Issue 7097 - Make element hiding filter objects ephemeral

lib/filterClasses.js

Index: lib/filterClasses.js
===================================================================
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -76,16 +76,26 @@
    * @type {string}
    */
   get type()
   {
     throw new Error("Please define filter type in the subclass");
   },
 
   /**
+   * Whether this object is discarded after use. If <code>false</code>, the
+   * object is retained in memory once created and every call to
+   * {@link Filter#fromText} returns the same instance. Defaults to
+   * <code>false</code>.
+   * @type {boolean}
+   * @package
+   */
+  ephemeral: false,
+
+  /**
    * Subscriptions to which this filter belongs.
    * @type {?(Subscription|Set.<Subscription>)}
    * @private
    */
   _subscriptions: null,
 
   /**
    * Whether the filter's subscriptions have already been added to the filter.
@@ -223,19 +233,21 @@
  */
 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} persistent Whether the filter object should be persisted in
+ *   memory.
  * @return {Filter}
  */
-Filter.fromText = function(text)
+Filter.fromText = function(text, persistent = true)

[Manish Jethani, 2018/11/18 06:19:14]

The idea here is that internally we'll always pass false, but UI for example
(for user-defined filters) will not pass anything so it'll default to true.

Rules for the ephemeral property:

 -  If persistent is true, ephemeral is false (otherwise it's the default value)
 -  The value cannot change once the filter object has been returned from here
 -  To persist state like disabled, hit count, etc., create a non-ephemeral
object first and then set the state property, otherwise it'll be lost
 -  Do not hold on to references to ephemeral objects because their state will
sooner or later be out of sync with reality (e.g. removed subscriptions will
still appear)

 {
   let filter = Filter.knownFilters.get(text);
   if (filter)
     return filter;
 
   if (text[0] == "!")
   {
     filter = new CommentFilter(text);
@@ -244,17 +256,22 @@
   {
     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 (persistent)
+    filter.ephemeral = false;
+
+  if (!filter.ephemeral)
+    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
@@ -1311,17 +1328,23 @@
  */
 function ElemHideFilter(text, domains, selector)
 {
   ElemHideBase.call(this, text, domains, selector);
 }
 exports.ElemHideFilter = ElemHideFilter;
 
 ElemHideFilter.prototype = extend(ElemHideBase, {
-  type: "elemhide"
+  type: "elemhide",
+
+  /**
+   * See Filter.ephemeral
+   * @inheritdoc
+   */
+  ephemeral: true
 });
 
 /**
  * Class for element hiding exceptions
  * @param {string} text see {@link Filter Filter()}
  * @param {string} [domains]  see {@link ElemHideBase ElemHideBase()}
  * @param {string} selector see {@link ElemHideBase ElemHideBase()}
  * @constructor