qt, build: Optimize string concatenation

The defined QT_USE_QSTRINGBUILDER macro means using the QStringBuilder
for efficient string concatenation in all Qt code by default.

src/Makefile.qt.include

@@ -288,7 +288,7 @@ RES_ANIMATION = $(wildcard $(srcdir)/qt/res/animation/spinner-*.png)
 
 BITCOIN_RC = qt/res/bitcoin-qt-res.rc
 
-BITCOIN_QT_INCLUDES = -DQT_NO_KEYWORDS
+BITCOIN_QT_INCLUDES = -DQT_NO_KEYWORDS -DQT_USE_QSTRINGBUILDER
 
 qt_libbitcoinqt_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) $(BITCOIN_QT_INCLUDES) \
   $(QT_INCLUDES) $(QT_DBUS_INCLUDES) $(QR_CFLAGS)

src/qt/optionsmodel.cpp

@@ -21,6 +21,7 @@
 #include <validation.h> // For DEFAULT_SCRIPTCHECK_THREADS
 
 #include <QDebug>
+#include <QLatin1Char>
 #include <QSettings>
 #include <QStringList>
 
@@ -244,7 +245,7 @@ static ProxySetting GetProxySetting(QSettings &settings, const QString &name)
 
 static void SetProxySetting(QSettings &settings, const QString &name, const ProxySetting &ip_port)
 {
-    settings.setValue(name, ip_port.ip + ":" + ip_port.port);
+    settings.setValue(name, QString{ip_port.ip + QLatin1Char(':') + ip_port.port});
 }
 
 static const QString GetDefaultProxyAddress()

src/qt/peertablemodel.cpp

@@ -114,7 +114,7 @@ QVariant PeerTableModel::data(const QModelIndex &index, int role) const
             return (qint64)rec->nodeStats.nodeid;
         case Address:
             // prepend to peer address down-arrow symbol for inbound connection and up-arrow for outbound connection
-            return QString(rec->nodeStats.fInbound ? "↓ " : "↑ ") + QString::fromStdString(rec->nodeStats.addrName);
+            return QString::fromStdString((rec->nodeStats.fInbound ? "↓ " : "↑ ") + rec->nodeStats.addrName);
         case ConnectionType:
             return GUIUtil::ConnectionTypeToQString(rec->nodeStats.m_conn_type, /* prepend_direction */ false);
         case Network:

src/qt/recentrequeststablemodel.cpp

@@ -14,6 +14,9 @@
 
 #include <utility>
 
+#include <QLatin1Char>
+#include <QLatin1String>
+
 RecentRequestsTableModel::RecentRequestsTableModel(WalletModel *parent) :
     QAbstractTableModel(parent), walletModel(parent)
 {
@@ -124,7 +127,11 @@ void RecentRequestsTableModel::updateAmountColumnTitle()
 /** Gets title for amount column including current display unit if optionsModel reference available. */
 QString RecentRequestsTableModel::getAmountTitle()
 {
-    return (this->walletModel->getOptionsModel() != nullptr) ? tr("Requested") + " ("+BitcoinUnits::shortName(this->walletModel->getOptionsModel()->getDisplayUnit()) + ")" : "";
+    if (!walletModel->getOptionsModel()) return {};
+    return tr("Requested") +
+           QLatin1String(" (") +
+           BitcoinUnits::shortName(this->walletModel->getOptionsModel()->getDisplayUnit()) +
+           QLatin1Char(')');
 }
 
 QModelIndex RecentRequestsTableModel::index(int row, int column, const QModelIndex &parent) const

src/qt/test/wallettests.cpp

@@ -236,7 +236,7 @@ void TestGUI(interfaces::Node& node)
 
             QCOMPARE(uri.count("amount=0.00000001"), 2);
             QCOMPARE(receiveRequestDialog->QObject::findChild<QLabel*>("amount_tag")->text(), QString("Amount:"));
-            QCOMPARE(receiveRequestDialog->QObject::findChild<QLabel*>("amount_content")->text(), QString("0.00000001 ") + QString::fromStdString(CURRENCY_UNIT));
+            QCOMPARE(receiveRequestDialog->QObject::findChild<QLabel*>("amount_content")->text(), QString::fromStdString("0.00000001 " + CURRENCY_UNIT));
 
             QCOMPARE(uri.count("label=TEST_LABEL_1"), 2);
             QCOMPARE(receiveRequestDialog->QObject::findChild<QLabel*>("label_tag")->text(), QString("Label:"));

src/qt/transactiondesc.cpp

@@ -26,6 +26,8 @@
 #include <stdint.h>
 #include <string>
 
+#include <QLatin1String>
+
 QString TransactionDesc::FormatTxStatus(const interfaces::WalletTx& wtx, const interfaces::WalletTxStatus& status, bool inMempool, int numBlocks)
 {
     if (!status.is_final)
@@ -38,16 +40,18 @@ QString TransactionDesc::FormatTxStatus(const interfaces::WalletTx& wtx, const i
     else
     {
         int nDepth = status.depth_in_main_chain;
-        if (nDepth < 0)
+        if (nDepth < 0) {
             return tr("conflicted with a transaction with %1 confirmations").arg(-nDepth);
-        else if (nDepth == 0)
-            return tr("0/unconfirmed, %1").arg((inMempool ? tr("in memory pool") : tr("not in memory pool"))) + (status.is_abandoned ? ", "+tr("abandoned") : "");
-        else if (nDepth < 6)
+        } else if (nDepth == 0) {
+            const QString abandoned{status.is_abandoned ? QLatin1String(", ") + tr("abandoned") : QString()};
+            return tr("0/unconfirmed, %1").arg(inMempool ? tr("in memory pool") : tr("not in memory pool")) + abandoned;
+        } else if (nDepth < 6) {
             return tr("%1/unconfirmed").arg(nDepth);
-        else
+        } else {
             return tr("%1 confirmations").arg(nDepth);
         }
     }
+}
 
 // Takes an encoded PaymentRequest as a string and tries to find the Common Name of the X.509 certificate
 // used to sign the PaymentRequest.

src/qt/transactiontablemodel.cpp

@@ -25,6 +25,8 @@
 #include <QDateTime>
 #include <QDebug>
 #include <QIcon>
+#include <QLatin1Char>
+#include <QLatin1String>
 #include <QList>
 
 
@@ -409,9 +411,9 @@ QVariant TransactionTableModel::txAddressDecoration(const TransactionRecord *wtx
 QString TransactionTableModel::formatTxToAddress(const TransactionRecord *wtx, bool tooltip) const
 {
     QString watchAddress;
-    if (tooltip) {
+    if (tooltip && wtx->involvesWatchAddress) {
         // Mark transactions involving watch-only addresses by adding " (watch-only)"
-        watchAddress = wtx->involvesWatchAddress ? QString(" (") + tr("watch-only") + QString(")") : "";
+        watchAddress = QLatin1String(" (") + tr("watch-only") + QLatin1Char(')');
     }
 
     switch(wtx->type)