2 files changed, 40 insertions, 7 deletions
diff --git a/src/corelib/tools/qstringlist.cpp b/src/corelib/tools/qstringlist.cpp
index eae9e0e5d9..a0b65ea554 100644
--- a/src/corelib/tools/qstringlist.cpp
+++ b/src/corelib/tools/qstringlist.cpp
@@ -447,6 +447,17 @@ void QtPrivate::QStringList_replaceInStrings(QStringList *that, const QRegularEx
 #endif // QT_NO_REGULAREXPRESSION
 #endif // QT_BOOTSTRAPPED
 
+static int accumulatedSize(const QStringList &list, int seplen)
+{
+    int result = 0;
+    if (!list.isEmpty()) {
+        for (const auto &e : list)
+            result += e.size() + seplen;
+        result -= seplen;
+    }
+    return result;
+}
+
 /*!
     \fn QString QStringList::join(const QString &separator) const
 
@@ -464,15 +475,9 @@ void QtPrivate::QStringList_replaceInStrings(QStringList *that, const QRegularEx
 */
 QString QtPrivate::QStringList_join(const QStringList *that, const QChar *sep, int seplen)
 {
-    int totalLength = 0;
+    const int totalLength = accumulatedSize(*that, seplen);
     const int size = that->size();
 
-    for (int i = 0; i < size; ++i)
-        totalLength += that->at(i).size();
-
-    if(size > 0)
-        totalLength += seplen * (size - 1);
-
     QString res;
     if (totalLength == 0)
         return res;
@@ -486,6 +491,27 @@ QString QtPrivate::QStringList_join(const QStringList *that, const QChar *sep, i
 }
 
 /*!
+    \fn QString QStringList::join(QLatin1String separator) const
+    \since 5.8
+    \overload join()
+*/
+QString QtPrivate::QStringList_join(const QStringList &list, QLatin1String sep)
+{
+    QString result;
+    if (!list.isEmpty()) {
+        result.reserve(accumulatedSize(list, sep.size()));
+        const auto end = list.end();
+        auto it = list.begin();
+        result += *it;
+        while (++it != end) {
+            result += sep;
+            result += *it;
+        }
+    }
+    return result;
+}
+
+/*!
     \fn QStringList QStringList::operator+(const QStringList &other) const
 
     Returns a string list that is the concatenation of this string
diff --git a/src/corelib/tools/qstringlist.h b/src/corelib/tools/qstringlist.h
index 87f15528bf..720d7d7419 100644
--- a/src/corelib/tools/qstringlist.h
+++ b/src/corelib/tools/qstringlist.h
@@ -73,6 +73,7 @@ public:
     inline int removeDuplicates();
 
     inline QString join(const QString &sep) const;
+    inline QString join(QLatin1String sep) const;
     inline QString join(QChar sep) const;
 
     inline QStringList filter(const QString &str, Qt::CaseSensitivity cs = Qt::CaseSensitive) const;
@@ -159,6 +160,7 @@ namespace QtPrivate {
     void Q_CORE_EXPORT QStringList_sort(QStringList *that, Qt::CaseSensitivity cs);
     int Q_CORE_EXPORT QStringList_removeDuplicates(QStringList *that);
     QString Q_CORE_EXPORT QStringList_join(const QStringList *that, const QChar *sep, int seplen);
+    Q_CORE_EXPORT QString QStringList_join(const QStringList &list, QLatin1String sep);
     QStringList Q_CORE_EXPORT QStringList_filter(const QStringList *that, const QString &str,
                                                Qt::CaseSensitivity cs);
 
@@ -200,6 +202,11 @@ inline QString QListSpecialMethods<QString>::join(const QString &sep) const
     return QtPrivate::QStringList_join(self(), sep.constData(), sep.length());
 }
 
+QString QListSpecialMethods<QString>::join(QLatin1String sep) const
+{
+    return QtPrivate::QStringList_join(*self(), sep);
+}
+
 inline QString QListSpecialMethods<QString>::join(QChar sep) const
 {
     return QtPrivate::QStringList_join(self(), &sep, 1);