Issue 7236 - Handle sub properties in abort-on-property snippets

lib/content/snippets.js

Index: lib/content/snippets.js
===================================================================
--- a/lib/content/snippets.js
+++ b/lib/content/snippets.js
@@ -693,24 +693,51 @@
   // 2176782336 is 36^6 which mean 6 chars [a-z0-9]
   // 60466176 is 36^5
   // 2176782336 - 60466176 = 2116316160. This ensure to always have 6
   // chars even if Math.random() returns its minimum value 0.0
   //
   return Math.floor(Math.random() * 2116316160 + 60466176).toString(36);
 }
 
-function wrapPropertyAccess(object, property, descriptor)
+function wrapPropertyAccess(object, property, descriptor, magic)
 {
-  let currentDescriptor = Object.getOwnPropertyDescriptor(object, property);
-  if (currentDescriptor && !currentDescriptor.configurable)
-    return false;
+  let dot = property.indexOf(".");
+  if (dot == -1)
+  {
+    // simple property case.
+    let currentDescriptor = Object.getOwnPropertyDescriptor(object, property);
+    if (currentDescriptor && !currentDescriptor.configurable)
+      return false;
+
+    Object.defineProperty(object, property, descriptor);
+    return true;
+  }
+  let prop = property.slice(0, dot);

[Manish Jethani, 2019/02/03 14:30:38]

We could just call this `name` instead of `prop`.

[hub, 2019/02/04 15:48:02]

Done.

+  property = property.slice(dot + 1);
+  let value = object[prop];
+  if (typeof value != "undefined")

[Manish Jethani, 2019/02/03 14:30:38]

What if `value` is `null`? I think we want to check `value != null`.

[hub, 2019/02/04 15:48:02]

Actually I think we want `value intanceof Object` here. Fixing the inconsistency
with below.

+    return wrapPropertyAccess(value, property, descriptor);
 
-  Object.defineProperty(object, property, descriptor);
-  return true;
+  let currentDescriptor = Object.getOwnPropertyDescriptor(object, prop);
+  if (currentDescriptor && currentDescriptor.set &&
+      magic && currentDescriptor.set.hasOwnProperty(magic))
+  {
+    return true;
+  }
+
+  let v;
+  let setter = a =>
+  {
+    v = a;
+    if (a instanceof Object)

[Manish Jethani, 2019/02/03 14:30:38]

This check is inconsistent with the one above. I think we can just check `a !=
null`. All other values will get coerced to object.

Oh wait, but `Object.defineProperty` will fail. Well then let's just check for
`a && typeof a == "object"`?

[hub, 2019/02/04 15:48:02]

`a instanceof Object` is false if a is null. Unlike `typeof a` that will be
`object` even for null.

[Manish Jethani, 2019/02/04 17:56:33]

We've been here before:

https://hg.adblockplus.org/adblockpluscore/file/91cd83c4c272/lib/content/snip...

instanceof is more expensive which is why we avoid it in Core. It doesn't matter
for snippets, but for consistency I think we can continue using `a && typeof a
== "object"`.

[hub, 2019/02/04 19:54:36]

So be it. And this actually make the test pass on Firefox.

+      wrapPropertyAccess(a, property, descriptor, magic);
+  };
+  setter[magic] = undefined;

[Manish Jethani, 2019/02/03 14:30:38]

If we just want to tag the setter, I think it's better to set it to `null`
rather than `undefined`.

[hub, 2019/02/04 15:48:03]

undefined is good. We check it with hasOwnProperty(). 

+  Object.defineProperty(object, prop, {get: () => v, set: setter});
 }
 
 /**
  * Overrides the <code>onerror</code> handler to discard tagged error messages
  * from our property wrapping.
  *
  * @param {string} magic The magic string that tags the error message.
  */
@@ -744,17 +771,17 @@
 
   let rid = randomId();
 
   function abort()
   {
     throw new ReferenceError(rid);
   }
 
-  if (wrapPropertyAccess(window, property, {get: abort, set() {}}))
+  if (wrapPropertyAccess(window, property, {get: abort, set() {}}, rid))
     overrideOnError(rid);
 }
 
 exports["abort-on-property-read"] = makeInjector(abortOnPropertyRead,
                                                  wrapPropertyAccess,
                                                  overrideOnError,
                                                  randomId);
 
@@ -776,17 +803,17 @@
 
   let rid = randomId();
 
   function abort()
   {
     throw new ReferenceError(rid);
   }
 
-  if (wrapPropertyAccess(window, property, {set: abort}))
+  if (wrapPropertyAccess(window, property, {set: abort}, rid))
     overrideOnError(rid);
 }
 
 exports["abort-on-property-write"] = makeInjector(abortOnPropertyWrite,
                                                   wrapPropertyAccess,
                                                   overrideOnError,
                                                   randomId);
 
@@ -839,15 +866,15 @@
     },
     set(value)
     {
       abort();
       currentValue = value;
     }
   };
 
-  if (wrapPropertyAccess(object, name, descriptor))
+  if (wrapPropertyAccess(object, name, descriptor, rid))
     overrideOnError(rid);
 }
 
 exports["abort-current-inline-script"] =
   makeInjector(abortCurrentInlineScript, wrapPropertyAccess, toRegExp,
                overrideOnError, regexEscape, randomId);