Issue 4499 - Consider $generichide exceptions when applying element hiding rules

lib/child/elemHide.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 326 matching lines @@
       {
         // We are too late, the window is gone already.
         return;
       }
 
       if (enabled)
       {
         let utils = window.QueryInterface(Ci.nsIInterfaceRequestor)
                           .getInterface(Ci.nsIDOMWindowUtils);
 
-        let specificOnly = filter;

[kzar, 2016/10/07 09:30:21]

I don't understand this line, isn't filter being given as filter.text by
elemHideFF.js for "elemhideEnabled"? How can we use the filter.text for
specificOnly?

[Wladimir Palant, 2016/10/07 09:37:49]

There are two kinds of filters that we can get in the response -
$elemhide/$document filters (disable element hiding altogether) or $generichide
filters (disable only generic filters). If enabled is true then it cannot be the
former. So if we have a filter at this point then a $generichide filter applies.

Not sure how this can be made more obvious, maybe send true/false/"specificonly"
for enabled? Combining boolean and string in the same field seems ugly. And I
don't really want to add more data to be sent.

[kzar, 2016/10/07 09:53:31]

Ah, I finally wrapped my head around it :). Well I suppose `let specificOnly =
!!filter;` might be a bit clearer? I guess a small comment here could also help
explain the thinking.

(I wonder why we need to check the contents of `filter` at all, won't it always
be truthy if enabled is true?)

[kzar, 2016/10/07 10:15:29]

(OK, I missed the final `return {enabled: true};` before. Now I see why you need
to check filter.)

[Wladimir Palant, 2016/10/07 10:53:05]

Done.

+        // If we have a filter hit at this point then it must be a $generichide
+        // filter - apply only specific element hiding filters.
+        let specificOnly = !!filter;
         if (!specificOnly)
         {
           if (!this.sheet)
           {
             this.sheet = Utils.styleService.preloadSheet(this.styleURL,
                 Ci.nsIStyleSheetService.USER_SHEET);
           }
 
           try
           {
@@ skipping 34 matching lines @@
       if (filter)
       {
         RequestNotifier.addNodeData(window.document, window.top, {
           contentType, docDomain, thirdParty, location, filter, filterType
         });
       }
     });
   }
 };
 observer.init();