Issue 6437 - Skip styles-only patterns on DOM mutations

lib/content/elemHideEmulation.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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
 const {textToRegExp, filterToRegExp, splitSelector} = require("../common");
 
 let MIN_INVOCATION_INTERVAL = 3000;
 const MAX_SYNCHRONOUS_PROCESSING_TIME = 50;
 const abpSelectorRegexp = /:-abp-([\w-]+)\(/i;
 
 function getCachedPropertyValue(object, name, defaultValueFunc = () => {})
 {
   let value = object[name];
-  if (value === undefined)

[hub, 2018/03/14 13:04:03]

there is the argument of value === undefined vs typeof value == "undefined" to
be settled here. It is cosmetic though.

[Manish Jethani, 2018/03/14 14:54:53]

Oh yeah, for the sake of consistency though I've made it use typeof now.

+  if (typeof value == "undefined")
     Object.defineProperty(object, name, {value: value = defaultValueFunc()});
   return value;
 }
 
 /** Return position of node from parent.
  * @param {Node} node the node to find the position of.
  * @return {number} One-based index like for :nth-child(), or 0 on error.
  */
 function positionInParent(node)
 {
@@ skipping 587 matching lines @@
     let generator = null;
 
     let processPatterns = () =>
     {
       let cycleStart = performance.now();
 
       if (!pattern)
       {
         if (!patterns.length)
         {
           if (selectors.length > 0)

[Manish Jethani, 2018/03/08 21:08:15]

We need to do this because of an existing bug, which happens more often with
these changes. Anyway it's a good idea not to call the functions if we don't
have to.

[Manish Jethani, 2018/03/08 21:28:34]

Sorry, I just checked, there is no bug. In any case, it would be a bug if we
didn't check for selectors.length here, because the length is 0 precisely when
there's a DOM mutation but no style sheet changes (what we're optimizing for),
but since the list of selectors is empty it would wipe out all existing
selectors in the document.

             this.addSelectorsFunc(selectors, selectorFilters);
           if (elements.length > 0)
             this.hideElemsFunc(elements, elementFilters);
           if (typeof done == "function")
             done();
           return;
         }
 
         pattern = patterns.shift();
 
@@ skipping 161 matching lines @@
           characterData: shouldObserveCharacterData(this.patterns),
           subtree: true
         }
       );
       this.document.addEventListener("load", this.onLoad.bind(this), true);
     }
   }
 };
 
 exports.ElemHideEmulation = ElemHideEmulation;