QTextStream: fix streaming of char16_t's

Clazy complains about all uses of QLatin1Char these days, but if one
actually applies the fixit to turn

   out << QLatin1Char(' ');

into

   out << u' ';

the space is now streamed as an int (20), not as a space.

Fix by providing an explicit char16_t overload.

[ChangeLog][QtCore][QTextStream] Added op<<(char16_t).

[ChangeLog][Important Behavior Changes] QTextStream streams char16_t's
as QChars now instead of outputting the numeric value. If you want to
preserve the old behavior, cast the char16_t to a numeric type, such
as ushort or int, and stream that. This is backwards-compatible.

Pick-to: 6.3
Change-Id: I42d422cdebb27d38ac1714b22ef186642ec407e7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/corelib/serialization/qtextstream.cpp

@@ -2287,6 +2287,15 @@ QTextStream &QTextStream::operator<<(char c)
     return *this;
 }
 
+/*!
+    \fn QTextStream &QTextStream::operator<<(char16_t c)
+    \overload
+    \since 6.3.1
+
+    Writes the Unicode character \a c to the stream, then returns a
+    reference to the QTextStream.
+*/
+
 /*!
     Writes the integer number \a i to the stream, then returns a
     reference to the QTextStream. By default, the number is stored in

src/corelib/serialization/qtextstream.h

@@ -169,6 +169,7 @@ public:
 
     QTextStream &operator<<(QChar ch);
     QTextStream &operator<<(char ch);
+    QTextStream &operator<<(char16_t ch) { return *this << QChar(ch); }
     QTextStream &operator<<(signed short i);
     QTextStream &operator<<(unsigned short i);
     QTextStream &operator<<(signed int i);

tests/auto/corelib/serialization/qtextstream/tst_qtextstream.cpp

@@ -94,6 +94,8 @@ private slots:
     // char operators
     void QChar_operators_FromDevice_data();
     void QChar_operators_FromDevice();
+    void char16_t_operators_FromDevice_data();
+    void char16_t_operators_FromDevice();
     void char_operators_FromDevice_data();
     void char_operators_FromDevice();
 
@@ -1918,6 +1920,31 @@ void tst_QTextStream::QChar_operators_FromDevice()
     QCOMPARE(writeBuf.buffer().constData(), write_output.constData());
 }
 
+// ------------------------------------------------------------------------------
+void tst_QTextStream::char16_t_operators_FromDevice_data()
+{
+    generateOperatorCharData(false);
+}
+
+// ------------------------------------------------------------------------------
+void tst_QTextStream::char16_t_operators_FromDevice()
+{
+    QFETCH(const QChar, qchar_output);
+    QFETCH(const QByteArray, write_output);
+    const char16_t char16_t_output = qchar_output.unicode();
+
+    QBuffer writeBuf;
+    writeBuf.open(QBuffer::WriteOnly);
+
+    QTextStream writeStream(&writeBuf);
+    writeStream.setEncoding(QStringConverter::Latin1);
+    writeStream << char16_t_output;
+    writeStream.flush();
+
+    QCOMPARE(writeBuf.buffer().size(), write_output.size());
+    QCOMPARE(writeBuf.buffer().constData(), write_output.constData());
+}
+
 // ------------------------------------------------------------------------------
 void tst_QTextStream::char_operators_FromDevice_data()
 {