Issue 6955 - Avoid making copies of common selector list

lib/elemHide.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 29 matching lines @@
 
 /**
  * This array caches the keys of filterBySelector table (selectors
  * which unconditionally apply on all domains). It will be null if the
  * cache needs to be rebuilt.
  * @type {?string[]}
  */
 let unconditionalSelectors = null;
 
 /**
  * Cached list of selectors that apply on any domain that neither has any

[Manish Jethani, 2018/09/17 09:28:43]

Here we are introducing the idea of "common" selectors. The precise definition
is in the JSDoc here.

  * domain-specific filters or exceptions nor is specifically excluded from any
  * generic filters or exceptions.
  * @type {?string[]}
  */
 let commonSelectors = null;
 
 /**
  * Map to be used instead when a filter has a blank domains property.
  * @type {Map.<string,boolean>}
  * @const
@@ skipping 148 matching lines @@
    * @param {boolean} [specificOnly] true if generic filters should not apply.
    * @returns {string[]} List of selectors.
    */
   getSelectorsForDomain(domain, specificOnly = false)
   {
     let selectors = [];
 
     let excluded = new Set();
     let currentDomain = domain ? domain.replace(/\.+$/, "").toLowerCase() : "";
 
-    let commonCase = true;
+    let commonCase = !specificOnly;
 
     // This code is a performance hot-spot, which is why we've made certain
     // micro-optimisations. Please be careful before making changes.
     while (true)
     {
       if (specificOnly && currentDomain == "")
         break;
+
+      if (commonCase && currentDomain != "" &&
+          ElemHideExceptions.domainHasExceptions(currentDomain))
+      {
+        commonCase = false;
+      }
 
       let filters = filtersByDomain.get(currentDomain);
       if (filters)
       {
         if (currentDomain != "")
           commonCase = false;
 
         for (let [filter, isIncluded] of filters)
         {
           if (!isIncluded)
           {
             excluded.add(filter);
           }
           else
           {
             let {selector} = filter;
-            if (excluded.size == 0 || !excluded.has(filter))
+            if ((excluded.size == 0 || !excluded.has(filter)) &&
+                !ElemHideExceptions.getException(selector, domain))
             {
-              let exception = ElemHideExceptions.getException(selector, domain);
-              if (!exception)
-                selectors.push(selector);
-              else if (commonCase && exception.domains)
-                commonCase = false;
+              selectors.push(selector);
             }
           }
         }
       }
 
       if (currentDomain == "")
         break;
 
       let nextDot = currentDomain.indexOf(".");
       currentDomain = nextDot == -1 ? "" : currentDomain.substr(nextDot + 1);
     }
 
     if (!specificOnly)
     {
       // Use the cache of common selectors if there are no filters or
       // exceptions that apply or don't apply specifically to this domain.
       if (commonCase)
       {
         if (!commonSelectors)
         {
-          let unconditional = getUnconditionalSelectors();
-          commonSelectors = Object.freeze(unconditional.concat(selectors));
+          commonSelectors =
+            Object.freeze(getUnconditionalSelectors().concat(selectors));
         }
 
         selectors = commonSelectors;
       }
       else
       {
-        let unconditional = getUnconditionalSelectors();
-        selectors = Object.freeze(unconditional.concat(selectors));
+        selectors = getUnconditionalSelectors().concat(selectors);
       }
     }
 
     return selectors;
   }
 };