Issue 6437 - Filter out patterns that do not match DOM mutations

lib/content/elemHideEmulation.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
@@ skipping 435 matching lines @@
   },
 
   get dependsOnCharacterData()
   {
     // Observe changes to character data only if there's a contains selector in
     // one of the patterns.
     return getCachedPropertyValue(
       this, "_dependsOnCharacterData",
       () => this.selectors.some(selector => selector.dependsOnCharacterData)
     );
+  },
+
+  matchesMutationTypes(mutationTypes)
+  {
+    let mutationTypeMatchMap = getCachedPropertyValue(
+      this, "_mutationTypeMatchMap",
+      () => new Map([

[Manish Jethani, 2018/03/20 09:41:33]

This is a cached property also so the map gets created only once.

+        // All types of DOM-dependent patterns are affected by mutations of
+        // type "childList".
+        ["childList", true],
+        ["attributes", this.maybeDependsOnAttributes],
+        ["characterData", this.dependsOnCharacterData]
+      ])
+    );
+
+    for (let mutationType of mutationTypes)
+    {
+      if (mutationTypeMatchMap.get(mutationType))
+        return true;
+    }
+
+    return false;
   }
 };
 
+function extractMutationTypes(mutations)
+{
+  let types = new Set();
+
+  for (let mutation of mutations)
+  {
+    types.add(mutation.type);
+
+    // There are only 3 types of mutations: "attributes", "characterData", and
+    // "childList".
+    if (types.size == 3)
+      break;
+  }
+
+  return types;
+}
+
 function filterPatterns(patterns, {stylesheets, mutations})
 {
   if (!stylesheets && !mutations)
     return patterns.slice();
 
+  let mutationTypes = mutations ? extractMutationTypes(mutations) : null;
+
   return patterns.filter(
     pattern => (stylesheets && pattern.dependsOnStyles) ||
-               (mutations && pattern.dependsOnDOM)
+               (mutations && pattern.dependsOnDOM &&
+                pattern.matchesMutationTypes(mutationTypes))
   );
 }
 
 function shouldObserveAttributes(patterns)
 {
   return patterns.some(pattern => pattern.maybeDependsOnAttributes);
 }
 
 function shouldObserveCharacterData(patterns)
 {
@@ skipping 332 matching lines @@
           characterData: shouldObserveCharacterData(this.patterns),
           subtree: true
         }
       );
       this.document.addEventListener("load", this.onLoad.bind(this), true);
     }
   }
 };
 
 exports.ElemHideEmulation = ElemHideEmulation;