Merge bitcoin-core/gui#313: qt: Optimize string concatenation by default

a02c970eb001b456d74ddc30750fe8b55348ddac qt, refactor: Revert explicit including QStringBuilder (Hennadii Stepanov)
3fd3a0fc87a81d42755246830124833e9ca3f0a9 qt, build: Optimize string concatenation (Hennadii Stepanov)

Pull request description:

  From [Qt docs](https://doc.qt.io/qt-5/qstring.html#more-efficient-string-construction):
  > ... multiple uses of the \[`QString`\] '+' operator usually means multiple memory allocations. When concatenating n substrings, where n > 2, there can be as many as n - 1 calls to the memory allocator.

  With this PR
  > ... the '+' will automatically be performed as the `QStringBuilder` '%' everywhere.

  The change in the `src/Makefile.qt.include` file does not justify submitting this PR into the main repo, IMHO.

ACKs for top commit:
  laanwj:
    Code review ACK a02c970eb001b456d74ddc30750fe8b55348ddac
  Talkless:
    utACK a02c970eb001b456d74ddc30750fe8b55348ddac, built successfully on Debian Sid with Qt 5.15.2, but did not check if any displayed strings are "wrong" after refactoring.
  jarolrod:
    ACK a02c970eb001b456d74ddc30750fe8b55348ddac

Tree-SHA512: cbb476ee96f27c3bd6e125efab74d8bf24bbdb4c30576b3feea45e203405f3bf5b497dd7d3e11361fc825fcbf4b893b152921a9efdeaf73b42d1865d85f0ae84

9 files changed, 31 insertions, 19 deletions

diff --git a/src/Makefile.qt.include b/src/Makefile.qt.include
index 30edb1e82d..9e471d61da 100644
--- a/src/Makefile.qt.include
+++ b/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)
diff --git a/src/qt/bitcoin.cpp b/src/qt/bitcoin.cpp
index dffdd5158b..69948402d0 100644
--- a/src/qt/bitcoin.cpp
+++ b/src/qt/bitcoin.cpp
@@ -50,7 +50,6 @@
 #include <QLocale>
 #include <QMessageBox>
 #include <QSettings>
-#include <QStringBuilder>
 #include <QThread>
 #include <QTimer>
 #include <QTranslator>
@@ -419,8 +418,8 @@ void BitcoinApplication::handleRunawayException(const QString &message)
 {
     QMessageBox::critical(
         nullptr, tr("Runaway exception"),
-        tr("A fatal error occurred. %1 can no longer continue safely and will quit.").arg(PACKAGE_NAME) %
-        QLatin1String("<br><br>") % GUIUtil::MakeHtmlLink(message, PACKAGE_BUGREPORT));
+        tr("A fatal error occurred. %1 can no longer continue safely and will quit.").arg(PACKAGE_NAME) +
+        QLatin1String("<br><br>") + GUIUtil::MakeHtmlLink(message, PACKAGE_BUGREPORT));
     ::exit(EXIT_FAILURE);
 }
 
@@ -430,8 +429,8 @@ void BitcoinApplication::handleNonFatalException(const QString& message)
     QMessageBox::warning(
         nullptr, tr("Internal error"),
         tr("An internal error occurred. %1 will attempt to continue safely. This is "
-           "an unexpected bug which can be reported as described below.").arg(PACKAGE_NAME) %
-        QLatin1String("<br><br>") % GUIUtil::MakeHtmlLink(message, PACKAGE_BUGREPORT));
+           "an unexpected bug which can be reported as described below.").arg(PACKAGE_NAME) +
+        QLatin1String("<br><br>") + GUIUtil::MakeHtmlLink(message, PACKAGE_BUGREPORT));
 }
 
 WId BitcoinApplication::getMainWinId() const
diff --git a/src/qt/guiutil.cpp b/src/qt/guiutil.cpp
index 0d73ea0ed0..55e57d425d 100644
--- a/src/qt/guiutil.cpp
+++ b/src/qt/guiutil.cpp
@@ -56,7 +56,6 @@
 #include <QShortcut>
 #include <QSize>
 #include <QString>
-#include <QStringBuilder>
 #include <QTextDocument> // for Qt::mightBeRichText
 #include <QThread>
 #include <QUrlQuery>
@@ -908,7 +907,7 @@ QString MakeHtmlLink(const QString& source, const QString& link)
 {
     return QString(source).replace(
         link,
-        QLatin1String("<a href=\"") % link % QLatin1String("\">") % link % QLatin1String("</a>"));
+        QLatin1String("<a href=\"") + link + QLatin1String("\">") + link + QLatin1String("</a>"));
 }
 
 void PrintSlotException(
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
index 70762ab6bc..abdf9e9ae6 100644
--- a/src/qt/optionsmodel.cpp
+++ b/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()
diff --git a/src/qt/peertablemodel.cpp b/src/qt/peertablemodel.cpp
index 6c4e326011..11441481bb 100644
--- a/src/qt/peertablemodel.cpp
+++ b/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:
diff --git a/src/qt/recentrequeststablemodel.cpp b/src/qt/recentrequeststablemodel.cpp
index 03531a1381..1ecc2f67ef 100644
--- a/src/qt/recentrequeststablemodel.cpp
+++ b/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
diff --git a/src/qt/test/wallettests.cpp b/src/qt/test/wallettests.cpp
index febfead6ad..26f568b16a 100644
--- a/src/qt/test/wallettests.cpp
+++ b/src/qt/test/wallettests.cpp
@@ -235,7 +235,7 @@ 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:"));
diff --git a/src/qt/transactiondesc.cpp b/src/qt/transactiondesc.cpp
index ece3a9cf48..02d220db20 100644
--- a/src/qt/transactiondesc.cpp
+++ b/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)
@@ -38,14 +40,16 @@ 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);
+        }
     }
 }
 
diff --git a/src/qt/transactiontablemodel.cpp b/src/qt/transactiontablemodel.cpp
index 0175c88e7f..b68ceaedbb 100644
--- a/src/qt/transactiontablemodel.cpp
+++ b/src/qt/transactiontablemodel.cpp
@@ -25,6 +25,8 @@
 #include <QDateTime>
 #include <QDebug>
 #include <QIcon>
+#include <QLatin1Char>
+#include <QLatin1String>
 #include <QList>
 
 
@@ -413,9 +415,9 @@ 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)