Issue 7096 - Make it possible to lazy initialize a filter's subscriptions

lib/filterClasses.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 64 matching lines @@
    * Filter type as a string, e.g. "blocking".
    * @type {string}
    */
   get type()
   {
     throw new Error("Please define filter type in the subclass");
   },
 
   /**
    * Subscriptions to which this filter belongs.
-   * @type {(Subscription|Set.<Subscription>)?}
+   * @type {?(Subscription|Set.<Subscription>)}
    * @private
    */
   _subscriptions: null,
 
   /**
    * Whether the filter's subscriptions have already been added to the filter.
    * @type {boolean}
    * @package
    */
   get subscriptionsAdded()
   {
     return this.hasOwnProperty("_subscriptions");
   },
   set subscriptionsAdded(value)
   {
-    this._subscriptions = this._subscriptions;
+    // Once set to true, this cannot be set back to false even if all
+    // subscriptions are removed.
+    if (value)
+      this._subscriptions = this._subscriptions;
   },
 
   /**
    * Yields subscriptions to which the filter belongs.
    * @yields {Subscription}
+   * @package
    */
   *subscriptions()
   {
     if (this._subscriptions)
     {
       if (this._subscriptions instanceof Set)
         yield* this._subscriptions;
       else
         yield this._subscriptions;
     }
   },
 
   /**
    * The number of subscriptions to which the filter belongs.
    * @type {number}
+   * @package
    */
   get subscriptionCount()
   {
     if (this._subscriptions instanceof Set)
       return this._subscriptions.size;
 
     return this._subscriptions ? 1 : 0;
   },
 
   /**
    * Adds a subscription to the set of subscriptions to which the filter
    * belongs.
    * @param {Subscription} subscription
+   * @package
    */
   addSubscription(subscription)
   {
     // Since we use truthy checks in our logic, we must avoid adding a
     // subscription that isn't a non-null object.
     if (subscription === null || typeof subscription != "object")
       return;
 
     if (this._subscriptions)
     {
       if (this._subscriptions instanceof Set)
         this._subscriptions.add(subscription);
       else if (subscription != this._subscriptions)
         this._subscriptions = new Set([this._subscriptions, subscription]);
     }
     else
     {
       this._subscriptions = subscription;
     }
   },
 
   /**
    * Removes a subscription from the set of subscriptions to which the filter
    * belongs.
    * @param {Subscription} subscription
+   * @package
    */
   removeSubscription(subscription)
   {
     if (this._subscriptions)
     {
       if (this._subscriptions instanceof Set)
       {
         this._subscriptions.delete(subscription);
 
         if (this._subscriptions.size == 1)
@@ skipping 1197 matching lines @@
 
   /**
    * Script that should be executed
    * @type {string}
    */
   get script()
   {
     return this.body;
   }
 });