Issue 6829 - Free filters when subscriptions are empty

lib/filterStorage.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 127 matching lines @@
    * Removes a filter subscription from the list
    * @param {Subscription} subscription filter subscription to be removed
    */
   removeSubscription(subscription)
   {
     for (let i = 0; i < FilterStorage.subscriptions.length; i++)
     {
       if (FilterStorage.subscriptions[i].url == subscription.url)
       {
         removeSubscriptionFilters(subscription);
+        for (let filter of subscription.filters)
+        {
+          if (filter.subscriptions.size == 0)
+            Filter.knownFilters.delete(filter.text);
+        }
 
         FilterStorage.subscriptions.splice(i--, 1);
         FilterStorage.knownSubscriptions.delete(subscription.url);
         FilterNotifier.triggerListeners("subscription.removed", subscription);
         return;
       }
     }
   },
 
   /**
@@ skipping 615 matching lines @@
       else if (this.wantObj === false && val)
         this.curObj.push(val.replace(/\\\[/g, "["));
     }
     finally
     {
       Filter.knownFilters = origKnownFilters;
       Subscription.knownSubscriptions = origKnownSubscriptions;
     }
   }
 };