Use QString::fromLatin1() less to avoid string allocations

QString::fromLatin1 always allocates memory, but there are
cases where we can avoid/reduce allocations or/and reduce
text size, e.g.:

QStringBuilder expressions
Fix: replace QString::fromLatin1 with QL1S

QString::fromLatin1().arg(String) pattern
Fix: replace with QStringBuilder

Overloaded functions with QL1S arg
Fix: replace QString::fromLatin1 with QL1S

In rare cases if there is no overloaded function
with QL1S and we have deal with string literal,
replace QString::fromLatin1 with QStringLiteral.

Change-Id: Iabe1a3cc0830f40ef78a0548afa4368583c31def
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/corelib/mimetypes/qmimeprovider.cpp

@@ -572,10 +572,9 @@ void QMimeBinaryProvider::loadMimeTypePrivate(QMimeTypePrivate &data)
 
     const QString file = data.name + QLatin1String(".xml");
     // shared-mime-info since 1.3 lowercases the xml files
-    QStringList mimeFiles = QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QString::fromLatin1("mime/") + file.toLower());
-    if (mimeFiles.isEmpty()) {
-        mimeFiles = QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QString::fromLatin1("mime/") + file); // pre-1.3
-    }
+    QStringList mimeFiles = QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QLatin1String("mime/") + file.toLower());
+    if (mimeFiles.isEmpty())
+        mimeFiles = QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QLatin1String("mime/") + file); // pre-1.3
     if (mimeFiles.isEmpty()) {
         qWarning() << "No file found for" << file << ", even though update-mime-info said it would exist.\n"
                       "Either it was just removed, or the directory doesn't have executable permission..."
@@ -807,7 +806,7 @@ bool QMimeXMLProvider::load(const QString &fileName, QString *errorMessage)
     QFile file(fileName);
     if (!file.open(QIODevice::ReadOnly | QIODevice::Text)) {
         if (errorMessage)
-            *errorMessage = QString::fromLatin1("Cannot open %1: %2").arg(fileName, file.errorString());
+            *errorMessage = QLatin1String("Cannot open ") + fileName + QLatin1String(": ") + file.errorString();
         return false;
     }
 

src/dbus/qdbusinternalfilters.cpp

@@ -116,8 +116,7 @@ static QString generateSubObjectXml(QObject *object)
     for ( ; it != end; ++it) {
         QString name = (*it)->objectName();
         if (!name.isEmpty() && QDBusUtil::isValidPartOfObjectPath(name))
-            retval += QString::fromLatin1("  <node name=\"%1\"/>\n")
-                      .arg(name);
+            retval += QLatin1String("  <node name=\"") + name + QLatin1String("\"/>\n");
     }
     return retval;
 }
@@ -192,8 +191,7 @@ QString qDBusIntrospectObject(const QDBusConnectionPrivate::ObjectTreeNode &node
             node.children.constEnd();
         for ( ; it != end; ++it)
             if (it->obj || !it->children.isEmpty())
-                xml_data += QString::fromLatin1("  <node name=\"%1\"/>\n")
-                            .arg(it->name);
+                xml_data += QLatin1String("  <node name=\"") + it->name + QLatin1String("\"/>\n");
     }
 
     xml_data += QLatin1String("</node>\n");

src/gui/image/qimagereader.cpp

@@ -569,7 +569,7 @@ bool QImageReaderPrivate::initHandler()
 
         do {
             file->setFileName(fileName + QLatin1Char('.')
-                    + QString::fromLatin1(extensions.at(currentExtension++).constData()));
+                    + QLatin1String(extensions.at(currentExtension++).constData()));
             file->open(QIODevice::ReadOnly);
         } while (!file->isOpen() && currentExtension < extensions.size());
 

src/gui/kernel/qkeysequence.cpp

@@ -1211,9 +1211,13 @@ QString QKeySequence::encodeString(int key)
 
 static inline void addKey(QString &str, const QString &theKey, QKeySequence::SequenceFormat format)
 {
-    if (!str.isEmpty())
-        str += (format == QKeySequence::NativeText) ? QCoreApplication::translate("QShortcut", "+")
-                                                    : QString::fromLatin1("+");
+    if (!str.isEmpty()) {
+        if (format == QKeySequence::NativeText)
+            str += QCoreApplication::translate("QShortcut", "+");
+        else
+            str += QLatin1Char('+');
+    }
+
     str += theKey;
 }
 

src/gui/text/qfontdatabase.cpp

@@ -2439,7 +2439,7 @@ int QFontDatabasePrivate::addAppFont(const QByteArray &fontData, const QString &
     }
 
     if (font.fileName.isEmpty() && !fontData.isEmpty())
-        font.fileName = QString::fromLatin1(":qmemoryfonts/") + QString::number(i);
+        font.fileName = QLatin1String(":qmemoryfonts/") + QString::number(i);
 
     registerFont(&font);
     if (font.families.isEmpty())

src/gui/text/qtextodfwriter.cpp

@@ -63,7 +63,7 @@ QT_BEGIN_NAMESPACE
 static QString pixelToPoint(qreal pixels)
 {
     // we hardcode 96 DPI, we do the same in the ODF importer to have a perfect roundtrip.
-    return QString::number(pixels * 72 / 96) + QString::fromLatin1("pt");
+    return QString::number(pixels * 72 / 96) + QLatin1String("pt");
 }
 
 // strategies

src/network/access/qhttpnetworkconnection.cpp

@@ -319,9 +319,9 @@ void QHttpNetworkConnectionPrivate::prepareRequest(HttpMessagePair &messagePair)
         if (systemLocale == QLatin1String("C"))
             acceptLanguage = QString::fromLatin1("en,*");
         else if (systemLocale.startsWith(QLatin1String("en-")))
-            acceptLanguage = QString::fromLatin1("%1,*").arg(systemLocale);
+            acceptLanguage = systemLocale + QLatin1String(",*");
         else
-            acceptLanguage = QString::fromLatin1("%1,en,*").arg(systemLocale);
+            acceptLanguage = systemLocale + QLatin1String(",en,*");
         request.setHeaderField("Accept-Language", acceptLanguage.toLatin1());
     }
 

src/network/kernel/qnetworkinterface_unix.cpp

@@ -488,7 +488,7 @@ static QList<QNetworkInterfacePrivate *> interfaceListing()
     interfaces = createInterfaces(interfaceListing);
     for (ifaddrs *ptr = interfaceListing; ptr; ptr = ptr->ifa_next) {
         // Find the interface
-        QString name = QString::fromLatin1(ptr->ifa_name);
+        QLatin1String name(ptr->ifa_name);
         QNetworkInterfacePrivate *iface = 0;
         QList<QNetworkInterfacePrivate *>::Iterator if_it = interfaces.begin();
         for ( ; if_it != interfaces.end(); ++if_it)

src/network/kernel/qnetworkproxy_generic.cpp

@@ -79,7 +79,7 @@ static bool ignoreProxyFor(const QNetworkProxyQuery &query)
         if (!peerHostName.startsWith('.'))
             peerHostName.prepend('.');
 
-        if (peerHostName.endsWith(QString::fromLatin1(token)))
+        if (peerHostName.endsWith(QLatin1String(token)))
             return true;
     }
 

src/platformsupport/devicediscovery/qdevicediscovery_static.cpp

@@ -135,7 +135,7 @@ bool QDeviceDiscoveryStatic::checkDeviceType(const QString &device)
 
     qCDebug(lcDD) << "doing static device discovery for " << device;
 
-    if ((m_types & Device_DRM) && device.contains(QString::fromLatin1(QT_DRM_DEVICE_PREFIX))) {
+    if ((m_types & Device_DRM) && device.contains(QLatin1String(QT_DRM_DEVICE_PREFIX))) {
         QT_CLOSE(fd);
         return true;
     }

src/plugins/platforms/haiku/qhaikuclipboard.cpp

@@ -91,7 +91,7 @@ QMimeData *QHaikuClipboard::mimeData(QClipboard::Mode mode)
 
             const status_t status = clipboard->FindData(name, B_MIME_TYPE, &data, &dataLen);
             if (dataLen && (status == B_OK)) {
-                const QString format = QString::fromLatin1(name);
+                const QLatin1String format(name);
                 if (format == QLatin1String("text/plain")) {
                     m_systemMimeData->setText(QString::fromLocal8Bit(reinterpret_cast<const char*>(data), dataLen));
                 } else if (format == QLatin1String("text/html")) {

src/plugins/platforms/xcb/qxcbmime.cpp

@@ -173,7 +173,7 @@ QVariant QXcbMime::mimeConvertToFormat(QXcbConnection *connection, xcb_atom_t a,
 //    qDebug() << "mimeConvertDataToFormat" << format << atomName << data;
 
     if (!encoding.isEmpty()
-        && atomName == format + QLatin1String(";charset=") + QString::fromLatin1(encoding)) {
+        && atomName == format + QLatin1String(";charset=") + QLatin1String(encoding)) {
 
 #ifndef QT_NO_TEXTCODEC
         if (requestedType == QVariant::String) {

src/plugins/sqldrivers/db2/qsql_db2.cpp

@@ -1665,7 +1665,8 @@ QString QDB2Driver::formatValue(const QSqlField &field, bool trimStrings) const
         }
         case QVariant::ByteArray: {
             QByteArray ba = field.value().toByteArray();
-            QString res = QString::fromLatin1("BLOB(X'");
+            QString res;
+            res += QLatin1String("BLOB(X'");
             static const char hexchars[] = "0123456789abcdef";
             for (int i = 0; i < ba.size(); ++i) {
                 uchar s = (uchar) ba[i];

src/printsupport/dialogs/qprintpreviewdialog.cpp

@@ -334,7 +334,7 @@ void QPrintPreviewDialogPrivate::init(QPrinter *_printer)
 
     QString caption = QCoreApplication::translate("QPrintPreviewDialog", "Print Preview");
     if (!printer->docName().isEmpty())
-        caption += QString::fromLatin1(": ") + printer->docName();
+        caption += QLatin1String(": ") + printer->docName();
     q->setWindowTitle(caption);
 
     if (!printer->isValid()

src/widgets/accessible/qaccessiblewidgets.cpp

@@ -830,7 +830,7 @@ QString QAccessibleTextWidget::attributes(int offset, int *startOffset, int *end
         family = family.replace('=', QLatin1String("\\="));
         family = family.replace(';', QLatin1String("\\;"));
         family = family.replace('\"', QLatin1String("\\\""));
-        attrs["font-family"] = QString::fromLatin1("\"%1\"").arg(family);
+        attrs["font-family"] = QLatin1Char('"') + family + QLatin1Char('"');
     }
 
     int fontSize = int(charFormatFont.pointSize());

src/widgets/kernel/qaction.cpp

@@ -63,7 +63,7 @@ QT_BEGIN_NAMESPACE
  */
 static QString qt_strippedText(QString s)
 {
-    s.remove( QString::fromLatin1("...") );
+    s.remove(QStringLiteral("..."));
     for (int i = 0; i < s.size(); ++i) {
         if (s.at(i) == QLatin1Char('&'))
             s.remove(i, 1);

src/widgets/widgets/qlcdnumber.cpp

@@ -188,8 +188,8 @@ static QString int2string(int num, int base, int ndigits, bool *oflow)
                 } while (n != 0);
                 len = ndigits - len;
                 if (len > 0)
-                s.fill(QLatin1Char(' '), len);
-                s += QString::fromLatin1(p);
+                    s += QString(len, QLatin1Char(' '));
+                s += QLatin1String(p);
             }
             break;
     }

src/widgets/widgets/qpushbutton.cpp

@@ -415,7 +415,7 @@ QSize QPushButton::sizeHint() const
     QString s(text());
     bool empty = s.isEmpty();
     if (empty)
-        s = QString::fromLatin1("XXXX");
+        s = QStringLiteral("XXXX");
     QFontMetrics fm = fontMetrics();
     QSize sz = fm.size(Qt::TextShowMnemonic, s);
     if(!empty || !w)