gui: add external signer path to options dialog

Author: Sjors

src/qt/forms/optionsdialog.ui

@@ -229,6 +229,36 @@
          </layout>
         </widget>
        </item>
+       <item>
+        <widget class="QGroupBox" name="groupBoxHww">
+         <property name="title">
+          <string>External Signer (e.g. hardware wallet)</string>
+         </property>
+         <layout class="QVBoxLayout" name="verticalLayoutHww">
+           <item>
+            <layout class="QHBoxLayout" name="horizontalLayoutHww">
+             <item>
+              <widget class="QLabel" name="externalSignerPathLabel">
+               <property name="text">
+                <string>&amp;External signer script path</string>
+               </property>
+               <property name="buddy">
+                <cstring>externalSignerPath</cstring>
+               </property>
+              </widget>
+             </item>
+             <item>
+              <widget class="QLineEdit" name="externalSignerPath">
+                <property name="toolTip">
+                  <string>Full path to a Bitcoin Core compatible script (e.g. C:\Downloads\hwi.exe or /Users/you/Downloads/hwi.py). Beware: malware can steal your coins!</string>
+                </property>
+              </widget>
+             </item>
+            </layout>
+           </item>
+         </layout>
+        </widget>
+       </item>
        <item>
         <spacer name="verticalSpacer_Wallet">
          <property name="orientation">

src/qt/optionsdialog.cpp

@@ -199,6 +199,7 @@ void OptionsDialog::setModel(OptionsModel *_model)
     connect(ui->prune, &QCheckBox::clicked, this, &OptionsDialog::togglePruneWarning);
     connect(ui->pruneSize, qOverload<int>(&QSpinBox::valueChanged), this, &OptionsDialog::showRestartWarning);
     connect(ui->databaseCache, qOverload<int>(&QSpinBox::valueChanged), this, &OptionsDialog::showRestartWarning);
+    connect(ui->externalSignerPath, &QLineEdit::textChanged, [this]{ showRestartWarning(); });
     connect(ui->threadsScriptVerif, qOverload<int>(&QSpinBox::valueChanged), this, &OptionsDialog::showRestartWarning);
     /* Wallet */
     connect(ui->spendZeroConfChange, &QCheckBox::clicked, this, &OptionsDialog::showRestartWarning);
@@ -233,6 +234,7 @@ void OptionsDialog::setMapper()
     /* Wallet */
     mapper->addMapping(ui->spendZeroConfChange, OptionsModel::SpendZeroConfChange);
     mapper->addMapping(ui->coinControlFeatures, OptionsModel::CoinControlFeatures);
+    mapper->addMapping(ui->externalSignerPath, OptionsModel::ExternalSignerPath);
 
     /* Network */
     mapper->addMapping(ui->mapPortUpnp, OptionsModel::MapPortUPnP);

src/qt/optionsmodel.cpp

@@ -117,6 +117,13 @@ void OptionsModel::Init(bool resetSettings)
         settings.setValue("bSpendZeroConfChange", true);
     if (!gArgs.SoftSetBoolArg("-spendzeroconfchange", settings.value("bSpendZeroConfChange").toBool()))
         addOverriddenOption("-spendzeroconfchange");
+
+    if (!settings.contains("external_signer_path"))
+        settings.setValue("external_signer_path", "");
+
+    if (!gArgs.SoftSetArg("-signer", settings.value("external_signer_path").toString().toStdString())) {
+        addOverriddenOption("-signer");
+    }
 #endif
 
     // Network
@@ -326,6 +333,8 @@ QVariant OptionsModel::data(const QModelIndex & index, int role) const
 #ifdef ENABLE_WALLET
         case SpendZeroConfChange:
             return settings.value("bSpendZeroConfChange");
+        case ExternalSignerPath:
+            return settings.value("external_signer_path");
 #endif
         case DisplayUnit:
             return nDisplayUnit;
@@ -445,6 +454,12 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
                 setRestartRequired(true);
             }
             break;
+        case ExternalSignerPath:
+            if (settings.value("external_signer_path") != value.toString()) {
+                settings.setValue("external_signer_path", value.toString());
+                setRestartRequired(true);
+            }
+            break;
 #endif
         case DisplayUnit:
             setDisplayUnit(value);

src/qt/optionsmodel.h

@@ -65,6 +65,7 @@ class OptionsModel : public QAbstractListModel
         Prune,                  // bool
         PruneSize,              // int
         DatabaseCache,          // int
+        ExternalSignerPath,     // QString
         SpendZeroConfChange,    // bool
         Listen,                 // bool
         OptionIDRowCount,