Issue 6562 - Remove filter keys from the element hiding code

lib/elemHide.js

Index: lib/elemHide.js
diff --git a/lib/elemHide.js b/lib/elemHide.js
index 9aa1ae3948540af980eda636d9530464c6951aa6..88aef4c93156a65a4b1558489c740f73a077e32a 100644
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -25,48 +25,36 @@ const {ElemHideException} = require("./filterClasses");
 const {FilterNotifier} = require("./filterNotifier");
 
 /**
- * Lookup table, filters by their associated key
- * @type {Filter[]}
- */
-let filterByKey = [];
-
-/**
- * Lookup table, keys of the filters by filter
- * @type {Map.<Filter,number>}
- */
-let keyByFilter = new Map();
-
-/**
- * Nested lookup table, filter (or false if inactive) by filter key by domain.
+ * Lookup table, active flag, by filter by domain.
  * (Only contains filters that aren't unconditionally matched for all domains.)
- * @type {Map.<string,Map.<number,(Filter|boolean)>>}
+ * @type {Map.<string,Map.<Filter,boolean>>}
  */
 let filtersByDomain = new Map();
 
 /**
- * Lookup table, filter key by selector. (Only used for selectors that are
+ * Lookup table, filter by selector. (Only used for selectors that are
  * unconditionally matched for all domains.)
- * @type {Map.<string,number>}
+ * @type {Map.<string,Filter>}
  */
-let filterKeyBySelector = new Map();
+let filterBySelector = new Map();
 
 /**
- * This array caches the keys of filterKeyBySelector table (selectors which
- * unconditionally apply on all domains). It will be null if the cache needs to
- * be rebuilt.
+ * 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.
  */
 let unconditionalSelectors = null;
 
 /**
- * Object to be used instead when a filter has a blank domains property.
+ * Map to be used instead when a filter has a blank domains property.
  */
 let defaultDomains = new Map([["", true]]);
 
 /**
- * Set containing known element hiding exceptions
- * @type {Set.<string>}
+ * Set containing known element hiding and exception filters
+ * @type {Set.<ElemHideBase>}
  */
-let knownExceptions = new Set();
+let knownFilters = new Set();
 
 /**
  * Lookup table, lists of element hiding exceptions by selector
@@ -84,39 +72,42 @@ let ElemHide = exports.ElemHide = {
    */
   clear()
   {
-    for (let collection of [keyByFilter, filtersByDomain, filterKeyBySelector,
-                            knownExceptions, exceptions])
+    for (let collection of [filtersByDomain, filterBySelector,
+                            knownFilters, exceptions])
     {
       collection.clear();
     }
-    filterByKey = [];
     unconditionalSelectors = null;
     FilterNotifier.emit("elemhideupdate");
   },
 
-  _addToFiltersByDomain(key, filter)
+  _addToFiltersByDomain(filter)
   {
     let domains = filter.domains || defaultDomains;
     for (let [domain, isIncluded] of domains)
     {
+      // There's no need to note that a filter is generically disabled.
+      if (!isIncluded && domain == "")
+        continue;
+
       let filters = filtersByDomain.get(domain);
       if (!filters)
         filtersByDomain.set(domain, filters = new Map());
-      filters.set(key, isIncluded ? filter : false);
+      filters.set(filter, isIncluded);
     }
   },
 
   /**
    * Add a new element hiding filter
-   * @param {ElemHideFilter} filter
+   * @param {ElemHideBase} filter
    */
   add(filter)
   {
+    if (knownFilters.has(filter))
+      return;
+
     if (filter instanceof ElemHideException)
     {
-      if (knownExceptions.has(filter.text))
-        return;
-
       let {selector} = filter;
       let list = exceptions.get(selector);
       if (list)
@@ -127,88 +118,66 @@ let ElemHide = exports.ElemHide = {
       // If this is the first exception for a previously unconditionally
       // applied element hiding selector we need to take care to update the
       // lookups.
-      let filterKey = filterKeyBySelector.get(selector);
-      if (typeof filterKey != "undefined")
-      {
-        this._addToFiltersByDomain(filterKey, filterByKey[filterKey]);
-        filterKeyBySelector.delete(selector);
-        unconditionalSelectors = null;
-      }
-
-      knownExceptions.add(filter.text);
-    }
-    else
-    {
-      if (keyByFilter.has(filter))
-        return;
-
-      let key = filterByKey.push(filter) - 1;
-      keyByFilter.set(filter, key);
-
-      if (!(filter.domains || exceptions.has(filter.selector)))
+      let unconditionalFilterForSelector = filterBySelector.get(selector);
+      if (unconditionalFilterForSelector)
       {
-        // The new filter's selector is unconditionally applied to all domains
-        filterKeyBySelector.set(filter.selector, key);
+        this._addToFiltersByDomain(unconditionalFilterForSelector);
+        filterBySelector.delete(selector);
         unconditionalSelectors = null;
       }
-      else
-      {
-        // The new filter's selector only applies to some domains
-        this._addToFiltersByDomain(key, filter);
-      }
     }
-
-    FilterNotifier.emit("elemhideupdate");
-  },
-
-  _removeFilterKey(key, filter)
-  {
-    if (filterKeyBySelector.get(filter.selector) == key)
+    else if (!(filter.domains || exceptions.has(filter.selector)))
     {
-      filterKeyBySelector.delete(filter.selector);
+      // The new filter's selector is unconditionally applied to all domains
+      filterBySelector.set(filter.selector, filter);
       unconditionalSelectors = null;
-      return;
     }
-
-    // We haven't found this filter in unconditional filters, look in
-    // filtersByDomain.
-    let domains = filter.domains || defaultDomains;
-    for (let domain of domains.keys())
+    else
     {
-      let filters = filtersByDomain.get(domain);
-      if (filters)
-        filters.delete(key);
+      // The new filter's selector only applies to some domains
+      this._addToFiltersByDomain(filter);
     }
+
+    knownFilters.add(filter);
+    FilterNotifier.emit("elemhideupdate");
   },
 
   /**
    * Removes an element hiding filter
-   * @param {ElemHideFilter} filter
+   * @param {ElemHideBase} filter
    */
   remove(filter)
   {
+    if (!knownFilters.has(filter))
+      return;
+
+    // Whitelisting filters
     if (filter instanceof ElemHideException)
     {
-      if (!knownExceptions.has(filter.text))
-        return;
-
       let list = exceptions.get(filter.selector);
       let index = list.indexOf(filter);
       if (index >= 0)
         list.splice(index, 1);
-      knownExceptions.delete(filter.text);
     }
+    // Unconditially applied element hiding filters
+    else if (filterBySelector.get(filter.selector) === filter)

[Manish Jethani, 2018/05/04 11:59:55]

Looking at the code above, the value returned by filterBySelector.get will
always be a non-null object. In that case we should change the strict equality
here to non-strict equality. There's no harm in keeping it, but when I see a
"===" I think there's a good reason for it to be there, it tells a story, but
here it's just noise.

(It would be the opposite if our style guide mandated "===" and made "==" the
exception.)

[kzar, 2018/05/04 12:06:10]

Done.

+    {
+      filterBySelector.delete(filter.selector);
+      unconditionalSelectors = null;
+    }
+    // Conditionally applied element hiding filters
     else
     {
-      let key = keyByFilter.get(filter);
-      if (typeof key == "undefined")
-        return;
-
-      delete filterByKey[key];
-      keyByFilter.delete(filter);
-      this._removeFilterKey(key, filter);
+      let domains = filter.domains || defaultDomains;
+      for (let domain of domains.keys())
+      {
+        let filters = filtersByDomain.get(domain);
+        if (filters)
+          filters.delete(filter);
+      }
     }
 
+    knownFilters.delete(filter);
     FilterNotifier.emit("elemhideupdate");
   },
 
@@ -234,16 +203,6 @@ let ElemHide = exports.ElemHide = {
     return null;
   },
 
-  /**
-   * Retrieves an element hiding filter by the corresponding protocol key
-   * @param {number} key
-   * @return {Filter}
-   */
-  getFilterByKey(key)
-  {
-    return (key in filterByKey ? filterByKey[key] : null);
-  },
-
   /**
    * Returns a list of selectors that apply on each website unconditionally.
    * @returns {string[]}
@@ -251,7 +210,7 @@ let ElemHide = exports.ElemHide = {
   getUnconditionalSelectors()
   {
     if (!unconditionalSelectors)
-      unconditionalSelectors = [...filterKeyBySelector.keys()];
+      unconditionalSelectors = [...filterBySelector.keys()];
     return unconditionalSelectors.slice();
   },
 
@@ -293,8 +252,11 @@ let ElemHide = exports.ElemHide = {
       selectors = this.getUnconditionalSelectors();
 
     let specificOnly = (criteria >= ElemHide.SPECIFIC_ONLY);
-    let seenFilters = new Set();
+    let excluded = new Set();
     let currentDomain = domain ? domain.toUpperCase() : "";
+
+    // 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 == "")
@@ -303,14 +265,17 @@ let ElemHide = exports.ElemHide = {
       let filters = filtersByDomain.get(currentDomain);
       if (filters)
       {
-        for (let [filterKey, filter] of filters)
+        for (let [filter, isIncluded] of filters)
         {
-          if (seenFilters.has(filterKey))
-            continue;
-          seenFilters.add(filterKey);
-
-          if (filter && !this.getException(filter, domain))
+          if (!isIncluded)
+          {
+            excluded.add(filter);
+          }
+          else if ((excluded.size == 0 || !excluded.has(filter)) &&
+                   !this.getException(filter, domain))
+          {
             selectors.push(filter.selector);
+          }
         }
       }