QStringRef: add truncate()

Missing part of QString API.

[ChangeLog][QtCore][QStringRef] Added truncate(int).

Change-Id: I49e218daf8f47fcd3dad131155e0abc8e2a133e5
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qstring.cpp

@@ -4880,7 +4880,7 @@ modifiable reference.
 
     If \a position is negative, it is equivalent to passing zero.
 
-    \sa chop(), resize(), left()
+    \sa chop(), resize(), left(), QStringRef::truncate()
 */
 
 void QString::truncate(int pos)
@@ -9375,6 +9375,20 @@ QStringRef QString::midRef(int position, int n) const
     return QStringRef();
 }
 
+/*!
+    \fn void QStringRef::truncate(int position)
+    \since 5.6
+
+    Truncates the string at the given \a position index.
+
+    If the specified \a position index is beyond the end of the
+    string, nothing happens.
+
+    If \a position is negative, it is equivalent to passing zero.
+
+    \sa QString::truncate()
+*/
+
 /*!
   \since 4.8
 

src/corelib/tools/qstring.h

@@ -1399,6 +1399,8 @@ public:
     QStringRef right(int n) const Q_REQUIRED_RESULT;
     QStringRef mid(int pos, int n = -1) const Q_REQUIRED_RESULT;
 
+    void truncate(int pos) Q_DECL_NOTHROW { m_size = qBound(0, pos, m_size); }
+
     bool startsWith(const QString &s, Qt::CaseSensitivity cs = Qt::CaseSensitive) const;
     bool startsWith(QLatin1String s, Qt::CaseSensitivity cs = Qt::CaseSensitive) const;
     bool startsWith(QChar c, Qt::CaseSensitivity cs = Qt::CaseSensitive) const;

tests/auto/corelib/tools/qstringref/tst_qstringref.cpp

@@ -82,6 +82,7 @@ private slots:
     void integer_conversion_data();
     void integer_conversion();
     void trimmed();
+    void truncate();
     void left();
     void right();
     void mid();
@@ -1839,6 +1840,30 @@ void tst_QStringRef::trimmed()
     QCOMPARE(b.trimmed().compare(QStringLiteral("a")), 0);
 }
 
+void tst_QStringRef::truncate()
+{
+    const QString str = "OriginalString~";
+    const QStringRef cref = str.midRef(0);
+    {
+        QStringRef ref = cref;
+        ref.truncate(1000);
+        QCOMPARE(ref, cref);
+        for (int i = str.size(); i >= 0; --i) {
+            ref.truncate(i);
+            QCOMPARE(ref.size(), i);
+            QCOMPARE(ref, cref.left(i));
+        }
+        QVERIFY(ref.isEmpty());
+    }
+
+    {
+        QStringRef ref = cref;
+        QVERIFY(!ref.isEmpty());
+        ref.truncate(-1);
+        QVERIFY(ref.isEmpty());
+    }
+}
+
 void tst_QStringRef::left()
 {
     QString originalString = "OrginalString~";