Issue 7452 - Do not cache element hiding filter objects by default

lib/filterClasses.js

Index: lib/filterClasses.js
===================================================================
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -126,16 +126,27 @@
     if (domains)
       domains.set("", !hasIncludes);
   }
 
   return domains;
 }
 
 /**
+ * Checks whether the given filter object should be cached in
+ * <code>{@link Filter.knownFilters}</code> based on properties of the object.
+ * @param {Filter} filter
+ * @returns {boolean}
+ */
+function shouldCacheFilter(filter)
+{
+  return !(filter instanceof ElemHideFilter);
+}
+
+/**
  * Abstract base class for filters
  *
  * @param {string} text   string representation of the filter
  * @constructor
  */
 function Filter(text)
 {
   this.text = text;
@@ -206,19 +217,21 @@
  */
 Filter.invalidCSPRegExp = /(;|^) ?(base-uri|referrer|report-to|report-uri|upgrade-insecure-requests)\b/i;
 
 /**
  * Creates a filter of correct type from its text representation - does the
  * basic parsing and calls the right constructor then.
  *
  * @param {string} text   as in Filter()
+ * @param {boolean} [forceCache] Whether to force-cache the filter object.
+ *   <em>For internal use only.<em>
  * @return {Filter}
  */
-Filter.fromText = function(text)
+Filter.fromText = function(text, forceCache = true)
 {
   let filter = Filter.knownFilters.get(text);
   if (filter)
     return filter;
 
   if (text[0] == "!")
   {
     filter = new CommentFilter(text);
@@ -227,17 +240,19 @@
   {
     let match = text.includes("#") ? Filter.contentRegExp.exec(text) : null;
     if (match)
       filter = ContentFilter.fromText(text, match[1], match[2], match[3]);
     else
       filter = RegExpFilter.fromText(text);
   }
 
-  Filter.knownFilters.set(filter.text, filter);
+  if (forceCache || shouldCacheFilter(filter))
+    Filter.knownFilters.set(filter.text, filter);
+
   return filter;
 };
 
 /**
  * Deserializes a filter
  *
  * @param {Object}  obj map of serialized properties and their values
  * @return {Filter} filter or null if the filter couldn't be created