Plugins: optimize string usage

Prefer QStringRef methods to avoid allocations.

Use startsWith/endsWith rather than comparing substrings;
and avoid substrings where references suffice.

Use new QStringList::join(QL1S).

Change-Id: I46c44aca96578633370006d613eb0ac13f7cfc03
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

8 files changed, 17 insertions, 18 deletions

diff --git a/src/plugins/bearer/nativewifi/qnativewifiengine.cpp b/src/plugins/bearer/nativewifi/qnativewifiengine.cpp
index 23656476bd..bb43072aba 100644
--- a/src/plugins/bearer/nativewifi/qnativewifiengine.cpp
+++ b/src/plugins/bearer/nativewifi/qnativewifiengine.cpp
@@ -459,7 +459,7 @@ void QNativeWifiEngine::disconnectFromId(const QString &id)
         return;
     }
 
-    QStringList split = interface.mid(1, interface.length() - 2).split('-');
+    const QVector<QStringRef> split = interface.midRef(1, interface.length() - 2).split(QLatin1Char('-'));
 
     GUID guid;
     guid.Data1 = split.at(0).toUInt(0, 16);
diff --git a/src/plugins/platforms/android/qandroidinputcontext.cpp b/src/plugins/platforms/android/qandroidinputcontext.cpp
index 06a9c8c488..2656d45d5f 100644
--- a/src/plugins/platforms/android/qandroidinputcontext.cpp
+++ b/src/plugins/platforms/android/qandroidinputcontext.cpp
@@ -866,7 +866,7 @@ const QAndroidInputContext::ExtractedText &QAndroidInputContext::getExtractedTex
     if (composeLength > 0) {
         //Qt doesn't give us the preedit text, so we have to insert it at the correct position
         int localComposePos = m_composingTextStart - blockPos;
-        blockText = blockText.left(localComposePos) + m_composingText + blockText.mid(localComposePos);
+        blockText = blockText.leftRef(localComposePos) + m_composingText + blockText.midRef(localComposePos);
     }
 
     int cpos = localPos + composeLength; //actual cursor pos relative to the current block
@@ -930,9 +930,8 @@ QString QAndroidInputContext::getTextAfterCursor(jint length, jint /*flags*/)
 QString QAndroidInputContext::getTextBeforeCursor(jint length, jint /*flags*/)
 {
     QVariant textBefore = queryFocusObjectThreadSafe(Qt::ImTextBeforeCursor, QVariant(length));
-    if (textBefore.isValid()) {
-        return textBefore.toString().right(length) + m_composingText;
-    }
+    if (textBefore.isValid())
+        return textBefore.toString().rightRef(length) + m_composingText;
 
     //compatibility code for old controls that do not implement the new API
     QSharedPointer<QInputMethodQueryEvent> query = focusObjectInputMethodQueryThreadSafe();
@@ -946,9 +945,9 @@ QString QAndroidInputContext::getTextBeforeCursor(jint length, jint /*flags*/)
 
     //### the preedit text does not need to be immediately before the cursor
     if (cursorPos <= length)
-        return text.left(cursorPos) + m_composingText;
+        return text.leftRef(cursorPos) + m_composingText;
     else
-        return text.mid(cursorPos - length, length) + m_composingText;
+        return text.midRef(cursorPos - length, length) + m_composingText;
 }
 
 /*
diff --git a/src/plugins/platforms/qnx/qqnxscreen.cpp b/src/plugins/platforms/qnx/qqnxscreen.cpp
index f8ae5121d1..46df500330 100644
--- a/src/plugins/platforms/qnx/qqnxscreen.cpp
+++ b/src/plugins/platforms/qnx/qqnxscreen.cpp
@@ -90,7 +90,7 @@ static QSize determineScreenSize(screen_display_t display, bool primaryScreen) {
 
     const QString envPhySizeStr = qgetenv("QQNX_PHYSICAL_SCREEN_SIZE");
     if (!envPhySizeStr.isEmpty()) {
-        const QStringList envPhySizeStrList = envPhySizeStr.split(QLatin1Char(','));
+        const auto envPhySizeStrList = envPhySizeStr.splitRef(QLatin1Char(','));
         const int envWidth = envPhySizeStrList.size() == 2 ? envPhySizeStrList[0].toInt() : -1;
         const int envHeight = envPhySizeStrList.size() == 2 ? envPhySizeStrList[1].toInt() : -1;
 
diff --git a/src/plugins/platforms/windows/qwindowsfontdatabase_ft.cpp b/src/plugins/platforms/windows/qwindowsfontdatabase_ft.cpp
index f7c8dbdf23..bc0e5cc523 100644
--- a/src/plugins/platforms/windows/qwindowsfontdatabase_ft.cpp
+++ b/src/plugins/platforms/windows/qwindowsfontdatabase_ft.cpp
@@ -137,10 +137,10 @@ static FontKeys &fontKeys()
             QString realKey = registryFontKey;
             realKey.remove(trueType);
             realKey.remove(sizeListMatch);
-            const QStringList fontNames = realKey.trimmed().split(QLatin1Char('&'));
+            const auto fontNames = QStringRef(&realKey).trimmed().split(QLatin1Char('&'));
             fontKey.fontNames.reserve(fontNames.size());
-            foreach (const QString &fontName, fontNames)
-                fontKey.fontNames.append(fontName.trimmed());
+            for (const QStringRef &fontName : fontNames)
+                fontKey.fontNames.append(fontName.trimmed().toString());
             result.append(fontKey);
         }
     }
diff --git a/src/plugins/platforms/xcb/qxcbmime.cpp b/src/plugins/platforms/xcb/qxcbmime.cpp
index f71c5464d0..3e9b0e1e4a 100644
--- a/src/plugins/platforms/xcb/qxcbmime.cpp
+++ b/src/plugins/platforms/xcb/qxcbmime.cpp
@@ -208,10 +208,10 @@ QVariant QXcbMime::mimeConvertToFormat(QXcbConnection *connection, xcb_atom_t a,
                   reinterpret_cast<const ushort *>(data.constData()), data.size() / 2);
             if (!str.isNull()) {
                 if (format == QLatin1String("text/uri-list")) {
-                    const QStringList urls = str.split(QLatin1Char('\n'));
+                    const auto urls = str.splitRef(QLatin1Char('\n'));
                     QList<QVariant> list;
-                    for (const QString &s : urls) {
-                        const QUrl url(s.trimmed());
+                    for (const QStringRef &s : urls) {
+                        const QUrl url(s.trimmed().toString());
                         if (url.isValid())
                             list.append(url);
                     }
diff --git a/src/plugins/platformthemes/gtk3/qgtk3dialoghelpers.cpp b/src/plugins/platformthemes/gtk3/qgtk3dialoghelpers.cpp
index 42d3c1f193..2030732e4b 100644
--- a/src/plugins/platformthemes/gtk3/qgtk3dialoghelpers.cpp
+++ b/src/plugins/platformthemes/gtk3/qgtk3dialoghelpers.cpp
@@ -463,10 +463,10 @@ void QGtk3FileDialogHelper::setNameFilters(const QStringList &filters)
 
     foreach (const QString &filter, filters) {
         GtkFileFilter *gtkFilter = gtk_file_filter_new();
-        const QString name = filter.left(filter.indexOf(QLatin1Char('(')));
+        const QStringRef name = filter.leftRef(filter.indexOf(QLatin1Char('(')));
         const QStringList extensions = cleanFilterList(filter);
 
-        gtk_file_filter_set_name(gtkFilter, name.isEmpty() ? extensions.join(QStringLiteral(", ")).toUtf8() : name.toUtf8());
+        gtk_file_filter_set_name(gtkFilter, name.isEmpty() ? extensions.join(QLatin1String(", ")).toUtf8() : name.toUtf8());
         foreach (const QString &ext, extensions)
             gtk_file_filter_add_pattern(gtkFilter, ext.toUtf8());
 
diff --git a/src/plugins/printsupport/cups/qppdprintdevice.cpp b/src/plugins/printsupport/cups/qppdprintdevice.cpp
index caa7382462..9efa83d409 100644
--- a/src/plugins/printsupport/cups/qppdprintdevice.cpp
+++ b/src/plugins/printsupport/cups/qppdprintdevice.cpp
@@ -63,7 +63,7 @@ QPpdPrintDevice::QPpdPrintDevice(const QString &id)
     if (!id.isEmpty()) {
 
         // TODO For now each dest is an individual device
-        QStringList parts = id.split(QLatin1Char('/'));
+        const auto parts = id.splitRef(QLatin1Char('/'));
         m_cupsName = parts.at(0).toUtf8();
         if (parts.size() > 1)
             m_cupsInstance = parts.at(1).toUtf8();
diff --git a/src/plugins/sqldrivers/sqlite/qsql_sqlite.cpp b/src/plugins/sqldrivers/sqlite/qsql_sqlite.cpp
index ef4ef2e93c..1cb0f10494 100644
--- a/src/plugins/sqldrivers/sqlite/qsql_sqlite.cpp
+++ b/src/plugins/sqldrivers/sqlite/qsql_sqlite.cpp
@@ -72,7 +72,7 @@ QT_BEGIN_NAMESPACE
 static QString _q_escapeIdentifier(const QString &identifier)
 {
     QString res = identifier;
-    if(!identifier.isEmpty() && identifier.left(1) != QString(QLatin1Char('"')) && identifier.right(1) != QString(QLatin1Char('"')) ) {
+    if (!identifier.isEmpty() && !identifier.startsWith(QLatin1Char('"')) && !identifier.endsWith(QLatin1Char('"'))) {
         res.replace(QLatin1Char('"'), QLatin1String("\"\""));
         res.prepend(QLatin1Char('"')).append(QLatin1Char('"'));
         res.replace(QLatin1Char('.'), QLatin1String("\".\""));