Issue 2878 - Element Hiding Helper is stuck in a bad state after a tab crash

lib/aardvark.js

 /*
  * This Source Code is subject to the terms of the Mozilla Public License
  * version 2.0 (the "License"). You can obtain a copy of the License at
  * http://mozilla.org/MPL/2.0/.
  */
 
 let {Prefs} = require("prefs");
 
 // Make sure to stop selection when we are uninstalled
 onShutdown.add(() => Aardvark.quit());
@@ skipping 236 matching lines @@
     this.doCommand("quit", null);
   },
 
   onMouseMove: function(event)
   {
     this.mouseX = event.screenX;
     this.mouseY = event.screenY;
 
     this.hideSelection();
     if (!this.browser)
-      return;   // hideSelection() called quit()

[saroyanm, 2015/08/10 14:58:12]

Nit: I think make sense to move comment before if statement, for consistency.

+    {
+      // hideSelection() called quit()
+      return;
+    }
 
     let x = event.clientX;
     let y = event.clientY;
 
     // We might have coordinates relative to a frame, recalculate relative to top window
     let node = event.target;
     while (node && node.ownerDocument && node.ownerDocument.defaultView && node.ownerDocument.defaultView.frameElement)
     {
       node = node.ownerDocument.defaultView.frameElement;
       let rect = node.getBoundingClientRect();
@@ skipping 122 matching lines @@
     {
       this.prevPos = pos;
       this.paintNode.addEventListener("MozAfterPaint", this.onAfterPaint, false);
     }
   },
 
   hideSelection: function()
   {
     try
     {
       if (this.boxElem.parentNode)

[saroyanm, 2015/08/10 14:58:12]

I wander if this is the only case where we are using CPOW when the tab is
crashed ? 
I've noticed that we also use "this.boxElem.parentNode" in selectElement, have
assumption that tab crash is connected to that CPOW.

[Wladimir Palant, 2015/08/10 21:10:11]

No, it's not, and the other places might still produce errors - but we'll
usually get here (either via onMouseMove or quit). This is merely an
intermediate solution until https://issues.adblockplus.org/ticket/2879 is fixed.

         this.boxElem.parentNode.removeChild(this.boxElem);
     }
     catch (e)
     {
       // Are we using CPOW whose process is gone? Quit!
+      // Clear some variables to prevent recursion (quit will call us again).
       this.boxElem = {};

[saroyanm, 2015/08/10 14:58:12]

Shouldn't we reset this.boxElem value and paintNode in quite() function  ?

[Wladimir Palant, 2015/08/10 21:10:11]

No, because quit() will call hideSelection() again - it would normally cause
infinite recursion.

       this.paintNode = null;
       this.quit();
       return;
     }
 
     if (this.paintNode)
       this.paintNode.removeEventListener("MozAfterPaint", this.onAfterPaint, false);
 
     this.paintNode = null;
     this.prevPos = null;
@@ skipping 358 matching lines @@
     // Show help box
     helpBox.showPopup(this.browser, -1, -1, "tooltip", "topleft", "topleft");
     return true;
   }
 }
 
 // Makes sure event handlers like Aardvark.onKeyPress always have the correct
 // this pointer set.
 for (let method of ["onMouseClick", "onMouseScroll", "onKeyPress", "onPageHide", "onMouseMove", "onAfterPaint", "quit"])
   Aardvark[method] = Aardvark[method].bind(Aardvark);