Issue 6957 - Return common style sheet for unknown domains

lib/elemHide.js

Index: lib/elemHide.js
===================================================================
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -58,29 +58,62 @@
 /**
  * The default style sheet that applies on all domains. This is based on the
  * value of <code>{@link unconditionalSelectors}</code>.
  * @type {?string}
  */
 let defaultStyleSheet = null;
 
 /**
+ * The common style sheet that applies on all unknown domains. This is a
+ * concatenation of the default style sheet and an additional style sheet based
+ * on selectors from all generic filters that are not in the
+ * <code>{@link unconditionalSelectors}</code> list.
+ * @type {?string}
+ */
+let commonStyleSheet = null;
+
+/**
  * Map to be used instead when a filter has a blank domains property.
  * @type {Map.<string,boolean>}
  * @const
  */
 let defaultDomains = new Map([["", true]]);
 
 /**
  * Set containing known element hiding filters
  * @type {Set.<ElemHideFilter>}
  */
 let knownFilters = new Set();
 
 /**
+ * All domains known to occur in exceptions
+ * @type {Set.<string>}
+ */
+let knownExceptionDomains = new Set();
+
+/**
+ * Returns the suffix of the given domain that is known. If no suffix is known,
+ * an empty string is returned.
+ * @param {?string} domain
+ * @returns {string}
+ */
+function getKnownSuffix(domain)
+{
+  while (domain && !filtersByDomain.has(domain) &&
+         !knownExceptionDomains.has(domain))
+  {
+    let index = domain.indexOf(".");
+    domain = index == -1 ? "" : domain.substring(index + 1);
+  }
+
+  return domain;
+}
+
+/**
  * Adds a filter to the lookup table of filters by domain.
  * @param {Filter} filter
  */
 function addToFiltersByDomain(filter)
 {
   let domains = filter.domains || defaultDomains;
   for (let [domain, isIncluded] of domains)
   {
@@ -107,27 +140,27 @@
   return unconditionalSelectors;
 }
 
 /**
  * Returns the list of selectors that apply on a given domain from the subset
  * of filters that do not apply unconditionally on all domains.
  *
  * @param {string} domain The domain.
- * @param {boolean} [specificOnly=false] Whether selectors from generic filters
- *   should be included.
+ * @param {boolean} specificOnly Whether selectors from generic filters should
+ *   be included.
  *
  * @returns {Array.<string>} The list of selectors.
  */
-function getConditionalSelectorsForDomain(domain, specificOnly = false)
+function getConditionalSelectors(domain, specificOnly)
 {
   let selectors = [];
 
   let excluded = new Set();
-  let currentDomain = domain ? domain.replace(/\.+$/, "").toLowerCase() : "";
+  let currentDomain = domain;
 
   // 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;
 
@@ -169,18 +202,47 @@
 function getDefaultStyleSheet()
 {
   if (!defaultStyleSheet)
     defaultStyleSheet = createStyleSheet(getUnconditionalSelectors());
 
   return defaultStyleSheet;
 }
 
-ElemHideExceptions.on("added", ({selector}) =>
+/**
+ * Returns the common style sheet that applies on all unknown domains.
+ * @returns {string}
+ */
+function getCommonStyleSheet()
 {
+  if (!commonStyleSheet)
+  {
+    commonStyleSheet = getDefaultStyleSheet() +
+                       createStyleSheet(getConditionalSelectors("", false));
+  }
+
+  return commonStyleSheet;
+}
+
+ElemHideExceptions.on("added", ({domains, selector}) =>
+{
+  commonStyleSheet = null;
+
+  if (domains)
+  {
+    for (let domain of domains.keys())
+    {
+      // Note: Once an exception domain is known it never becomes unknown, even
+      // when all the exceptions containing that domain are removed. This is a
+      // best-case optimization.
+      if (domain != "")
+        knownExceptionDomains.add(domain);
+    }
+  }
+
   // If this is the first exception for a previously unconditionally applied
   // element hiding selector we need to take care to update the lookups.
   let unconditionalFilterForSelector = filterBySelector.get(selector);
   if (unconditionalFilterForSelector)
   {
     addToFiltersByDomain(unconditionalFilterForSelector);
     filterBySelector.delete(selector);
     unconditionalSelectors = null;
@@ -193,34 +255,41 @@
  * @class
  */
 exports.ElemHide = {
   /**
    * Removes all known filters
    */
   clear()
   {
-    for (let collection of [filtersByDomain, filterBySelector, knownFilters])
+    commonStyleSheet = null;
+
+    for (let collection of [filtersByDomain, filterBySelector, knownFilters,
+                            knownExceptionDomains])
+    {
       collection.clear();
+    }
 
     unconditionalSelectors = null;
     defaultStyleSheet = null;
 
     filterNotifier.emit("elemhideupdate");
   },
 
   /**
    * Add a new element hiding filter
    * @param {ElemHideFilter} filter
    */
   add(filter)
   {
     if (knownFilters.has(filter))
       return;
 
+    commonStyleSheet = null;
+
     let {selector} = filter;
 
     if (!(filter.domains || ElemHideExceptions.hasExceptions(selector)))
     {
       // The new filter's selector is unconditionally applied to all domains
       filterBySelector.set(selector, filter);
       unconditionalSelectors = null;
       defaultStyleSheet = null;
@@ -239,16 +308,18 @@
    * Removes an element hiding filter
    * @param {ElemHideFilter} filter
    */
   remove(filter)
   {
     if (!knownFilters.has(filter))
       return;
 
+    commonStyleSheet = null;
+
     let {selector} = filter;
 
     // Unconditially applied element hiding filters
     if (filterBySelector.get(selector) == filter)
     {
       filterBySelector.delete(selector);
       unconditionalSelectors = null;
       defaultStyleSheet = null;
@@ -288,22 +359,39 @@
    * @param {boolean} [specificOnly=false] Whether selectors from generic
    *   filters should be included.
    *
    * @returns {ElemHideStyleSheet} An object containing the CSS code and the
    *   list of selectors.
    */
   generateStyleSheetForDomain(domain, specificOnly = false)
   {
-    let selectors = getConditionalSelectorsForDomain(domain, specificOnly);
-    let code = specificOnly ? createStyleSheet(selectors) :
-                 (getDefaultStyleSheet() + createStyleSheet(selectors));
+    let code = null;
+    let selectors = null;
+
+    if (domain[domain.length - 1] == ".")
+      domain = domain.replace(/\.+$/, "");
+
+    domain = domain.toLowerCase();
 
-    if (!specificOnly)
+    if (specificOnly)
+    {
+      selectors = getConditionalSelectors(domain, true);
+      code = createStyleSheet(selectors);
+    }
+    else
+    {
+      let knownSuffix = getKnownSuffix(domain);
+
+      selectors = getConditionalSelectors(knownSuffix, false);
+      code = knownSuffix == "" ? getCommonStyleSheet() :
+               (getDefaultStyleSheet() + createStyleSheet(selectors));
+
       selectors = getUnconditionalSelectors().concat(selectors);
+    }
 
     return {code, selectors};
   }
 };
 
 /**
  * Splits a list of selectors into groups determined by the value of
  * <code>{@link selectorGroupSize}</code>.