if (i)
diff --git a/tests/auto/qstringlist/tst_qstringlist.cpp b/tests/auto/qstringlist/tst_qstringlist.cpp
index 8429303..fb28bf4 100644
--- a/tests/auto/qstringlist/tst_qstringlist.cpp
+++ b/tests/auto/qstringlist/tst_qstringlist.cpp
@@ -77,6 +77,7 @@ private slots:
     void streamingOperator();
     void join() const;
     void join_data() const;
+    void join_emptiness() const;
 };
 
 extern const char email[];
@@ -311,5 +312,14 @@ void tst_QStringList::join_data() const
                 << QString("a b c");
 }
 
+void tst_QStringList::join_emptiness() const
+{
+    QStringList list;
+    QString string = list.join(QString());
+
+    QCOMPARE(string.isEmpty(), true);
+    QCOMPARE(string.isNull(), true);
+}
+
 QTEST_APPLESS_MAIN(tst_QStringList)
 #include "tst_qstringlist.moc"