Add multiple change output preference

Limit to 3 if enabled.

gui/qt/main_window.py

@@ -2744,9 +2744,23 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
             if self.wallet.use_change != usechange_result:
                 self.wallet.use_change = usechange_result
                 self.wallet.storage.put('use_change', self.wallet.use_change)
+                multiple_cb.setEnabled(self.wallet.use_change)
         usechange_cb.stateChanged.connect(on_usechange)
         usechange_cb.setToolTip(_('Using change addresses makes it more difficult for other people to track your transactions.'))
-        tx_widgets.append((usechange_cb, None))
+
+        def on_multiple(x):
+            multiple = x == Qt.Checked
+            if self.wallet.multiple_change != multiple:
+                self.wallet.multiple_change = multiple
+                self.wallet.storage.put('multiple_change', multiple)
+        multiple_change = self.wallet.multiple_change
+        multiple_cb = QCheckBox(_('Multiple'))
+        multiple_cb.setEnabled(self.wallet.use_change)
+        multiple_cb.setToolTip(_('If appropriate, and the "privacy" coin chooser is selected, use up to 3 change addresses.'))
+        multiple_cb.setChecked(multiple_change)
+        multiple_cb.stateChanged.connect(on_multiple)
+        tx_widgets.append((usechange_cb, multiple_cb))
+
 
         showtx_cb = QCheckBox(_('View transaction before signing'))
         showtx_cb.setChecked(self.show_before_broadcast())

lib/wallet.py

@@ -159,6 +159,8 @@ class Abstract_Wallet(PrintError):
         # saved fields
         self.seed_version          = storage.get('seed_version', NEW_SEED_VERSION)
         self.use_change            = storage.get('use_change',True)
+        self.multiple_change       = storage.get('multiple_change', False)
+
         self.use_encryption        = storage.get('use_encryption', False)
         self.seed                  = storage.get('seed', '')               # encrypted
         self.labels                = storage.get('labels', {})
@@ -973,8 +975,9 @@ class Abstract_Wallet(PrintError):
                 return tx
 
         # Let the coin chooser select the coins to spend
+        max_change = 3 if self.multiple_change else 1
         coin_chooser = self.coin_chooser(config)
-        tx = coin_chooser.make_tx(coins, outputs, change_addrs,
+        tx = coin_chooser.make_tx(coins, outputs, change_addrs[:max_change],
                                   fee_estimator, dust_threshold)
 
         # Sort the inputs and outputs deterministically