[electrum] add the option to always add new addresses to wallet when …

…scanning beyond gap

Summary:
Users have requested a better solution for generating more addresses without having to use console command.
This adds a checkbox to the "Scan More Addresses" tool. Users can optionnaly check it to save all the newly scanned addresses to the wallet, no matter if any tx history was found for any following address.

Note that as a result of this the wallet will monitor more unused addresses than the usual 20 (default gap limit), so it is not something I recommend doing for wallets with already a large history.

Depends on D15848

Test Plan:
use the Scan More Addresses tool  with the new checkbox toggled. Make sure the expected number of new addresses is added to the Address tab.
Try scanning for only receive addresses, only change addresses, and both.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15849

electrumabc_gui/qt/scan_beyond_gap.py

@@ -73,6 +73,7 @@ def __init__(self, main_window):
             QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Fixed
         )
         vbox.addWidget(label)
+
         vbox.addStretch(1)
         hbox = QtWidgets.QHBoxLayout()
         label = QtWidgets.QLabel(_("Number of addresses to scan:"))
@@ -90,15 +91,31 @@ def __init__(self, main_window):
         hbox.addWidget(self.which_cb)
         hbox.addStretch(1)
         vbox.addLayout(hbox)
+
+        self.always_add_addresses_cb = QtWidgets.QCheckBox(
+            _("Always add scanned addresses to the wallet")
+        )
+        self.always_add_addresses_cb.setToolTip(
+            _(
+                "Add the scanned addresses even if no new history is found. Leave this "
+                "unchecked if unsure, because subscribing to more addresses may "
+                "needlessly slow down your wallet."
+            )
+        )
+        vbox.addWidget(self.always_add_addresses_cb)
+
         self.prog = QtWidgets.QProgressBar()
         self.prog.setMinimum(0)
         self.prog.setMaximum(100)
         vbox.addWidget(self.prog)
+
         self.prog_label = QtWidgets.QLabel()
         vbox.addWidget(self.prog_label)
+
         self.found_label = QtWidgets.QLabel()
         vbox.addWidget(self.found_label)
         vbox.addStretch(1)
+
         self.cancel_but = QtWidgets.QPushButton(_("Cancel"))
         self.scan_but = QtWidgets.QPushButton(_("Start Scan"))
         vbox.addLayout(Buttons(self.cancel_but, self.scan_but))
@@ -107,7 +124,7 @@ def __init__(self, main_window):
         self.scan_but.clicked.connect(self.scan)
 
         self.thread = threading.Thread(target=self.scan_thread, daemon=True)
-        self._thread_args = (None,) * 2
+        self._thread_args = (None,) * 3
         self.stop_flag = False
         self.canceling = False
         self.stage2 = False
@@ -157,9 +174,11 @@ def scan(self):
         self.which_cb.setDisabled(True)
         self.num_sb.setDisabled(True)
         self.found_label.setText("")
-        total = self.num_sb.value()
-        which = self.which_cb.currentIndex()
-        self._thread_args = (total, which)
+        self._thread_args = (
+            self.num_sb.value(),
+            self.which_cb.currentIndex(),
+            self.always_add_addresses_cb.isChecked(),
+        )
         self.thread.start()
 
     def progress_slot(self, pct, scanned, total, found):
@@ -240,8 +259,8 @@ def _addr_has_history(self, address, network):
         )
 
     def scan_thread(self):
-        total, which = self._thread_args
-        assert total is not None and which is not None
+        total, which, always_add = self._thread_args
+        assert all(arg is not None for arg in self._thread_args)
         wallet = self.main_window.wallet
         network = wallet.network
         assert network
@@ -270,14 +289,16 @@ def scan_thread(self):
                     )
                     if self.stop_flag:
                         return
-                    if self._addr_has_history(addr, network):
+                    has_history = self._addr_has_history(addr, network)
+                    if has_history:
                         self.print_error(
                             "FOUND:",
                             addr,
                             "(Change)" if is_change else "(Receiving)",
                             n,
                         )
                         num_found += 1
+                    if has_history or always_add:
                         if is_change:
                             change_end = n
                         else:
@@ -286,7 +307,7 @@ def scan_thread(self):
                     self.progress_sig.emit(ct * 100 // total, ct, total, num_found)
                 i += 1
             num_added = 0
-            if num_found:
+            if num_found or (always_add and (recv_end or change_end)):
                 num_added = self._add_addresses(recv_end, change_end)
             self.done_sig.emit(num_found, num_added)
         except ServerError as e: