Issue 6423 - Observe only relevant mutation types

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 284 matching lines @@
       yield [selector, subtree];
   }
 };
 
 function isSelectorHidingOnlyPattern(pattern)
 {
   return pattern.selectors.some(s => s.preferHideWithSelector) &&
     !pattern.selectors.some(s => s.requiresHiding);
 }
 
+function shouldObserveAttributes(patterns)
+{
+  // Observe changes to attributes if either there's a plain selector that
+  // looks like an attribute selector in one of the patterns
+  // (e.g. "a[href='https://example.com/']")
+  // or there's a properties selector nested inside a has selector
+  // (e.g. "div:-abp-has(:-abp-properties(color: blue))")
+  return patterns.some(
+    pattern => pattern.selectors.some(
+      selector => (selector instanceof PlainSelector &&
+                   /\[.+\]/.test(selector._selector))||

[Manish Jethani, 2017/10/22 22:58:13]

This check for attribute selector syntax can give false positives in very rare
cases, but it doesn't matter since this is just an optimization anyway.

+                  (pattern.selectors[0] instanceof HasSelector &&

[Manish Jethani, 2017/10/22 22:58:13]

I realize that the second check is essentially
pattern.selectors[0].dependsOnStyle. I think this logic generally should be
moved into the respective classes.

[Manish Jethani, 2017/10/23 00:12:09]

Done.

+                   selector instanceof PropsSelector)
+    )
+  );
+}
+
+function shouldObserveCharacterData(patterns)
+{
+  // Observe changes to character data only if there's a contains selector in
+  // one of the patterns.
+  return patterns.some(
+    pattern => pattern.selectors.some(
+      selector => selector instanceof ContainsSelector
+    )
+  );
+}
+
 function ElemHideEmulation(addSelectorsFunc, hideElemsFunc)
 {
   this.document = document;
   this.addSelectorsFunc = addSelectorsFunc;
   this.hideElemsFunc = hideElemsFunc;
   this.observer = new MutationObserver(this.observe.bind(this));
 }
 
 ElemHideEmulation.prototype = {
   isSameOrigin(stylesheet)
@@ skipping 265 matching lines @@
         this.patterns.push({selectors, text: pattern.text});
     }
 
     if (this.patterns.length > 0)
     {
       this.queueFiltering();
       this.observer.observe(
         this.document,
         {
           childList: true,
-          attributes: true,
-          characterData: true,
+          attributes: shouldObserveAttributes(this.patterns),
+          characterData: shouldObserveCharacterData(this.patterns),
           subtree: true
         }
       );
       this.document.addEventListener("load", this.onLoad.bind(this), true);
     }
   }
 };
 
 exports.ElemHideEmulation = ElemHideEmulation;