gui: toggle chain via menu

The selected chain is stored in the QSettings for mainnet.

doc/release-notes.md

@@ -129,7 +129,11 @@ GUI changes
 -----------
 
 - UTXOs which are locked via the GUI are now stored persistently in the
-  wallet database, so are not lost on node shutdown or crash. (#23065)
+  wallet database, so are not lost on node shutdown or crash. (bitcoin-core/gui#23065)
+
+- Toggle chain from mainnet to testnet, signet or regtest. The GUI now always sets `-chain`,
+  so any occurrences of `-testnet`, `-signet` or `-regtest` in `bitcoin.conf` should
+  be replace with `chain=test`, `chain=signet` or `chain=regtest` respectively. (bitcoin-core/gui#414)
 
 Low-level changes
 =================

src/qt/bitcoin.cpp

@@ -562,6 +562,10 @@ int GuiMain(int argc, char* argv[])
     // - QSettings() will use the new application name after this, resulting in network-specific settings
     // - Needs to be done before createOptionsModel
 
+    QSettings settings;
+    std::string chain = settings.value("chain", "main").toString().toStdString();
+    gArgs.SoftSetArg("-chain", chain);
+
     // Check for chain settings (Params() calls are only valid after this clause)
     try {
         SelectParams(gArgs.GetChainName());

src/qt/bitcoingui.cpp

@@ -454,6 +454,46 @@ void BitcoinGUI::createMenuBar()
     appMenuBar = menuBar();
 #endif
 
+    // Add chain selection submenu
+    QAction* chain_selection_action{nullptr};
+    QMenu* chain_selection_menu{nullptr};
+    chain_selection_action = new QAction(tr("&Switch chain"), this);
+    chain_selection_action->setStatusTip(tr("Restart application using a different (test) network"));
+    chain_selection_menu = new QMenu(this);
+
+    connect(chain_selection_menu, &QMenu::aboutToShow, [this, chain_selection_menu] {
+        chain_selection_menu->clear();
+        const std::vector<std::pair<QString, QString>> chains = {{"main", "&Bitcoin"}, {"test", "&Testnet"}, {"regtest", "&Regtest"}, {"signet", "&Signet"}};
+        for (auto chain : chains) {
+            const bool is_current = gArgs.GetChainName() == chain.first.toStdString();
+            QAction* action = chain_selection_menu->addAction(chain.second);
+            action->setCheckable(true);
+            action->setChecked(is_current);
+            action->setEnabled(!is_current);
+
+            connect(action, &QAction::triggered, [this, chain] {
+                //: Switch to the mainnet, testnet, signet or regtest chain.
+                QMessageBox::StandardButton btn_ret_val = QMessageBox::question(this, tr("Switch chain"),
+                    //: Switching between mainnet, testnet, signet or regtest chain requires a restart.
+                    tr("Client restart required to switch chain.\n\nClientClient will be shut down. Do you want to proceed?"),
+                    QMessageBox::Yes | QMessageBox::Cancel, QMessageBox::Cancel);
+
+                if (btn_ret_val == QMessageBox::Cancel) return;
+
+                // QSettings are stored seperately for each network. Switch application name
+                // to mainnet before storing the selected chain.
+                QScopedPointer<const NetworkStyle> networkStyle(NetworkStyle::instantiate("main"));
+                assert(!networkStyle.isNull());
+                QApplication::setApplicationName(networkStyle->getAppName());
+
+                QSettings settings;
+                settings.setValue("chain", chain.first);
+                QApplication::quit();
+            });
+        }
+    });
+    chain_selection_action->setMenu(chain_selection_menu);
+
     // Configure the menus
     QMenu *file = appMenuBar->addMenu(tr("&File"));
     if(walletFrame)
@@ -471,6 +511,8 @@ void BitcoinGUI::createMenuBar()
         file->addAction(m_load_psbt_clipboard_action);
         file->addSeparator();
     }
+    file->addAction(chain_selection_action);
+    file->addSeparator();
     file->addAction(quitAction);
 
     QMenu *settings = appMenuBar->addMenu(tr("&Settings"));