Issue 6992 - Remove keyword-by-filter map

lib/matcher.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";
 
 /**
  * @fileOverview Matcher class implementing matching addresses against
  *               a list of filters.
  */
 
 const {WhitelistFilter} = require("./filterClasses");
 
 /**
+ * Regular expression for matching a keyword in a filter.
+ * @type {RegExp}
+ */
+const keywordRegExp = /[^a-z0-9%*][a-z0-9%]{3,}(?=[^a-z0-9%*])/;
+
+/**
+ * Regular expression for matching all keywords in a filter.
+ * @type {RegExp}
+ */
+const allKeywordsRegExp = new RegExp(keywordRegExp, "g");
+
+/**
+ * Checks whether a particular filter is slow.
+ * @param {RegExpFilter} filter
+ * @returns {boolean}
+ */
+function isSlowFilter(filter)
+{
+  return !filter.pattern || !keywordRegExp.test(filter.pattern);
+}
+
+exports.isSlowFilter = isSlowFilter;
+
+/**
  * Blacklist/whitelist filter matching
  */
 class Matcher
 {
   constructor()
   {
     /**
      * Lookup table for filters by their associated keyword
      * @type {Map.<string,(Filter|Set.<Filter>)>}
      */
@@ skipping 62 matching lines @@
    * @param {Filter} filter
    * @returns {string} keyword or an empty string if no keyword could be found
    */
   findKeyword(filter)
   {
     let result = "";
     let {pattern} = filter;
     if (pattern == null)
       return result;
 
-    let candidates = pattern.toLowerCase().match(
-      /[^a-z0-9%*][a-z0-9%]{3,}(?=[^a-z0-9%*])/g
-    );
+    let candidates = pattern.toLowerCase().match(allKeywordsRegExp);
     if (!candidates)
       return result;
 
     let hash = this.filterByKeyword;
     let resultCount = 0xFFFFFF;
     let resultLength = 0;
     for (let i = 0, l = candidates.length; i < l; i++)
     {
       let candidate = candidates[i].substr(1);
       let filters = hash.get(candidate);
@@ skipping 222 matching lines @@
 
 exports.CombinedMatcher = CombinedMatcher;
 
 /**
  * Shared {@link CombinedMatcher} instance that should usually be used.
  * @type {CombinedMatcher}
  */
 let defaultMatcher = new CombinedMatcher();
 
 exports.defaultMatcher = defaultMatcher;