qt: Add GUIUtil::ExceptionSafeConnect function

Throwing an exception from a slot invoked by Qt's signal-slot connection
mechanism is considered undefined behavior, unless it is handled within
the slot. The GUIUtil::ExceptionSafeConnect function should be used for
exception handling within slots.

src/qt/guiutil.cpp

@@ -902,4 +902,15 @@ QString MakeHtmlLink(const QString& source, const QString& link)
         QLatin1String("<a href=\"") % link % QLatin1String("\">") % link % QLatin1String("</a>"));
 }
 
+void PrintSlotException(
+    const std::exception* exception,
+    const QObject* sender,
+    const QObject* receiver)
+{
+    std::string description = sender->metaObject()->className();
+    description += "->";
+    description += receiver->metaObject()->className();
+    PrintExceptionContinue(exception, description.c_str());
+}
+
 } // namespace GUIUtil

src/qt/guiutil.h

@@ -9,18 +9,23 @@
 #include <fs.h>
 #include <net.h>
 #include <netaddress.h>
+#include <util/check.h>
 
+#include <QApplication>
 #include <QEvent>
 #include <QHeaderView>
 #include <QItemDelegate>
 #include <QLabel>
 #include <QMessageBox>
+#include <QMetaObject>
 #include <QObject>
 #include <QProgressBar>
 #include <QString>
 #include <QTableView>
 
+#include <cassert>
 #include <chrono>
+#include <utility>
 
 class QValidatedLineEdit;
 class SendCoinsRecipient;
@@ -332,6 +337,53 @@ namespace GUIUtil
      */
     QString MakeHtmlLink(const QString& source, const QString& link);
 
+    void PrintSlotException(
+        const std::exception* exception,
+        const QObject* sender,
+        const QObject* receiver);
+
+    /**
+     * A drop-in replacement of QObject::connect function
+     * (see: https://doc.qt.io/qt-5/qobject.html#connect-3), that
+     * guaranties that all exceptions are handled within the slot.
+     *
+     * NOTE: This function is incompatible with Qt private signals.
+     */
+    template <typename Sender, typename Signal, typename Receiver, typename Slot>
+    auto ExceptionSafeConnect(
+        Sender sender, Signal signal, Receiver receiver, Slot method,
+        Qt::ConnectionType type = Qt::AutoConnection)
+    {
+        return QObject::connect(
+            sender, signal, receiver,
+            [sender, receiver, method](auto&&... args) {
+                bool ok{true};
+                try {
+                    (receiver->*method)(std::forward<decltype(args)>(args)...);
+                } catch (const NonFatalCheckError& e) {
+                    PrintSlotException(&e, sender, receiver);
+                    ok = QMetaObject::invokeMethod(
+                        qApp, "handleNonFatalException",
+                        blockingGUIThreadConnection(),
+                        Q_ARG(QString, QString::fromStdString(e.what())));
+                } catch (const std::exception& e) {
+                    PrintSlotException(&e, sender, receiver);
+                    ok = QMetaObject::invokeMethod(
+                        qApp, "handleRunawayException",
+                        blockingGUIThreadConnection(),
+                        Q_ARG(QString, QString::fromStdString(e.what())));
+                } catch (...) {
+                    PrintSlotException(nullptr, sender, receiver);
+                    ok = QMetaObject::invokeMethod(
+                        qApp, "handleRunawayException",
+                        blockingGUIThreadConnection(),
+                        Q_ARG(QString, "Unknown failure occurred."));
+                }
+                assert(ok);
+            },
+            type);
+    }
+
 } // namespace GUIUtil
 
 #endif // BITCOIN_QT_GUIUTIL_H