GUI: Update nDisplayUnit to keep old versions in sync

Author: luke-jr

src/qt/bitcoinunits.cpp

@@ -323,8 +323,7 @@ CAmount BitcoinUnits::maxMoney()
     return MAX_MONEY;
 }
 
-namespace {
-std::variant<qint8, QString> ToSetting(BitcoinUnit unit)
+std::variant<qint8, QString> BitcoinUnits::ToSetting(BitcoinUnit unit)
 {
     switch (unit) {
     case BitcoinUnit::BTC:  return qint8{0};
@@ -338,6 +337,7 @@ std::variant<qint8, QString> ToSetting(BitcoinUnit unit)
     assert(false);
 }
 
+namespace {
 BitcoinUnit FromQint8(qint8 num)
 {
     switch (num) {
@@ -366,7 +366,7 @@ BitcoinUnit BitcoinUnits::FromSetting(const QString& s, BitcoinUnit def)
 
 QDataStream& operator<<(QDataStream& out, const BitcoinUnit& unit)
 {
-    auto setting_val = ToSetting(unit);
+    auto setting_val = BitcoinUnits::ToSetting(unit);
     if (const QString* setting_str = std::get_if<QString>(&setting_val)) {
         return out << qint8{0} << *setting_str;
     } else {

src/qt/bitcoinunits.h

@@ -63,6 +63,8 @@ class BitcoinUnits: public QAbstractListModel
 
     //! Get list of units, for drop-down box
     static QList<Unit> availableUnits();
+    //! String for setting(s)
+    static std::variant<qint8, QString> ToSetting(Unit unit);
     //! Convert setting(s) string to unit
     static Unit FromSetting(const QString&, Unit def);
     //! Long name

src/qt/optionsmodel.cpp

@@ -667,6 +667,15 @@ void OptionsModel::setDisplayUnit(const QVariant& new_unit)
     } else {
         settings.setValue("DisplayBitcoinUnitKnots", QVariant::fromValue(m_display_bitcoin_unit));
     }
+    {
+        // For older versions:
+        auto setting_val = BitcoinUnits::ToSetting(m_display_bitcoin_unit);
+        if (const QString* setting_str = std::get_if<QString>(&setting_val)) {
+            settings.setValue("nDisplayUnit", *setting_str);
+        } else {
+            settings.setValue("nDisplayUnit", std::get<qint8>(setting_val));
+        }
+    }
     Q_EMIT displayUnitChanged(m_display_bitcoin_unit);
 }