qt: add menu item to view closing transaction of channel

electrum/gui/qt/channels_list.py

@@ -119,6 +119,11 @@ class ChannelsList(MyTreeView):
             if chan.peer_state == peer_states.GOOD:
                 menu.addAction(_("Close channel"), lambda: self.close_channel(channel_id))
             menu.addAction(_("Force-close channel"), lambda: self.force_close(channel_id))
+        else:
+            txid = chan.get_closing_txid()
+            closing_tx = self.lnworker.lnwatcher.db.get_transaction(txid)
+            if closing_tx:
+                menu.addAction(_("View closing transaction"), lambda: self.parent.show_transaction(closing_tx))
         if chan.is_redeemed():
             menu.addAction(_("Remove"), lambda: self.remove_channel(channel_id))
         menu.exec_(self.viewport().mapToGlobal(position))

electrum/lnchannel.py

@@ -311,6 +311,11 @@ class Channel(Logger):
         # the closing txid has been saved
         return self.get_state() >= channel_states.CLOSED
 
+    def get_closing_txid(self):
+        item = self.lnworker.channel_timestamps.get(self.channel_id.hex())
+        funding_txid, funding_height, funding_timestamp, closing_txid, closing_height, closing_timestamp = item
+        return closing_txid
+
     def is_redeemed(self):
         return self.get_state() == channel_states.REDEEMED