gui: warn about old channel backups on wallet startup

Implement a mechanism to show one-time warnings to the user on
startup of the wallet to inform them about critical changes.

Use this mechanism to inform them about the changed lightning
channel backup scheme.

Author: f321x

electrum/gui/qml/components/main.qml

@@ -698,6 +698,28 @@ ApplicationWindow
         }
     }
 
+    function showStartupWarnings() {
+        if (!Daemon.currentWallet)
+            return
+        let warnings = Daemon.currentWallet.startupWarnings
+        // show the warnings one after another, as the dialogs are not modal
+        function showWarning(i) {
+            if (i >= warnings.length)
+                return
+            let dialog = app.messageDialog.createObject(app, {
+                title: warnings[i].title,
+                iconSource: Qt.resolvedUrl('../../icons/warning.png'),
+                text: warnings[i].message
+            })
+            dialog.closed.connect(function() {
+                showWarning(i + 1)
+            })
+            dialog.open()
+            Daemon.currentWallet.acknowledgeWarning(warnings[i].key)
+        }
+        showWarning(0)
+    }
+
     Connections {
         target: Daemon
         function onWalletRequiresPassword(name, path) {
@@ -734,6 +756,7 @@ ApplicationWindow
         }
         function onWalletLoaded() {
             app._loadingWalletContext = null  // either biometric auth or manual auth was successful
+            showStartupWarnings()
         }
     }
 

electrum/gui/qml/qewallet.py

@@ -528,6 +528,18 @@ def lightningNumPeers(self):
             return self.wallet.lnworker.lnpeermgr.num_peers()
         return 0
 
+    @pyqtProperty('QVariantList', notify=dataChanged)
+    def startupWarnings(self):
+        return [{
+            'key': warning.key,
+            'title': warning.title,
+            'message': warning.message,
+        } for warning in self.wallet.get_startup_warnings()]
+
+    @pyqtSlot(str)
+    def acknowledgeWarning(self, key: str):
+        self.wallet.acknowledge_warning(key)
+
     @pyqtSlot()
     def enableLightning(self):
         self.wallet.init_lightning(password=self.password)

electrum/gui/qt/__init__.py

@@ -331,6 +331,7 @@ def _create_window_for_wallet(self, wallet):
         self.build_tray_menu()
         w.warn_if_testnet()
         w.warn_if_watching_only()
+        w.show_startup_warnings()
         return w
 
     def count_wizards_in_progress(func):

electrum/gui/qt/main_window.py

@@ -681,6 +681,11 @@ def on_cb(_x):
         if cb_checked:
             self.config.DONT_SHOW_TESTNET_WARNING = True
 
+    def show_startup_warnings(self):
+        for warning in self.wallet.get_startup_warnings():
+            self.show_warning(warning.message, title=warning.title)
+            self.wallet.acknowledge_warning(warning.key)
+
     def open_wallet(self):
         try:
             wallet_folder = self.get_wallet_folder()

electrum/lnworker.py

@@ -95,7 +95,7 @@
 
 if TYPE_CHECKING:
     from .network import Network
-    from .wallet import Abstract_Wallet
+    from .wallet import Abstract_Wallet, WalletWarning
     from .channel_db import ChannelDB
     from .simple_config import SimpleConfig
 
@@ -1123,6 +1123,33 @@ def has_anchor_channels(self) -> bool:
         return any(chan.has_anchors() and not chan.is_closed()
                    for chan in self.channels.values())
 
+    def get_lightning_startup_warnings(self) -> Sequence['WalletWarning']:
+        from .wallet import WalletWarning
+        warnings = []
+        if not self.has_deterministic_node_id() and self.has_anchor_channels():
+            # backups exported before we started storing the payment_basepoint privkey
+            # (backup v3) cannot sweep the to_remote output of an anchor channel
+            warnings.append(WalletWarning(
+                key='ln_outdated_channel_backups',
+                title=_('Outdated channel backups'),
+                message=''.join([
+                    _("The Lightning channels of this wallet cannot be recovered from seed."), ' ',
+                    _("Channel backups that were exported with an older version of Electrum "
+                      "cannot be used to request a force close of these channels."), '\n\n',
+                    _("Please export new channel backups and store them in a safe place."),
+                ])))
+        if any(not cb.can_sweep_their_ctx_to_remote() for cb in self.channel_backups.values()):
+            warnings.append(WalletWarning(
+                key='ln_unusable_channel_backups',
+                title=_('Unusable channel backups'),
+                message=''.join([
+                    _("This wallet contains channel backups that cannot be used to request a force close, "
+                      "because they were exported with an older version of Electrum."), ' ',
+                    _("Please import new backups, exported by the wallet these channels belong to."), '\n\n',
+                    _("If you have lost access to that wallet, please open an issue on GitHub."),
+                ])))
+        return warnings
+
     @property
     def features(self) -> 'LnFeatures':
         return self.lnpeermgr.features

electrum/wallet.py

@@ -379,6 +379,12 @@ class TxWalletDetails(NamedTuple):
     is_related_to_wallet: bool
 
 
+class WalletWarning(NamedTuple):
+    key: str      # stable identifier, used to remember that the user has seen this warning
+    title: str
+    message: str
+
+
 @dataclass(kw_only=True, slots=True, frozen=True)
 class PiechartBalance:
     confirmed: int    # confirmed and matured and NOT frozen
@@ -517,6 +523,22 @@ def save_backup(self, backup_dir):
         new_db.write()
         return new_path
 
+    def get_startup_warnings(self) -> Sequence[WalletWarning]:
+        """Warnings that should be shown to the user once, when the wallet is opened in a GUI."""
+        warnings = []  # type: List[WalletWarning]
+        if self.lnworker:
+            warnings += self.lnworker.get_lightning_startup_warnings()
+        acknowledged = self.db.get('acknowledged_warnings', [])
+        return [warning for warning in warnings if warning.key not in acknowledged]
+
+    def acknowledge_warning(self, key: str) -> None:
+        """Remember that the user has seen this warning, so that it is not shown again."""
+        acknowledged = self.db.get('acknowledged_warnings', [])
+        if key in acknowledged:
+            return
+        self.db.put('acknowledged_warnings', list(acknowledged) + [key])
+        self.save_db()
+
     def has_lightning(self) -> bool:
         return bool(self.lnworker)